| 1. |
- Abbasi, R., et al.
(författare)
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The IceCube data acquisition system : Signal capture, digitization, and timestamping
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 601:3, s. 294-316
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Tidskriftsartikel (refereegranskat)abstract
- IceCube is a km-scale neutrino observatory under construction at the South Pole with sensors both in the deep ice (InIce) and on the surface (IceTop). The sensors, called Digital Optical Modules (DOMs). detect, digitize and timestamp the signals from optical Cherenkov-radiation photons. The DOM Main Board (MB) data acquisition subsystem is connected to the central DAQ in the IceCube Laboratory (ICL) by a single twisted copper wire-pair and transmits packetized data on demand. Time calibration is maintained throughout the array by regular transmission to the DOMs of precisely timed analog signals, synchronized to a central GPS-disciplined clock. The design goals and consequent features, functional capabilities, and initial performance of the DOM MB, and the operation of a combined array of DOMs as a system, are described here. Experience with the first InIce strings and the IceTop stations indicates that the system design and performance goals have been achieved. (c) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Abbasi, R., et al.
(författare)
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Solar energetic particle spectrum on 2006 December 13 determined by IceTop
- 2008
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 689:1, s. L65-L68
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Tidskriftsartikel (refereegranskat)abstract
- On 2006 December 13 the IceTop air shower array at the South Pole detected a major solar particle event. By numerically simulating the response of the IceTop tanks, which are thick Cerenkov detectors with multiple thresholds deployed at high altitude with no geomagnetic cutoff, we determined the particle energy spectrum in the energy range 0.6-7.6 GeV. This is the first such spectral measurement using a single instrument with a well-defined viewing direction. We compare the IceTop spectrum and its time evolution with previously published results and outline plans for improved resolution of future solar particle spectra.
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| 3. |
- Achterberg, A., et al.
(författare)
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Detection of atmospheric muon neutrinos with the IceCube 9-string detector
- 2007
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 76:2, s. 027101-
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Tidskriftsartikel (refereegranskat)abstract
- The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino detector under construction at the geographic South Pole. The dominant population of neutrinos detected in IceCube is due to meson decay in cosmic-ray air showers. These atmospheric neutrinos are relatively well understood and serve as a calibration and verification tool for the new detector. In 2006, the detector was approximately 10% completed, and we report on data acquired from the detector in this configuration. We observe an atmospheric neutrino signal consistent with expectations, demonstrating that the IceCube detector is capable of identifying neutrino events. In the first 137.4 days of live time, 234 neutrino candidates were selected with an expectation of 211 +/- 76.1(syst)+/- 14.5(stat) events from atmospheric neutrinos.
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| 4. |
- Abbasi, R., et al.
(författare)
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Search for point sources of high energy neutrinos with final data from AMANDA-II
- 2009
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 79, s. 062001-
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Tidskriftsartikel (refereegranskat)abstract
- We present a search for point sources of high energy neutrinos using 3.8 yr of data recorded by AMANDA-II during 2000-2006. After reconstructing muon tracks and applying selection criteria designed to optimally retain neutrino-induced events originating in the northern sky, we arrive at a sample of 6595 candidate events, predominantly from atmospheric neutrinos with primary energy 100 GeV to 8 TeV. Our search of this sample reveals no indications of a neutrino point source. We place the most stringent limits to date on E(-2) neutrino fluxes from points in the northern sky, with an average upper limit of E(2)Phi(nu mu)+nu(tau)<= 5.2x10(-11) TeV cm(-2) s(-1) on the sum of nu(mu) and nu(tau) fluxes, assumed equal, over the energy range from 1.9 TeV to 2.5 PeV.
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| 5. |
- Ackermann, M., et al.
(författare)
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Search for ultra-high-energy neutrinos with amanda-II
- 2008
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 675:2, s. 1014-1024
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Tidskriftsartikel (refereegranskat)abstract
- A search for diffuse neutrinos with energies in excess of 10(5) GeV is conducted with AMANDA-II data recorded between 2000 and 2002. Above 10(7) GeV, the Earth is essentially opaque to neutrinos. This fact, combined with the limited overburden of the AMANDA-II detector ( roughly 1.5 km), concentrates these ultra-high-energy neutrinos at the horizon. The primary background for this analysis is bundles of downgoing, high-energy muons from the interaction of cosmic rays in the atmosphere. No statistically significant excess above the expected background is seen in the data, and an upper limit is set on the diffuse all-flavor neutrino flux of E-2 Phi(90%CL) < 2.7x10(-7) GeV cm(-2) s(-1) sr(-1) valid over the energy range of 2x10(5) to 10(9) GeV. A number of models that predict neutrino fluxes from active galactic nuclei are excluded at the 90% confidence level.
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| 6. |
- Abbasi, R., et al.
(författare)
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SEARCH FOR HIGH-ENERGY MUON NEUTRINOS FROM THE "NAKED-EYE" GRB 080319B WITH THE IceCube NEUTRINO TELESCOPE
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 701:2, s. 1721-1731
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Tidskriftsartikel (refereegranskat)abstract
- We report on a search with the IceCube detector for high-energy muon neutrinos from GRB 080319B, one of the brightest gamma-ray bursts (GRBs) ever observed. The fireball model predicts that a mean of 0.1 events should be detected by IceCube for a bulk Lorentz boost of the jet of 300. In both the direct on-time window of 66 s and an extended window of about 300 s around the GRB, no excess was found above background. The 90% CL upper limit on the number of track-like events from the GRB is 2.7, corresponding to a muon neutrino fluence limit of 9.5 x 10(-3) erg cm(-2) in the energy range between 120 TeV and 2.2 PeV, which contains 90% of the expected events.
