V.Philipps, SEWG Gas balance and fuel removal, JET, 22.7.08 Energy Research – Plasma Physics |...

V.Philipps, SEWG Gas balance and fuel removal, JET, 22.7.08 Energy Research – Plasma Physics | Association EURATOM – FZJ

Ion Cyclotron Wall Conditioning (ICWC) and T removal in TEXTOR

A. Lyssoivan, G. Sergienko, V. Philipps, G. Van Wassenhove, R. Koch, H.G.Esser, C.Schulz


Motivation

Wall conditioning in the presence of permanent magnetic field (inter-shot conditioning) must be developed for /onboard in ITER to allow

plasma start up in particular after special events like disruptions, leaks, openings

reduce long term T-inventory (T-housekeeping strategy)

Ion Cyclotron Wall Conditioning (ICWC) is approved for integration into the ITER baseline using ITER ICRF heating system.

Further development of the ITER relevant ICWC scenarios with conventional ICRF antennas is an important and urgent task.


R&D on ICWC Optimization

ICWC Plasma Production Wall conditioning removal Mechanisms

AntennaCoupling

GRFplRF PP

PlasmaHomogeneity/ Extension

• Homogenity• Flux spectrum • Fast Ions Generation

1. High Ion Cyclotron Harmonics, =nci, n>>12. Mode Conversion, = ci

BT+BV, BV<<BT


ICRF plasma can be produced at any BT-field and in any gas mixture

used in TEXTOR: He, He+H2, O2, O2+He, NH3+D2, NH3+He

=10cH+ (low field BT0.2 T): High coupling achieved (0.8), density (>21017 m-3) and homogeneity

ICRF Plasma Characterization


0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60

1

2

3

4

5

6

7TEXTOR- (He+H2)-plasma +Bv

- (He+H2)-plasma

- He-plasma

HD

Rem

oval

Rat

e[1

0

mol

/(skW

)]16

BT [ T

=cH+ (BT2.3 T): less coupling, improvement achieved by proper He/H2 mixtures (mode conversion in He+H2 and overlaying a small vertical magnetic field)


AUG: ICRF Plasma Characterization

Mode conversion scenario in (He+H2)-plasmas:

Higher antenna coupling (up to 3 times)

Better homogeneity and extension in radial direction

Better performance at two frequencies

(He+H2)-plasma vs He-plasma

BT+BV vs BT

Vertical magnetic field improves plasma homogeneity in poloidal direction and extends it towards divertor

He, f=30 MHz He+H2, f=30 MHz He+H2, f1=30 MHz+f2=36.5 MHz

I II III

BT BT

BV

BT=2.4 T, BV=0 BT=2.4 T, BV0.02 T


TEXTOR walls were preloaded in D2 GDC before each “ cleaning” in H2+He ICWC plasmas

Isotope exchange : D2 + H = HD


ICWC has been tested in TEXTOR in

He

H2, D2

He+ H2

He+O2

N2+ H2/D2

D2+ NH3

He+ NH3

Most effective methods


Injected O2

Maximum allowable pressure determines effectivity

He injection

O2 injection CO formation

CO outgassing


Formed CO


ICWC plasmas reliably produced in different gases and Bt

For carbon removal, He/O2 oxygen most effective

He/H2 mixtures best for final cleaning action

He/NH3 has some effectivity, better then H2/N2 (all nitrogen absorbed in TEXTOR)

The main constraint with this type of wall conditioning is still the homogeneity (despite the improvements in recent years)

AUG found about 25% effectively affected by the cleaning

Similar values estimated in TEXTOR

Further improvements possible: horizontal magnetic field, several or sweeping frequencies)


Proposal for the JET FT 2009:

JET Task Force – Fusion Technology Proposal for WP-2009Development of Ion Cyclotron Wall Conditioning (ICWC) Technique for ITERProposers:, A.Lyssoivan, V.Philipps , D.Douai, S.Bremond, P.Coad, C.Grisolia, R.Koch, I.Monakhov, J.-M.Noterdaeme, J.Ongena, V.Rohde, G.Sergienko Aim: Develop efficient wall cleaning/conditioning technique for ITER in the presence of permanent high magnetic field using standard ICRH antennas

V.Philipps, SEWG Gas balance and fuel removal, JET, 22.7.08 Energy Research – Plasma Physics |...

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