| 111. |
- Hellesen, Carl, 1980-, et al.
(author)
-
Measurements of fast ions and their interactions with MHD activity using neutron emission spectroscopy
- 2010
-
In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:8, s. 084006-
-
Journal article (peer-reviewed)abstract
- Ion cyclotron radio frequency (ICRF) heating can produce fast ion populations with energies reaching up to several megaelectronvolts. Here, we present unique measurements of fast ion distributions from an experiment with 3rd harmonic ICRF heating on deuterium beams using neutron emission spectroscopy (NES). From the experiment, very high DD neutron rates were observed, using only modest external heating powers. This was attributed to acceleration of deuterium beam ions to energies up to about 2-3 MeV, where the DD reactivity is on a par with that of the DT reaction. The high neutron rates allowed for observations of changes in the fast deuterium energy distribution on a time scale of 50 ms. Clear correlations were seen between fast deuterium ions in different energy ranges and magnetohydrodynamic activities, such as monster sawteeth and toroidal Alfven eigen modes (TAE). Specifically, NES data showed that the number of deuterons in the region between 1 and 1.5 MeV were decaying significantly during strong TAE activity, while ions with lower energies around 500 keV were not affected. This was attributed to resonances with the TAE modes.
|
|
| 112. |
- Kiptily, V., et al.
(author)
-
Doppler broadening of gamma ray lines and fast ion distribution in JET plasmas
- 2010
-
In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:8, s. 084001-
-
Journal article (peer-reviewed)abstract
- The Doppler broadening of individual γ-ray lines was measured with a high purity germanium detector in JET plasma experiments. High-resolution γ-ray spectrometry of nuclear reactions between energetic D, 3 He and 4 He ions accelerated by ion cyclotron resonance heating and main plasma impurities such as carbon and beryllium has been used. The nuclear reactions giving rise to γ-rays have been identified and an effective temperature of the heated ions has been obtained in JET discharges. This technique could be used for fast ion and fusion alpha-particle studies in ITER.
|
|
| 113. |
- Muraro, A., et al.
(author)
-
Neutron radiography as a non-destructive method for diagnosing neutron converters for advanced thermal neutron detectors
- 2016
-
In: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 11:C03033
-
Journal article (peer-reviewed)abstract
- Due to the well-known problem of He-3 shortage, a series of different thermal neutron detectors alternative to helium tubes are being developed, with the goal to find valid candidates for detection systems for the future spallation neutron sources such as the European Spallation Source (ESS). A possible He-3-free detector candidate is a charged particle detector equipped with a three dimensional neutron converter cathode (3D-C). The 3D-C currently under development is composed by a series of alumina (Al2O3) lamellas coated by 1 mu m of B-10 enriched boron carbide (B4C). In order to obtain a good characterization in terms of detector efficiency and uniformity it is crucial to know the thickness, the uniformity and the atomic composition of the B4C neutron converter coating. In this work a non-destructive technique for the characterization of the lamellas that will compose the 3D-C was performed using neutron radiography. The results of these measurements show that the lamellas that will be used have coating uniformity suitable for detector applications. This technique (compared with SEM, EDX, ERDA, XPS) has the advantage of being global (i.e. non point-like) and non-destructive, thus it is suitable as a check method for mass production of the 3D-C elements.
|
|
| 114. |
- Nocente, M, et al.
(author)
-
Calculated neutron emission spectrum with knock-on effects for RF heated (He-3)D plasmas
- 2011
-
In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 51:6, s. 063011-
-
Journal article (peer-reviewed)abstract
- The neutron emission from (He-3)D plasmas with RF heating is calculated using a model that includes supra-thermal (knock-on) components of the deuteron population. The RF generation of fast He-3 ions is described and the knock-on components were determined with the help of newly derived He-3 + d scattering cross sections. Results are presented on the neutron emission spectrum and its contributions from different deuteron velocity components. It is shown that knock-on leaves an observable feature in the spectrum with a clear dependence on absorbed RF power. The importance of the nuclear interaction in the elastic cross section is demonstrated. The results represent a step forward in the use of neutron emission spectroscopy to diagnose fusion plasmas with minority supra-thermal components in their fuel ion composition.
|
|
| 115. |
- Nocente, M., et al.