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| 7. |
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| 8. |
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| 9. |
- Abe, O, et al.
(författare)
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Effects of chemotherapy and hormonal therapy for early breast cancer on recurrence and 15-year survival: an overview of the randomised trials
- 2005
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Ingår i: The Lancet. - 1474-547X. ; 365:9472, s. 1687-1717
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Tidskriftsartikel (refereegranskat)abstract
- Background Quinquennial overviews (1985-2000) of the randomised trials in early breast cancer have assessed the 5-year and 10-year effects of various systemic adjuvant therapies on breast cancer recurrence and survival. Here, we report the 10-year and 15-year effects. Methods Collaborative meta-analyses were undertaken of 194 unconfounded randomised trials of adjuvant chemotherapy or hormonal therapy that began by 1995. Many trials involved CMF (cyclophosphamide, methotrexate, fluorouracil), anthracycline-based combinations such as FAC (fluorouracil, doxombicin, cyclophosphamide) or FEC (fluorouracil, epirubicin, cyclophosphamide), tamoxifen, or ovarian suppression: none involved taxanes, trastuzumab, raloxifene, or modem aromatase inhibitors. Findings Allocation to about 6 months of anthracycline-based polychemotherapy (eg, with FAC or FEC) reduces the annual breast cancer death rate by about 38% (SE 5) for women younger than 50 years of age when diagnosed and by about 20% (SE 4) for those of age 50-69 years when diagnosed, largely irrespective of the use of tamoxifen and of oestrogen receptor (ER) status, nodal status, or other tumour characteristics. Such regimens are significantly (2p=0 . 0001 for recurrence, 2p<0 . 00001 for breast cancer mortality) more effective than CMF chemotherapy. Few women of age 70 years or older entered these chemotherapy trials. For ER-positive disease only, allocation to about 5 years of adjuvant tamoxifen reduces the annual breast cancer death rate by 31% (SE 3), largely irrespective of the use of chemotherapy and of age (<50, 50-69, &GE; 70 years), progesterone receptor status, or other tumour characteristics. 5 years is significantly (2p<0 . 00001 for recurrence, 2p=0 . 01 for breast cancer mortality) more effective than just 1-2 years of tamoxifen. For ER-positive tumours, the annual breast cancer mortality rates are similar during years 0-4 and 5-14, as are the proportional reductions in them by 5 years of tamoxifen, so the cumulative reduction in mortality is more than twice as big at 15 years as at 5 years after diagnosis. These results combine six meta-analyses: anthracycline-based versus no chemotherapy (8000 women); CMF-based versus no chemotherapy (14 000); anthracycline-based versus CMF-based chemotherapy (14 000); about 5 years of tamoxifen versus none (15 000); about 1-2 years of tamoxifen versus none (33 000); and about 5 years versus 1-2 years of tamoxifen (18 000). Finally, allocation to ovarian ablation or suppression (8000 women) also significantly reduces breast cancer mortality, but appears to do so only in the absence of other systemic treatments. For middle-aged women with ER-positive disease (the commonest type of breast cancer), the breast cancer mortality rate throughout the next 15 years would be approximately halved by 6 months of anthracycline-based chemotherapy (with a combination such as FAC or FEC) followed by 5 years of adjuvant tamoxifen. For, if mortality reductions of 38% (age <50 years) and 20% (age 50-69 years) from such chemotherapy were followed by a further reduction of 31% from tamoxifen in the risks that remain, the final mortality reductions would be 57% and 45%, respectively (and, the trial results could well have been somewhat stronger if there had been full compliance with the allocated treatments). Overall survival would be comparably improved, since these treatments have relatively small effects on mortality from the aggregate of all other causes. Interpretation Some of the widely practicable adjuvant drug treatments that were being tested in the 1980s, which substantially reduced 5-year recurrence rates (but had somewhat less effect on 5-year mortality rates), also substantially reduce 15-year mortality rates. Further improvements in long-term survival could well be available from newer drugs, or better use of older drugs.
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| 10. |
- Abbasi, R, et al.
(författare)
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Determination of the atmospheric neutrino flux and searches for new physics with AMANDA-II
- 2009
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 79, s. 102005-
-
Tidskriftsartikel (refereegranskat)abstract
- The AMANDA-II detector, operating since 2000 in the deep ice at the geographic South Pole, has accumulated a large sample of atmospheric muon neutrinos in the 100 GeV to 10 TeV energy range. The zenith angle and energy distribution of these events can be used to search for various phenomenological signatures of quantum gravity in the neutrino sector, such as violation of Lorentz invariance or quantum decoherence. Analyzing a set of 5511 candidate neutrino events collected during 1387 days of livetime from 2000 to 2006, we find no evidence for such effects and set upper limits on violation of Lorentz invariance and quantum decoherence parameters using a maximum likelihood method. Given the absence of evidence for new flavor-changing physics, we use the same methodology to determine the conventional atmospheric muon neutrino flux above 100 GeV.
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| 11. |
- Abbasi, R, et al.
(författare)
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Extending the Search for Neutrino Point Sources with IceCube above the Horizon
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:22, s. 221102-
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Tidskriftsartikel (refereegranskat)abstract
- Point source searches with the IceCube neutrino telescope have been restricted to one hemisphere, due to the exclusive selection of upward going events as a way of rejecting the atmospheric muon background. We show that the region above the horizon can be included by suppressing the background through energy-sensitive cuts. This improves the sensitivity above PeV energies, previously not accessible for declinations of more than a few degrees below the horizon due to the absorption of neutrinos in Earth. We present results based on data collected with 22 strings of IceCube, extending its field of view and energy reach for point source searches. No significant excess above the atmospheric background is observed in a sky scan and in tests of source candidates. Upper limits are reported, which for the first time cover point sources in the southern sky up to EeV energies.
