Neutral Beam Injection Experiments in the HL1M Tokamak

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Neutral Beam Injection Experiments in the HL-1M
Tokamak

• Longwen Yan, Guangjiu Lei, Jiquan Zhang, Tao
  Jiang, Yan Zhou, Mingliang Shi, Saofeng Jiang,
  Xuantong Ding, Yong Liu

The Talk of CFS Seminar in March, 2003
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Outline

• Objectives
• NBI experiments in tokamaks
• NBI system and its performance in HL-1M
• The experimental results of NBI in HL-1M
• Analyses of NBI heating effects in HL-1M
• Conclusion and discussion

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Objectives

• Commissioning between NBI system and HL-1M plasma
  
• Heating plasma temperature by NBI
• Optimization of NBI parameters to obtain good
  heating effects
• Experience to develop HL-2A NBI system
• Training scientists

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NBI Experiments in Tokamaks

• 40MW, 120keV in TFTR, Ti044keV, Te013keV
• 24MW, 140/160keV (H/D) in JET, Ti020keV,
  Te010keV, QDT1
• 20MW, 80keV in DIII-D, Ti020keV, BNH20
• 40MW/120keV, 10MW/500keV(NNBI) in JT-60,
  Ti045keV, Te010.6keV, QDT1.25
• 2.1MW, 40keV in PLT, Ti05.5keV, Te03.5keV
• 0.7MW with 38 degree to plasma axis in JFT-2M
• 0.6MW in TFR, Ti0 increase 0.1-0.3keV
• 0.5MW in HL-1M, Ti0 increase 0.1-0.35keV

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NBI system in HL-1M

• 1. Ion source
• 2. Bellow
• 3. Vacuum valve
• 4. Neutralizer
• 5. Magnetic shield
• 6. Deflecting magnet
• 7. Ion dump
• 8. Vacuum valve
• 9. Fast shutter
• 10. Bellow
• 11. Drift duct
• 12. Plasma
• 13. Titanium bar
• 14. Vacuum tank

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Performance of NBI system in HL-1M

• Perpendicular injection
• Designed 1MW/35keV, 1.1MW/25keV in Exp.
• NBI 0.8MW, 25keV, 200ms
• Focus length is 3.5m horizon and 4.5 vertically
• Beam divergence is 0.50 horizon or 1.30
  vertically
• Beam decay length near focus is 2.5cm horizon
• Size of arc chamber is 33x20x13 in cm
• Grid surface is 25x12cm2 with 48 transparency
• Gas pressure 0.2Pa and exit current 200mA.cm-2

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Two Modes of Ion Source of NBI

• Mode I
• IA50-350A
• VA41-54V
• Mode II
• IA500-1200A
• VA39-53V
• Transition zone
• IA350-550A
• VA54-39V

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Shot 7039 with NBI of Mode I

• 370-520ms for NBI
• Ii25A, Vi21kV
• 80-90 of neutrali-zation efficiency
• PNBI 400 kW
• ne(2.6-3.4)x1019m-3
• Twice protection of NBI system
• Gas puffing dropped
• No Tea rise

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Ion temperature for shot 7039

• Ti0600?800eV after NBI of mode I
• No Te0 increase
• Little suprathermal ions
• Ti0 quickly rise after NBI
• Carbon emission and radiation power keep
  invariant during NBI

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Shot 7641 with NBI of Mode II

• 314-409ms for NBI
• Ii24A, Vi17kV
• 80-90 of neutrali-zation efficiency
• PNBI 320 kW
• ne(2-3.2)x1019m-3
• Gas puffing dropped
• Tea drop during NBI
• Current quench by NBI of Mode II

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Ion temperature for shot 7641

• Ti0600?750eV in 30ms after NBI of mode II
• Ti0 quickly rise after NBI
• Little suprathermal ions
• Ti0 dropping before current quench
• Carbon emission and radiation power gradually
  rise during NBI

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Electron Temperatures during NBI

• Te0 increases a little during NBI
• Te first drops before NBI being ended
• Electrons should absorb most NBI power due to low
  Te0
• Relatively low Te increment needs further studying

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Radiation power rise during NBI

• Symmetry profile before NBI
• Profile contracts during NBI
• Radiation obviously rise at HFS and then profile
  extends
• Radiation focuses on HFS means new impurity
  source
• Prad/POHgt1 at edge lead to disruption

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Analyses of NBI heating effects

• Half width of banana orbit at 20keV is 9cm/H and
  13cm/D
• e-fold decay length is 26cm if nel6x1019 m-3 in
  HL-1M
• Carbon production by heat sublimation may be
  neglected if Tslt1800K
• Carbon production due to physics sputtering is
  omitted if beam energy Ebgt4keV
• Carbon impurity by chemical sputtering is a few
  percentages near 550 0C
• Ts550 0C if 200kW NBI reaches the tiles for
  40-60ms

• Heat diffusion time across graphite protection
  tiles (tdiff) is given as

The surface temperature (Ts) rise on the tiles is
estimated if tdiffgtgttNBI
Here d, k, K and Ps are thickness, thermal
diffusivity, thermal conductivity and heat flux,
respectively
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Summary and Discussion

• Two modes of ion source are explored in HL-1M
• 0.5MW, 35keV, 200ms achieved for NBI system
• Ti increases 30-80 for Mode I without disruption
• Ti increases 10-25 for Mode II with disruption
• Density gradually rise for Mode I and II during
  NBI
• Carbon impurity and radiation power increase with
  time for Mode II during NBI
• No obvious rise for Te during NBI
• Edge temperature drop a little during NBI
• Chemical sputtering should be main impurity
  source to quench current because of its yield may
  reach a few percentages near 550 0C