Achievements of the first year of plasma operation with the

JET ITER-Like Wall2011/2012

Mathias GrothAalto University, School of Science, Dep. Applied PhysicsFor JET TFE1 and TFE2 leaders, and JET-EFDA contributors

2

Outline

• Purpose of the JET ITER-like wall (ILW) project

• Installation of ILW and operational constraints

• Primary achievements during first year operation:

– Demonstration of reduction of fuel (tritium) retention

– W sources and accumulation in core

• Review of campaigns in 2011/12, and preliminary timeline for 2013

All W wall considered for DEMO:

1. To provide sufficient lifetime (plasma-wall interaction/neutrons)

2. Best possible power handling

Risk to operational flexibility too high for ITER

AUG

3

W divertor and Be wall selected for ITER DT:

1. To maximise operating space (Be)

2. To reduce T retention compared to CFCJET

ITER

Tungsten plasma-facing components are foreseen in future fusion reactors

New JET Capabilities in addition to ILWNeutral beam upgrade: 35MW, 20s Pellets for ELM control: 50HzEnhanced spectroscopic coverage – especially W

• Be erosion and transport into the divertor

• Be-W mixing and Be:D layer formation D (T) retention⇒

• Transport into remote areas ⇒D (T) retention in plasma-shadowed areas

• W erosion, prompt re-deposition, and core W contamination

• Transient transport: W melt layer motion, stability and loss

• Be/W dust formation

The ILW project addresses some of the most urgent physics issues for ITER

4

5

10x

(4 months)

Roth NF 2004

Significant reduction of tritium retention was predicted for W plasma-facing components

66

Last JET pulses with all-carbon plasma-facing components ended in October 2009

77

Installation of the JET ITER-like wall (ILW) was completed on May 8, 2011

88

Bulk W

W-coated CFC

9

Solid Be Surface temperature < 900oC <22MJm-2s-1/2 (impact energy)

W-coated CFC Temperature <1200oC (carbidisation)ELMs: <5 MJ m-2 s-1/2

W stacks Surface temperature limit<1200oC-2200oC 20-35MJm-2s-1/2, Fixings, <350oC, <60MJ/m2/stack

Be

Be

W+

CF

C

W+CFC

Bu

lk W

Be

The new Be/W wall imposes more stringent power and energy limits than

the CFC wall

JET in the ILW configuration was successfully started up in September 2011

• Sets of reference discharges have been performed on weekly basis to monitor wall conditions (emission from C, Be, W, O)

11

JET wall temperature

10x

Gas balance results: Is the absolute value low enough? True long term value could be much lower (surface analysis)

ITER

JET C-wall & ILW

10x

NBIH-mode

Type I

ICRHH-mode

Type III

L-mode

The retention of deuterium in the vessel walls is reduced by 10x in the ILW compared to CFC

12

Outer divertor CIII just after X-point formation

10x

The reduction in retention strongly correlates with the reduction in carbon in the plasma

• Low plasma temperature = very low erosion

• W erosion is usually dominated by impurity sputtering: Be, C, O

Ion impact energy

Ei = 3ZTe + 2Ti

Prompt re-deposition helps maintaining low W in plasmas

W+

W

High sputtering threshold energy makes tungsten an attractive material for reactors

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t[s]

2.80

2.75

2.70

2.65

R[m]

Central density

#80768

4.7

6.0

3.5

ne d

l [1

019 m

-2]

Inte

nsit

y

[arb

. u

nit

s]

Tdiv P∝ heat / ncore

D (410.0nm)

WI (400.8nm)Inte

nsit

y [

arb

. u

nit

s]

#80846

55 60 65

55 60 t[s]

WI 400.8nm

#80768

WI 400.8nm

0

W source strength increases with increasing plasma temperature in front of divertor

targets

15

ELM frequency too low W accumulates in the ⇒

centre T⇒ e collapsed

Time(s)

82880

Te

(keV

)P

ow

er (

MW

)

JET-ILW

PNBI

Be

II (

arb

.) ELMs

Te (0)

Te (~0.6)