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| 12. |
- Abbasi, R, et al.
(författare)
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FIRST NEUTRINO POINT-SOURCE RESULTS FROM THE 22 STRING ICECUBE DETECTOR
- 2009
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Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 701, s. L47-L51
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Tidskriftsartikel (refereegranskat)abstract
- We present new results of searches for neutrino point sources in the northern sky, using data recorded in 2007-2008 with 22 strings of the IceCube detector (approximately one-fourth of the planned total) and 275.7 days of live time. The final sample of 5114 neutrino candidate events agrees well with the expected background of atmospheric muon neutrinos and a small component of atmospheric muons. No evidence of a point source is found, with the most significant excess of events in the sky at 2.2 sigma after accounting for all trials. The average upper limit over the northern sky for point sources of muon-neutrinos with E-2 spectrum is E-2 Phi(v mu) < 1.4 x 10(-11) TeV cm(-2) s(-1), in the energy range from 3 TeV to 3 PeV, improving the previous best average upper limit by the AMANDA-II detector by a factor of 2.
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| 13. |
- Abbasi, R, et al.
(författare)
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Limits on a Muon Flux from Neutralino Annihilations in the Sun with the IceCube 22-String Detector
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:20, s. 201302-
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Tidskriftsartikel (refereegranskat)abstract
- A search for muon neutrinos from neutralino annihilations in the Sun has been performed with the IceCube 22-string neutrino detector using data collected in 104.3 days of live time in 2007. No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured neutralinos in the Sun and converted to limits on the weakly interacting massive particle (WIMP) proton cross sections for WIMP masses in the range 250-5000 GeV. These results are the most stringent limits to date on neutralino annihilation in the Sun.
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| 14. |
- Aguilar, J. A., et al.
(författare)
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First results of the instrumentation line for the deep-sea ANTARES neutrino telescope
- 2006
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 26:4-5, s. 314-324
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Tidskriftsartikel (refereegranskat)abstract
- In 2005, the ANTARES Collaboration deployed and operated at a depth of 2500 m a so-called Mini Instrumentation Line equipped with Optical Modules (MILOM) at the ANTARES site. The various data acquired during the continuous operation from April to December 2005 of the MILOM confirm the satisfactory performance of the Optical Modules, their front-end electronics and readout system. as well as the calibration devices of the detector. The in situ measurement of the Optical Module time response yields a resolution better than 0.5 ns. The performance of the acoustic positioning system, which enables the spatial reconstruction of the ANTARES detector with a precision of about 10 cm, is verified. These results demonstrate that with the full ANTARES neutrino telescope the design angular resolution of better than 0.3 degrees can be realistically achieved.
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| 15. |
- Aguilar, J. A., et al.
(författare)
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The data acquisition system for the ANTARES neutrino telescope
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 570:1, s. 107-116
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Tidskriftsartikel (refereegranskat)abstract
- The ANTARES neutrino telescope is being constructed in the Mediterranean Sea. It consists of a large three-dimensional array of photo-multiplier tubes. The data acquisition system of the detector takes care of the digitisation of the photo-multiplier tube signals, data transport, data filtering, and data storage. The detector is operated using a control program interfaced with all elements. The design and the implementation of the data acquisition system are described. (c) 2006 Elsevier B.V. All rights reserved.
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| 16. |
- Ageron, M., et al.
(författare)
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The ANTARES optical beacon system
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 578:3, s. 498-509
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Tidskriftsartikel (refereegranskat)abstract
- ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It consists of a three-dimensional array of photomultiplier tubes that can detect the Cherenkov light induced by charged particles produced in the interactions of neutrinos with the surrounding medium. High angular resolution can be achieved, in particular, when a muon is produced, provided that the Cherenkov photons are detected with sufficient timing precision. Considerations of the intrinsic time uncertainties stemming from the transit time spread in the photomultiplier tubes and the mechanism of transmission of light in sea water lead to the conclusion that a relative time accuracy of the order of 0.5 ns is desirable. Accordingly, different time calibration systems have been developed for the ANTARES telescope. In this article, a system based on Optical Beacons, a set of external and well-controlled pulsed light sources located throughout the detector, is described. This calibration system takes into account the optical properties of sea water, which is used as the detection volume of the ANTARES telescope. The design, tests, construction and first results of the two types of beacons, LED and laser-based, are presented. (C) 2007 Elsevier B.V. All rights reserved.
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| 17. |
- Aguilar, J A, et al.
(författare)
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Study of large hemispherical photomultiplier tubes for the ANTARES neutrino telescope
- 2005
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 555:1-2, s. 132-141
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Tidskriftsartikel (refereegranskat)abstract
- The ANTARES neutrino telescope, to be immersed depth in the Mediterranean Sea, will consist of a three-dimensional matrix of 900 large area photomultiplier tubes housed in pressure-resistant glass spheres. The selection of the optimal photomultiplier was a critical step for the project and required an intensive phase of tests and developments carried out in close collaboration with the main manufacturers worldwide. This paper provides an overview of the tests performed by the collaboration and describes in detail the features of the photomultiplier tube chosen for ANTARES. (c) 2005 Elsevier B.V. All rights reserved.
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| 18. |
- Aguilar, J A, et al.
