Electron cyclotron emission radiometer upgrade on the DIII-D tokamak

Abstract

The electron cyclotron emission (ECE) heterodyne radiometer diagnostic on DIII-D has been upgraded with the addition of eight channels for a total of 40. The new, higher frequency channels allow measurements of electron temperature into the magnetic axis in discharges at maximum field, 2.15 T. The complete set now extends over the full usable range of second harmonic emission frequencies at 2.0 T, covering radii from the outer edge inward to the location of third harmonic overlap on the high-field side. Full coverage permits the measurement of heat pulses and magnetohydrodynamic fluctuations on both sides of the magnetic axis. In addition, the symmetric measurements are used to fix the location of the magnetic axis in tokamak magnetic equilibrium reconstructions. Also, the new, higher frequency channels have been used to determine central Te with good time resolution in low-field, high-density discharges using third harmonic ECE in the optically gray and optically thick regimes.

Central flattening of the fast-ion profile in reversed-shear DIII-D discharges

“…At the magnetic axis, the peak of the fast-ion distribution function occurs at a pitch of v /v = 0.68, so an appreciable fraction of the fastion distribution can resonate with a TAE at v = v A /3 [9,10]. Figure 3 shows representative electron temperature profiles from Thomson scattering [11] and electron cyclotron emission (ECE) [12] diagnostics, electron density from Thomson scattering and CO 2 interferometry [13], and ion temperature, toroidal rotation, and carbon density profiles from chargeexchange recombination spectroscopy [14]. The dominant impurity is carbon in these discharges and Z eff 1.3.…”

“…The profile of the total plasma pressure p tot is obtained from EFIT [25] reconstructions of the MHD equilibrium that are consistent with the MSE data, with external magnetics data, and with isotherms of the electron temperature as measured by a 40-channel electron cyclotron emission (ECE) [12] radiometer ( figure 1(a)). The thermal pressure p th from the T e , n e , T i and carbon density measurements (figure 3) is subtracted from the MHD pressure profile to obtain the fast-ion pressure profile p f (figure 4) [26,27].…”

Diverse wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit

“…Radial profiles are measured by a 40-channel electron cyclotron emission (ECE) radiometer diagnostic. 13 Toroidal mode numbers are measured by a toroidal array of Mirnov coils at the outer midplane. 14 A database is constructed from 48 discharges acquired during two days of dedicated experiments.…”

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

“…Eigenfunction information is provided by an ECE radiometer that measures electron temperature fluctuationsT e on a radial chord near the midplane, 40 an ECE imaging diagnostic that measuresT e in two rectangular regions, 41 and a beam emission spectroscopy (BES) diagnostic that measures electron density fluctuationsñ e at 64 variable locations. 42 Toroidal mode numbers are inferred from a toroidal array of magnetic coils and from the Doppler shift and temporal evolution of upsweeping RSAEs.…”