XP 603: Long pulse DND discharge development with rtEFIT

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XP 603 Long pulse DND discharge development with
rtEFIT
Columbia U Comp-X General Atomics INEL Johns
Hopkins U LANL LLNL Lodestar MIT Nova
Photonics NYU ORNL PPPL PSI SNL UC Davis UC
Irvine UCLA UCSD U Maryland U New Mexico U
Rochester U Washington U Wisconsin Culham Sci
Ctr Hiroshima U HIST Kyushu Tokai U Niigata
U Tsukuba U U Tokyo JAERI Ioffe
Inst TRINITI KBSI KAIST ENEA, Frascati CEA,
Cadarache IPP, Jülich IPP, Garching U Quebec

• Presented by D. A. Gates
• At NSTX Research Forum
• July 26-27, 2006

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XP 603 Long pulse DND

• XP run on 3 different days (6 hours, 4 hours, 8
  hours in March, April and June respectively)
• 75 shot numbers, 51 plasmas
• 3 distinct goals
• Early H-mode
• Higher ? 2.5 (tall plasma)
• Very high ? 2.7 at 5.5kGauss (large outer gap)

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rtEFIT statistics

• rtEFIT now dominant control algorithm
• 66 of all discharges under rtEFIT control
• rtEFIT control has enabled increased reliability
  for long pulse discharges

2006 rtEFIT vs. non-rtEFIT integrated current
All years, all shots Integrated current
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First day, early H-mode

• Experiment failed due to PF1A power supply
  anomaly
• Unable to ramp power supplies according to
  requested waveforms
• Ip flat-spot with earlier beams also failed
  (because step 1 failed)
• Current scan was successful, but did not increase
  pulse length
• Did create interesting low loop voltage shot at
  800kA
• Same power supply failure has recked other XPs
  (e.g. Stans triangularity scan in 2005)

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Higher ?, long pulse

• Developed long pulse discharge with ? 2.5
• Very reproducible
• Higher bootstrap fraction than similar plasmas at
  lower ?
• Set Ip pulse length record at 1MA (since
  surpassed) of 1.15s
• 7/8 1MA plasma attempts had pulse lengths greater
  than 1 second
• Plasma very similar to the cross-section proposed
  in the 5 year plan

Five year plan cross-section
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Higher ? with large outer gap

• Achieved world record controlled plasma
  elongation of ? 3
• Also maintained a plasma with li 0.4
• Increased outer gap to 25cm
• Did not achieve desired ?p
• Did not achieve the desired goal of high
  bootstrap fraction
• fbs ?1/2?p

7
Plasma shows signs of ideal instability
Shot 121241, ? 3

• The maximum achievable ?N dropped to 3.8
• This was coincident with moving the plasma far
  from the conducting shell
• It seems likely that the cause of the decreased ?
  limit is the loss of wall stabilization
• Stability calculations are planned