(författare)
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Transmission of light in deep sea water at the site of the ANTARES neutrino telescope
- 2005
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 23:1, s. 131-155
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Tidskriftsartikel (refereegranskat)abstract
- The ANTARES neutrino telescope is a large photomultiplier array designed to detect neutrino-induced upward-going muons by their Cherenkov radiation. Understanding the absorption and scattering of light in the deep Mediterranean is fundamental to optimising the design and performance of the detector. This paper presents measurements of blue and UV light transmission at the ANTARES site taken between 1997 and 2000. The derived values for the scattering length and the angular distribution of particulate scattering were found to be highly correlated, and results are therefore presented in terms of an absorption length;,ab, and an effective scattering length lambda(sct)(eff). The values for blue (UV) light are found to be lambda(abs) similar or equal to 60(26) m, lambda(sct)(eff similar or equal to) 265(122) m, with significant (similar to15%) time variability. Finally, the results of ANTARES simulations showing the effect of these water properties on the anticipated performance of the detector are presented. (C) 2004 Elsevier B.V. All rights reserved.
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| 19. |
- Stork, D., et al.
(författare)
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Overview of transport, fast particle and heating and current drive physics using tritium in JET plasmas
- 2005
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 45:10, s. S181-S194
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority tritium (T) plasmas (n(T)/n(D) < 3%). Thermal tritium particle transport coefficients (D-T, nu(T)) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities and in the region of internal transport barriers (ITBs) in reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q(95) 2.8 and triangularity delta = 0.2, the T particle transport scales in a gyro-Bohm manner in the inner plasma (r/a < 0.4), whilst the outer plasma particle transport scaling is more Bohm-like. Dimensionless parameter scans show contrasting behaviour for the trace particle confinement (increases with collisionality, nu* and beta) and bulk energy confinement (decreases with nu* and is independent of beta). In an extended ELMy H-mode data set, with rho*, nu*, and q varied but with neo-classical tearing modes (NTMs) either absent or limited to weak, benign core modes (4/3 or above), the multiparameter fit to the normalized diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives D-T/B-phi similar to rho*(2.46) nu*(-0.23) beta(-1.01) q(2.03). In hybrid scenarios (q(min) similar to 1, low positive shear, no sawteeth), the T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma and hybrid scenarios) in the outer plasma region, a correlation of high values of D-T with high values Of nu(T) is seen. The normalized diffusion coefficients for the hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalized tritium diffusion scales with normalized poloidal Larmor radius (rho(theta)* = q rho*) in a manner close to gyro-Bohm (similar to rho(sigma)*(3)), with an added inverse P dependence. The effects of ELMs, sawteeth and NTMs on the T particle transport are described. Fast-ion confinement in current-hole (CH) plasmas was tested in TTE by tritium neutral beam injection into JET CH plasmas. gamma-rays from the reactions of fusion alpha and beryllium impurities (Be-9(alpha, n gamma)C-12) characterized the fast fusion-alpha population evolution. The gamma-decay times are consistent with classical alpha plus parent fast triton slowing down times (tau(Ts) + tau(alpha s)) for high plasma currents (I-p > 2 MA) and monotonic q-profiles. In CH discharges the gamma-ray emission decay times are much lower than classical (tau(Ts) + tau(alpha s)), indicating alpha confinement degradation, due to the orbit losses and particle orbit drift predicted by a 3-D Fokker-Planck numerical code and modelled using TRANSP.
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| 20. |
- Wortman, J. R., et al.
(författare)
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The 2008 update of the Aspergillus nidulans genome annotation: A community effort
- 2009
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Ingår i: Fungal Genetics and Biology. - : Elsevier BV. - 1096-0937 .- 1087-1845. ; 46, s. S2-S13
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Tidskriftsartikel (refereegranskat)abstract
- The identification and annotation of protein-coding genes is one of the primary goals of whole-genome sequencing projects, and the accuracy of predicting the primary protein products of gene expression is vital to the interpretation of the available data and the design of downstream functional applications. Nevertheless, the comprehensive annotation of eukaryotic genomes remains a considerable challenge. Many genomes submitted to public databases, including those of major model organisms, contain significant numbers of wrong and incomplete gene predictions. We present a community-based reannotation of the Aspergillus nidulans genome with the primary goal of increasing the number and quality of protein functional assignments through the careful review of experts in the field of fungal biology. (C) 2009 Elsevier Inc. All rights reserved.
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| 21. |
- Hobirk, J., et al.
(författare)
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Improved confinement in JET hybrid discharges
- 2009
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Ingår i: 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts. - 9781622763368 ; , s. 150-153
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Konferensbidrag (refereegranskat)
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| 22. |
- Kiptily, V. G., et al.
(författare)
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Recent progress in fast ion studies on JET
- 2009
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:6
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents recent results on fast ion studies on JET. A set of diagnostics for both confined and lost fast ions was employed for investigating the response of fast ions to MHD modes and for studying their behaviour in plasmas with toroidal field ripple and in shear-reversed plasmas. A dependence of the losses on MHD mode amplitude was deduced from the experimental data. A study of various plasma scenarios has shown that a significant redistribution of the fast ions happens during changes in the profile of the safety factor from shear-reversed to monotonic. Significant changes in the losses of ICRH accelerated protons were found to be associated with L-H confinement transitions in plasmas. After an L-H transition, an abrupt decrease in the ICRH proton losses was observed. In plasmas with an internal transport barrier, the loss of ICRH accelerated ions was found to increase as the barrier forms. Further results concerning fast ion losses were obtained during JET experiments in which the magnitude of the TF ripple was varied. The ripple losses of fusion products appear similar to classical losses, and are in agreement with modelling.
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| 23. |
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| 24. |
- Liang, Y., et al.
