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Title: Progress in controlling ICRF-edge interactions in ASDEX upgrade

Abstract

RF measurements during variation of the strap voltage balance of the original 2-strap ICRF antenna in ASDEX Upgrade at constant power are consistent with electromagnetic calculations by HFSS and TOPICA, more so for the latter. RF image current compensation is observed at the antenna limiters in the experiment at a local strap voltage of about half of the value of the remote strap, albeit with a non-negligible uncertainty in phasing. The RF-specific tungsten (W) source at the broad-limiter 2-strap antenna correlates strongly with the RF voltage at the local strap at the locations not connected to opposite side of the antenna along magnetic field lines. The trends of the observed increase of the RF loading with injection of local gas are well described by a combined EMC3-Eirene – FELICE calculations, with the most efficient improvement confirmed for the outer-midplane valves, but underestimated by about 1/3. The corresponding deuterium density tailoring is also likely responsible for the decrease of local W sources observed in the experiment.

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]; ;  [2]; ; ;  [1];  [3]; ;  [4] more »;  [5]; « less
  1. Max-Planck-Institut für Plasmaphysik, Boltzmannstr.2, D-85748 (Germany)
  2. CCFE, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
  3. (Belgium)
  4. CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
  5. Institute of Plasma Physics and Laser Microfusion, Hery 23 Str., 01-497 Warsaw (Poland)
Publication Date:
OSTI Identifier:
22496182
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1689; Journal Issue: 1; Conference: 21. topical conference on radio frequency power in plasmas, Lake Arrowhead, CA (United States), 27-29 Apr 2015; Other Information: (c) 2015 EURATOM; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANTENNAS; ASDEX TOKAMAK; BALANCES; DENSITY; DEUTERIUM; ELECTRIC POTENTIAL; HYPERFINE STRUCTURE; ICR HEATING; IMAGES; INJECTION; ION CYCLOTRON-RESONANCE; MAGNETIC FIELDS; RADIOWAVE RADIATION; TUNGSTEN; VALVES

