Ar puff

D2 puff

Pumping

概述

This work is supported by National Magnetic Confinement Fusion Science Program of China under contract no. 11405214, and the China National Fusion Project for ITER under grant nos. 2014GB106000, 2013GB106002 and 2014GB106003.

\ The local closure effect of the divertor structure has been studied on the detachment density in CFETR by using the scrape-offlayer plasma simulation (SOLPS) code. The divertor geometry near the striking point was set as a semicircle structure. The local closure ofstriking point was changed by reducing the radius of the semicircle step by step with all the other parameters fixed the same. The simulationresults reveal that the heat flux show great differences in low density case and high density case. In low density case, the applied of semicirclestructure (r~10cm) can hardly change the heat flux of the striking point. Yet, for the high density case, the semicircle structure will greatly reducethe temperature of the striking point, thus enhance the density of the neutral gas. In other words, the increased local closure effect willsignificantly reduce the heat flux of the striking point and help reduce the threshold density of the detachment.

Study of local closure effect of the Divertor structure on Detachment Density in CFETR

D.F.Konga,X.J.Liua,R.Dinga,C.F.Sang b, S.F. Maoc, V.Chan c,X.Gaoa,c,J.G.LiaaInstituteofPlasmaPhysics,ChineseAcademyofSciences,230031HefeiAnhui,PRChinabSchoolofPhysicsandOptoelectronicEngineering,DalianUniversityofTechnology,Dalian116024,People’sRepublicofChina.cUniversityofScienceandTechnologyofChina,Hefei230026,People’sRepublicofChina

ASIPP

Discussion

Acknowledgement

ResultsSetup of simulations

Divertor geometry configuration

Abstract

üUpstream profiles• A set of upstream profiles including

(ne, nD+, P, Te and Ti ) can be got which is good agreement with the results from OMFIT in pedestal region.

• Ti is much higher than Te due to higher qi, which is reasonable for CFETR with low edge collisionality (ν<<50).

• Furthermore, EPED model is rather more concern about the structure of pressure in pedestal than the profiles of Temperature and density.

72

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,//, 2

7÷÷ø

öççè

æ»

ei

Deieui

LqT

k 0 060 2000i ek k» << »

üThermal conductivity coefficients:

üTransport coefficients• For pedestal region, D, χe, χi and v are

determined by fitting the Te, Ti, ne and P profiles given by OMFIT.

• For SOL region, D, χe, χi and v are assumed and make sure the power decay length at OMP similar to the value predicted by T. Eich et al and smooth connection with the core values at separatrix.

𝝀𝒒𝑺𝒑𝒊𝒕𝒛𝒆𝒓 = 𝟐

𝟕𝝀𝑻𝒆~6.6mm

(#Kallenbach etal,JNM 2015)𝝀𝒒(𝟏𝟒) = 𝟎. 𝟔𝟑𝑩𝒑𝒐𝒍9𝟏.𝟏𝟗𝐦𝐦~0.78mm

(Eichetal,NF 53(2013))XGC1 result?(C.S.ChangetalNucl.Fusion57(2017)116023)

semicircle

𝒏𝒆

ü In summary, the increased local closure effect will significantly reduce the heat flux of the striking point and help reduce the threshold density of the detachment.

𝒏𝒆

𝑷𝒕𝒂𝒈𝒆𝒕 𝑷𝒕𝒂𝒈𝒆𝒕

𝑻𝒆

𝒁𝒆𝒇𝒇

flatsemicircle

flat semicircle

Electron temperature

Low density case: 𝟑×𝟏𝟎𝟏𝟗𝒎9𝟑 High density case: 𝟔×𝟏𝟎𝟏𝟗𝒎9𝟑

flat semicircle

Neutrals density

D.F. Kong et al., The 2nd IAEA- Technical Meeting on Divertor Concepts, 13-16 Nov 2017, Suzhou, China

SOLPrivatefluxzone

• In low density case: the increased local closure wouldn’t affect the peak power anddensity on the target;

• In high density case: the increased local closure effect can significantly suppress peaktemperature, thus the peak power on the target. Yet, the temperature of plasma farout is still high.

The semicirclestructure willhelp toconcentrate theneutrals on thestrike point.

The semicirclestructuresuppresstemperature onthe strike point.

Flat case semicircle case

• D2 and Ar puff are included in simulations;• The divertor target assume to be W;• All parameters are kept the same between flat case and semicircle case during the

simulations.

r=2cmr=5cmr=10cmr=20cm

Parameters CFETR with high Bt

Ip (MA) 10MAR/a(m) 6.6/1.8Bt(T) 6

<ne>(1019m-3) 9.8Beta_n 3.2q_95 5.2f_bs 84%

P_in (MW) 54P_EC(MW) 20P_NB(MW) 34

Q_fus 15.5H_98 1.35P_fus 840MWZeff 2.0

Y.X. Wan et.al. Nucl. Fusion 57 (2017) 102009

1. Fix 𝝀𝒒, the local closure will be changed by altering the radiusof semicircle from 2cm, 5cm, 10cm to 20cm step by step.

2. Fix radius of semicircle, scan the 𝝀𝒒. Explore the relationshipbetween 𝝀𝒒 and radius (local closure).

Ar puff

D2 puff

Pumping