Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode

doi:10.1088/1674-1056/25/10/105204

Abstract Alfvénic gap eigenmode (AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this eigenmode, due to easy diagnostic access and simple geometry, and the idea is to arrange a periodic array of magnetic mirrors along the plasma cylinder and introduce a local defect to break the field periodicity. The present work validates this idea by reproducing a clear AGE inside a spectral gap, and more importantly details the influence of the number and depth (or modulation factor) of magnetic mirror on the characteristics of AGE. Results show that AGE is suppressed by other modes inside the spectral gap when the number of magnetic mirrors is below a certain value, which leads to a weakened Bragg's effect. The structure and frequency of AGE remain unchanged for a decreased number of magnetic mirrors, as long as this number is enough for the AGE formation. The width of spectral gap and decay constant (inverse of decay length) of AGE are linearly proportional to the depth of magnetic mirror, implying easier observation of AGE through a bigger mirror depth. The frequency of AGE shifts to a lower range with the depth increased, possibly due to the unfrozen plasma with field line and the invalidity of small-perturbation analysis. Nevertheless, it is exciting to find that the depth of field modulation can be increased to form AGE for a very limited number of magnetic mirrors. This is of particular interest for the experimental implementation of AGE on a low-temperature plasma cylinder with limited length.

Keywords: Alfvénic gap eigenmode magnetic mirror Bragg's effect

Received: 26 March 2016
Revised: 18 May 2016
Accepted manuscript online:

PACS:	52.35.Bj	(Magnetohydrodynamic waves (e.g., Alfven waves))
	52.55.Jd	(Magnetic mirrors, gas dynamic traps)
	52.25.Xz	(Magnetized plasmas)

Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 11405271, 11372104, 75121543, 11332013, 11372363, and 11502037).

Corresponding Authors: Lei Chang
E-mail: leichang_plasma@163.com

Cite this article:

Lei Chang(苌磊), Ning Hu(胡宁), Jianyao Yao(姚建尧) Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode 2016 Chin. Phys. B 25 105204

[1]	Heidbrink W W 2008 Phys. Plasmas 15 055501
[2]	Duong H H, Heidbrink W W, Strait E J, Petrie T W, Lee R, Moyer R A and Watkins J G 1993 Nucl. Fusion 33 749
[3]	White R B, Fredrickson E, Darrow D, Zarnstorff M, Wilson R, Zweben S, Hill K, Chen Y and Fu G 1995 Phys. Plasmas 2 2871
[4]	Cheng C Z, Chen L and Chance M S 1985 Ann. Phys. 161 21
[5]	Zhang Y, Heidbrink W W, Boehmer H, McWilliams R, Chen G, Breizman B N, Vincena S, Carter T, Leneman D, Gekelman W, Pribyl P and Brugman B 2008 Phys. Plasmas 15 012103
[6]	Chang L, Breizman B N and Hole M J 2013 Plasma Phys. Control. Fusion 55 025003
[7]	Chang L 2014 “The impact of magnetic geometry on wave modes in cylindrical plasmas”, Ph. D. Dissertation (Canberra: The Australian National University) (in English)
[8]	Ginzburg V L 1970 The propagation of electromagnetic waves in plasmas, 2nd edn. (Oxford: Pergamon Press) p. 19
[9]	Breizman B N and Arefiev A V 2000 Phys. Rev. Lett. 84 3863
[10]	Chen G, Arefiev A V, Bengtson R D, et al. 2006 Phys. Plasmas 13 123507

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Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode

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