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

HL-2A Outline  Introduction  EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup  LHCD experiments  LHCD &ECCD experiments  Summary

HL-2A Introduction HL-2A is a normal Tokamak device of China, located in SWIP Chengdu Sichuan Province. Its main parameters ： B t =2.7T, t=5s, R=1.65m, r=0.4m, T e =5keV, I p =450kA, n e =6*10 19 m -3 HL-2M is on building

HL-2A 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

HL-2A Introduction LH system ： 2*500kW klystrons 2*12 antenna n || =2.75 f=2.45GHz

HL-2A Outline  Introduction  EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup  LHCD experiments  LHCD &ECCD experiments  Summary

HL-2A EC experiments EC antenna structure of HL-2A 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

HL-2A In ECRH condition, I p =I OH +I b +I EC Where I OH =V l / R V l is loop voltage R is the plasma resistance I b ≈c ɛ 1/2  p I p is Bootstrap current c≈1/3 is proportionality constant ɛ is the aspect radio I EC is driving current ECCD experiments For the plasma is approximate constant, R&  p is constant We know that I EC0 =0 when EC is injected in vertical direction So the driving current in different direction can be obtained by I EC ≈(1-c ɛ 1/2  p )(I p -V l I p0 /V l 0 ) Where I p0 &V l 0 are separately plasma current and loop voltage in vertical injection condition

HL-2A ECCD experiments ShotΦ (degree) dI OH /dt (kA/s) I EC (kA)  EC (10 19 A m -2 W -1 ) ECCD efficiency has an optimized inject angle

HL-2A ECRH experiments H mode is obtained for the first time on HL-2A in 2009 （ shot ） 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 ? ECRH NBI

HL-2A 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

HL-2A 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 Long SMBI

HL-2A ECRH experiments LCO phenomenon with ELMs feature NBI H-mode kHz Bt~1.31T, r/a~0.3, P ECRH ~1.6MW During ECRH ， the displacement is 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

HL-2A ECRH experiments 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 NBI ECRH In the ECRH H mode experiments, pump out phenomenon is a big problem ECRH Te ↑ ne ↓ Power threshold ↑ electron-ion collision rate ↓ Ti ↓ Harder L-H transition

HL-2A Pre-ionization & Assisted Startup On HL-2A, in order to build up scenarios for ECRH pre-ionization and assisted startup to relax the conditions 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

HL-2A 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

HL-2A 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.

HL-2A Pre-ionization & Assisted Startup Shot: O1-mode P=200kW t=108ms, 117ms Shot: X2-mode P=600kW t=108ms, 117ms angle 0°, Shot: X2-mode P=800kW t=126ms, 135ms angle 20°  The minimum ECRH powers O1- mode ： 200kW X2- mode ： 300kW  Parameter influence wall condition prefilled gas pressure field null structure toroidal injection angle

HL-2A Outline  Introduction  EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup  LHCD experiments  LHCD &ECCD experiments  Summary

HL-2A In LHCD condition, I p =I OH +I b +I LH Where I OH =V l / R While without LHCD, I p0 =I OH0 + I b0 For the plasma current is feed back controlled, I p should be the same as that without LHCD. I b is considered to be constant and small (less than 10% I p ) I p = I p0, I b = I b0, I p ≈ I OH =V l / R, So, I LH =I OH0 -I OH Which means I LH ≈ I p Δ V l /V l But the fact is a little more complex. Ip is not controlled completely. LHCD experiments

HL-2A I LH is formed by 2 components: I LH =I ΔVl + ΔI p Where ΔI p can be read from data Typical LHCD result on HL-2A

HL-2A LHCD experiments Shot LHCD power （ kW ）  LH (10 19 Am -2 W -1 ) RC （ % ） limiter （ cm ） Ne (10 19 m -3 ) LHCD efficiency on HL-2A

HL-2A Outline  Introduction  EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup  LHCD experiments  LHCD &ECCD experiments  Summary

HL-2A LHCD &ECCD experiments Full CD obtained by LHCD&ECCD shot RC （ % ） With ECCD NO NO NO YES YES YES YES YES 9779Ip disturb YES 9780Ip disturb YES YES YES ECCD improve absorption of LHW 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.

HL-2A Outline  Introduction  EC experiments ECCD experiments ECRH experiments Pre-ionization and Assisted Startup  LHCD experiments  LHCD &ECCD experiments  Summary

HL-2A 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

HL-2A