(författare)
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Active control of type-I edge localized modes on JET
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 49:12B, s. B581-B589
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Tidskriftsartikel (refereegranskat)abstract
- The operational domain for active control of type-I edge localized modes (ELMs) with an n = 1 external magnetic perturbation field induced by the ex-vessel error field correction coils on JET has been developed towards more ITER-relevant regimes with high plasma triangularity, up to 0.45, high normalized beta, up to 3.0, plasma current up to 2.0 MA and q(95) varied between 3.0 and 4.8. The results of ELM mitigation in high triangularity plasmas show that the frequency of type-I ELMs increased by a factor of 4 during the application of the n = 1 fields, while the energy loss per ELM, Delta W/W, decreased from 6% to below the noise level of the diamagnetic measurement (<2%). No reduction of confinement quality (H98Y) during the ELM mitigation phase has been observed. The minimum n = 1 perturbation field amplitude above which the ELMs were mitigated increased with a lower q(95) but always remained below the n = 1 locked mode threshold. The first results of ELM mitigation with n = 2 magnetic perturbations on JET demonstrate that the frequency of ELMs increased from 10 to 35 Hz and a wide operational window of q95 from 4.5 to 3.1 has been found.
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| 25. |
- Litaudon, X., et al.
(författare)
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Prospects for steady-state scenarios on JET
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 47:9, s. 1285-1292
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Tidskriftsartikel (refereegranskat)abstract
- In the 2006 experimental campaign, progress has been made on JET to operate non-inductive scenarios at higher applied powers (31 MW) and density (n(1) similar to 4 x 10(19) m(-3)), with ITER-relevant safety factor (q(95) similar to 5) and plasma shaping, taking advantage of the new divertor capabilities. The extrapolation of the performance using transport modelling benchmarked on the experimental database indicates that the foreseen power upgrade (similar to 45 MW) will allow the development of non-inductive scenarios where the bootstrap current is maximized together with the fusion yield and not, as in present-day experiments, at its expense. The tools for the long-term JET programme are the new ITER-like ICRH antenna (similar to 15 MW), an upgrade of the NB power (35 MW/20s or 17.5 MW/40s), a new ITER-like first wall, a new pellet injector for edge localized mode control together with improved diagnostic and control capability. Operation with the new wall will set new constraints on non-inductive scenarios that are already addressed experimentally and in the modelling. The fusion performance and driven current that could be reached at high density and power have been estimated using either 0D or 1-1/2D validated transport models. In the high power case (45 MW), the calculations indicate the potential for the operational space of the non-inductive regime to be extended in terms of current (similar to 2.5 MA) and density (n(1) > 5 x 10(19) m(-3)), with high beta(N) (beta(N) > 3.0) and a fraction of the bootstrap current within 60-70% at high toroidal field (similar to 3.5 T).
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| 26. |
- Dorlo, Thomas P C, et al.
(författare)
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Pharmacokinetics of miltefosine in Old World cutaneous leishmaniasis patients.
- 2008
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Ingår i: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 52:8, s. 2855-60
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Tidskriftsartikel (refereegranskat)abstract
- The pharmacokinetics of miltefosine in leishmaniasis patients are, to a great extent, unknown. We examined and characterized the pharmacokinetics of miltefosine in a group of patients with Old World (Leishmania major) cutaneous leishmaniasis. Miltefosine plasma concentrations were determined in samples taken during and up to 5 months after the end of treatment from 31 Dutch military personnel who contracted cutaneous leishmaniasis in Afghanistan and were treated with 150 mg miltefosine/day for 28 days. Samples were analyzed with a validated liquid chromatography-tandem mass spectrometry assay with a lower limit of quantification (LLOQ) of 4 ng/ml. Population pharmacokinetic modeling was performed with nonlinear mixed-effect modeling, using NONMEM. The pharmacokinetics of miltefosine could best be described by an open two-compartment disposition model, with a first elimination half-life of 7.05 days and a terminal elimination half-life of 30.9 days. The median concentration in the last week of treatment (days 22 to 28) was 30,800 ng/ml. The maximum duration of follow-up was 202 days after the start of treatment. All analyzed samples contained a concentration above the LLOQ. Miltefosine is eliminated from the body much slower than previously thought and is therefore still detectable in human plasma samples taken 5 to 6 months after the end of treatment. The presence of subtherapeutic miltefosine concentrations in the blood beyond 5 months after treatment might contribute to the selection of resistant parasites, and moreover, the measures for preventing the teratogenic risks of miltefosine treatment should be reconsidered.
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| 27. |
- Lamalle, P. U., et al.
