Ion heating and magnetohydrodynamic dynamo fluctuations in the reversed-field pinch

Abstract

Ion temperatures have been measured in the Madison Symmetric Torus (MST) [Dexter et aL, Fusion Technol. 19, 131 ( 199 1 j] reversed-field pinch (RFP) with a five channel charge exchange analyzer. The characteristic anomalously high ion temperature of RFP discharges has been observed in the MST. The ion heating expected from ion-electron collisions is calculated and shown to be too small to explain the measured ion temperatures. The charge exchange determined ion temperature is also compared to measurements of the thermally broadened CV 227.1 nm line. The ion temperature, Ti~250 eV for 1=360 kA, increases by more than 100% during discrete dynamo bursts in MST discharges. Magnetic field fluctuations in the range OS-5 MHz were also measurd during the dynamo bursts. Structure in the fluctuation frequency spectrum at the ion cyclotron frequency suggests that the mechanism of ion heating involves the dissipation of dynamo fluctuations at ion cyclotron frequencies.

Local Measurement of Nonclassical Ion Heating during Magnetic Reconnection

“…In the Earth's magnetosphere, reconnection is believed to occur in the day-side magnetopause and in the magnetotail, where charged particles can be accelerated along field lines toward the polar regions, giving rise to the aurora [5]. In laboratory plasmas such as reverse-field pinches, enhanced ion heating has been seen to correlate with magnetic fluctuations associated with reconnection and dynamo activity [6].…”

Fast magnetic reconnection with anomalous ion heating and its application

“…caused by those reconnections and their mode cascades up to ion-gyromode number causes the anomalous ion heating [15]. Stenzel performed a famous laboratory experiment of magnetic reconnection using a discharge current between electrodes as a current-sheet.…”

Reversed-field pinch studies in the Madison Symmetric Torus

“…We have measured proton heating in MST with a five-channel charge-exchange analyzer (CXA) [26], and CV ion heating with a VUV spectrometer, both with fast time resolution (10 #s), and have found that the ion temperature exhibits rapid increases during discrete dynamo bursts [9,10] (Fig. 4) which are also periods of increased magnetic activity.…”

“…The Ohmic power input in the RFP is increased over that of a tokamak due to geometric effects and the dynamo [2,3,4,5], which may also supply the extra power drawn directly by ions in 'anomalous' heating [6,7,8,9,10]. As a result, an RFP " reactor may reach ignition with only Ohmic power input [11,12].…”