In extreme cases, the temperature collapsed due to W accumulation

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JET-ILW

Te

(keV

)P

ow

er (

MW

)

Time(s)

81765

Te (0)

Te (~0.6)

In other cases, the plasma survived influx of tungsten

ELM frequency higher than previous case ⇒plasma recovered after W influx, but Te well below 1 keV

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

2011 C28 C28 C28 C28

2012 C29 C29 C29 C30a C30b C30b C30c Shutdown

First plasmas in the ILW were successfully run in September 2011

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• Successful execution of C28a: monitoring of evolution of Be/W wall in simple Ohmic plasmas

• Delay of neutral beams in C28b operation with ICRF only: ⇒ICRF coupling, first H-modes, characterisation of W sputtering, limiter plasmas for heat flux to main chamber surfaces ...

• Low-power operation with NBI commenced in December 2011 ⇒PNBI > 12 MW started in February 2012

• Loss of cryo plant in mid-April 2012 operations without ⇒divertor pumping throughout May 2012 restart with NBI in ⇒June 2012

• Extension of plasma operation until the end of July 2012: last two weeks execution of same plasma to achieve steady-state wall conditions tile removal for surface analysis⇒

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

2011 C28 C28 C28 C28

2012 C29 C29 C29 C30a C30b C30b C30c

2013 C31 C31 C32 C32 C33 C33

Current forward-planning of campaigns in 2013 focus on further exploitation of new

capabilities

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• Assuming routine operation at 2.5 MA and PNBI up to 25 MW is established in 2012, experiments in 2013 will focus on:• W melt experiment support for ITER’s decision on the day-one ⇒

armour material• Further exploitation of ITER operating scenarios in the ILW:

hybrids, Ip > 3.0 MA, ...

• Divertor power handling via impurity seeding• Intervention in late October (remote handling only) to:

• Removal of special bulk-W lamella used in melt experiment• Second massive gas injection system• Reinstallation of ITER-like antenna

Shutdown

19

Scientifically, our association has been strongly involved in the JET ILW project

• Experiments:- 4 researchers acting as scientific coordinator of experiments,

including a 2-week long mini-campaign - Successful commissioning of high-energy neutral particle

analyser need to better connect data to simulations⇒- SIMS surface analysis of JET tiles at VTT

• Modelling:

- Edge modelling utilising comprehensive suites of codes: two modelling meetings in spring and autumn of 2011 (7 participants from University of Helsinki and Aalto link modelling into ⇒experimental programme

- Fast particles (2-3 researchers) ILW adapted in ASCOT ⇒- Core and edge-core integrated transport (2 researchers)

• Two TFLs covering SOL physics and fusion technology

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• The JET ITER-like wall project successfully started up in September of 2011 and produced the first set of high-level results: Demonstration of factor-of-10 lower fuel (tritium) retention

• Gradual step-up of auxiliary power first high-confinement ⇒plasmas with PNBI > 20 MW achieved in April 2012

• Thus far, machine limits reached in few events only: melting of Be at the top, runaway beam hitting the inner wall limiter

• This year’s campaign will conclude in July 2012 with an experiment aiming at steady-state wall conditions tile removal ⇒in autumn

• Next year’s campaign is planned to cover the period April – October 2013

• Tekes continue to be very visible in the JET programme: edge and fast particle modelling, experiments, surface analysis, diagnostics

Conclusions

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Backup slides

22

80000 80500 81000 81500 82000 82500 830000,0

0,4

0,8

1,2

1,6

2,0

2,4

BeII/D - outer divertor legBe

II [5

27

nm

] / D

JPN

0

2

4

6

8

KS3O

CII/D - outer divertor leg

CII

[51

5n

m] /

D accidental cryo

warmp-up

KS3O

Be flux mirrors carbon

JET-ILW: Monitoring pulses

Carbon content initially reduced by factor of 3, then remain steady-state throughout

campaign

23

JET-C with Be evaporationJET-ILW

no Be evap.

Oxygen content was slightly reduced when introducing Be (oxygen getter)