Two-dimensional ion temperature measurement by application of tomographic reconstruction to Doppler spectroscopy

Abstract

A novel 2D ion temperature measurement for toroidal plasmas has been developed by use of cost-effective discrete tomography reconstruction of 2D ion Doppler spectroscopy composed of a polychromator with an ICCD camera and optical fibres. The 2D projection of the line spectrum collected by 35 (7 × 5) optical fibres is transformed into the r-z profile of the local spectrum by means of the Abel inversion at each wavelength and finally into the 2D (r-z) profile of the ion temperature. Numerical tests of its algorithm indicate that the reconstruction error for a peaked temperature profile is smaller than 15% if the chord-integrated signals have noise smaller than 5%. This system successfully measured the peaked ion temperature profile of a torus plasma on the r-z plane under the condition of negligibly small plasma flow.

Recent progress of magnetic reconnection research in the MAST spherical tokamak

“…16 For those laboratory experiments, evidence of plasma acceleration toward the outflow direction was observed as a split line-integrated distribution function in 0D, 17 1D, and 2D bidirectional toroidal acceleration during counter helicity spheromak merging 18,19 and in-plane Mach probe measurement around the X-point with and without the guide field. [20][21][22] In the recent TS-3 experiment, 2D ion and electron heating characteristics were revealed 23,24 as bulk heating of ions downstream and localized electron heating around the X-point. The energy inventory has been investigated in both push merging 3,25 and pull reconnection.…”

“…Tokyo collaboration addressed this issue by the temporary repurposing of an existing collecting lens to provide a 32 chord tomographic ion Doppler spectroscopy capability on the midplane with a radial range spanning the diffusion region. 3,23,39 Here, this paper addresses the recent major progress of detailed profile measurement of both electron and heating using those fine diagnostics during a high field reconnection experiment in MAST. Figure 1 illustrates the geometric setting of the merging/ reconnection experiment in the MAST spherical tokamak (ST).…”

Energy Flux due to Electromagnetic Fluctuations during Guide Field Magnetic Reconnection

“…The ion temperature T i deduced from a neutral line (H β : 486.135 nm) spectrum measured using the IDSP (ion dynamics spectroscopy probe [15]) is 3 -35 eV. Note that this emission line is reasonable for the ion Doppler spectroscopy in this experiment because the collision time between H + and H is much shorter than the reconnection time scale [16]. The ion flow velocity measured by a Mach probe is −30 -40 km/s.…”

Recent Progress in High Resolution 2D Imaging Measurements of Reconnection Heating during Merging Plasma Startup in TS-3

“…However in MAST, due to the absence of in-situ magnetic field measurements during reconnection, investiga-tion of the detailed heating/transport mechanism was not possible. The clear results from 130CH-YAG/300CH-Ruby Thomson scattering [34][35][36][37] and 32CH ion Doppler tomography diagnostics [38,39] provided new insights into magnetic reconnection, fine structure formation such as highly peaked structure around X-point and poloidallyring-like hollow ion temperature profile [33] by the coupling of outflow heating mechanism and toroidal confinement [18], but those processes have not yet been investigated comprehensively due to the absence of proper magnetic diagnostics. Based on the feedback, a recent TS-3 experiment made a further diagnostics upgrade for MASTlike high resolution imaging measurement and has started detailed investigation of guide field reconnection with a guide field ratio similar to that in MAST.…”