Measurements with divertor probes on COMPASS ...

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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 ●



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 ●









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() 









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



Double roof with 5o and 10o regions to distinguish q|| from q 

● ● ● ●

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





● ●

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

● ●

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

● ●

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



Inserting deeper yields ● The same  q,near ●

The same q,main



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