Citation Formats

Bobkov, Vl., E-mail: bobkov@ipp.mpg.de, Ochoukov, R., Bilato, R., Braun, F., Carralero, D., Dux, R., Faugel, H., Fünfgelder, H., Jacquot, J., Lunt, T., Potzel, S., Pütterich, Th., Jacquet, Ph., Monakhov, I., Zhang, W., Noterdaeme, J.-M., Stepanov, I., Department of Applied Physics, Gent University, 9000 Gent, Colas, L., Meyer, O., Czarnecka, A., and and others. Progress in controlling ICRF-edge interactions in ASDEX upgrade. United States: N. p., 2015. Web. doi:10.1063/1.4936469.
Bobkov, Vl., E-mail: bobkov@ipp.mpg.de, Ochoukov, R., Bilato, R., Braun, F., Carralero, D., Dux, R., Faugel, H., Fünfgelder, H., Jacquot, J., Lunt, T., Potzel, S., Pütterich, Th., Jacquet, Ph., Monakhov, I., Zhang, W., Noterdaeme, J.-M., Stepanov, I., Department of Applied Physics, Gent University, 9000 Gent, Colas, L., Meyer, O., Czarnecka, A., & and others. Progress in controlling ICRF-edge interactions in ASDEX upgrade. United States. doi:10.1063/1.4936469.
Bobkov, Vl., E-mail: bobkov@ipp.mpg.de, Ochoukov, R., Bilato, R., Braun, F., Carralero, D., Dux, R., Faugel, H., Fünfgelder, H., Jacquot, J., Lunt, T., Potzel, S., Pütterich, Th., Jacquet, Ph., Monakhov, I., Zhang, W., Noterdaeme, J.-M., Stepanov, I., Department of Applied Physics, Gent University, 9000 Gent, Colas, L., Meyer, O., Czarnecka, A., and and others. 2015. "Progress in controlling ICRF-edge interactions in ASDEX upgrade". United States. doi:10.1063/1.4936469.
@article{osti_22496182,
title = {Progress in controlling ICRF-edge interactions in ASDEX upgrade},
author = {Bobkov, Vl., E-mail: bobkov@ipp.mpg.de and Ochoukov, R. and Bilato, R. and Braun, F. and Carralero, D. and Dux, R. and Faugel, H. and Fünfgelder, H. and Jacquot, J. and Lunt, T. and Potzel, S. and Pütterich, Th. and Jacquet, Ph. and Monakhov, I. and Zhang, W. and Noterdaeme, J.-M. and Stepanov, I. and Department of Applied Physics, Gent University, 9000 Gent and Colas, L. and Meyer, O. and Czarnecka, A. and and others},
abstractNote = {RF measurements during variation of the strap voltage balance of the original 2-strap ICRF antenna in ASDEX Upgrade at constant power are consistent with electromagnetic calculations by HFSS and TOPICA, more so for the latter. RF image current compensation is observed at the antenna limiters in the experiment at a local strap voltage of about half of the value of the remote strap, albeit with a non-negligible uncertainty in phasing. The RF-specific tungsten (W) source at the broad-limiter 2-strap antenna correlates strongly with the RF voltage at the local strap at the locations not connected to opposite side of the antenna along magnetic field lines. The trends of the observed increase of the RF loading with injection of local gas are well described by a combined EMC3-Eirene – FELICE calculations, with the most efficient improvement confirmed for the outer-midplane valves, but underestimated by about 1/3. The corresponding deuterium density tailoring is also likely responsible for the decrease of local W sources observed in the experiment.},
doi = {10.1063/1.4936469},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1689,
place = {United States},
year = 2015,
month =
}
  • The ICRF system on ASDEX Upgrade is equipped with an arc detector based on the observation of frequencies between 5 and 25 MHz in the RF feeding line [R1]. On some shots, the detector was triggered in an anomalous way: tenths of detections over several hundreds of milliseconds on detectors of all antennas at the same time [R2]. It was suggested that these frequencies were not excited by arcs but came from the plasma. We installed a RF probe inside the vacuum vessel and connected it to a fast acquisition system. We indeed observed frequencies during ICRF heating of severalmore » shots. We present here the features of these frequencies, their possible conditions of existence in terms of plasma and RF parameters (magnetic field, density, temperature, RF frequency, power injected) and we compare the source of these frequencies with known phenomena like ICE, CAE and surface waves.« less
  • Simulations were carried out with the 3D plasma transport code EMC3-EIRENE, to study the deuterium gas (D{sub 2}) puff effects on edge density and the coupling of Ion Cyclotron Range of Frequency (ICRF) power in ASDEX Upgrade. Firstly we simulated an inter-ELM phase of an H-mode discharge with a moderate (1.2 × 10{sup 22} electrons/s) lower divertor gas puff. Then we changed the gas source positions to the mid-plane or top of machine while keeping other conditions the same. Cases with different mid-plane or top gas valves are investigated. Our simulations indicate that compared to lower divertor gas puffing, themore » mid-plane gas puff can enhance the local density in front of the antennas most effectively, while a rather global (toroidally uniform) but significantly smaller enhancement is found for top gas puffing. Our results show quantitative agreement with the experiments.« less
  • A new multichannel frequency modulated continuous-wave reflectometry diagnostic has been successfully installed and commissioned on ASDEX Upgrade to measure the plasma edge electron density profile evolution in front of the Ion Cyclotron Range of Frequencies (ICRF) antenna. The design of the new three-strap ICRF antenna integrates ten pairs (sending and receiving) of microwave reflectometry antennas. The multichannel reflectometer can use three of these to measure the edge electron density profiles up to 2 × 10{sup 19} m{sup −3}, at different poloidal locations, allowing the direct study of the local plasma layers in front of the ICRF antenna. ICRF power coupling,more » operational effects, and poloidal variations of the plasma density profile can be consistently studied for the first time. In this work the diagnostic hardware architecture is described and the obtained density profile measurements were used to track outer radial plasma position and plasma shape.« less
  • The present paper reviews the recent results achieved in the ICRF-DC experiments performed in helium/hydrogen mixtures in the non-circular tokamaks ASDEX Upgrade and JET and first tests of the ICRF discharges in helium/oxygen mixtures in the circular tokamak TEXTOR. Special emphasis was given to study the physics of ICRF discharges. A new recipe for safe and reliable RF plasma production [<ne>{approx}(3-5)x1017 m-3, Te{approx}(3-5) eV] with improved antenna coupling efficiency (by 1.5-3 times) and improved radial/poloidal homogeneity was proposed and successfully tested: coupling the RF power in the FW-IBW mode conversion scenario in plasmas with two ion species. The first resultsmore » on ICRF wall conditioning in helium/hydrogen and in helium/oxygen mixtures are analyzed.« less
  • ICRF has been applied at power levels up to of 4 MW for plasma heating with good results in the L- and H-modes, alone and in combination with NI. Mainly minority heating has been applied so far, in some cases combined with second harmonic. Modulation experiments allowed to determine the power absorption efficiency, deposition profiles and the local heat conduction. The ICRF was also shown to have further interesting and beneficial effects on the plasma: the central impurity concentration of tungsten injected by Laser Blow Off was reduced, and a transiently improved energy confinement at the beginning of the NBImore » pulse was stabilized. The influence of plasma variations on the RF system and methods allowing stable operation, e.g. during the ELMy H-mode, were studied. Coupling measurements were also used to examine SOL characteristics. Experiments comparing antennas with and without Faraday screen show only minor differences of their electrical properties and heating characteristics. {copyright} {ital 1996 American Institute of Physics.}« less