PISCES Laser Transient Systems

Transcription

1 Laser Transient Systems Karl R. Umstadter for Team Center for Energy Research University of California San Diego, USA February 11, 2009

2 Overview Introduction Use of Laser Heat Pulses PA Short Pulse Update PA Long Pulse Initial Results PB Long Pulse Install

3 Introduction When an ELM occurs in tokamaks, up to 30% of the pedestal energy can be deposited on the plasma facing boundary Result is heating & material loss due to sublimation, evaporation and melt splashing of plasma facing components and Expansion of the ejected material into the plasma

4 IFE/MFE Transients & Experiments Q LP 5.E-9 J. Linke, F. Escourbiac, I.V. Mazul, R. Nygren, M. Rodig, J. SchlosseR, S. Suzuki, J Nucl. Mat (2007)

5 A Γ~ D + /cm 2 s -1 n ~ D + /cm 3 Te ~ 5-10eV V bias ~ up to 250V R p ~ 4cm A & Beam Delivery Laser Path

6 Introduction Calculations indicate that a pulsed laser system can be used to simulate the surface effects of the heat pulse of ELMs Surface temperature during an ELM is a function of the energy density of deposition and thermal conduction to the bulk during and following the deposition Lasers of varied pulsewidth can be utilized to mock transients such as ELMs and IFE wall impacts.

7 Temperature (C) E-08 Q-Switch Nd:YAG as ELM Mimic ELM (300usec) ELM+60usec YAG (5nsec) YAG+1nsec YAG Pulse Simulates Surface Heating Well 1.0E E-06 Longer duration results in deeper heat transport May effect retention 1.0E-05 Depth in Target (m) 1.0E E-03 Surface temperature during an ELM is a function of the energy density of deposition and thermal conduction to the bulk during and following the deposition Best expressed as an Energy Impact Value with units MJ/m 2 -s 1/2

8 Mimic of ELM Transient on W Laser Exposure of W at 200C for 60min Laser Parameters 5nsec 4mm spot 166mJ per Shot ~10 8 W/cm Pulses Absorbed Energy Impact ~58 MJ/m 2 s 1/2 R W (λ=1064nm) ~ 70% ELM Equivalent 1MJ/m 0.3msec Plasma Parameters Total Fluence ~ D + /m 2 Ion Energy ~100eV

9 SEM Surface Analysis

10 Plasma + Heat Pulse Enhancement Absorbed Energy Impact ~45 MJ/m 2 s 1/2 + F~ D + /m 2 T surf ~ 50ºC LASER SPOT LASER ONLY LASER + PLASMA

11 Mass Loss (mg) Erosion of W PFC under Simulated ELM Transients at High Repetition Rate (low fluence between ELMs) Laser + Plasma Laser Only Plasma Only 3000 Transients with Absorbed Energy Impact ~45 MJ/m 2 s 1/2 F~ D + /m 2 T surf ~ 50ºC Ion Energy [ev] (Vbias-Vplasma)

12 Effects of D Loading on Damage SAMPLE F = 5 x /m 2 F = 5 x /m 2 F = 2 x /m 2 Fluence to surface between heating transients V bias =125V Γ=2x10 22 /m 2 -sec T e =11eV n e =2x10 24 /m 3

13 Summary of Observations Fluence to -A targets between transients greater than operating tokamaks - approaching ITER Neutral and Ionized W found in range of mm to several cm in front of surface allows study of transport & redeposition Synergistic effect between thermal transients & plasma exposure leads to enhanced material removal Synergistic effect depends upon D fluence between transients

14 Long Pulse Laser New Laser System msec pulse E pulse = J Installation on A Compare results to short-pulse results Test diagnostic systems Installation on B for Mixed Materials Studies Alloying of Materials Effect on Surface Nanostructures

15 Long Pulse Nd:YAG as ELM Mimic msec 1msec 5msec 10msec Temp (C) E-06 1.E-05 1.E-04 1.E-03 1.E-02 depth (m) Maximum system parameters at each pulse duration

16 PA Long Pulse Output beam collimated (divergence reduced) Laser safety windows installed Beam entirely enclosed outside vacuum No goggle operation Heat exchanger repaired Aux air cooling added (AC) Triggering system for remote/camera operation

17 Initial Experiments 25J 5msec Laser Hz 5 kw 50MJ/m 2 s 1/2 75V Bias Total Fluence ~10 26 D + /m 2 Room Temperature >500ºC

18 Surface Profiles 70E+3 RT 550C Height (nm) 35E+3 000E+0-35E+3-70E Position (um)

19 PB Implementation Update Spectroscopy Window with Laser Glass Shutter (Interlocked) Enclosure Pyrometer Laser Optics Laser-Safe Plastic Operators Window

20 Questions Karl R. Umstadter Team M.Baldwin, R.Doerner, J. Hanna, E. Hollmann, D. Nishijima, G.R.Tynan, and J. Yu