by Zeke Unterberg Presented to FES Fusion Material Workshop Oak Ridge TN July 2016 E rosion deposition amp reerosion continuously evolve impurity source distribution as material migrates during plasma exposure ID: 810459
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Slide1
W migration in magnetic confinement devices
by
Zeke Unterberg
Presented to
FES Fusion Material Workshop
Oak Ridge, TN
July 2016
Slide2Erosion, deposition, & re-erosion continuously evolve impurity source distribution as material migrates during plasma exposure
Need to understand, interpret, & predict this surface evolution
Schmid
et
al., IAEA AMPMI, 2014
M
aterial migration causes PFC materials to rapidly change from what was installed
Slide3Detailed understanding necessary as we move to longer pulsed devices in order to deal with large re-deposits of material
Management of large quantities of
migrated material
will be necessary to prevent disrupting operation (“slag management”)
Estimates of CX-induced Net
First Wall Erosion Rate [NWER]
†
(Courtesy of
Stangeby & Buchenhauer)Device Pheat [MW]Annual runtime [s/yr]BerylliumNWER [kg/yr]BoronNWER [kg/yr]CarbonNWER [kg/yr]TungstenNWER [kg/yr]DIII-D201040.130.110.080.16JT-60SA341040.220.190.150.27EAST241051.61.20.821.8ITER10010677, 29*, 60***6444, 53*, 54***92, 41*, 46***Vulcan2010712010070150FNSF-AT100107610500340740Reactor4002.5e1076500530037007900, 5000**
†
Based on 5% power loss & 300eV T neutrals; see
Buchenhauer
et al, FES PMI workshop 2015
*
Kukushkin
el al., FED 2011 **
Lackner
, EU EFP Workshop on Tungsten 2009; ***
Behrisch
et al., JNM 2003
Slide4Erosion & migration depend on fluxes to surfaces that change with location
Migration is a multi-dimensional problem in space & time, therefore needs appropriate diagnostics
Complicated by wide ranges of magnitudes/energies
Complexity of in-/ex-situ diagnosis has severely restricted progress
Pitts et
al.,
PPCF, 2005;
Behrisch
et al., JNM, 2003ITER erosion modeling by different incident species on a variety of material surfaces Incident flux distributionErosion rate distribution
Slide5In divertor
tokamaks, most material migrates from main chamber
into divertor region
Both high-Z & low-Z material eventually end up in
divertorExact nature of re-deposition is seen to depend on plasma conditions, divertor geometry & speciesPoints to requirement of much better diagnostics
Pitts et
al.,
PPCF
, 2005Meisl et al., Phys.Scr. 2016WallDYN modelingof ITER N2 migrationWallDYN modeling ofJET ILW Be migration
Slide6Transient events also play a major role in material migration
T
ransients include ELMs, disruptions, dust and/or UFOs
ELMs have been investigated the most; still lots more to doDust/slag, especially in long pulse devices, will need to be addressed for impact on nuclear safety
Abrams, PSI,
2016
S
ubmitted to NF
DenHarder et al., NF, 2016JET comparison of W sources vs core contentDIII-D comparison of W source profile vs ELM frequency, fELMfELM = 130 HzfELM = 35 Hz?
Slide7Research needs/thrusts
L
ong pulse (high
fluence) dictate need to fully characterize & predict surface evolution Code
validation by experiment is extremely limited, to-dateBoth local (e.g. ERO) & global (e.g. WallDYN) erosion/migration codes need to be benchmarked in various devices & geometriesCoupling of these activities is needed on linear & toroidal devices for both short & long pulsesDiagnostic development/implementation to measure fluxes with space & time resolution in controlled conditions Simple in-situ surface diagnostics neededEasy to replicate to get as wide coverage as possible
Spatial & temporal measurements needed of
ELMs &
main- chamber
C-X fluxes