Density profile sensitivity study of ASDEX Upgrade ICRF Antennas with the TOPICA code

Abstract

Abstract. During operation of the ASDEX Upgrade (AUG) ion cyclotron radio frequency (ICRF) system, Tungsten (W)-coated poloidal limiters and structures connected along magnetic field lines to the antenna can be sources of W, which is attributed to sputtering by ions accelerated in radio frequency (RF) sheaths. In order to analyze and optimize the ICRF antenna performance, accurate and efficient simulation tools are necessary. TOPICA code was developed for analysis of ICRF antenna systems with plasma loading conditions modeled with 1D FELICE code. This paper presents an initial comparative analysis of two AUG ICRF antennas for a set of model plasma density profiles (with varying density gradient and antenna cut-off distance). The antennas are presently installed in AUG and differ in that one was partially optimized using HFSS code to reduce E // near fields. Power transferred to plasma and sheath driving RF potentials are computed.

A detailed comparison of antenna impedance measurements on ASDEX Upgrade with the ion cyclotron range of frequencies antenna code TOPICA

“…TOPICA meas meas (7) is 2.9% for the upper line and 1.4% for the lower line. It can also be seen that there is a relatively large (but roughly constant) difference in the phase of the reflection coefficient between the simulated and measured results, i.e.…”

“…The directional couplers and V max probes 7 , which are located near the estimated position of the voltage maximum on each line, constitute the standard diagnostics, from which the loading resistance is normally computed via the definition [14…”

“…In recent years, TOPICA has been extensively tested against experimental results obtained on Alcator C-Mod [1], Tore Supra [3], DIII-D [4], JET [5] and ASDEX Upgrade [6]. It is not straightforward to directly compare the results of these studies, since they differ in the quantities being compared: coupling resistance per unit length in Tore Supra, effective conductance in JET, complex voltage reflection coefficient in Alcator C-Mod and loading resistance in DIII-D; in the case of ASDEX Upgrade, a voltage reflection coefficient measured behind the matching network was used (in addition, two other studies investigated the performance of both the baseline and the wide limiter antenna in ASDEX Upgrade in terms of coupling and radiofrequency (RF) potentials, namely [7] and [8], but no comparisons with the experiment are quoted). The agreement with experimental data has usually been rather good.…”

“…One of the state-of-the art codes used to evaluate the ITER antenna performance is TOPICA (TOrino POlytechnic Ion Cyclotron Antenna), which handles an arbitrarily shaped three-dimensional antenna model [1], facing a hot, multispecies plasma in slab geometry described by a modified version of the FELICE (Finite ELement Ion Cyclotron Emulator) code, which includes finite Larmor radius (FLR) effects up to second order in the ratio of the ion Larmor radius to the typical perpendicular wavelength [2]. In recent years, TOPICA has been extensively tested against experimental results obtained on Alcator C-Mod [1], Tore Supra [3], DIII-D [4], JET [5] and ASDEX Upgrade [6]; it is not straightforward to directly compare the results of these studies, since they differ in the quantities being compared: coupling resistance per unit length in Tore Supra, effective conductance in JET, complex voltage reflection coefficient in Alcator C-Mod, loading resistance in DIII-D; in the case of ASDEX Upgrade, a voltage reflection coefficient measured behind the matching network was used (in addition two other studies investigated the performance of both the baseline and the wide limiter antenna at ASDEX Upgrade in terms of coupling and RF potentials, namely [7] and [8], but no comparisons with experiment are quoted). The agreement with experimental data has usually been rather good.…”