Possible TCV contributions to EUPWI activities

1
Possible TCV contributions toEU-PWI activities

• R. A. Pitts for the TCV Team(including
  contribution from HAS G. Veres)
• Centre de Recherches en Physique des Plasmas
• Ecole Polytechnique Fédérale de Lausanne,
  Switzerland
• Association EURATOM-Swiss Confederation

2
Outline

• Brief reminder of main TCV characteristics
• Heating systems
• First wall
• Expected contributions to EU-PWI
• Ongoing and future work on SOL transport
• Transients
• Disruption mitigation
• Particle balance, material migration?

3
The TCV tokamak

• R 0.88m a 0.25m
• BT 1.5T Ip 1.2MA
• 0.9lt k lt2.8 -0.6lt d lt0.9

• X3 118GHz
• 3 ? 0.5MW, 2s
• Top launch ECH
• ncut-off 11.5?1019m-3

• X2 82.7GHz
• 6 ? 0.5MW, 2s
• Side launch ECH, ECCD
• ncut-off 4.2?1019m-3

4
TCV first wall

• All graphite machine
• 90 of first wall tiled with polycrystalline
  graphite (1400 individual elements)
• Cold walls (during operation)
• Regularly boronised (220?C, Glow with 10
  B2D6/90 He)
• Pulse length typically 1.2 s
• Always intershot He glow (required for reliable
  breakdown)

5
Origin of SOL transport (I)

• Measurements of turbulent particle flux, Gturb,
  in Ohmic plasmas, Ip340 kA, single lower null
  divertor geometry

Typical standard SNL divertor config ?

• At the wall radius (important for main chamber
  recycling) transport is well described by
  effective convective velocity
• Veff Gturb/n, with Veff independent of n

? Need to try and extend to H-mode
6
Origin of SOL transport (II)

• Comparison with 2D e.s. fluid model ESEL, with ?B
  effects (interchange drive)

• Density field evolution shows radial propagation
  of blobs

• Predicted sharp rise and trailing edge of density
  agree with measured temporal evolution of large
  amplitude bursts at wall radius
• Agreement also on profiles of ne, dne/ne, pdf
  moments

separatrix
wall
? Intermittent SOL transport is due to
interchange driven radial motion of blobsMore
experimental work planned on influence of wall
gap, H-mode etcExtend ESEL simulations to higher
density
7
SOL flows (I)

• Unambiguous experimental data
• Complement now with modelling ? SOLPS5 with
  drifts
• Can the code reproduce experiment?
• If not, is it consistent internally?
• X. Bonnin begins first visit to CRPP this week to
  implement drifts into SOLPS5 for TCV

wall
8
SOL flows (II)
10 cm
0 cm
-10 cm
OUTER divertor

• Done only with reversed Bj
• Will now be repeated in forward field (this year)
• Characterise magnitude of field independent
  offset role for material migration
• In H-mode also

9
Transients new IR system (I)

• New fast IR camera just installed on TCV
• Views the vessel floor from above
• Same camera also purchased by AUG
• Will be used for transient and steady state work
• ELMs and disruptions (natural and mitigated)
• Sheath transmission factors
• Possibility of dust detection using a second,
  slower camera laterally viewing outer divertor?

Si relay optics7 lenses in 3 groups
Camera specifications
10
Transients new IR system (II)

• Camera installed end October
• Still awaiting first dedicated ELMing H-modes
  (ohmic)
• Higher power X3 H-modes in 2007
• No disruption work yet
• But high levels of dust seen on first few shots
  after 3 month vessel opening (but after vessel
  bakeout and boronisation)

Combine slower Merlin microbolometer IR with new
top viewing system to track dust particles
infer temperature from IR emission ? S.
Krashenninikov, IAEA 2006
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Transients new array of wall probes

• Low field side, outer midplane
• 100 kHz acquisition frequency
• Poloidal array above and below midplane of
  standard SNL
• Spatial resolution 15 mm
• Can be used to study ELM propagation and main
  chamber recycling

LP arraysLower divertor 26Inner divertor
34Low-field-side wall 19

• New fast Photron visible camera also now
  installed on TCV will be used in conjunction
  with the LFS array

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Type III ELMs clear filaments
26746, Jsat

• Data analysis just begun
• Shots with varying outer gap width
• Use poloidal probe distribution to estimate
  radial propagation speed
• Every ELM different!
• Rich structure
• HAS will participate in analysis of this data

Outer divertor
Inner divertor
LFS Wall
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Larger ELMs now accessible on TCV

• X3 heating yields large ELMs
• Up to 20 of total stored plasma energy per ELM ?
  10 kJ/ELM
• Average energy loss per Type III 200 J/ELM!
• Will combine main chamber LP measurements with
  divertor IR to investigate ELM transport

Total heating pwer
Da
Type I?
Type III
Type III
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ELM modelling

• SOLPS5 model of inter-ELM SOL established
• First ELM simulations now underway
• Will compare with outer target IR thermography

Upstream pedestalSOL
ne
Inner divertor Outer divertor
Te
c?, D?
r - rsep
B. Gulejova, PSI 2006
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Fast impurity injection valve

• Planned installation, 2007
• HAS leading hardware development (G. Veres)
• To be used for disruption and impurity transport
  studies
• Study of disruption dynamics
• Fast radiation distribution (AXUV)
• Heat fluxes (IR)
• Injection in first instance from a top lateral
  port
• Noble gases and H2, D2
• Use fast Photron camera for observation of
  disruption dynamics

Gasinjection
7 camera AXUV diode system 2 x 140 LOS (total
radiation and filtered Da (under
development)).Time resolution 10 ms. Data
analysis in collaboration with HAS
16
Valve testing at KFKI
Vacuumpump
Velocity probe 2(movable radially)
Velocity probe 3
Gas flow
Fly tube 2 m
skimmer
Valve
Vacuum pump
Nozzle
Velocity probe 1
G. Veres, HAS
17
Detection principle timing
20 M O
20 M O
100 K O
Ud-2 kV
Glow discharge between two electrodes
With Skimmer
Without Skimmer
18
Effectiveness as a disruption generator

• 0D estimates with KPRAD
• Courtesy of D. Whyte (MIT)
• Uniform distribution of impurities
• Assume effective disruption if core Te reduced to
  10 eV in a few ms
• With the chosen valve for TCV
• He probably not effective
• Ne probably effective
• Ar will be effective
• Note no Halo current measurement on TCV

10 eV
Measured number of injected particles in a 10 ms
pulse
19
Particle balance migration

• Particle balance
• Never done on TCV!
• New cold and hot cathode gauges installed this
  summer to make a start though post pulse
  acquisition not yet implemented
• Migration
• Have proposed a 13C migration experiment (outer
  midplane injection into Type III ELMing H-mode)
• Would occur end March 2007 before next long TCV
  shutdown
• Has advantage that many samples can be removed
  from the machine
• Requires assistance for sample analysis however
  (J. Likonen and M. Rubel contacted)