NSTX dust experiments and DUSTT modeling R'D' Smirnov, A'Yu' Pigarov, S'I' Krasheninnikov UCSD A'L'

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NSTX dust experiments and DUSTT modelingR.D.
Smirnov, A.Yu. Pigarov, S.I. Krasheninnikov
(UCSD)A.L. Roquemore, C.H. Skinner, D.K.
Mansfield (PPPL)

• Motivation
• Theory and some experiments showed that
  significant amount of mobile dust can penetrate
  deeply into plasma and contaminate plasma in
  fusion devices
• Major trouble causes big dust particles which can
  contaminate and even disrupt the plasma due to
  large material intake and long dwell time
• Predictive simulations of dust in ITER require
  development and benchmarking of dust transport
  and dust-plasma interaction models
• Real time dust diagnostics are needed for ITER.
  Tracking and photometry of dust and ablation
  cloud with cameras can be used for dust and
  plasma diagnostics
• ITPA DSOL-(21?) Introduction of pre-characterized
  dust for dust transport studies in the divertor
  SOL. Multi-tokamak effort.

Camera image of dust in NSTX
DUSTT modeled dust trajectories
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Outstanding Dust Issues to be addressed

• Dust Ablation and Impurities
• Ablation and fragmentation of dust of various
  materials in plasmas
• Penetration of dust material in the core
• Disruption mitigation
• Tritium retention

• Dust Characterization and Transport
• Dust formation mechanisms
• Mobilized dust amount, sizes and velocities
• Dust acceleration, charging and heating in fusion
  plasmas
• Collisions with walls
• Dust removal

• Diagnostics
• Real time dust diagnostics in fusion plasmas
• Control of surface dust accumulation
• Dust in plasmas as mobile probes

DustT code provides some modeling capabilities
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Proposed experiments

• Dosed injection of well characterized dust of
  different sizes using Mansfields dropper and
  pellet injector
• Precise 3D tracking of dust in plasma using
  multiple cameras
• Use Li dust and dust of different ITER related
  materials (C, W) for penetration studies and
  verification of dust ablation and radiation
  models
• Introduced safe amounts C up to 30mg (as in
  DIII-D), W up to 100 µg (to be mixed with low-Z
  materials)
• Dust radiation photometry with cameras for dust
  temperature measurements
• Imaging of line radiation from the ablation cloud
  (CII, WI) for studies of dust-plasma interactions
  and transport of ablated dust material
• Required time ½ day (at the end of campaign if W)
  piggy back.
• Goals
• Matching experimental data with DustT modeling
  for dust trajectories and radiation
• Deriving relations between plasma parameters,
  dust characteristics and dynamics in tokamak
  plasmas
• Compare experimental and modeling distribution
  functions of dust over sizes
• Development and benchmarking of DustT models for
  large grains
• Comparative analysis of intrinsic and injected
  dust particles

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Tungsten dust injection limit

• How much of tungsten dust
• can be safely injected in NSTX?
• Dust radius Rd1µm, grain mass Md8.1x10-11g ?
  2.6x1011 atoms
• Plasma temperature Te500eV, density ne5x1019m-3
• Tungsten power loss coefficient Prad10-31W m3
  /ion (Z20)
• Assume conservatively that all dusts tungsten
  penetrates the core and ?10 of heating power
  Ph3MW may be radiated by tungsten ions
• N ? Ph / (Prad ne) 6x1016 atoms 20µg
• 2.3x105 dust grains (Rd1µm) or 200 dust
  grains (Rd10µm)
• Number of grains may be enough to trace
  trajectories, but
• requires precisely dosed injection