| 1. |
- Meyer, H., et al.
(författare)
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Overview of physics results from MAST
- 2009
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:10, s. 104017-
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Tidskriftsartikel (refereegranskat)abstract
- Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities P-NBI <= 3.8 MW H-mode at I-P = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I-P and more strongly with B-t than in the ITER IPB98(y, 2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original designed total throughput capacity. The anomalous momentum diffusion, chi(phi), is linked to the ion diffusion, chi(i), with a Prandtl number close to P-phi approximate to chi(phi)/chi(i) approximate to 1, although chi(i) approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, E-r, show that the position of steepest gradients in electron pressure and E-r (i.e. shearing rate) are coincident, but their magnitudes are not linked. The T-e pedestal width on MAST scales with root beta(ped)(pol) rather than rho(pol). The edge localized mode (ELM) frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of four external coils (n = 1, 2). A new internal 12 coil set (n <= 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfven eigenmodes. Fast particle instabilities also affect the off-axis NBI current drive, leading to fast ion diffusion of the order of 0.5 m(2) s(-1) and a reduction in the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a ST generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST.
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| 2. |
- Lloyd, B., et al.
(författare)
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Overview of physics results from MAST
- 2007
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 47:10, s. S658-S667
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Tidskriftsartikel (refereegranskat)abstract
- Substantial advances have been made on the Mega AmpÚre Spherical Tokamak (MAST). The parameter range of the MAST confinement database has been extended and it now also includes pellet-fuelled discharges. Good pellet retention has been observed in H-mode discharges without triggering an ELM or an H/L transition during peripheral ablation of low speed pellets. Co-ordinated studies on MAST and DIII-D demonstrate a strong link between the aspect ratio and the beta scaling of H-mode energy confinement, consistent with that obtained when MAST data were merged with a subset of the ITPA database. Electron and ion ITBs are readily formed and their evolution has been investigated. Electron and ion thermal diffusivities have been reduced to values close to the ion neoclassical level. Error field correction coils have been used to determine the locked mode threshold scaling which is comparable to that in conventional aspect ratio tokamaks. The impact of plasma rotation on sawteeth has been investigated and the results have been well-modelled using the MISHKA-F code. Alfvén cascades have been observed in discharges with reversed magnetic shear. Measurements during off-axis NBCD and heating are consistent with classical fast ion modelling and indicate efficient heating and significant driven current. Central electron Bernstein wave heating has been observed via the O-X-B mode conversion process in special magnetically compressed plasmas. Plasmas with low pedestal collisionality have been established and further insight has been gained into the characteristics of filamentary structures at the plasma edge. Complex behaviour of the divertor power loading during plasma disruptions has been revealed by high resolution infra-red measurements.
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| 3. |
- Salamanca, I., et al.
(författare)
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Spectroscopic monitoring of active galactic nuclei. III. Size of the broad line region in NGC 3227
- 1994
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 282:3, s. 742-752752
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Tidskriftsartikel (refereegranskat)abstract
- For pt.II see ibid., vol.269, no.1-2, p.39-53 (1993). The authors present the results of a five-month monitoring campaign of the active galactic nucleus in NGC 3227. The Hbeta and Halpha emission lines and the optical continuum have been analysed. The optical AGN continuum and the broad-line region (BLR) emission in NGC 3227 appear to vary by about 40% on a timescale of 1.5 month. The levels of the broad-line emission and the 675.0 nm continuum are well correlated, a fact consistent with the assumption that the BLR material is photoionised by the central continuum source. Cross-correlation analyses between the light curves of the 675.0 nm AGN continuum and the BLR H emission indicate that the lag of the BLR emission with respect to the continuum variations is 17plusmn7 days. This result suggests that the BLR clouds that are affected by the changes in the flux of the central ionising source lie about 17 light days away from it
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| 4. |
- Dietrich, M., et al.
(författare)
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Monitoring of active galactic nuclei. IV. The Seyfert 1 galaxy NGC 4593
- 1994
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 284:1, s. 33-4343
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Tidskriftsartikel (refereegranskat)abstract
- Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution Halpha and Hbeta spectra and direct images in the Johnson U, B, V, R and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The Halpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions known so far
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| 5. |
- ERKENS, U, et al.
(författare)
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MONITORING OF ACTIVE GALACTIC NUCLEI .6. THE QUASAR MKN-876
- 1995
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Ingår i: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER VERLAG. - 0004-6361. ; 296:1, s. 90-98
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present the results of a 6 month monitoring campaign of Mkn 876, a low luminosity quasar with M(abs) approximate to -24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line a
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| 6. |
- Erkens, U., et al.
