Supported by

1

Supported by
XP817 Transient CHI Solenoid free Plasma
Startup and Coupling to Induction
R. Raman, B.A. Nelson, D. Mueller, T.R. Jarboe,
M.G. Bell et al., University of
Washington Princeton Plasma Physics Laboratory
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 JAEA Hebrew
U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST
POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP,
Jülich IPP, Garching ASCR, Czech Rep U Quebec
NSTX FY08 Results Review August 6-7, 2008 (PPPL)
2
Transient CHI Axisymmetric reconnection leads to
formation of closed flux surfaces

• Demonstration of closed flux current generation
• Aided by gas and EC-Pi injection from below
  divertor plate region
• Demonstration of coupling to induction (2008)
• Aided by staged capacitor bank capability

3
FY08 Result Proof-of-Principle Demonstration of
Coupling a CHI Started Discharge to Induction

• 8 Total days 2 days commissioning
  conditioning
• 2 days Testing without Cryo pumping
  capability
• 4 days Full capability
• March 10 Commissioned new CHI hardware
• - Staged capacitor bank operation
• - Fast voltage monitoring system
• March 11 Conditioned the lower divertor plates
• - Operated in stuffed injector mode
• - Conducted first D2GDC (in recent history)
• March 12 First day of main XP
• - Inductive discharge development that had
  reduced CS pre-charge
• - Started CHI discharge with some pre-charge in
  CS
• - Reproduced good Te CHI discharges with zero CS
  pre-charge
• - Saw first evidence for coupling to OH (good Te
  and ne signals)

4
CHI Started Discharges after Inductive Coupling
Transition into H-mode and are more reproducible
with Li Conditioning

• March 31 Inductively coupled discharges reach
  180kA and reach Te 100eV
• April 9 Inductively started discharges reach Ip
  600kA and Te 500eV
• - Used position feedback control to increase
  current
• June 2,3 Operated without Cryo Pumping and
  without Boronization
• - Vessel base pressure 10x higher than usual (4
  x 10-7 Torr)
• - June 2- Tested CHI discharge formation in He
  then switched to D2 plasmas, Ip 400kA in poor
  reproducibility discharges
• - June 3 - First use of Li evaporation for CHI
• - Discharges became reproducible and reached Ip
  600kA
• - Tested use of HHFW for heating during the
  coupling phase to induction
• July 8 Used Cryo pumping and 10mg/min Li
  evaporation
• - Central electron temperature reached 1keV
• - Ip reached 725kA, discharges transitioned into
  H-modes
• - Discharges with 2min HeGDC 6min Li were more
  reproducible than Li-only cases

5
March 12 First Evidence of CHI Coupling to
Induction

• Final four shots coupled to induction
• Te and ne (from Thomson) showed plasma to be
  resting on outer vessel during inductive phase
• Later confirmed by EFIT
• On last shot increased vertical field moved
  plasma further inboard verifying Thomson and EFIT
  results

6
March 31 Demonstrated First Good Coupling of CHI
Produced Discharge to Induction (in NSTX)

• Started with Final discharge from March 12
• Used 7.5kJ of capacitor bank energy to initiate
  CHI discharge
• Used pre-programmed PF coil currents to maintain
  equilibrium
• Discharges gt40ms were ramping up in Ip but
  vertically unstable

7
CHI started discharge couples to induction and
transitions to an H-mode demonstrating
compatibility with high-performance plasma
operation

• Te Ne from Thomson
• Ti from CHERS
• Central Te reaches 800eV
• Central Ti gt 700eV
• Note the broad density
• profile during H-mode phase

• Discharge is under full plasma equilibrium
  position control
• Loop voltage is preprogrammed

CHERS R. Bell Thomson B. LeBlanc
8
Discharges with Li Conditioning are More
Reproducible and reach Higher Currents after
Inductive Coupling
Li makes breakdown more reproducible and the
improvements are due to reduced recycling
(similar to the effect of Ti-gettering on HIT-II)
9
Need auxiliary heating or metal divertor plates
to compensate for increased radiated power with
more capacitors

• Low-z impurity radiation increases with more
  capacitors
• High Te in spheromaks (500eV) obtained with metal
  electrodes
• Test with partial metal outer divertor plates
  during FY09
• Reverse TF polarity to make outer vessel cathode
• Upper divertor radiation also increases with more
  capacitors
• Need to reduce absorber arcs
• Absorber field nulling coils to be used during
  FY09
• Assess benefits of partial metal plates
  Absorber coils
• Discharge clean divertor with high current DC
  power supply
• Use 350kW ECH during FY11

Plasma Current
128400 5mF (7.6kJ) 128401 10mF (15.3kJ) 129402
15mF (22.8kJ)
10
First Demonstration of Compatibility of CHI with
High-Performance Inductive Operation in a Large ST

• Transient CHI is a proven method to generate
  closed flux (160kA to date)
• Startup inductive coupling at 100kA
  demonstrated on NSTX HIT-II
• CHI initiated and inductively ramped current
  reached 700kA in H-mode
• Peak Te 0.9keV obtained in discharges coupled to
  induction
• Need to reduce Low-Z impurity radiation to
  increase current
• Electrode conditioning to be improved for FY09
• Reduce absorber arcs using Absorber PF coils
• Use outer metal divertor plates needed for Liquid
  Li system
• Beyond 2009
• 350kW ECH higher power HHFW will help
  considerably
• Results from metal outer plate tests during 2009
  will provide additional data on effect of Low-Z
  impurities
• Higher voltage needed to increase startup current
• Higher TF will increase current multiplication
  factor

Closed flux startup currents of about 500kA is
possible in NSTX through hardware improvements
(not a physics limitation)