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Heating & Current Driving by LHW and ECW study on HL-2A

Heating & Current Driving by LHW and ECW study on HL-2A. Bai Xingyu, HL-2A heating team. Outline. Introduction EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup LHCD experiments LHCD &ECCD experiments Summary.

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Heating & Current Driving by LHW and ECW study on HL-2A

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  1. Heating & Current Driving by LHW and ECW study on HL-2A Bai Xingyu, HL-2A heating team

  2. Outline • Introduction • EC experiments • ECCD experiments • ECRH experiments • Pre-ionization and Assisted Startup • LHCD experiments • LHCD &ECCD experiments • Summary

  3. HL-2A is a normal Tokamak device of China, located in SWIP Chengdu Sichuan Province. Its main parameters： Bt=2.7T, t=5s, R=1.65m, r=0.4m, Te=5keV, Ip=450kA, ne=6*1019m-3 Introduction HL-2M is on building

  4. Introduction • EC system： • 68GHz : • 6*500kW gyrotrons • 2 antenna in 2 windows • Rotatable mirror • Duration 1s*4+1.5s*2 • 140GHz : • 2*1MW gyrotrons • 1 shared antenna • Rotatable mirror • Duration 3s 8 gyrotrons for ECRH

  5. Introduction • LH system： • 2*500kW klystrons • 2*12 antenna • n||=2.75 • f=2.45GHz

  6. Outline • Introduction • EC experiments • ECCD experiments • ECRH experiments • Pre-ionization and Assisted Startup • LHCD experiments • LHCD &ECCD experiments • Summary

  7. EC experiments • EC antenna (new)： • Rotatable in P direction: • Lower 2 mirrors • 1MW/140GHz only • Rotatable in T direction: • All mirrors • Left for right & right for left EC antenna structure of HL-2A

  8. ECCD experiments In ECRH condition, Ip=IOH+Ib+IEC Where IOH=Vl / R Vl is loop voltage R is the plasma resistance Ib≈cɛ1/2 bp Ip is Bootstrap current c≈1/3 is proportionality constant ɛ is the aspect radio IEC is driving current For the plasma is approximate constant, R& bp is constant We know that IEC0=0 when EC is injected in vertical direction So the driving current in different direction can be obtained by IEC≈(1-cɛ1/2 bp)(Ip-Vl Ip0/Vl 0) Where Ip0&Vl 0 are separately plasma current and loop voltage in vertical injection condition

  9. ECCD experiments ECCD efficiency has an optimized inject angle

  10. ECRH experiments ECRH NBI H mode is obtained for the first time on HL-2A in 2009 （shot 11333） H mode can be obtained by ECRH and NBI or only NBI on HL-2A PEC=1.62MW，PNBI=0.26MW (22151) NBI power is much less than the H mode threshold (MIN NBI power is 570kW for L-H transition) The output power of EC system (3MW/68GHz) can reach 2.5MW Can H mode be obtained only by ECRH ?

  11. ECRH experiments ECRH-H mode W7-AS [V. Erckmann, PRL1993] 0.45MW/140GHz/X2 DIII-D [J. Lohr, PRL1988] 60GHz/0.9MW/X2 r/a - 0~0.3 ASDEX-U [F. Ryter, NF2009] 140GHz/>1.3MW/X2 r/a=0~0.3

  12. Long SMBI ECRH experiments SMBI makes ne increase rapidly. limit cycle oscillation (LCO) appears in the following ne-decrease section Conditions: • Siliconized wall • Ne is controlled above 1.5 by SMBI • Displacement and X point angle control • Bt=1.34，inject point r/a=0.45 • ECRH power1.5MW

  13. 22909 NBI H-mode ECRH experiments LCO phenomenon with ELMs feature 23065 Bt~1.31T, r/a~0.3, PECRH ~1.6MW During ECRH，the displacementis controlled minus to avoid cutting off. Ne is feedback controlled 1.75 by SMBI. LCO frequency is 2-3kHz. Once (700ms~800ms) 1kHz component appears. And the oscillation waveform has ELMs feature 1kHz