(författare)
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Monitoring of active galactic nuclei. VI. The quasar Mrk 876
- 1995
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 296:1, s. 90-9898
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Tidskriftsartikel (refereegranskat)abstract
- For pt. V see ibid., vol. 285, no. 3, p. 857-67 (1994). We present the results of a 6 month monitoring campaign of Mrk 876, a low luminosity quasar with M absap-24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line and continuum light curves are presented. Mrk 876 showed a decrease of 17% in the continuum over the whole observing period whereas the line flux of Hbeta and Halpha stayed constant. This implies, that the radius of the broad line region is larger than 6 light months. Coadded spectra of Hbeta and Halpha are presented which confirm an extreme asymmetry of the line profiles to the red. With respect to much earlier spectra the line profiles changed considerably
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| 7. |
- Jackson, N., et al.
(författare)
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Monitoring of active galactic nuclei. I. The quasars 1302-102 and 1217+023
- 1992
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 262:1, s. 17-2525
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Tidskriftsartikel (refereegranskat)abstract
- Presents the results of a five-month spectroscopic monitoring campaign of two radio-loud quasars PKS 1217+023 and PKS 1302-102. There is a pronounced lack of variability in 1302-102 apart from a possible small change in the continuum level near the end of the monitoring period, but 1217+023 underwent a 20% continuum decrease in the middle of the campaign. No line variability at all was observed. The co-added data represent two of the best spectra yet obtained of any radio-loud quasar other than 3C 273, and the shape of the Hbeta line and the presence underneath it of other contaminating lines are well determined. The Hbeta broad line in 1302-102 is redshifted by 3 Aring with respect to the narrow line region and there is evidence for a separate broad Hbeta feature on top of the main Hbeta emission in both quasars. This feature is stronger in 1217+023 than in 1302-102
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| 8. |
- Koratkar, A, et al.
(författare)
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The disappearing broad absorption lines and variable emission lines in NGC 3516
- 1996
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Ingår i: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 470:1, s. 378-393
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Seyfert 1 galaxy NGC 3516 was monitored during 1993 February 16-May 13 by IUE every 4 days for the first month, and then every 2 days for 2 months giving a total of 40 observations. This paper gives the initial results from this campaign, (1) The broa
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| 9. |
- Penston, M. V., et al.
(författare)
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The extended narrow line region of NGC 4151. I. Emission line ratios and their implications
- 1990
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 236:1, s. 53-6262
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents the first results from long-slit spectra of the Seyfert galaxy NGC 4151 which give average diagnostic ratios of weak lines in the extended narrow line region (ENLR) of that galaxy and the first direct density measurement in an ENLR. These data confirm that the ENLR is kinematically undisturbed gas in the disc of the galaxy which is illuminated by an ionizing continuum stronger by a factor of 13 than a power law interpolated between observed ultraviolet and X-ray fluxes. Explanations of this apparent excess include a hot thermal continuum, time variations and an anisotropic radiation field. The authors give reasons for favouring anisotropy which might be caused by shadowing by a thick accretion disc or by relativistic beaming. Shadowing by a molecular torus is unlikely, given the absence of an infrared signal from the reradiated flux absorbed by any torus. Anisotropy would have important implications for the bolometric luminosity and nature of active galactic nuclei
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| 10. |
- Stirpe, G. M., et al.
(författare)
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Monitoring of active galactic nuclei. V. The Seyfert 1 galaxy Markarian 279
- 1994
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 285:3, s. 857-867867
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Tidskriftsartikel (refereegranskat)abstract
- For pt. IV see ibid., vol.284, no.1, p.33-43 (1994). Reports on the Lovers of Active Galaxies' (LAG) monitoring of the Seyfert 1 galaxy Markarian 279 from January to June 1990. The source, which was in a very bright state, gradually weakened after the first month of monitoring: the Halpha and Hbeta flux decreased by 20% and 35% respectively, and the continuum under Halpha by 30%. The luminosity-weighted radius of the broad line region (BLR), as derived from the cross-correlation function, is of the order of 10 light days. This result is very uncertain because the features in the light curves are very shallow, but it is unlikely that the radius of the BLR is more than 1 light month. The profile variations of Halpha confirm that the prevailing motions are not radial. The data of the present campaign and those obtained in previous years, when the source was in a much weaker state, show that the red asymmetry of the Balmer lines correlates positively with the broad line flux. This new effect is briefly discussed
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