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Title	173: Confinement and fast ion diffusion in high betaN, steady-state scenario discharges
Name:	John Ferron ferron@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Steady State Heating and Current Drive	Presentation time:	Not requested
Co-Author(s):		ITPA Joint Experiment :	No
Description:	Produce dedicated discharges for a study of confinement in steady-state scenario discharges at high betaN. Obtain discharges where an optimized comparison of predicted and measured fast ion density profiles can be made. Optimize the discharges for all of the fast ion diagnostics including FIDA and the fast ion loss detectors. Compare losses from on-axis and off-axis beams. Also produce discharges optimized for obtaining fluctuation data for understanding of thermal transport. Do a scan of q_min. Look at confinement during the scan, and the scaling of the ratio of the transport code stored energy to the EFIT stored energy. Look for systematic discrepancies in measurements of the thermal stored energy. Correlate confinement to fluctuation levels for fast ion driven instabilities. Look for parameter regimes where fast ion losses can be minimized while still operating at high q_min >2. Coordinate this experiment with other experiments to measure the NBCD profile at high betaN.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	See the "Description" paragraph.
Background:	Analysis of the high betaN steady-state scenario discharges requires calculation of the noninductive current density profiles from models. In order to calculate the neutral beam current density profile, the beam deposition profile must be calculated and this calculated profile must be assumed to be correct. However, typically if the measured thermal pressure and the calculated fast ion pressure profiles are summed, the on-axis pressure and the total stored energy are inconsistent with equilibrium reconstructions using EFIT with magnetics and MSE data. It is necessary to assume an anomalous fast ion diffusion profile in order to obtain agreement. It is highly desirable to evaluate whether this technique of using an anomalous diffusion profile actually produces fast ion density profiles from the model that match the experiment. Otherwise, analysis of the steady-state scenario discharges and calculation of the noninductive current fraction involves significant uncertainty because the total neutral beam driven current is not well known. The problem is particularly significant at high betaN. In addition, at q_min >2 in discharges with off-axis neutral beam injection, global confinement seems to be reduced as a result of enhanced fast ion transport while thermal confinement seems to be at expected H-mode levels. We need to understand the scaling of thermal and fast ion confinement in these discharges and where there are parameter regimes where good confinement is present so that high betaN can be achieved with the available neutral beam power.
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