Diamagnetic double-loop method for a highly sensitive measurement of energy stored in a Stellarator plasma

Abstract

In this article we describe a diamagnetic double-loop method for measurement of the energy stored in a magnetized plasma. Two concentric diamagnetic loops enclose a plasma column. The advantage of this method is the capability to eliminate to a high extent the background magnetic field and the effect of eddy currents in the measurement of relatively small diamagnetic signals. This method was applied to initial plasmas produced in the helical axis stellarator Heliotron J. A stored energy of 0.7 kJ was measured with a resolution of ±0.02 kJ at rippling magnetic field of 1 T in a plasma heated by rf discharges up to 400 kW. This diamagnetic double-loop method improved the signal to noise ratio of the conventional single loop method sixfold. The magnetic diagnostics hardware, experimental results, and an error estimate are presented.

Local and integral disruption forces on the tokamak wall

“…The variation of B 0 2 is often ignored in the disruptions studies, see the discussions and references in [18,19,22,23,25]. This can be justified in many tasks of plasma equilibrium because the so-called diamagnetic effect is always weak in tokamaks and stellarators [46][47][48][49], and small dB 0 has no visible effect on the equilibrium configuration.…”

Diamagnetic measurements and plasma energy in toroidal systems

“…In tokamaks and stellarators the external field can be controlled to some extent [8,9,28], and δB e can be partly determined by this control. In principle, δB e can be measured by using local probes outside the plasma or the diamagnetic double loops [6]. The double loops give also two values of δ gap with different S gap , which could allow one to find δS pl .…”

“…Diamagnetic measurements are a useful tool for determining the plasma stored energy in tokamaks and stellarators [1][2][3][4][5][6][7][8][9]. For interpretation a simple formula is used,…”

Diamagnetic diagnostics of rapid events in the T-15MD tokamak

“…Similar double-loop configurations have been in use in the tokamaks Tore Supra [11], KSTAR [16,19], HL-2A [21], J-TEXT [26], WEST [27] and stellarators Heliotron J [9], U-2M and U-3M [22].…”

“…The standard approach to this task is to arrange supplementary measurements allowing the evaluation of B e . These can be done with either so-called compensation coils [2, 3, 10, 12-15, 17-21, 23-25, 27-29] by-passing the plasma and reacting on t B e ¶ ¶ / only, or a second diamagnetic loop [2,9,11,16,19,21,22,26,27] d2 covering a different area compared to the other one d1.…”