Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements

We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D-alpha (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble the original fast-ion velocity distribution functions but nevertheless show their coarsest features. For CTS or FIDA systems with many simultaneous views on the same measurement volume, the resemblance improves with the number of available views, even if the resolution in each view is varied inversely proportional to the number of views, so that the total number of measurements in all views is the same. With a realistic four-view system, tomographies of a beam ion velocity distribution function at ASDEX Upgrade reproduce the general shape of the function and the location of the maxima at full and half injection energy of the beam ions. By applying our method to real many-view CTS or FIDA measurements, one could determine tomographies of 2D fast-ion velocity distribution functions experimentally

Combination of fast-ion diagnostics in velocity-space tomographies:Paper

Fast-ion Dα (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fastion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods

Radiation in impurity-seeded discharges in the JET MkI, MkIIA and MkIIGB divertors

Radiative cooling by seeded impurities is a way to reduce the power load on divertor targets. Impurity-seeding experiments carried out in the JET MkI, MkIIA and MkIIGB divertors are discussed, in particular in terms of their radiative properties. A reassessment of the radiation levels in about 235 discharges, seeded predominantly with nitrogen or neon, leads to the conclusion that radiation levels have been underestimated in some impurity-seeded plasmas in MkI and MkIIA. Apart from increased radiation levels, the consequences of the reassessment for the interpretation of impurity-seeded plasmas are limited. With the new estimates the understanding of the power balance and the fit to Matthews' scaling law for Z(eff) are improved. The techniques for improved estimates of the total radiated power and radiated power in the divertor region are discussed and it is shown that weighted summation of bolometer line integrals is unreliable for impurity-seeded discharges in JET. (C) 2003 J. Pamela. Published by Elsevier Science B.V. All rights reserved

Radiation in impurity-seeded discharges in the JET MkI, MkIIA and MkIIGB divertors

Radiative cooling by seeded impurities is a way to reduce the power load on divertor targets. Impurity-seeding experiments carried out in the JET MkI, MkIIA and MkIIGB divertors are discussed, in particular in terms of their radiative properties. A reassessment of the radiation levels in about 235 discharges, seeded predominantly with nitrogen or neon, leads to the conclusion that radiation levels have been underestimated in some impurity-seeded plasmas in MkI and MkIIA. Apart from increased radiation levels, the consequences of the reassessment for the interpretation of impurity-seeded plasmas are limited. With the new estimates the understanding of the power balance and the fit to Matthews' scaling law for Z(eff) are improved. The techniques for improved estimates of the total radiated power and radiated power in the divertor region are discussed and it is shown that weighted summation of bolometer line integrals is unreliable for impurity-seeded discharges in JET. (C) 2003 J. Pamela. Published by Elsevier Science B.V. All rights reserved