Retarding field energy analyzers for the ion temperature measurements in the SOL plasmas of the tokamak ISTTOK and the TJ-II stellarator
Measurements of the ion temperature in the plasma boundary of fusion devices typically employs the Retarding Field Analyzer (RFA) that is based on selective rejecting or retarding the plasma ions by a varying braking electric field. Normally, the RFA comprises an input slit and collector electrode with two or more separately biased fine grids placed in front of it. With an assumption of Maxwellian ion distribution, the exponential decay of the RFA collector currentvoltage characteristic is determined by the ion temperature. This contribution describes 1- and 3channels RFAs for the ion temperature measurements in the scrape-off-layer of the tokamak ISTTOK and the TJ-II stellarator. Selected results of the ion temperature measurements on the ISTTOK and the TJ-II are presented. In addition, limitations related to the RFA operation (including the alignment along magnetic field direction and plasma loading) are considered.
Retarding field energy analyzer for the Saskatchewan Torus-Modified plasma boundary.
The retarding field energy analyzer (RFA) is a simple and reliable diagnostic technique to measure the ion temperature in the scrape-off layer and edge of magnetic fusion devices. Design and operation features of a single-sided (facing the ion flow) RFA for ion temperature measurements in the Saskatchewan Torus-Modified (STOR-M) tokamak are described. Its compact size (21 x 15 x 20 mm3) allows RFA measurements without perturbing plasma significantly. Both ion and electron temperature have been measured by RFA in the STOR-M tokamak. A method is proposed to correct the effects of ion flow on the ion temperature using the simultaneously measured Mach number. The measured electron temperature is consistent with the previously reported Langmuir probe data. Abnormal behavior of the RFA has been observed in both ion and electron modes when RFA is inserted deep into the plasma.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)