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Overview of HSX Experimental Operations
| Author: | Anderson D.T. |
| Coauthor: | A. Abdou, A. Almagri, F.S.B. Anderson, D. Brower, J. Canik, C. Deng, S.P. Gerhardt, W. Guttenfelder, |
| Institution : | University of Wisconsin-Madison |
| Abstract text: | At line-averaged densities of ~1.5 x 1018 m-3 (50 kW injected power) the Thomson scattering measures Te0 ~600 eV. The profile is peaked in agreement with power deposition from ray tracing calculations. Even higher values are observed in lower density QHS discharges and are potentially the result of a large non-thermal tail population, as supported by hard x-ray and electron cyclotron emission measurements. In higher density discharges (~ 2 x 1018 m-3) the ECE is in good agreement with the Thomson system and the kinetic stored energy is in agreement with the diamagnetic loop. Density scans at constant ECH power showed the central Te to be roughly independent of density. The ASTRA code is being used to model the HSX discharges to investigate the role of anomalous transport. The independence of Te0 is suggestive of an anomalous thermal conductivity which scales as 1/n (Alcator-like scaling). Power scaling by varying the ECH power shows that, except at lowest densities, both Te0 and the stored energy scale as the power, also supportive of this model. A 3-D version of the neutral particle DEGAS code has been implemented for HSX in collaboration with ORNL. The code has been used to analyze the signals from the toroidal and poloidal H-a arrays. Diffusion coefficients inferred from the H-a data are of the order 104 cm2/s and in agreement with perturbative calculations/measurements made using a modulated gas feed. Density and power scans show that this anomalous diffusivity is negligibly dependent upon power, but scales as n-0.6. Flows induced with a biased electrode show more flow with less drive in the QHS configuration compared to the mirror-mode and a factor of three reduced damping rate. Evidence of two time scales in the flow evolution has been observed and correlated to directions of symmetry on the magnetic surfaces. |
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