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XP615: Active Stabilization of the Resistive Wall Mode at Low Aspect Ratio

XP615: Active Stabilization of the Resistive Wall Mode at Low Aspect Ratio. Goals (Part I): Operate new RWM feedback system on 0.9–1.0 MA DND target All aspects of RWM control system / RWM sensors worked well. Good target plasmas with wide n=1 free window; high b N up to 6.

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XP615: Active Stabilization of the Resistive Wall Mode at Low Aspect Ratio

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  1. XP615: Active Stabilization of the Resistive Wall Mode at Low Aspect Ratio • Goals (Part I): • Operate new RWM feedback system on 0.9–1.0 MA DND target • All aspects of RWM control system / RWM sensors worked well. • Good target plasmas with wide n=1 free window; high bN up to 6. • Both locked/rotating RFA/RWM were observed/tracked by feedback. • Vary RWM feedback phase/gain to show control system influence • Ip = 1.0 MA target showed “best” phase <~ 270o • Ip = 0.9 MA target more conclusive / finer scan; best phase = 225o • “Best” phase depends on whether mode is rotating or not • Reduce plasma rotation with n = 3 braking to excite RWM if needed • RFA observed / RWM excited without braking in most cases • Ip = 0.9 MA target with phase = 250o, 225o required braking to excite mode

  2. Setting RWM feedback relative phase in the range ~ 250osuperior for longer pulse, higher bN vs. ~ 0o • Phase scan • Varied through 360o, finer scan in 270o range; 225o appears to be “best” • n = 3 braking required to generate RWM when phase set to most favorable settings b collapse (250o) bN = 6 b collapse (290o) bN = 4.9 Feedback on dBp(n=1) (T) b collapse (0o) bN = 4.7

  3. Generated relatively low rotation plasmas at high bN ~ 5.7 20 No n=1 rotating mode n=1 feedback (270o phase) bN = 5.7 10 Wf (kHz) 119758 0 40 t = 0.5 – 0.65s 30 n=3 DC (0.8kA) applied field n=1 rotating mode onset 20 Wf (kHz) 10 119674 0 1.0 1.2 1.4 1.6 R(m)

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