1. Achievements of the first year of plasma operation with the
JET ITER-Like Wall
2011/2012
Mathias Groth
Aalto University, School of Science, Dep. Applied Physics
For 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

3. Tungsten plasma-facing components are foreseen in future fusion reactors
ITER
All W wall considered for DEMO:
To provide sufficient lifetime (plasma-wall interaction/neutrons)
Best possible power handling
Risk to operational flexibility too high for ITER
AUG
W divertor and Be wall selected for ITER DT:
To maximise operating space (Be)
To reduce T retention compared to CFC
JET
New JET Capabilities in addition to ILW Neutral beam upgrade: 35MW, 20s Pellets for ELM control: 50Hz Enhanced spectroscopic coverage – especially W 3

4. The ILW project addresses some of the most urgent physics issues for ITER
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
Role of remaining impurities: residual C and O
Variation in time

5. Significant reduction of tritium retention was predicted for W plasma-facing components
10x
(4 months)
Roth NF 2004

6. Last JET pulses with all-carbon plasma-facing components ended in October 20096

7. Installation of the JET ITER-like wall (ILW) was completed on May 8, 20117

8. Bulk W
W-coated CFC 8

9. The new Be/W wall imposes more stringent power and energy limits than the CFC wall
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 MJm-2s-1/2,
Fixings, <350oC, <60MJ/m2/stack Be Be Be
W+CFC
W+CFC
Bulk W

10. 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. The retention of deuterium in the vessel walls is reduced by 10x in the ILW compared to CFC
JET wall temperature
JET C-wall & ILW
ICRH H-mode
Type III
NBI H-mode
Type I
L-mode
10x
Gas balance results: Is the absolute value low enough?  True long term value could be much lower (surface analysis)
ITER
10x

12. The reduction in retention strongly correlates with the reduction in carbon in the plasma
Outer divertor CIII just after X-point formation
10x

13. Prompt re-deposition helps maintaining low W in plasmas
High sputtering threshold energy makes tungsten an attractive material for reactors
Ion impact energy
Ei = 3ZTe + 2Ti
Prompt re-deposition helps maintaining low W in plasmas W+ W
Low plasma temperature = very low erosion
W erosion is usually dominated by impurity sputtering: Be, C, O

14. W source strength increases with increasing plasma temperature in front of divertor targets
Tdiv ∝ Pheat / ncore
Dd (410.0nm)
WI (400.8nm)
Intensity [arb. units]
#80846
Central density
6.0
ne dl [1019 m-2]
3.5
4.7
#80768 55 60
t[s]
R[m]
2.80
2.75
2.70
2.65
WI 400.8nm
WI 400.8nm
[arb. units]
Intensity
#80768 55 60 65
t[s] 14

15. In extreme cases, the temperature collapsed due to W accumulation
82880
Te (keV)
Power (MW)
JET-ILW
PNBI
Be II (arb.)
ELMs
Te (0)
Te (~0.6)
ELM frequency too low ⇒ W accumulates in the centre ⇒ Te collapsed
Time(s)

16. In other cases, the plasma survived influx of tungsten
JET-ILW
81765
ELM frequency higher than previous case ⇒ plasma recovered after W influx, but Te well below 1 keV
Power (MW)
Te (0)
Te (keV)
Te (~0.6)
Time(s)

17. First plasmas in the ILW were successfully run in September 2011
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2011
C28
2012
C29
C30a
C30b
C30c
Shutdown
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

18. Current forward-planning of campaigns in 2013 focus on further exploitation of new capabilities
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2011
C28
2012
C29
C30a
C30b
C30c
2013
C31
C32
C33
Shutdown
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

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

20. Conclusions
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

21. Backup slides

22. Carbon content initially reduced by factor of 3, then remain steady-state throughout campaign
JET-ILW: Monitoring pulses
Be flux mirrors carbon

23. Oxygen content was slightly reduced when introducing Be (oxygen getter)
JET-ILW no Be evap.
JET-C with Be evaporation