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Title: Multimachine data–based prediction of high-frequency sensor signal noise for resistive wall mode control in ITER

Abstract

The high-frequency noise measured by magnetic sensors, at levels above the typical frequency of resistive wall modes, is analyzed across a range of present tokamak devices including DIII-D, JET, MAST, ASDEX Upgrade, JT-60U, and NSTX. A high-pass filter enables identification of the noise component with Gaussian-like statistics that shares certain common characteristics in all devices considered. A conservative prediction is made for ITER plasma operation of the high-frequency noise component of the sensor signals, to be used for resistive wall mode feedback stabilization, based on the multimachine database. The predicted root-mean-square n = 1 (n is the toroidal mode number) noise level is 10 4 to 10 5 G/s for the voltage signal, and 0.1 to 1 G for the perturbed magnetic field signal. The lower cutoff frequency of the Gaussian pickup noise scales linearly with the sampling frequency, with a scaling coefficient of about 0.1. As a result, these basic noise characteristics should be useful for the modeling-based design of the feedback control system for the resistive wall mode in ITER.

Authors:
ORCiD logo [1];  [2];  [3];  [3];  [4];  [3];  [5];  [5];  [6];  [7];  [8]
  1. Culham Science Centre, Abingdon (United Kingdom); Southwest Institute of Physics, Chengdu (China); Chalmers Univ. of Technology, Gothenburg (Sweden)
  2. Columbia Univ., New York, NY (United States)
  3. Culham Science Centre, Abingdon (United Kingdom)
  4. ITER Organization, St. Paul Lez Durance Cedex (France)
  5. Max Planck Inst. for Plasma Physics, Garching (Germany)
  6. Japan Atomic Energy Agency, Ibaraki (Japan)
  7. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  8. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
CCFE, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.; Southwestern Inst Phys, POB 432, Chengdu 610041, Peoples R China.; Chalmers, Dept Earth & Space Sci, SE-41296 Gothenburg, Sweden; Columbia Univ, Dept Appl Phys & Appl Math, New York, NY 10027 USA; .ITER Org, Route Vinon Verdon,CS90046, F-13067 St Paul Les Durance, France; Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany; Japan Atom Energy Agcy, 801-1 Mukouyama, Naka, Ibaraki 3110193, Japan
OSTI Identifier:
1340286
Alternate Identifier(s):
OSTI ID: 1376866
Grant/Contract Number:
AC02-09CH11466; FC02-04ER54698; FG02-99ER54524
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Fusion Science and Technology
Additional Journal Information:
Journal Volume: 70; Journal Issue: 3; Journal ID: ISSN 1536-1055
Publisher:
American Nuclear Society
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; sensor noise; resistive wall mode; diii-d tokamak; feedback stabilization; plasma rotation; active; feedback; external-modes; RMW

Citation Formats

Liu, Yueqiang, Sabbagh, S. A., Chapman, I. T., Gerasimov, S., Gribov, Y., Hender, T. C., Igochine, V., Maraschek, M., Matsunaga, G., Okabayashi, M., and Strait, E. J. Multimachine data–based prediction of high-frequency sensor signal noise for resistive wall mode control in ITER. United States: N. p., 2017. Web. doi:10.13182/fst15-207.
Liu, Yueqiang, Sabbagh, S. A., Chapman, I. T., Gerasimov, S., Gribov, Y., Hender, T. C., Igochine, V., Maraschek, M., Matsunaga, G., Okabayashi, M., & Strait, E. J. Multimachine data–based prediction of high-frequency sensor signal noise for resistive wall mode control in ITER. United States. doi:10.13182/fst15-207.
Liu, Yueqiang, Sabbagh, S. A., Chapman, I. T., Gerasimov, S., Gribov, Y., Hender, T. C., Igochine, V., Maraschek, M., Matsunaga, G., Okabayashi, M., and Strait, E. J. Mon . "Multimachine data–based prediction of high-frequency sensor signal noise for resistive wall mode control in ITER". United States. doi:10.13182/fst15-207. https://www.osti.gov/servlets/purl/1340286.
@article{osti_1340286,
title = {Multimachine data–based prediction of high-frequency sensor signal noise for resistive wall mode control in ITER},
author = {Liu, Yueqiang and Sabbagh, S. A. and Chapman, I. T. and Gerasimov, S. and Gribov, Y. and Hender, T. C. and Igochine, V. and Maraschek, M. and Matsunaga, G. and Okabayashi, M. and Strait, E. J.},
abstractNote = {The high-frequency noise measured by magnetic sensors, at levels above the typical frequency of resistive wall modes, is analyzed across a range of present tokamak devices including DIII-D, JET, MAST, ASDEX Upgrade, JT-60U, and NSTX. A high-pass filter enables identification of the noise component with Gaussian-like statistics that shares certain common characteristics in all devices considered. A conservative prediction is made for ITER plasma operation of the high-frequency noise component of the sensor signals, to be used for resistive wall mode feedback stabilization, based on the multimachine database. The predicted root-mean-square n = 1 (n is the toroidal mode number) noise level is 104 to 105 G/s for the voltage signal, and 0.1 to 1 G for the perturbed magnetic field signal. The lower cutoff frequency of the Gaussian pickup noise scales linearly with the sampling frequency, with a scaling coefficient of about 0.1. As a result, these basic noise characteristics should be useful for the modeling-based design of the feedback control system for the resistive wall mode in ITER.},
doi = {10.13182/fst15-207},
journal = {Fusion Science and Technology},
number = 3,
volume = 70,
place = {United States},
year = {Mon Mar 27 00:00:00 EDT 2017},
month = {Mon Mar 27 00:00:00 EDT 2017}
}

