Investigation of impurity transport using laser blow-off technique in the HL-2A Ohmic and ECRH plasmas

Abstract

Impurity transports in two neighboring discharges with and without electron cyclotron resonance heating (ECRH) are studied in the HL-2A tokamak by laser blow-off (LBO) technique. The progression of aluminium ions as the trace impurity is monitored by soft x-ray (SXR) and bolometer detector arrays with good temporal and spatial resolutions. Obvious difference in the time trace of the signal between the Ohmic and ECRH L-mode discharges is observed. Based on the numerical simulation with one-dimensional (1D) impurity transport code STRAHL, the radial profiles of impurity diffusion coefficient D and convective velocity V are obtained for each shot. The result shows that the diffusion coefficient D significantly increases throughout the plasma minor radius for the ECRH case with respect to the Ohmic case, and that the convection velocity V changes from negative (inward) for the Ohmic case to partially positive (outward) for the ECRH case. The result on HL-2A confirms the pump out effect of ECRH on impurity profile as reported on various other devices.

Prospects of X-ray imaging spectrometers for impurity transport: Recent results from the stellarator Wendelstein 7-X (invited)

“…[12][13][14] In the latter experiment, trace amounts of impurities are injected into the plasma and either the temporal or the combined spatio-temporal impurity emission is recorded using several diagnostics, providing impurity decay times [13][14][15] and impurity transport parameters from a comparison with transport code calculations. [16][17][18][19][20][21][22][23][24][25] Compared with other diagnostics, X-ray imaging spectrometers are particularly well suited for impurity transport investigations for several reasons: On the one hand, their high resolution allows precise measurements of the radial electric field, [26][27][28] being a critical parameter in stellarators as its radial profile determines different transport regimes, e.g., ion or electron root confinement. 29,30 On the other hand, the selectivity of imaging spectrometers to a single impurity species in a particular charge state allows for a direct measurement of impurity fluxes and impurity transport parameters, as recently shown for Ar impurities.…”

Argon impurity transport studies at Wendelstein 7-X using x-ray imaging spectrometer measurements

“…A comparison of measured impurity abundances with simulated ones using various transport codes yields estimations on diffusive and convective transport coefficients [9][10][11][12][13][14][15][16][17][18].…”

“…Impurity transport experiments typically consist of injecting impurity species into the plasma and monitoring its temporal and/or radial distribution, using several diagnostics. A comparison of measured impurity abundances with simulated ones using various transport codes yields estimations on diffusive and convective transport coefficients [9][10][11][12][13][14][15][16][17][18]. Alternatively, fluxes and transport coefficients can be derived from the knowledge of total impurity densities, as shown for impurity transport [19,20] and also for electron transport [21], neglecting external sink and source terms.…”

Simulation of helium supersonic molecular beam injection in tokamak plasma*

“…Four kinds of corresponding radiation energy loss densities (all in units of W•m −3 ) are included in this paper and are shown below: [30,31] P…”