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Solenoid-free Plasma Start-up in NSTX using Transient CHI

Office of Science. Supported by. Solenoid-free Plasma Start-up in NSTX using Transient CHI. College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL

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Solenoid-free Plasma Start-up in NSTX using Transient CHI

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  1. Office of Science Supported by Solenoid-free Plasma Start-up in NSTX using Transient CHI College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec R. Raman1, T.R. Jarboe1, B.A. Nelson1, M.G. Bell2, D.Mueller2, R. Maqueda3 , R. Kaita2, B. LeBlanc2, J. Menard2, T. Bigelow4, M. Nagata5, S. Sabbagh6, M.J. Schaffer7, V. Soukhanowskii8, H.R. Wilson2 and the NSTX Research Team 1University of Washington, Seattle, WA, USA 2Princeton Plasma Physics Lab., Princeton, NJ,USA 3Nova Photonics, USA 4Oak Ridge National Laboratory, Oak Ridge, TN, USA 5University of Hyogo, Japan 6Columbia University, New York, NY, USA 7General Atomics, San Diego, CA, USA 8Lawrence Livermore National Laboratory, Livermore, CA, USA NSTX Results Review PPPL, Princeton, NJ, 12-13 December, 2005 Work supported by DOE contract numbers DE-FG02-99ER54519 AM08, DE-FG03-96ER54361 Raman, Dec05

  2. Solenoid-free plasma startup is essential for the viability of the ST concept • Elimination of the central solenoid simplifies the engineering design of tokamaks (Re: ARIES AT & RS) • CHI is capable of both plasma start-up and edge current in a pre-established diverted discharge - Edge current profile for high beta discharges Raman, Dec05

  3. Implementation of Transient CHI Expect axisymmetric reconnection at the injector to result in formation of closed flux surfaces Raman, Dec05 Fast camera: R. Maqueda

  4. Improved pre-ionization to a level that results in injected gas amount similar to that used for pre-fill for inductive plasmas • Novel pre-ionization system • 10x reduced gas injection than in 2004 • Fast Crowbar system • 50mF, 1.5kV capacitor bank • 15mF used in experiments EC-Pi glow along the center stack Shot 116565 1.4 Torr.L gas injection EC-Pi glow in gap between divertor plates. No voltage is applied. Divertor gap Shot 116570 0.7 Torr.L gas injection Raman, Dec05

  5. 6 ms 8 ms 10 ms 12 ms 15 ms 17 ms Closed flux current generation by Transient CHI • Plasma current amplified many times over the injected current. • Camera images at 12 to 17ms shows clear detachment of plasma from injector region Hiroshima University (N. Nishino) Camera Images: R. Kaita (PPPL) Raman, Dec05

  6. 13ms 17ms 13ms 13ms 17ms 17ms Electron temp. & density profiles during the current persistence phase Movement of discharge towards CS seen in the density profile, consistent with the camera image >60kA of closed flux current generated using Transient CHI Unambiguous closed flux current generation is clearly demonstrated by these discharges. Phantom Camera Images: R. Maqueda (Nova Photonics) Thomson scattering: B. LeBlanc (PPPL) Raman, Dec05

  7. 20ms 10ms 14ms 16ms 17ms 19ms 32ms 22ms 35ms 40ms Some discharges have current persistence well beyond 20ms 5 to 19ms: Plasma forms and shrinks 20 to 35ms: Plasma expands along CS 35 to 400ms: Plasma shrinks, becomes faint Raman, Dec05

  8. Fast camera movie of a short duration transient CHI discharge As time progresses, the CHI produced plasma gradually shrinks in size and forms a ring around the center stack Raman, Dec05

  9. Plasma Current (kA) Injector Current (kA) Some discharges persist for t > 200ms • After plasma shrinks, it continues to persist for nearly 400ms. • Plasma parameters for this persisting plasma have not • yet been measured. Raman, Dec05

  10. Summary • Generation of a solenoid-free closed flux current discharge by CHI clearly demonstrated in NSTX • 60kA of closed flux current generated using only 7kJ of capacitor bank energy • Optimization at more energy should easily result in closed flux currents of >200kA • At this current level, expect HHFW and NBI to couple to CHI produced discharges for non-inductive current ramp-up • In some discharges, the current channel shrinks to a small size and persists for more than 200ms Raman, Dec05

  11. 12ms 18ms 15ms 13ms 16ms 12ms Thomson scattering Te & ne profiles show progression towards a less hollow profile at later times, consistent with CHI startup The black traces are at the earlier time, and the red traces are at the later time • CHI startup initially drives current along the edge • After reconnection in the injector region, the initially hollow profile should become less hollow with time as current diffuses in Raman, Dec05 Thomson scattering: B. LeBlanc (PPPL)

  12. Shot 118334 at 26ms Shot 118342 at 11ms Preliminary EFIT reconstructions For discharge 118334, that has about 15 to 20kA persisting beyond t = 20ms, EFIT indicates the presence of a discharge along the center stack. EFIT: S. Sabbagh (Columbia U) Raman, Dec05

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