SUNIST SUNIST- Sino UNIted Spherical Tokamak Status of SUNIST spherical tokamak in 2006 HE Yexi, ZHANG Liang, *FENG Chunhua, FU Hongjun, GAO Zhe, TAN Yi, WANG Wenhao, *WANG Long, *YANG Xuanzong, XIE Lifeng (o), (fax) SUNIST United Laboratory Department of Engineering Physics, Tsinghua University, Beijing , P.R.China *Institute of Physics, Chinese Academy of Science, Beijing , P.R.China This work was supported by National Nature and Science Fund of China (Grant numbers: and ), and International Atomic Energy Agency (Research contract No /R0). The 2 nd Research Coordinate Meeting on Joint Research Using Small Tokamak, IAEA October , Beijing

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result ECR plasma current startup the 1st step modification for double swing operation of B OH Further plan

SUNIST spherical tokamak SUNIST SUNIST main parameters: major radiusR0.3 m minor radiusa0.23 m Aspect ratio A ~ 1.3 elongationκ ~ 1.6 toroidal field （ R 0 ） B T 0.15T plasma current I P 0.05 MA flux (double swing)ΔΦ0.06 Vs SUNIST spherical tokamak

SUNIST spherical tokamak magnets and power supply UNIST SUNIST coilturn L(  H)R(m  ) I D (kA)V C (V)Capacitor(mF) TF (1280) HF /1280 EF /1201(2)/476(18.8) Vacuum vessel and BV magnet assembling toroidal magnet pre-assembling Cross section and designed magnetic surface SUNIST spherical tokamak

SUNIST spherical tokamak vacuum and vacuum vessel SUNIST main parameters – vacuum vessel: outer diameter1.2m inner diameter0.13m height1.2m volume~ 1m 3 surface area~ 2.3m 2 vacuum pumps: TMP (1000l//s) sputtering Ti pump (200l/s) cryogenic pump (1500l/s to N 2 ) wall conditioning: baking: PTC （ Curie point C) glowing discharge, siliconization background pressure: ~ 6×10 -5 P a (between shots) leaking rate on cross seal: ≯ 2×10 -7 P a m 3 /s SUNIST spherical tokamak

SUNIST Typical Discharge in single swing mode SUNIST spherical tokamak

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result ECR plasma current startup the 1st step modification for double swing operation of B OH Further plan

SUNIST Typical discharge of ECR startup in 2005 Preliminary result Microwave: P out < 100kW, t pulse ~ 30 ms, f = 2.45 GHz background pressure ~ 1  Pascal hydrogen pressure ~ 1  Pascal during discharge

SUNIST Improving vacuum condition Preliminary result top view of the movement of the piezo valve installed a cryogenic pump (CRYO- PLEX 8LP), background pressure down to 5~8x10 -5 P a (between shots) pulsed gas puffing, moving valve to chamber, shorter puffing duration (~2ms) and shorter interval between filling and P RF (~3ms) siliconization, S i H 4 + H e, DC glow discharge the piezo valve vacuum vessel Conduit for pumping t 0 ~30ms ~8ms puffing pulse power pulse t0 ~3ms ~2ms

SUNIST Preliminary result spiky still oscillations of H  and microwave reflection causing during lower B v BV effect on ECR startup current startup with a later B V current startup with one-up B V Typical discharge of ECR startup in 2006

SUNIST The effect of B V to H  emission and wave reflection Preliminary result with Bv (~30G) without Bv

SUNIST Dependence of plasma current on vertical field Preliminary result

SUNIST Electrode arrangement Preliminary result

SUNIST Typical discharge with electrode assistance Preliminary result

SUNIST Plasma current counteracted by electrode current Preliminary result

SUNIST Performances of preliminary ECR current startup Preliminary result The effects of B V on plasma current startup on SUNIST: - B V applied leading P RF _ plasma current is just spikes. The dependence of driven I P on vertical field is consistent with the toroidal plasma current produced by B V drift effect in ECR plasma. - B V applied during ECR plasma _ plasma current has higher value, longer duration. - B V influences on H  and reflection of P RF. The effect of electrode discharge to ECR plasma current - in co-direction _ I P could increase above 10% (Fig. 7). - in counter-direction _ I P would be counteracted more obviously (Fig.8).

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result ECR plasma current startup the 1st step modification for double swing operation of B OH Further plan

modification for double swing operation of B OH UNIST SUNIST Modifications of the circuit shutdown the SCR increasing ramp-down rate To From t I ohm,I’ C 13.6mF 3000V SCR D Coil 519uH SCR’ C’ 500uF 3000V L’ 12uH R 200mOhm 0 I max I’ t C 13.6mF 3000V SCR D Coil 519uH

modification for double swing operation of B OH UNIST SUNIST With < 10kA I ohm and 200 mohm R, ~20kA I p is generated and a small flat-top revealed that could be adjusted by R and IP. Compare to normal ramp- up ohmic discharge, >10kA I ohm ~30kA I p If loop voltage can be kept, the plasma current can be maintained.

modification for double swing operation of B OH UNIST SUNIST Adding a capacitor bank in order to reverse Iohm, and get longer duration of Ip C 13.6mF 3000V SCR SCR’ C’ 500uF 3000V L’ 12uH R 200mOhm SCR’’ C’’ 1.28F 300V I ohm 0 t IpIp

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result ECR plasma current startup the 1st step modification for double swing operation of B OH Further plan

SUNIST Further plan 1upgrade system *modification of ohmic field power supply to double swing mode *upgrade diagnostics: H  and SX arrays, visible and UV spectroscopy,  W interferometer and reflectometer… *magnet discharge and plasma configuration controls 2SUNIST discharge performance *operation regime, equilibrium and MHD *edge plasma *vacuum vessel conditioning effects to discharge 3current startup and RF wave effect on plasma *ECR current startup with or without electrode assistance and B V effects *possibility transit to typical discharge from non induced start plasma current *Alfven wave effects on low aspect ratio toroidal plasma.

SUNIST SUNIST- Sino UNIted Spherical Tokamak Status of SUNIST spherical tokamak in 2006 The 2 nd Research Coordinate Meeting on Joint Research Using Small Tokamak, IAEA October , Beijing THANKS