(författare)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 46:2, s. 391-400
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on ITER-relevant ion cyclotron resonance frequency (ICRF) physics investigated on JET in 2003 and early 2004. Minority heating of helium three in hydrogen plasmas-(He-3)H-was systematically explored by varying the 3 He concentration and the toroidal phasing of the antenna arrays. The best heating performance (a maximum electron temperature of 6.2 keV with 5 MW of ICRF power) was obtained with a preferential wave launch in the direction of the plasma current. A clear experimental demonstration was made of the sharp and reproducible transition to the mode conversion heating regime when the 3 He concentration increased above similar to 2%. In the latter regime the best heating performance (a maximum electron temperature of 8 keV with 5 MW of ICRF power) was achieved with dipole array phasing, i.e. a symmetric antenna power spectrum. Minority heating of deuterium in hydrogen plasmas-(D)H-was also investigated but was found inaccessible because this scenario is too sensitive to impurity ions with Z/A = 1/2 such as C6+, small amounts of which directly lead into the mode conversion regime. Minority heating of up to 3% of tritium in deuterium plasmas was systematically investigated during the JET trace tritium experimental campaign (TTE). This required operating JET at its highest possible magnetic field (3.9 to 4 T) and the ICRF system at its lowest frequency (23 MHz). The interest of this scenario for ICRF heating at these low concentrations and its efficiency at boosting the suprathermal neutron yield were confirmed, and the measured neutron and gammay ray spectra permit interesting comparisons with advanced ICRF code simulations. Investigations of finite Larmor radius effects on the RF-induced high-energy tails during second harmonic (omega = 2 omega(c)) heating of a hydrogen minority in D plasmas clearly demonstrated a strong decrease in the RF diffusion coefficient at proton energies similar to 1 MeV in agreement with theoretical expectations. Fast wave heating and current drive experiments in deuterium plasmas showed effective direct electron heating with dipole phasing of the antennas, but only small changes of the central plasma current density were observed with the directive phasings, in particular at low single pass damping. New investigations of the heating efficiency of ICRF antennas confirmed its strong dependence on the parallel wavenumber spectrum. Advances in topics of a more technological nature are also summarized: ELM studies using fast RF measurements, the successful experimental demonstration of a new ELM-tolerant antenna matching scheme and technical enhancements planned on the JET ICRF system for 2006, they being equally strongly driven by the preparation for ITER.
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| 28. |
- Lamalle, P.U, et al.
(författare)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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Ingår i: Nucl. Fusion. ; 46, s. 391-
-
Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) has been used for millennia in many applications, primarily in artisanal mining and as an electrode in the chlor–alkali industry. It is anthropogenically emitted as a pollutant from coal fired power plants and naturally emitted, primarily from volcanoes. Its unique chemical characteristics enable global atmospheric transport and it is deposited after various processes, ultimately ending up in one of its final sinks, such as incorporated into deep sediment or bioaccumulated, primarily in the marine environment. All forms of Hg have been established as toxic, and there have been no noted biological benefits from the metal.Throughout time, there have been notable incidents of Hg intoxication documented, and the negative health effects have been documented to those chronically or acutely exposed. Today, exposure to Hg is largely diet or occupationally dependent, however, many are exposed to Hg from their amalgam fillings. This paper puts a tentative monetary value on Hg polluted food sources in the Arctic, where local, significant pollution sources are limited, and relates this to costs for strategies avoiding Hg pollution and to remediation costs of contaminated sites in Sweden and Japan. The case studies are compiled to help policy makers and the public to evaluate whether the benefits to the global environment from banning Hg and limiting its initial emission outweigh the benefits from its continued use or lack of control of Hg emissions. The cases we studied are relevant for point pollution sources globally and their remediation costs ranged between 2500 and 1.1 million US$ kg−1 Hg isolated from the biosphere. Therefore, regulations discontinuing mercury uses combined with extensive flue gas cleaning for all power plants and waste incinerators is cost effective.
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| 29. |
- Liang, Y., et al.
(författare)
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Active control of type-I edge-localized modes with n=1 perturbation fields in the JET tokamak
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:26
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Tidskriftsartikel (refereegranskat)abstract
- Type-I edge-localized modes (ELMs) have been mitigated at the JET tokamak using a static external n=1 perturbation field generated by four error field correction coils located far from the plasma. During the application of the n=1 field the ELM frequency increased by a factor of 4 and the amplitude of the D-alpha signal decreased. The energy loss per ELM normalized to the total stored energy, Delta W/W, dropped to values below 2%. Transport analyses shows no or only a moderate (up to 20%) degradation of energy confinement time during the ELM mitigation phase.
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| 30. |
- Mantica, P., et al.
(författare)
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Experimental Study of the Ion Critical-Gradient Length and Stiffness Level and the Impact of Rotation in the JET Tokamak
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:17
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were carried out in the JET tokamak to determine the critical ion temperature inverse gradient length (R/L-Ti = R vertical bar del T-i vertical bar/T-i) for the onset of ion temperature gradient modes and the stiffness of Ti profiles with respect to deviations from the critical value. Threshold and stiffness have been compared with linear and nonlinear predictions of the gyrokinetic code GS2. Plasmas with higher values of toroidal rotation show a significant increase in R/L-Ti, which is found to be mainly due to a decrease of the stiffness level. This finding has implications on the extrapolation to future machines of present day results on the role of rotation on confinement.
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| 31. |
- Mantica, P., et al.
(författare)
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Experimental Study of the Ion Critical Gradient Length and Stiffness Level and the Impact of Rotational Shear in the JET Tokamak
- 2008
-
Ingår i: Proceedings of the 22nd IAEA Fusion Energy Conference.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Experiments have been carried out in the JET tokamak in order to determine the critical iontemperature inverse gradient length (R/LTi =R|∇Ti|/Ti) for the onset of Ion Temperature Gradientmodes and the stiffness of Ti profiles with respect to deviations from the critical value. The existenceof a threshold in R/LTi has been assessed and its value found in close agreement with linear GS2gyro-kinetic calculations. The ion stiffness level is high and keeps R/LTi close to the linear thresholdirrespective of the amount of core ion heating. This finding is not in agreement with non-linear GS2calculations, yielding significantly higher R/LTi values than the linear threshold. Comparison ofplasmas with different values of toroidal rotation indicates a significant increase in R/LTi in rotatingplasmas. Various observations allow to conclude that such increase is mainly due to a decrease ofthe stiffness level with increasing rotation, rather than to a mere up-shift of the threshold, as commonlypredicted by theory. This finding has implications on the interpretation of present day experimentalresults on the effect of rotation on confinement as well as on extrapolations to future machines.
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| 32. |
- Tala, T., et al.
