Characterization and calibration of the Thomson scattering diagnostic suite for the C-2W field-reversed configuration experiment

International Atomic Energy Agency Nuclear Fusion Nucl. Fusion 58 (2018) 126026 (8pp) https://doi.org/10.1088/1741-4326/aae5df
First experimental measurements of a new fast ion driven micro-burst instability in a field-reversed configuration plasma
B.H. Deng1,a , J.D. Douglass1, T. Roche1, E.V. Belova2, M. Beall1,
M.W. Binderbauer1, R. Clary1, S.A. Dettrick1, H. Gota1 , E. Granstedt1, S. Korepanov1, R.M. Magee1, A. Necas1, M. Onofri1, S. Putvinski1,
A. Smirnov1, Y. Song1, T. Tajima1, M.C. Thompson1, M. Tuszewski1, A.D. Van Drie1, X. Yang1, K. Zhai1, W. Horton3 and The TAE Team1
1 TAE Technologies, Inc., Rancho Santa Margarita, CA, United States of America
2 Princeton Plasma Physics Laboratory, Princeton, NJ, United States of America
3 Institute for Fusion Studies, University of Texas at Austin, Austin, TX, United States of America
E-mail: bhdeng2002@yahoo.com
Received 8 July 2018, revised 19 September 2018 Accepted for publication 3 October 2018 Published 22 October 2018
Abstract
In modern field-reversed configuration (FRC) experiments (Binderbauer et al 2015 Phys. Plasmas 22 056110) at TAE Technologies, classical FRC instabilities are suppressed
by advanced neutral beam injection and edge biasing methods, leading to high plasma confinement and fast ion pressure built-up which is comparable to the bulk plasma pressure. In some of these high performance FRC plasmas, a new macroscopically non-destructive fast ion driven micro-burst instability is observed as periodic small amplitude bursts with frequency down chirping in the diamagnetic drift frequency range, repeating about every 0.1 to 0.5 ms. The occurrence of these micro-bursts and burst-free operation can be controlled by changing the injected neutral beam energy. Major observed characteristics of this new instability are presented. Possible explanation of the phenomenon is suggested.
Keywords: fast ion driven instability, field-reversed configuration, micro-burst, far-infrared laser interferometry, rotational instability, angular momentum, fishbone
(Some figures may appear in colour only in the online journal)
1. Introduction
The field-reversed configuration (FRC) is a magnetic con- finement fusion concept which has the advantages of simple geometry and high beta. In conventional FRC experiments the classical instabilities with the lowest toroidal mode numbers of n = 1 and 2 limit the FRC lifetime to less than 1ms [1]. In recent years advanced FRC experiments are conducted in the C-2 and C-2U machines at TAE Technologies, and the advance- ments achieved have significantly raised the prospect for FRCs to become a realistic magnetic confinement fusion reactor con- cept. In these experiments the classical FRC instabilities are
a Author to whom any correspondence should be addressed.
suppressed by neutral beam injection (NBI) and edge biasing methods to achieve high performance FRC operation regimes with the FRC plasmas sustained by advanced NBI to a lifetime beyond 10ms [2–5]. Both the bulk plasma and fast ions have significantly improved confinement properties, and the fast ion pressure builds up to a level comparable to that of the bulk plasma. In this upgraded high performance FRC plasma sce- nario, previously undocumented plasma physics phenomena emerge, including a new macroscopically non-destructive fast ion driven micro-burst instability which is first observed by the far-infrared (FIR) laser interferometer and later by the bolometer arrays and edge magnetic probes. This paper reports the initial plasma results of this new instability in C-2U FRC plasmas. In section 2 the experimental setup is outlined and
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