1. Merging Start-up and Sustainment Experiments on UTST 15 th Intl. Workshop on Spherical Tori 2009, Madison, WI, Oct. 22, 2009 T. Yamada 1, R. Imazawa 2, S. Kamio 1, R. Hihara 1, K. Abe 1, M. Sakumura 1, Q. H. Cao 1, H. Sakakita 3, H. Koguchi 3, S. Kiyama 3, Y. Hirano 3, T. Oosako 1, H. Kobayashi 1, T. Wakatsuki 4, B. I. An 4, Y. Nagashima 1, M. Inomoto 1, A. Ejiri 1, Y. Takase 1 and Y. Ono 1 1 Graduate School of Frontier Sciences, The University of Tokyo 2 Graduate School of Engineering, The University of Tokyo 3 National Institute of Advanced Industrial Science and Technology 4 Graduate School of Science, The University of Tokyo

2. Outline Overview of the UTST experiment Recent progress of the UTST experiment  290-ch. simultaneous measurement  PF + Acceleration coils  Neutral Beam Injection Summary

3. Overview of the UTST experiment

4. Objective of the UTST Plasma UTST (Kashiwa campus) (Hongo campus) TST-2 (Takase-Ejiri Lab.) RF heating technique Merging technique NB injection from AIST

5. Generating a High  ST By magnetic reconnection, the magnetic field energy is converted to the plasma kinetic energy, and the plasma  is increased up to 50%. Two Merging STs

6. Double Null Merging (DNM) Method At UTST, DNM start-up is performed by outer PF coils. Null-points formed PF Ion heating by Magnetic Reconnection PF coils generate plasmas High  ST Merging

7. The UTST Plasma Merging Device 2 m 0.7 m ACC2 (4 turns) EF2 (8 turns) PF3 (3 turns) ACC1 (4 turns) PF1 (8 turns) Washer gun (for pre-ionization) PF2 (3 turns) EF1 (8 turns) CS (95 turns) TF (8 turns) Pickup coil array B t : 64 channels B z : 64 channels PF4 (8 turns) Pickup coil array B t : 81 channels B z : 81 channels

8. Typical Discharge of the UTST Plasma Gas (H 2 ) Anode Cathode Plasma Washers Insulator Washer gun is used for pre-ionization. Two main discharge scenarios. a.DNM start-up discharge (PF). b.DNM start-up + CS assist discharge (PF + CS). Seed plasma in a spiral magnetic field.

9. TF (/turn)EF (/turn) Washer gun PF (/turn) Plasma current (CW) a. PF discharge Plasma current up to 40 kA was obtained by DNM method, by using PF coils.

10. b. PF+CS discharge TF (/turn)EF (/turn) Washer gun PF (/turn) Plasma current (CW) CS (/turn) current[kA] Plasma current reached 170 kA by using the CS coil to assist the DNM start-up (PF) discharge.

11. Recent progress of the UTST experiment

12. 1. Two-dimensional Pickup Coil Arrays Glass tube By using B t and B z pickup coil arrays, many variables can be calculated. An Example of poloidal flux, , produced by EF coils, measured by the pickup coils. Pickup coil array B t : 64 chs. B z : 64 chs. Pickup coil array B t : 81 chs. B z : 81 chs. Expansion of the digitizer made it possible to measure all the 290 channels simultaneously.

13. Improvement of the measurement B z and B t are reconstructed by Precision of B z and B t measurement has been improved.  and  are measured by generating toroidal or vertical magnetic fields. Good agreement between B z with B t and B z w/o B t.

14. a. Results on PF discharge Fast camera images Two STs are merged together to form a single ST

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16. b. Results on PF + CS discharge 4.70 ms 4.71 ms 4.72 ms 4.73 ms4.74 ms Fast camera images The merged plasma reached up to 170 kA.

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18. To be reported in APS DPP, PP8.00099 (Atlanta, GA). 2. PF discharge + Acceleration coils ACC2 ACC1 By using acceleration coils on PF discharge, current sheet was observed. Acceleration coils increase the plasma merging speed. Current sheet ?! PF + CS + ACC is under preparation.

19. 3. Neutral Beam Injection 160 mm NB's acceleration electrode (concave type, F = 1250 mm) UTST NB A general view of the experiment device Neutralization chamber Jointed to UTST Ion source

20. 10 ms 500 kW Neutral beam power Neutral Beam Injection focus NB UTST Top view of NB and UTST Fast camera image Plasma current Test of the neutral beam device and test injection into the UTST device have been finished. Higher density will be required for effective results.

21. Plasma startup by double null merging method was successfully observed in the UTST plasma merging experiment. Plasma current up to 40 kA was achieved, and the merging of magnetic surfaces was observed. With CS assist, plasma current reached 170 kA. By using Acceleration coils, current sheet was observed. Neutral beam injection has just started. Summary Pre-ionization at the upper region is needed for balancing STs. Power supplies to the coils will be increased. More diagnostics. Future Works