(författare)
-
Toroidal and poloidal momentum transport studies in tokamaks
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 49:12B, s. B291-B302
-
Tidskriftsartikel (refereegranskat)abstract
- The present status of understanding of toroidal and poloidal momentum transport in tokamaks is presented in this paper. Similar energy confinement and momentum confinement times, i.e. tau(E)/tau(phi)approximate to 1 have been reported on several tokamaks. It is more important though, to study the local transport both in the core and edge plasma separately as, for example, in the core plasma, a large scatter in the ratio of the local effective momentum diffusivity to the ion heat diffusivity chi(phi eff)/chi(i.eff) among different tokamaks can be found. For example, the value of effective Prandtl number is typically around chi(phi eff)/chi(i.eff)approximate to 0.2 on JET while still tau(E)/tau(phi)approximate to 1 holds. Perturbative NBI modulation experiments on JET have shown, however, that a Prandtl number chi(phi)/chi(i) of around 1 is valid if there is an additional, significant inward momentum pinch which is required to explain the amplitude and phase behaviour of the momentum perturbation. The experimental results, i.e. the high Prandtl number and pinch, are in good qualitative and to some extent also in quantitative agreement with linear gyro-kinetic simulations. In contrast to the toroidal momentum transport which is clearly anomalous, the poloidal velocity is usually believed to be neo-classical. However, experimental measurements on JET show that the carbon poloidal velocity can be an order of magnitude above the predicted value by the neo-classical theory within the ITB. These large measured poloidal velocities, employed for example in transport simulations, significantly affect the calculated radial electric field and therefore the E x B flow shear and hence modify and can significantly improve the simulation predictions. Several fluid turbulence codes have been used to identify the mechanism driving the poloidal velocity to such high values. CUTIE and TRB turbulence codes and also the Weiland model predict the existence of an anomalous poloidal velocity, peaking in the vicinity of the ITB and driven dominantly by the flow due to the Reynold's stress. It is worth noting that these codes and models treat the equilibrium in a simplified way and this affects the geodesic curvature effects and geodesic acoustic modes. The neo-classical equilibrium is calculated more accurately in the GEM code and the simulations suggest that the spin-up of poloidal velocity is a consequence of the plasma profiles steepening when the ITB grows, following in particular the growth of the toroidal velocity within the ITB.
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| 33. |
- Challis, C. D., et al.
(författare)
-
High βN JET H-modes for steady-state application
- 2007
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Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - : European Physical Society. - 9781622763344 ; , s. 2118-2121
-
Konferensbidrag (refereegranskat)
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| 34. |
- de Vries, P. C., et al.
(författare)
-
Effect of toroidal field ripple on the formation of internal transport barriers
- 2008
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 50:6
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of a toroidal field (TF) ripple on the formation and performance of internal transport barriers (ITBs) has been studied in JET. It was found that the TF ripple had a profound effect on the toroidal plasma rotation. An increased TF ripple up to delta = 1% led to a lower rotation and reduced the rotational shear in the region where the ITBs were formed. ITB triggering events were observed in all cases and it is thought that the rotational shear may be less important for this process than, for example, the q-profile. However, the increase in the pressure gradient following the ITB trigger was reduced in discharges with a larger TF ripple and consequently a lower rotational shear. This suggests that toroidal rotation and its shear play a role in the growth of the ITB once it has been triggered.
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| 35. |
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| 36. |
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| 37. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Modeling of resistive wall mode and its control in experiments and ITER
- 2006
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 13:5
-
Tidskriftsartikel (refereegranskat)abstract
- Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut, Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.
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| 38. |
- Mayoral, M. L., et al.
(författare)
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Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak
- 2006
-
Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 46:7, s. S550-S563
-
Tidskriftsartikel (refereegranskat)abstract
- During the initial operation of the International Thermonuclear Experimental Reactor (ITER), it is envisaged that activation will be minimized by using hydrogen (H) plasmas where the reference ion cyclotron resonance frequency (ICRF) heating scenarios rely on minority species such as helium (He-3) or deuterium (D). This paper firstly describes experiments dedicated to the study of He-3 heating in H plasmas with a sequence of discharges in which 5 MW of ICRF power was reliably coupled and the He-3 concentration, controlled in real-time, was varied from below 1% up to 10%. The minority heating (MH) regime was observed at low concentrations (up to 2%). Energetic tails in the He-3 ion distributions were observed with effective temperatures up to 300 keV and bulk electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and bulk electron temperatures up to 8 keV. Secondly, experiments performed to study D minority ion heating in H plasmas are presented. This MH scheme proved much more difficult since modest quantities of carbon
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| 39. |
- Mayoral, M L, et al.
(författare)
-
ICRF heating for the non-activated phase of ITER : From inverted minority to mode conversion regime
- 2005
-
Ingår i: Radio Frequency Power in Plasmas. ; , s. 122-129
-
Konferensbidrag (refereegranskat)abstract
- In the initial phase of ITER H plasmas will be used in order to avoid activating the machine. The reference ICRF heating scenarios rely on minority species such as Helium (3 He) or deuterium (D). These schemes' distinctive feature comes from the presence of the fast magnetosonic wave ion-ion hybrid resonance/cut-off pair, between the antennas and the minority cyclotron layer. In order to document these unusual heating schemes, ICRF experiments were carried out recently on JET. First, the use of He-3 ions in H plasmas was investigated with a sequence of discharges in which 5 MW of ICRF power was coupled to the plasma and the 3 He concentration was varied from below 1% up to 10%. The inverted minority heating regime was observed at low concentrations (up to similar to 2%). Energetic tails in the 3 He distribution were observed with effective temperatures up to 300 keV and central electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and central electron temperature up to 8 keV. All these experiments systematically used power modulation techniques to assess the radial profiles of the wave absorption by the electrons. Secondly, experiments to study the ICRF heating of D minority ions in H were performed. This heating scheme proved much more difficult since modest quantities of C6+ impurity, which has the same Z/A ratio than die D minority ions, led us directly into the mode conversion regime. This effect preventing any absorption by D ions at minority cyclotron layer, could make die (D)H scenario not suitable for the non-active phase of ITER.