(author)
-
Cross section of the d + He-3 -> alpha plus p reaction of relevance for fusion plasma applications
- 2010
-
In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:5, s. 055001-
-
Journal article (peer-reviewed)abstract
- The cross section of the d + He-3 -> alpha + p fusion reaction has been determined with regard to its systematic variation with energy (E-CM) based on the available experimental data. Information is provided on the angular distribution d sigma/d Omega (theta(p), E) at energies up to E-CM = 8.0 MeV and the total cross section sigma(E-CM) for the range E-CM = 3.0-8.0 MeV. The relevance of the presented results for fusion plasmas heated with RF heating of He-3 minority in D and DT plasmas is discussed.
|
|
| 116. |
- Nocente, M, et al.
(author)
-
Reaction analysis of neutron emission from D and DT plasmas with/without 3 He
- 2013
-
In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:5
-
Journal article (peer-reviewed)abstract
- The effects of nuclear elastic scattering (knock-on) from energetic light ions on the neutron emission spectrum in fusion plasmas are studied. The knock-on spectral features in D and DT plasmas without and with radio frequency heating on a 3 He minority component are determined through Monte Carlo simulations. The neutron production magnitudes are determined relative to those due to fuel ions in the thermal bulk state (down to the level of 10 −5 ), and the interference of higher order terms in the outlying spectral regions where these dominate is evaluated. The study completes the mapping of nuclear reaction and elastic scattering effects on the neutron emission spectrum including first-, second- and third-order processes. Included are the cross-couplings between dd and dt fusion reactions as manifested in the full neutron spectrum ( E n = 0–20 MeV) for DT plasmas of varying isotopic composition. This study determines the relationship between components of the neutron emission spectra and those of the underlying ion velocity distributions, which provides a general basis for judging the plasma diagnostic information that can potentially be extracted from measurement and analysis of such neutron data.
|
|
| 117. |
- Ognissanto, F., et al.
(author)
-
Line integration effects on ion temperatures in tokamak plasmas measured with neutron emission spectroscopy
- 2008
-
In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:10, s. 10E511-
-
Journal article (peer-reviewed)abstract
- The line integrated line emission measured by neutron spectrometers at JET along sight lines in the vertical and horizontal planes has been simulated in Monte Carlo calculations to determine the relationship between the measured (effective) ion temperature (T-eff) relative to the peak value of the profile (T-0). The general sight line dependence of (T-eff) was expressed analytically for circular plasmas which was used to explain the simulated results for the actual JET sight lines. The analytical model with parametrization of sight lines and plasma profiles is described and the results are used to discuss dual sight line measurements that can be tested at JET and its forward implications for study burning (nearly thermal) plasmas of ITER.
|
|
| 118. |
- Ognissanto, F, et al.
(author)
-
The elastic He-3+d cross section of relevance for knock-on effects in radio frequency heated (He-3)D plasmas
- 2011
-
In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 269:8, s. 786-792
-
Journal article (peer-reviewed)abstract
- The cross section for d+He-3 elastic scattering has been determined for the angular range 20-180 degrees (CM) for beam energies E-d = 0.05 to 11 MeV through combined use of experimental data, Coulomb scattering and extrapolations. The results are used to study, for instance, how the cross section is affected by nuclear interaction contributions. Implications of these results on the calculation of knock on effects in (He-3)D plasmas subjected to RF heating and their manifestations in the spectrum of the d + d fusion neutron emission are discussed.
|
|
| 119. |
- Sjöstrand, Henrik, et al.
(author)
-
Fusion Power Measurement using a Combined Neutron Spectrometer-Camera System at JET
- 2010
-
In: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 57:2, s. 162-175
-
Journal article (peer-reviewed)abstract
- Fusion power production is the ultimate goal of fusion research, and its determination is crucial in any fusion energy application. In this paper the principles of collimated neutron flux measurements for fusion plasma power determination are described. In this method, a high-resolution neutron spectrometer provides an absolutely calibrated neutron flux, and a neutron profile monitor ("camera") gives information on the neutron emission profile of the plasma. The total neutron flux seen by the spectrometer is discussed in terms of direct and scattered flux, and a model is set up to evaluate the magnitude of these different components. Particular care is taken to estimate the uncertainties involved, both in the model and the measurements. The method is put to practical use at JET, where a magnetic proton recoil spectrometer and a neutron profile monitor are available. Results from JET's trace tritium experimental campaign in 2003 are presented and show that the systematic uncertainties in fusion power measurements are reduced in comparison to what has been presented for foil activation systems. A systematic error of 6% is reported here. For ITER these results imply that the fusion power can be redundantly measured and with better accuracies than for traditional methods.
|
|
| 120. |
|
|