  14. ECRH experiments In the ECRH H mode experiments, pump out phenomenon is a big problem Pump out phenomenon: Ne decreases while ECRH power increases and remain stable at a certain value. In the new profile, ne decreases in core and increases on the edge. Ne profile is changed from peaking to hollow ECRH Te↑ electron-ion collision rate↓ ne ↓ Ti ↓ ECRH NBI Power threshold ↑ Harder L-H transition

  15. Pre-ionization & Assisted Startup OnHL-2A, in order to build up scenarios for ECRH pre-ionization and assisted startup to relax theconditions required to breakdown and startup plasma on HL-2M, and to clarify the ITPA IOS2.3 open issue, ECRH pre-ionization and assisted startup experiments have been carried out during 2010, 2011 and 2012 experiment campaigns

  16. Pre-ionization & Assisted Startup • Waveform for min ECRH power and pure ohmic start up • Min breakdown voltage ：0.5V • Toroidal Electric field ：0.05V/m ( 1/6 ITER value) • Tt is the smallest value ever obtained by Tokamak • Min breakdown voltage of ohmic: 3.4V • The minimum breakdown voltage was reduced much

  17. ITPA IOS2.3 open issue The earlier application of loop voltage does not delay or hinder the avalanche formation on HL-2A, and even better than that of later application of loop voltage. There is no problem for earlier application of loop voltage. Why shorter delay times for earlier application? Loop voltage may accelerate the initial free electrons (about 0.03 eV) to a higher energy value close to subcritical energy, so the X2 mode absorption rate become higher, which causes the earlier breakdown.

  18. Shot: 14444 O1-mode P=200kW t=108ms, 117ms Shot: 16289 X2-mode P=600kW t=108ms, 117ms angle 0°, Shot: 16617 X2-mode P=800kW t=126ms, 135ms angle 20° Pre-ionization & Assisted Startup • Parameter influence • wall condition • prefilled gas pressure • field null structure • toroidal injection angle • The minimum ECRH powers • O1- mode：200kW • X2- mode：300kW

  19. Outline • Introduction • EC experiments • ECCD experiments • ECRH experiments • Pre-ionization and Assisted Startup • LHCD experiments • LHCD &ECCD experiments • Summary

  20. LHCD experiments In LHCD condition, Ip=IOH+Ib+ILH Where IOH=Vl / R While without LHCD, Ip0=IOH0+ Ib0 For the plasma current is feed back controlled, Ip should be the same as that without LHCD. Ib is considered to be constant and small (less than 10% Ip ) Ip = Ip0, Ib = Ib0 , Ip≈IOH=Vl / R, So, ILH=IOH0-IOH Which means ILH ≈ IpΔVl /Vl But the fact is a little more complex. Ip is not controlled completely.

  21. LHCD experiments Typical LHCD result on HL-2A ILH is formed by 2 components: ILH =IΔVl + ΔIp Where ΔIp can be read from data

  22. LHCD experiments LHCD efficiency on HL-2A

  23. Outline • Introduction • EC experiments • ECCD experiments • ECRH experiments • Pre-ionization and Assisted Startup • LHCD experiments • LHCD &ECCD experiments • Summary

  24. LHCD &ECCD experiments Why ECCD can improve LHW absorption？ Pump out phenomenon makes particle move out, which increase edge density. That form a puffing gas effect on the edge, which make LHW coupling better. Full CD obtained by LHCD&ECCD ECCD improve absorption of LHW

  25. Outline • Introduction • EC experiments • ECCD experiments • ECRH experiments • Pre-ionization and Assisted Startup • LHCD experiments • LHCD &ECCD experiments • Summary

  26. Summary • EC experiments was carried out on HL-2A • ECCD efficiency was estimated and compared with theory • H mode experiments by ECRH only was tried. LCO phenomenon with ELMs feature was obtained • Pre-ionization and assisted startup experiment by ECW was carried out. The smallest Toroidal electric field ever in Tokamak is obtained. The result shows that earlier application of loop voltage does not delay or hinder the avalanche formation, even better, which solves ITPA IOS2.3 open issue • LHCD experiments was carried out on HL-2A • LHCD efficiency was estimated • LHCD &ECCD experiments was carried out also • Full CD was observed • ECCD improve LHCD coupling phenomenon was achieved and analyzed

  27. Thank you!

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