The 2 nd IAEA Technical Meeting on Divertor Concepts, 13 to 16 November, 2017, Suzhou China Conceptual Design of Magnetic Island Divertor in the J-TEXT tokamak Bo Rao 1, Yonghua Ding 1, Song Zhou 1, Nengchao Wang 1, Yunfeng Liang 1,2,3 and J-TEXT team 1 State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China 2 Forschungszentrum Jülich GmbH, Association EURATOM-FZ Jülich, Institut für Energieforschung-Plasmaphysik, Trilateral Euregio Cluster, D-52425 Jülich, Germany 3 Institute of Plasma Physics Chinese Academy of Sciences Email: borao@hust.edu.cn 1
Motivation Ref.: Y Feng, et al. PPCF 2011 Plasma ions flow in the two divertor legs with opposite toroidal velocities, however, the two adjacent legs in a island divertor (ID) are much closer to each other, which cause momentum loss. The connection length in SOL of a ID is much longer than that in poloidal divertor. Reduce interactions between plasma and first wall materials Increase perpendicular transport 2
Motivation Can we get a ID in the tokamak edge? It is more difficult, especially in a divertor tokamak, however, much easier in limiter configurations. The edge transport in the regions with closed surface, islands and stochastic regions is much different. Edge recycling, thermal power decay length (λq) and also impurity behaviors may be optimized. Stochastic region island target Ref.: Y Feng, et al. PPCF 2011 3
J-TEXT tokamak Parameters R = 1.05m; a = 0.26m (Limiter); I p =350 ka (220 ka now);b T =3.0T (2.2T now); n e =0.1-0.8 10 20 m -3 (5 10 19 m -3 now); T e (0) ~1keV; Diagnostics ECE, ECE imaging (USTC) Polarimeter-interferometer XICS Reciprocating Langmuir Probe ERD, CIII arrays IR TV 4
Methods Choose a plasma equilibrium with edge q slightly larger than 4 (4.06). Calculate field of ID coils Construct the flux coordinate, the field component perpendicular the magnetic surface, and then take Fourier Transform Take flied line tracing to observe island width, connection length and calculate edge transport 2D Plasma Equilibrium Flux coordinate (ψ,ω,φ ) Perpendicular component to magnetic surface Bq(ω,φ) DFT Maximize m/n =4/1 Calculate vacuum magnetic field of island divertor coils (BR,BZ,Bφ ) Filed line tracing Connection length, transport evaluation, possible heat deposition on targets 5
Possible solution 1 r, m Saddle coils outside the vacuum vessel wall 4 poloidal 4 toroidal A 1.5~2 cm 4/1 island can be obtained with 5 ka current 4/1 (1.5~cm) 3/1 2/1 6
Possible solution 2 Modular coils inside the vacuum vessel 8 Z configuration coils Widths and positions of conducting loops change with the magnetic field line Coil conductor Field line on q=4 surface 7
Possible solution 2 r, m Modular coils inside the vacuum vessel 1kA Large 5/1 is produced together with 4/1, lead to a wide stochastic region. 4/1 (1.5~cm) 3/1 2/1 θ, degs. 8
Existing RMP coils on J-TEXT Connection mode 1 8 groups, 24 coils in total Connection mode 1: 2/1 resonant mode dominated Connection mode 2: 1/1 and 3/1 dominated Connection mode 2 9
2/1 and 3/1 compensation Magnetic perturbations with low mode numbers are those we must pay enough attention to. They can interact intensively with core plasmas and even cause disruptions. In our design, 2/1 component is expected to be compensated with the existing RMP coils. 3/1 perturbation or island may obviously change the edge transport, so the 3/1 perturbation is hope to be controllable. 2/1 perturbation produced by existing RMP 3/1 perturbation produced by existing RMP 10
Experimental Plan In the near future, optimize the magnetic field spectrum to get a flexible island configuration, and also a reliable engineering design Use present limiter as the simplified target, and observe plasma transport near the island regions and the heat flux distribution IR camera, CCD AXUV, CIII, CV, Ha Plasma limiter Electrostatic Probe arrays 11
Thanks for your attention! 12