PISCES Laser Transient Systems - University of California...

UCSD Center for Energy Research K.Umstadter – PELS

PISCES

PISCES Laser Transient Systems

Karl R. Umstadter for PISCES Team

Center for Energy ResearchUniversity of California – San Diego, USA

February 11, 2009


PISCES

Overview

• Introduction

• Use of Laser Heat Pulses

• PA Short Pulse Update

• PA Long Pulse Initial Results

• PB Long Pulse Install


PISCESIntroduction

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


PISCES

IFE/MFE Transients & Experiments

J. Linke, F. Escourbiac, I.V. Mazul, R. Nygren, M. Rodig, J. SchlosseR, S. Suzuki, J Nucl. Mat. 367–370 (2007) 1422–1431

PISCES

5.E-9

Q

LP


PISCES

PISCES A & Beam Delivery

Laser PathPISCES A

Γ~1017 – 1019 D+/cm2 s-1

n ~ 1012 D+/cm3

Te ~ 5-10eVVbias ~ up to 250V Rp ~ 4cm


PISCESIntroduction

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.


PISCES

0

500

1000

1500

2000

2500

3000

3500

1.0E

-08

1.0E

-07

1.0E

-06

1.0E

-05

1.0E

-04

1.0E

-03

Depth in Target (m)

Tem

pera

ture

(C)

ELM (300usec)ELM+60usecYAG (5nsec)YAG+1nsec

Q-Switch Nd:YAG as ELM Mimic

YAG Pulse Simulates Surface Heating Well

Longer duration results in deeper

heat transport

May effect retention

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/m2-s1/2


PISCES

Mimic of ELM Transient on W

Laser Exposure of W at 200C for 60min

• Laser Parameters5nsec4mm spot166mJ per Shot~108 W/cm2

1200 Pulses

• Plasma ParametersTotal Fluence ~ 1026 D+/m2

Ion Energy ~100eV

Absorbed Energy Impact~58 MJ/m2 s1/2

RW (λ=1064nm) ~ 70%

ELM Equivalent1MJ/m2 @ 0.3msec


PISCES

SEM Surface Analysis


PISCES

Plasma + Heat Pulse Enhancement

F~ 1026 D+/m2

Tsurf ~ 50ºC

Absorbed Energy Impact~45 MJ/m2 s1/2

+

LASER ONLY LASER + PLASMA

LASERSPOT


PISCES

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 30 60 90 120 150Ion Energy [eV] (Vbias-Vplasma)

Mas

s Lo

ss (m

g)

Laser + PlasmaLaser OnlyPlasma Only

Erosion of W PFC under Simulated ELM Transients at High Repetition Rate

F~ 1026 D+/m2

Tsurf ~ 50ºC

3000 Transients withAbsorbed Energy Impact

~45 MJ/m2 s1/2

(low fluence between ELMs)


PISCES

Effects of D Loading on Damage

F = 5x1022/m2

F = 5x1023/m2

F = 2x1024/m2

Vbias=125VΓ=2x1022/m2-sec

Te=11eVne=2x1024/m3

SAM

PLE

Fluence to surfacebetween heating

transients


PISCES

Summary of Observations

• Fluence to PISCES-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


PISCES

Long Pulse Laser

• New Laser System• 0.3 - 20msec pulse• Epulse = 1.5 - 50 J

• Installation on PISCES A• Compare results to short-pulse

results• Test diagnostic systems

• Installation on PISCES B for Mixed Materials Studies –

Alloying of MaterialsEffect on Surface “Nanostructures”


PISCESLong Pulse Nd:YAG as ELM Mimic

0

1000

2000

3000

4000

5000

1.E-06 1.E-05 1.E-04 1.E-03 1.E-02depth (m)

Tem

p (C

)

0.3msec1msec5msec10msec

Maximum system parameters at each pulse duration


PISCES

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


PISCES

Initial Experiments

• 25J – 5msec - 1200 Laser Pulses @1/3 Hz5 kW – 50MJ/m2s1/2

• 75V Bias – Total Fluence ~1026 D+/m2

Room Temperature >500ºC


PISCES

Surface Profiles

-70E+3

-35E+3

000E+0

35E+3

70E+3

-500 0 500 1000 1500 2000 2500 3000 3500 4000

Position (um)

Hei

ght (

nm)

RT

550C


PISCES

PB Implementation Update

LaserOptics

EnclosurePyrometer

Spectroscopy Window with Laser Glass Shutter (Interlocked)

Laser-Safe Plastic Operators Window


PISCES

Questions

Karl R. [email protected]

PISCES TeamM.Baldwin, R.Doerner, J. Hanna, E. Hollmann,

D. Nishijima, G.R.Tynan, and J. Yu

PISCES Laser Transient Systems - University of California...

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