ASIPP

1. HT-7 belt limiter ASIPP Investigation of EAST Divertor Asymmetry in Plasma Detachment & Target Power Loading Using B2/Eirene Houyang Guo, Sizhen Zhu and Jiangang Li Seminar presented at AS-IPP, Hefei, 10/10/2006

2. HT-7 belt limiter Acknowledgements • Jiangang Li, Baonian Wan, Yuanxi Wan, • Sizhen Zhu for support of this work. • Youzhen He, Weiping Huang, Qing Li, • Ying Zhang for facilitating my visit. • And all of you!

3. HT-7 belt limiter Introduction • A major concern for EAST and future high- • powered steady-state machines such as • ITER is the power handling capability of • divertor target plates. • Localized injection of highly radiating • impurities such as Ne may provide as a • means of reducing power fluxes to the • divertor targets and actively controlling • inner/outer divertor asymmetry in power • loading.

4. HT-7 belt limiter Outline • EAST divertor geometry and major modeling • parameters for B2/Eirene – SOLPS4.0. • Basic performance of EAST divertor in • terms of target power loading and impurity • screening for both single-null and • double-null configurations. • Active control of plasma detachment and • target power loading using neon puffing. • Summary and conclusions.

5. HT-7 belt limiter Unique Features of EAST • High power • 1st phase: 10 MW • 2nd phase: 20 MW • (with NB) • AndLong pulse • 1000 s, sustained by • LHCD

6. HT-7 belt limiter EAST was built to allow both single null and double null divertor operations

7. HT-7 belt limiter Basic Divertor Functions • Exhaust power and particles • (including helium ash in a reactor) • Provide sufficient screening for • impurities to minimize core • contamination

8. A major concern for EAST and ITER is divertor power handling capability - Provided by Dr. Damao Yao

9. Modeling of Divertor Performance Using B2/Eirene – SOLPS 4.0 • B2/Eirene code package – SOLPS 4.0 •  A multi-fluid codeB2for electrons and ions, and •  A Monte-Carlo codeEirenefor neutrals • Major control parameters •  Total heat fluxes from confined core: • Ps  4 MW (equally split between the i and e channels) • Ps,out  3Ps,innfor double dull configuration • ns = 0.5  3.51019 m-3 •  ITER-like cross-field transport: • D = 0.3 m2s-1 • i  e  1.0 m2s-1

10. Impurity Sources (1) Intrinsic Carbon  Physical sputtering  Chemical sputtering Ych = 2% (2) Active neon puffing  To reduce target power loading  Control divertor inner/outer asymmetry

11. Comparison between single null (SN) & double null (CDN) configurations • As expected, CDN • reduces peaked heat • fluxes to both targets. • Zs is also reduced • for CDN. • However, plasma • detaches at inner target • occurs at a much lower • density for CDN, thus • resulting in strong • divertor asymmetry.

12. ns = 1.51019 m-3 CDN operation leads to stronger divertor asymmetry • Plasma is fully detached • from inner target, with heat • flux to the target dramatically • reduced. • Heat flux at the outer strike • point is substantially reduced • - a key feature of vertical • divertor, but remains high • elsewhere. • Localized gas puffing from outer divertor may accelerate detachment, further reducing heat flux to the outer divertor.

13. HT-7 belt limiter Consequences of Divertor Asymmetry Full plasma detachment at inner target may lead to confinement degradation due to excessive neutral influxes around X-point to the core.  Further, most of the outer divertor plasma still remains attached, with substantial power flux going to the outer target, which is undesirable for long pulse operation.

14. Ne Localized neon puffing is used as a means to reduce heat flux to outer target • Ne is introduced from • outerlower divertor. • Ne is well restricted to the • vicinity of lower divertor • due to strong divertor • screening for Ne. • However, significant • radiation from neon is • also present in the inner • divertor, presumably due • to leakage of Ne through • private region or around • X-point.

15. Nevertheless, Ne puffing dramatically reduces heat fluxes to the outer target It is remarkable that neon puffing does not appear to affect much the edge impurity content, suggesting very strong divertor screening for neon under modeled conditions.

16. Work in progress: Reduce neon leakage into inner divertor • To further reduce heat flux to the outer target and divertor asymmetry: • Optimizing Ne puffing location to maximize Ne ionization inside outer divertor. • Inducing SOL flow by mid- plane fueling & pumping. • A physical septum may help preventing direct Ne leakage from outboard into inboard.

17. HT-7 belt limiter Summary & Conclusions  A major concern for EAST and future high-powered steady-state machines such as ITER is the power handling capability of divertor target plates.  As expected, double null operation distributes output power more widely, reducing peak target power loading.  However, double null leads to early detachment at inner target, resulting in strong divertor asymmetry.  Ne puffing from outer divertor dramatically reduces peak heat flux to the target, without affecting much Zeff.  To further reduce outer target power loading and divertor asymmetry, Ne leakage into inner divertor must be minimized.