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Counter-Injection Campaign S.M. Kaye et al., 12/15/03

Counter-Injection Campaign S.M. Kaye et al., 12/15/03. Motivation/Background 25% lower L-H power threshold (DIII-D) Quiescent H-modes (AUG, DIII-D, MAST) Reduction in short wavelength mode activity (DIII-D) Transport barrier at large r/a (DIII-D, MAST)

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Counter-Injection Campaign S.M. Kaye et al., 12/15/03

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  1. Counter-Injection CampaignS.M. Kaye et al., 12/15/03 • Motivation/Background • 25% lower L-H power threshold (DIII-D) • Quiescent H-modes (AUG, DIII-D, MAST) • Reduction in short wavelength mode activity (DIII-D) • Transport barrier at large r/a (DIII-D, MAST) • QH-modes obtained during first day of counter injection (MAST) • Little impurity accumulation possible (MAST) • Distant walls? • Potential advantages • Produce quasi-steady target discharges with good confinement • Improved electron confinement • Broad p(r) • Greater stability • Increased bootstrap current fraction 1

  2. There is No Dearth of Physics Topics to Study • Physics Topics • Fast ion confinement – exp’t/modeling comparison • L-H threshold – the effect of fast ion loss in Er generation • Development of quiescent (ELM-free) H-mode targets with good density control (reduced beam source) • Development of ITBs at large r/a coupled with edge barriers • Thermal confinement/local transport/microturbulence differences between co and counter-injection • Effect of rotation, j(r), p(r) differences • Stability properties • ELM suppression/Edge Harmonic Oscillations • Low-n stability • Effect of rotation on low-n and RWM stability • Effect of Bpol­ direction reversal on mode locking • Synergy between HHFW and NBI on direction of NBCD. • RF loading asymmetry – inherent asymmetry in the antenna, or due to B-field geometry? • Characterization of plasma edge (including edge turbulence) 2

  3. Engineering Considerations • For full BT, Ip reversal • Change links and protection systems (1 day) - weekend • ISTP-001 to commission change (1/2 day) • Plasma control system checkout/plasma development (~1 day; procedure being developed) • Some tasks desire BT reversal only • RF asymmetry studies • Diamagnetic loop compensation measurements • Two step process (will have to to engineering/c.s. checks at each step) • Reverse BT, normal Ip • Reverse BT, reverse Ip • Full reversal first then two-step switch back (less run time sacrificed?) 3

  4. Strawman Schedule (~ 3 run weeks) • Weekend – switchover • Mon/Tues – ISTPs, control system checkout, begin OH/NBI operation • Th/Fri – Fast ion confinement (vary beam source, Ip, PNBI) • Transport studies (1-2 days) • Stability studies (1-2 days) • RF studies (1-2 days) • HHFW/NB (htg and cd) compatibility • Boundary physics (1 day) • Switch to normal Ip (1/2 day) • System checkout (~ 1 day) • RF loading asymmetry studies (1 day) • Diamagnetic loop compensation (1/2 day) 4

  5. Schedule (cont’d) • Propose to run counter-campaign in mid-run to take advantage of potential benefits for during remainder of run • If good plasma conditions not achieved within 1 week, may want to switch back • Need to commit one week initially • Devote some time to understand why counter is not working • If good results obtained, extend to 2 (or possibly 3) weeks 5

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