Solenoidfree Plasma Startup in NSTX using Transient CHI

1
Solenoid-free Plasma Start-up in NSTX using
Transient CHI

• 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

College WM 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
47th 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
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

3
Implementation of Transient CHI
Expect axisymmetric reconnection at the injector
to result in formation of closed flux surfaces
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
5
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)
6
Electron temp. density profiles during the
current persistence phase
Movement of discharge towards CS seen in the
density profile, consistent with the camera
image gt60kA 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)
7
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
8
Some discharges persist for t gt 200ms

• After plasma shrinks, it continues to persist for
  nearly 400ms.
• Plasma parameters for this persisting plasma have
  not
• yet been measured.

9
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 gt200kA
• 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
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

Thomson scattering B. LeBlanc (PPPL)
11
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
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)