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XP 905: Current Profile Modifications and Fast Ion Loss from BAAEs/EPMs

XP 905: Current Profile Modifications and Fast Ion Loss from BAAEs/EPMs. D. Darrow, et al. April 8, 2009. EPMs. 119624. BAAE/EPM bursts expel NB ions & may redistribute current.

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XP 905: Current Profile Modifications and Fast Ion Loss from BAAEs/EPMs

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  1. XP 905: Current Profile Modifications and Fast Ion Loss from BAAEs/EPMs D. Darrow, et al. April 8, 2009

  2. EPMs 119624 BAAE/EPM bursts expel NB ions & may redistribute current • Bursts are often seen during Ip ramp up, causing neutron drops and possibly contributing to rapid j(r) redistribution • Important for NHTX, VNS, & ITER to quantify j(r) transport due to modes

  3. Frequency chirp Multi-n Mode chirps & has multiple n • Neutron drops & fast ion loss concurrent with multi-n overlap Mirnov coil data Frequency (kHz)

  4. Bursts also seen during Ip flattop—simplest situation to study

  5. Experimental plan-1 • Reload 2008 shot with bursts during flattop: 127393 (alternates: 127383, or 127397) • 900 kA, 0.44 T, 3 beams at 90 kV • Check for presence of bursts

  6. Experimental plan-2 • If no bursts: • Reduce Ip by steps of 100 kA until bursts recur • With bursts present, increase gas puff to increase ne in steps of ≤1x1019 m-3 to reduce mode fast ion drive & increase interval between bursts. Goal: 50 ms between bursts. [2 hour limit on this step] • If 50 ms spacing not attained: • Increase Ip in steps of ≤100 kA until 50 ms spacing attained [2 hour limit on search]

  7. Experimental plan-3 • Work with 50 ms separated bursts, if attained, otherwise measure effect of series of bursts • Document effects of bursts on j(r), fast ion loss

  8. Experimental plan-4 • Document mode numbers, profiles & amplitudes • Reserve 2 hours for: Repeat shots with n=3 braking to get data on mode structure near wrot=0

  9. Key diagnostics • MSE: j(r, t) • Mirnov coils: mode n, freq, & amplitude • FIDA: fNB(E, r, t) • NPA: fNB(E, r, t) • CHERS:wrot(R, t) (for fast ion loss torque) • Neutron detectors: Sn(t) • sFLIP: Gloss(E, c, t) • SXR array: mode structure • FIReTIP: mode structure • Reflectometer: mode structure? (H-mode) • High-k scattering: mode structure info

  10. Analysis emphases • MSE: Focus on effect of single burst or cumulative effect of multiple bursts, depending upon what is obtained; identify amount of current transported to or from each flux surface • Mode profile diagnostics: fit best mode radial profiles and compare with NOVA predictions for BAAE under those conditions; compare also at lowest attainable toroidal rotation: how well do modes match BAAE theory?

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