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  • The high frequency noise, above the frequency of typical resistive wall modes, from magnetic pickup coils is analysed across a range of present tokamak devices including DIII-D, JET, MAST, ASDEX Upgrade, JT-60U and NSTX. Application of a high-pass filter enables identification of the noise component with Gaussian-like statistics, that shares certain common characteristics in all devices considered. A conservative prediction is made for ITER plasmas based on the multi-machine database, for the high-frequency noise component of the sensor signals, for the purpose of feedback stabilisation of the resistive wall mode. The predicted root-mean-square n=1 (n is the toroidal mode number)more » noise level is 104 -105Gauss/second for the voltage signal, and 0.1-1Gauss for the perturbed magnetic field signal. The lower cutoff frequency of the Gaussian pickup noise scales linearly with the sampling frequency, with the scaling coefficient of about 0.1. These basic noise characteristics should be useful for the modelling based design of the feedback control system for the resistive wall mode in ITER.« less
  • Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, et al., Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved betweenmore » MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.« less
  • A new model-based dynamic resistive wall mode (RWM) identification and feedback control algorithm has been developed. While the overall RWM structure can be detected by a model-based matched filter in a similar manner to a conventional sensor-based scheme, it is significantly influenced by edge-localized-modes (ELMs). A recent study suggested that such ELM noise might cause the RWM control system to respond in an undesirable way. Thus, an advanced algorithm to discriminate ELMs from RWM has been incorporated into this model-based control scheme, dynamic Kalman filter. Specifically, the DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] resistive vessel wall wasmore » modeled in two ways: picture frame model or eigenmode treatment. Based on the picture frame model, the first real-time, closed-loop test results of the Kalman filter algorithms during DIII-D experimental operation are presented. The Kalman filtering scheme was experimentally confirmed to be effective in discriminating ELMs from RWM. As a result, the actuator coils (I-coils) were rarely excited during ELMs, while retaining the sensitivity to RWM. However, finding an optimized set of operating parameters for the control algorithm requires further analysis and design. Meanwhile, a more advanced Kalman filter based on a more accurate eigenmode model has been developed. According to this eigenmode approach, significant improvement in terms of control performance has been predicted, while maintaining good ELM discrimination.« less
  • One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-{ital n} ideal magnetohydrodynamic instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Previous experiments have demonstrated that plasmas with a nearby conducting wall can remain stable to the n=1 ideal external kink above the beta limit predicted with the wall at infinity. Recently, extension of the wall stabilized lifetime {tau}{sub L} to more than 30 times the resistive wall timemore » constant {tau}{sub w} and detailed, reproducible observation of the n=1 RWM have been possible in DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159] plasmas above the no-wall beta limit. The DIII-D measurements confirm characteristics common to several RWM theories. The mode is destabilized as the plasma rotation at the q=3 surface decreases below a critical frequency of 1{endash}7 kHz ({approximately}1{percent} of the toroidal Alfv{acute e}n frequency). The measured mode growth times of 2{endash}8 ms agree with measurements and numerical calculations of the dominant DIII-D vessel eigenmode time constant {tau}{sub w}. From its onset, the RWM has little or no toroidal rotation ({omega}{sub mode}{le}{tau}{sub w}{sup {minus}1}{lt}{omega}{sub plasma}), and rapidly reduces the plasma rotation to zero. These slowly growing RWMs can in principle be destabilized using external coils controlled by a feedback loop. In this paper, the encouraging results from the first open loop experimental tests of active control of the RWM, conducted in DIII-D, are reported. {copyright} {ital 1999 American Institute of Physics.}« less