1. Raman, APS051 Solenoid-free Plasma Start-up in NSTX using Transient CHI R. Raman 1, T.R. Jarboe 1, B.A. Nelson 1, M.G. Bell 2, D.Mueller 2, R. Maqueda 3, R. Kaita 2, B. LeBlanc 2, J. Menard 2, T. Bigelow 4, M. Nagata 5, S. Sabbagh 6, M.J. Schaffer 7, V. Soukhanowskii 8, H.R. Wilson 2 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 47 th Meeting of the American Physical Society, DPP Denver, Colorado, 24 – 28 October, 2005 Work supported by DOE contract numbers DE-FG02-99ER54519 AM08, DE-FG03-96ER54361 Supported by Office of Science 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

2. Raman, APS052 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

3. Raman, APS053 Implementation of Transient CHI Expect axisymmetric reconnection at the injector to result in formation of closed flux surfaces Fast camera: R. Maqueda

4. Raman, APS054 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 in gap between divertor plates. No voltage is applied. Shot 116565 1.4 Torr.L gas injection Shot 116570 0.7 Torr.L gas injection EC-Pi glow along the center stack Divertor gap

5. Raman, APS055 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 6 ms8 ms10 ms 12 ms15 ms17 ms Hiroshima University (N. Nishino) Camera Images: R. Kaita (PPPL)

6. Raman, APS056 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. Electron temp. & density profiles during the current persistence phase Phantom Camera Images: R. Maqueda (Nova Photonics) Thomson scattering: B. LeBlanc (PPPL) 13ms17ms 13ms17ms 13ms 17ms

7. Raman, APS057 Some discharges have current persistence well beyond 20ms 10ms 14ms 16ms 17ms 19ms 20ms 22ms 32ms 35ms 40ms 5 to 19ms: Plasma forms and shrinks 20 to 35ms: Plasma expands along CS 35 to 400ms: Plasma shrinks, becomes faint

8. Raman, APS058 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. Plasma Current (kA) Injector Current (kA)

9. Raman, APS059 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

10. Raman, APS0510 Thomson scattering T e & n e profiles show progression towards a less hollow profile at later times, consistent with CHI startup 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 12ms18ms 13ms 15ms 12ms 16ms Thomson scattering: B. LeBlanc (PPPL) The black traces are at the earlier time, and the red traces are at the later time

11. Raman, APS0511 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

12. Raman, APS0512 Preliminary EFIT reconstructions Shot 118334 at 26msShot 118342 at 11ms 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)