P.C. Stangeby. University of Toronto, Institute for Aerospace Studies, Toronto, M3H 5T6, Canada. Narrow heat flux channels in the COMPASS limiter scrape-off ...
Narrow heat flux channels in the COMPASS limiter scrape-off layer J. Horacek, P. Vondracek, R. Panek, R. Dejarnac, M. Komm, P. Hacek, J. Havlicek, M. Hron, M. Imrisek, F. Janky Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 1782/3, 182 00, Prague 8, Czech Republic Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
R.A. Pitts, M. Kocan ITER Organization, Route de Vinon-sur-Verdon, CS 9004,613067 St. Paul Lez Durance Cedex, France
R.J. Goldston Princeton Plasma Physics Laboratory, Princeton New Jersey 08543, USA
P.C. Stangeby University of Toronto, Institute for Aerospace Studies, Toronto, M3H 5T6, Canada
J. Horacek: Steep heat flux on COMPASS limiter
| 1/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
Optimum shape of innerwall limiter is logarithmic ●
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ITER first wall is shaped for start-up and ramp-down in limiter configuration → HFS is preferred. 1st wall toroidal shaping on ITER is designed to spread power uniformly for a single SOL heat flux decay length q. toroidal
q=-q||/ rq||=? Main SOL q scaling is subject of recent works [O3 Ricci] etc. Multi-machine database has been constructed by ITPA Div/SOL. Tor J. Horacek: Steep heat flux on COMPASS limiter
| 2/17 | PSI conference, Kanazawa, Japan
oidal x
| 26.5.2014
Near SOL much steeper than main SOL ●
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JET HFS limiter was designed for a single main SOL q~1cm. Melting observed on some tile apexes during HFS limiter plasmas! JET IR camera shows qmain >>qnear !
G. Arnoux, Phys. Scr. T159 (2014) 014009
ITER Organization launched a working group to investigate the HFS limiter power deposition Experiments on ● COMPASS ● TCV [Nespoli P-095] ● D-IIID [Stangeby, O5] ● C-Mod (in progress)
J. Horacek: Steep heat flux on COMPASS limiter
Main SOL G. Arnoux et al. Nucl. Fusion (2013) 073016.
| 3/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
COMPASS experimental setup
IR camera viewing COMPASS central column Graphite tiles 18 toroidal x 3 vertical
J. Horacek: Steep heat flux on COMPASS limiter
| 4/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
First observation of rounded limiter T → Theodor → q [MW/m2]
limiter toroidal profile
Vertical
rounded
Toroidal ●
q||(r)=q /sin()
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J. Horacek: Steep heat flux on COMPASS limiter
First indication for narrow q.
EFIT & limiter geometry → and r here vary only vertically The FOV limited → unable to see the main SOL Problems with misalignment (toroidal tilt) → experimental program launched with various limiter insertions, inclinations and toroidal shaping
| 5/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
2nd step: double-roof limiter rounded
roof
18 Langmuir probes
limiter toroidal profile
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Double roof with 5o and 10o regions to distinguish q|| from q
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Main SOL now visible in IR Variable tilt assures toroidal symmetry All directions of Ip & Btor Embedded Langmuir probes to see: ● q =T J || e sat ●
J. Horacek: Steep heat flux on COMPASS limiter
Local non-ambipolar currents to limiter
| 6/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
2nd step: double-roof limiter rounded
roof
limiter toroidal profile
Generic 2- q heat flux profile
q||0,near q||0,main
q,main
IR data fitting with double-exponential
q=sin()q||0near(e-r/near+e-r/main/Rq) Rq=q||0near/q||0main is the measure of
q,near
J. Horacek: Steep heat flux on COMPASS limiter
importance of the narrow feature.
| 7/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
2nd step: double-roof limiter rounded
roof
limiter toroidal profile
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J. Horacek: Steep heat flux on COMPASS limiter
It can be radially inserted up to 40mm this strengthen the narrow feature Narrow feature observed by IR in all discharges without exception Profiles vary with Ip and insertion We see toroidal asymmetry (30% at LCFS) which flips with Ip
| 8/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
3rd step: Logarithmic double-roof rounded
roof
log & roof
limiter toroidal profile
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Narrow feature still preserved The heat is reversed: lowest at the apex
Vertical
q
Toroidal J. Horacek: Steep heat flux on COMPASS limiter
| 9/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
4th step: recessed-roof rounded
roof
log & roof recessed 2-roof
limiter toroidal profile
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Insertions: -2, 0, 4 mm ITER relevant shape and expected misalignments
Toroi da
J. Horacek: Steep heat flux on COMPASS limiter
lx
| 10/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
IR camera observation of HFS limiters rounded
roof
log & roof recessed 2-roof
limiter toroidal profile
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Inserting deeper yields ● The same q,near ●
The same q,main
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Higher Rq as it intercepts more of the narrow feature
Insertion = 40mm
el. side
q,near a few mm
Insertion = 0
J. Horacek: Steep heat flux on COMPASS limiter
Ion side
| 11/17 | PSI conference, Kanazawa, Japan
| 26.5.2014
Clear scalings for recessed limiters (ITER-relevant) Recessed = the limiter is part of the inner wall insertion
