Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

A. V. Melnikov; M. Ochando; E. Ascasibar; F. Castejon; A. Cappa; L. G. Eliseev; C. Hidalgo; L. I. Krupnik; A. Lopez-Fraguas; M. Liniers; S. E. Lysenko; J. L. De Pablos; S. V. Perfilov; S. E. Sharapov; D. A. Spong; J. A. Jimenez; M. V. Ufimtsev; B. N. Breizman

doi:10.1088/0029-5515/54/12/123002

Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

A. V. Melnikov, M. Ochando, E. Ascasibar, F. Castejon, A. Cappa, L. G. Eliseev, C. Hidalgo, L. I. Krupnik, A. Lopez-Fraguas, M. Liniers, S. E. Lysenko, J. L. De Pablos, S. V. Perfilov, S. E. Sharapov, D. A. Spong, J. A. Jimenez, M. V. Ufimtsev, B. N. Breizman

Plasma Theory and Modeling

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Abstract

Excitation of modes in the Alfvénic frequency range, 30 kHz < f_AE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with variation during discharges has shown strong effects on the mode frequency via both vacuum changes and induced net plasma current. A drastic frequency increase from ∼50 to ∼250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for f_AE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

Original language	English
Article number	123002
Journal	Nuclear Fusion
Volume	54
Issue number	12
DOIs	https://doi.org/10.1088/0029-5515/54/12/123002
State	Published - Dec 1 2014

Funding

Funders	Funder number
Engineering and Physical Sciences Research Council	EP/I501045/1

Keywords

Alfvén modes
rotational transformation
stellarator

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1088/0029-5515/54/12/123002

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Melnikov, A. V., Ochando, M., Ascasibar, E., Castejon, F., Cappa, A., Eliseev, L. G., Hidalgo, C., Krupnik, L. I., Lopez-Fraguas, A., Liniers, M., Lysenko, S. E., De Pablos, J. L., Perfilov, S. V., Sharapov, S. E., Spong, D. A., Jimenez, J. A., Ufimtsev, M. V., & Breizman, B. N. (2014). Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II. Nuclear Fusion, 54(12), Article 123002. https://doi.org/10.1088/0029-5515/54/12/123002

@article{d0a889d7f11c479ab86d2a9ff1b27499,

title = "Effect of magnetic configuration on frequency of NBI-driven Alfv{\'e}n modes in TJ-II",

abstract = "Excitation of modes in the Alfv{\'e}nic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with variation during discharges has shown strong effects on the mode frequency via both vacuum changes and induced net plasma current. A drastic frequency increase from ∼50 to ∼250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfv{\'e}n eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.",

keywords = "Alfv{\'e}n modes, rotational transformation, stellarator",

author = "Melnikov, {A. V.} and M. Ochando and E. Ascasibar and F. Castejon and A. Cappa and Eliseev, {L. G.} and C. Hidalgo and Krupnik, {L. I.} and A. Lopez-Fraguas and M. Liniers and Lysenko, {S. E.} and {De Pablos}, {J. L.} and Perfilov, {S. V.} and Sharapov, {S. E.} and Spong, {D. A.} and Jimenez, {J. A.} and Ufimtsev, {M. V.} and Breizman, {B. N.}",

note = "Publisher Copyright: {\textcopyright} 2014 IAEA, Vienna.",

year = "2014",

month = dec,

day = "1",

doi = "10.1088/0029-5515/54/12/123002",

language = "English",

volume = "54",

journal = "Nuclear Fusion",

issn = "0029-5515",

publisher = "IOP Publishing",

number = "12",

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Melnikov, AV, Ochando, M, Ascasibar, E, Castejon, F, Cappa, A, Eliseev, LG, Hidalgo, C, Krupnik, LI, Lopez-Fraguas, A, Liniers, M, Lysenko, SE, De Pablos, JL, Perfilov, SV, Sharapov, SE, Spong, DA, Jimenez, JA, Ufimtsev, MV & Breizman, BN 2014, 'Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II', Nuclear Fusion, vol. 54, no. 12, 123002. https://doi.org/10.1088/0029-5515/54/12/123002

TY - JOUR

T1 - Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

AU - Melnikov, A. V.

AU - Ochando, M.

AU - Ascasibar, E.

AU - Castejon, F.

AU - Cappa, A.

AU - Eliseev, L. G.

AU - Hidalgo, C.

AU - Krupnik, L. I.

AU - Lopez-Fraguas, A.

AU - Liniers, M.

AU - Lysenko, S. E.

AU - De Pablos, J. L.

AU - Perfilov, S. V.

AU - Sharapov, S. E.

AU - Spong, D. A.

AU - Jimenez, J. A.

AU - Ufimtsev, M. V.

AU - Breizman, B. N.

PY - 2014/12/1

Y1 - 2014/12/1

N2 - Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with variation during discharges has shown strong effects on the mode frequency via both vacuum changes and induced net plasma current. A drastic frequency increase from ∼50 to ∼250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

AB - Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with variation during discharges has shown strong effects on the mode frequency via both vacuum changes and induced net plasma current. A drastic frequency increase from ∼50 to ∼250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

KW - Alfvén modes

KW - rotational transformation

KW - stellarator

UR - http://www.scopus.com/inward/record.url?scp=84914674453&partnerID=8YFLogxK

U2 - 10.1088/0029-5515/54/12/123002

DO - 10.1088/0029-5515/54/12/123002

M3 - Article

AN - SCOPUS:84914674453

SN - 0029-5515

VL - 54

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 12

M1 - 123002

ER -

Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

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