Ion temperature, heating and scaling relations at the Extrap-T1 reversed-field pinch

Abstract

Investigations of the temperatures of the in situ impurity ions C 4+ , C 2+ , O 4+ , O 3+ and O 2+ have been performed at the Extrap-T1 reversed-field pinch (RFP) via measurements of the Doppler broadening of emission lines in the near-UV wavelength region. Ion temperatures of the high ionization stages are found to be of the order of the electron temperature.This means that ion heating can be connected with RFP dynamo activity giving rise to the non-Spitzer part of the power input. Power input to the ions of the order of the non-Spitzer part of the total power input is required to explain the high ion temperatures. MHD effects could be responsible for this heating. We present scaling of the observed C 4+ ion temperatures with plasma current I φ , electron density n e , pinch parameter and magnetic fluctuations. We also present an empirical scaling law in which the ion temperature can be expressed as T i ∝ I φ × (I φ /n e ) × 4 . Keeping constant, this gives a constant ion beta poloidal β θ,i = 2µ 0 p /B θ (a) 2 .

Ion heating during reconnection in the Madison Symmetric Torus reversed field pinch

“…As a result, ion heating is often observed to accompany magnetic reconnection in both laboratory and astrophysical plasmas. Ion heating associated with magnetohydrodynamic ͑MHD͒ fluctuation activity and magnetic reconnection has been observed in a number of laboratory experiments-such as in the tokamak, 1 the reversed field pinch ͑RFP͒, [2][3][4][5][6] the spheromak, 7,8 and the spherical tokamak 9,10 -as well as in the solar corona 11,12 and in the Earth's magnetosphere. 13 In many cases, magnetic reconnection and the associated heating occur impulsively in the form of a sudden event following a long quiescent period during which the plasma evolves slowly.…”

Statistical analysis of variations in impurity ion heating at reconnection events in the Madison Symmetric Torus

“…[3][4][5] Ion heating has been observed in laboratory plasmas, including plasma merging experiments, 6 the magnetic reconnection experiment (MRX), 7 and sawtooth crashes in Reversed Field Pinch (RFP) plasmas. [8][9][10][11] One particular RFP experiment in which ion heating has been observed and studied is the Madison Symmetric Torus (MST). 12 MST produces toroidally shaped plasmas with a major radius R!=!1.5!m and minor radius r!=!0.52!m.…”

Spatially Resolved Measurements of Ion Heating during Impulsive Reconnection in the Madison Symmetric Torus

“…Ion heating associated with MHD fluctuation activity and magnetic reconnection is also observed in a number of laboratory experiments. These include magnetic fusion devices such as the tokamak [4], the reversed field pinch (RFP) [5][6][7][8][9], the spheromak [10,11], and the spherical tokamak [12,13], as well as high energy density plasmas [14] and basic plasma experiments designed specifically to study reconnection [15,16]. Magnetic reconnection (and subsequent heating) often occurs in impulsive events, both in nature (e.g., solar flares and magnetospheric substorms) and in laboratory plasmas (e.g., sawtooth crashes in the tokamak [17] and the RFP [18]).…”