Achievements of the first year of plasma operation with the JET ITER-Like Wall 2011/2012

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 AUG • 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 ITER • 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 ILWNeutral beam upgrade: 35MW, 20s Pellets for ELM control: 50HzEnhanced 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

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 2009 6

7. Installation of the JET ITER-like wall (ILW) was completed on May 8, 2011 7

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 BeSurface temperature < 900oC <22MJm-2s-1/2 (impact energy) W-coated CFCTemperature <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 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 ITER Gas balance results: Is the absolute value low enough? True long term value could be much lower (surface analysis) JET wall temperature JET C-wall & ILW ICRHH-mode Type III NBIH-mode Type I L-mode 10x 10x

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

13. 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 #80846 Dd (410.0nm) Intensity [arb. units] WI (400.8nm) Tdiv ∝ Pheat / ncore Central density 6.0 ne dl [1019 m-2] 4.7 3.5 #80768 55 60 t[s] R[m] 2.80 2.75 2.70 2.65 WI 400.8nm WI 400.8nm Intensity [arb. units] #80768 0 55 60 65 t[s] 14

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