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| 40. |
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| 41. |
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| 42. |
- Charrier, D. S. H., et al.
(författare)
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Bimolecular recombination in ambipolar organic field effect transistors
- 2009
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 10:5, s. 994-997
-
Tidskriftsartikel (refereegranskat)abstract
- In ambipolar organic field effect transistors (OFET) the shape of the channel potential is intimately related to the recombination zone width W, and hence to the electron-hole recombination strength. Experimentally, the recombination profile can be assessed by scanning Kelvin probe microscopy (SKPM). However, surface potentials as measured by SKPM are distorted due to spurious capacitive couplings. Here, we present a (de)convolution method with an experimentally calibrated transfer function to reconstruct the actual surface potential from a measured SKPM response and vice versa. Using this scheme, we find W = 0.5 mu m for a nickel dithiolene OFET, which translates into a recombination rate that is two orders of magnitude below the value expected for Langevin recombination. (C) 2009 Elsevier B.V. All rights reserved.
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| 43. |
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| 44. |
- de Vries, P. C., et al.
(författare)
-
Effect of toroidal field ripple on plasma rotation in JET
- 2008
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 48:3
-
Tidskriftsartikel (refereegranskat)abstract
- Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect.
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| 45. |
- Eriksson, L. G., et al.
(författare)
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On ion cyclotron current drive for sawtooth control
- 2006
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 46:10, s. S951-S964
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Tidskriftsartikel (refereegranskat)abstract
- Experiments using ion cyclotron current drive (ICCD) to control sawteeth are presented. In particular, discharges demonstrating shortening of fast ion induced long sawteeth reported in (Eriksson et al 2004 Phys. Rev. Lett. 92 235004) by ICCD have been analysed in detail. Numerical simulations of the ICCD driven currents are shown to be consistent with the experimental observations. They support the hypothesis that an increase in the magnetic shear, due to the driven current, at the surface where the safety factor is unity was the critical factor for the shortening of the sawteeth. In view of the potential utility of ICCD, the mechanisms for the current drive have been further investigated experimentally. This includes the influence of the averaged energy of the resonating ions carrying the current and the spectrum of the launched waves. The results of these experiments are discussed in the light of theoretical considerations.
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| 46. |
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| 47. |
- Lonnroth, J. S., et al.
(författare)
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Effects of ripple-induced ion thermal transport on H-mode plasma performance
- 2007
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 49:3, s. 273-295
-
Tidskriftsartikel (refereegranskat)abstract
- A recent series of dimensionless pedestal identity experiments at JET and JT-60U failed to produce a match in the dimensional pedestal parameters and edge-localized mode (ELM) frequency despite a good match in the main dimensionless plasma parameters. This paper describes the progress made in understanding these experimental results. First, it is investigated whether differences in the magnetohydrodynamic stability of the pedestal, including those potentially arising from the 10% difference in the aspect ratio between the two tokamaks, can explain the results. The potential effects of differences in plasma rotation between the two machines are also examined. Given the result that these mechanisms fail to explain the experimental observations and the fact that JT-60U features considerably stronger toroidal magnetic field ripple than JET, the bulk of the paper, however, discusses the effects of ripple losses. The analysis shows that ripple losses of thermal ions can affect H-mode plasma performance very sensitively. Orbit-following simulations indicate that losses due to diffusive transport give rise to a wide radial distribution of enhanced ion thermal transport, whereas non-diffusive losses have a very edge-localized distribution. In predictive transport simulations with an energy sink term in the continuity equation for the ion pressure representing non-diffusive losses, reduced performance as well as an increase in the ELM
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| 48. |
- Mantsinen, M. J., et al.
(författare)
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Fast ion distributions driven by polychromatic ICRF waves on JET
- 2005
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 47:9, s. 1439-1457
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Tidskriftsartikel (refereegranskat)abstract
- Experiments have been carried out on the JET tokamak to investigate fast He-3 and hydrogen minority ion populations accelerated by ion cyclotron range of frequencies (ICRF) waves launched with multiple frequencies (i.e. up to four frequencies separated by up to approximate to 15%). This 'polychromatic' heating is compared with single-frequency, 'monochromatic', ICRF heating of reference discharges with similar power levels. Information on the fast ion populations is provided by two-dimensional gamma-ray emission tomography and the measurements are compared with numerical modelling. Polychromatic heating with resonances in the plasma centre (R-res approximate to R-0) and on the low magnetic-field side (LFS) (R-res > R-0) is found to produce predominantly high-energy standard trapped ions, while resonances on the high magnetic-field side (R-res < R-0) increase the fraction of high-energy passing ions. Monochromatic heating with a central resonance produces stronger gamma-ray emission with the maximum emission in the midplane close to, and on the LFS of, the resonance, in agreement with the calculated radial distribution of fast ion orbits. Both the fast ion tail temperature and energy content are found to be lower with polychromatic waves. Polychromatic ICRF heating has the advantage of producing smaller-amplitude and shorter-period sawteeth, consistent with a lower fast ion pressure inside the q = 1 surface, and higher ion to electron temperature ratios.
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| 49. |
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| 50. |
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