the effect of divertor detachment on hydrocarbon sources in jet l-mode discharges

ITPA D-SOL Meeting, Garching, May 7-10, 2007 S. Brezinsek 10/05/2007

TF E

The effect of divertor detachment on hydrocarbon sources in JET L-mode discharges

MotivationPlasma configuration and settings Applied diagnosticsDetachment characterisationHydrocarbon chemistryConclusion

Outline:

S. Brezinsek, A.G. Meigs, J. Rapp, R. Felton, A. Huber, S. Jachmich, V. Philipps, A. Pospieszczyk, R. Pugno, O. Schmitz, G. Sergienko,

M. F. Stamp, and EFDA-JET Contributors


TF EIntroduction

Motivation: A semi-detached outer divertor is foreseen as the operating regime for ITER. Reduction of the hydrocarbon flux (& chemical sputtering) in AUG and DIII-D with detached outer divertor of observed. Comparison with the hotter target (~180°C) of JET would help to close the gap to ITER. ITPA D-SOL task

Goals: i) Controlled and steady-state outer divertor detachment operation.ii) Characterisation of the detached outer divertor.iii) Hydrocarbon chemistry under detached plasma conditions.

Brezinsek et al. Phys. Scripta 2007


TF E Settings and Configuration

Settings: L-mode (I=1.7MA, B=2.7T, PNBI=1.7MW)

Deuterium plasma Outer strike point fixed on the LBSRP –

optimised for diagnostics Strong deuterium fuelling in the PFR Local methane injection at the OSP

(only a few shots) LBSRP


TF EPlasma scenario

Partial detachment and full detachment scenario is made with feedback controlafter approaching the programmed density in the density ramp.

Time evolution:

attached

full detachment (fb)

partial detachment (fb)

GIM14 injection

61.0 s 64.0 s56.0 s 59.0 s

NBI 1.7 MW

density rampwith D fuelling

in the PFR2

attached

67.0 s

no puff

detached

61.0 s 64.0 s56.0 s 59.0 s 67.0 s

prefill

density limit disruption

pulsed injectionthrough a singleinlet (pneumatic)


TF EDiagnostics

OSP is fixed on the LP close to GIM 14 location (local injection in the SOL) KS3 and GIM 14 used for in-situ calibration of hydrocarbons (octant 5) KT3 (octant 8) and KY4D used for detachment characterisation

KT3

GIM14

KS3

Diagnostics:

Divertor spectroscopy (KT3, KS3) Langmuir probes (KY4D) CCD camera with D filter (KL1) IR camera (KL7) Divertor bolometry (KB5) Gas injection module (GIM14)


TF EDetachment characterisation (Langmuir Probes)

Ion saturation current at injection location Degree of detachment

Roll over in ion saturation current indicates “start” of detachment

Complete detachment of the outer divertor at ~62 s

Density ramp:


TF EDetachment characterisation (Langmuir Probes)

Attached plasma (close to roll over) Complete detached plasma

High density and hot plasmaPeak ion flux: 1.7*1023 m2s-1

Neutral flux in the sub-divertor: 0.8*1022m2s-1

Plasma (too) hot for recombination?Peak ion flux: 3.4*1022 m2s-1

Neutral flux in the sub-divertor: 2*1022m2s-1

Plasma parameters in the outer divertor (LBSRP):

KY4D


TF EDetachment characterisation (spectroscopy)

Paschencontinuum

Paschen recombination lines

PFR SOL

KT3C #70574

Spatial distribution (tile 5)

semi detached

full detached

roll over (LP)

Paschen line (8->3)

Plasma parameters from Balmer recombination line analysis:Te ~ 1-2 eV ne ~ 2-3 1020 m-3

Tim

e [s

]

Tim

e [s

]

Radius [a.u.]Wavelength [A]

Much colder and denser than plasma parameters from Langmuir probes

Deuterium volume recombination in the outer divertor:

Wavelength [A]

Paschen recombination line analysis

Inte

nsi

ty [

arb

. un

its]


TF E

Emission pattern in the outer divertor: D and CD

D CD – Gerö band

roll over (LP)

Strong drop ofintrinsic CD light!

KT3B #70574

PFR SOLPFR SOL

roll over (LP)Tim

e [s

]

Radius [a.u.]

Tim

e [s

]

Radius [a.u.]

Spatial distribution:

Radius [a.u.] Radius [a.u.]Time [s]Time [s]

Inte

nsi

ty [

arb

. un

its]

Inte

nsi

ty [

arb

. un

its]


TF EHydrocarbon chemistry in the outer divertor

Integrated CD and D intensities:

Hydrocarbon emission (and flux) dropped prior to ion flux roll over No complete suppression of the hydrocarbon flux in complete detachment Possible reasons: flux dependence / threshold energy for Ychem

KT3B #70574

density ramp


TF EAttached – Detached oscillation (with feedback)

Spatial distribution D Spatial distribution CD

attached

detachedKT3B #70578

Tim

e [s

]

Radius [a.u.]

Tim

e [s

]

Radius [a.u.]

Spatial distribution during attached – detached oscillation:

Density feedback set to the density at the roll over time Switch between attached and detached regime (gain too high) Oscillation of D and CD (same for C2 and D2)


TF ELocal methane injection through GIM14

KS3A #70579

Hydrocarbon particle flux quantification:

Reduction of CD light is related to reduction of particles! (Same for C2!) Injected amount is too high (valve operation restriction) Absolute quantification not yet done (need of calibration)

Extrinsic sourceis detectable!

Photon efficiencies inattached and detachedcase are comparable!

detached

CII

CD

Dattacheddetached

D

CD

CII

CD D

attached


TF EConclusion

• Detached and volume recombined outer divertor plasma established• Plasma parameters from spectroscopy and Langmuir probes differ

Outer divertor plasma scenario:

Hydrocarbon chemistry:

• Hydrocarbon “footprint” drops prior to roll over of the ion flux• Extrinsic source is detectable Substantial reduction of the erosion yield But absolute quantification not yet done

• Effect of flux dependence (ions and atoms at low energies)• Energy threshold of chemical sputtering?

• Similar behaviour with respect to DIII-D and AUG experiments – but hydrocarbon flux is still detectable during detachment

Comparison with other experiments:

the effect of divertor detachment on hydrocarbon sources in jet l-mode discharges

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