Recent Results on the SUNIST and Device Upgrade

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1 The 8 th General Scientific Assembly of the Asia Plasma and Fusion Association Guilin, China, 1-4 Nov. 211 (APFA 211 ) Recent Results on the SUNIST and Device Upgrade Zhe GAO ( 高喆 ) 1 and the SUNIST group 1,2 1) Department of Engineering Physics, Tsinghua University, Beijing, China 2) Institute of Physics, Chinese Academic of Science, Beijing, China This work is supported by the Major State Basic Research Development Program from MOST of China under Grant No. 28CB71784, 29GB152 and 21GB172, NSFC under Grant No , and

Brief introduction to the SUNIST Sino United Spherical Tokamak Managed by

of Physics, Chinese Academy of Sciences(IoP, CAS) Close collaborated with SWIP,

15 T I P ~ 5 ka n e ~ 1 1 19 m -3 Major diagnostics Langmuir probes /magnetic

diode array Visible Spectrometers (2 ~ 1 nm) Missions/Major interests Properties

current startup and drive Startup by electron cyclotron waves Alfven waves current

2 Brief introduction to the SUNIST Sino United Spherical Tokamak Managed by Department of Engineering Physics, Tsinghua University (Tsinghua U) and Institute of Physics, Chinese Academy of Sciences(IoP, CAS) Close collaborated with SWIP, ASIPP and other universities. Typical parameters R /a~.3m /.23 m B T <.15 T I P ~ 5 ka n e ~ m -3 Major diagnostics Langmuir probes /magnetic probes 94GHz interferometer /26-4GHz reflectometer Fast camera (513 fps) /H a diode array Visible Spectrometers (2 ~ 1 nm) Missions/Major interests Properties of ST plasmas Edge plasma fluctuation MHD activities and its control Non-inductive current startup and drive Startup by electron cyclotron waves Alfven waves current drive Overview of the SUNIST device Section view of the SUNIST device The vacuum vessel of SUNIST SUNIST 2

3 Outline Recent research progress ECW startup: experiment and modeling Preliminary results of AW experiments MHD activities Device upgrade Vacuum chamber Field power supplies Future plan Summary SUNIST 3

ECW startup: experiment Experimental setup and results 2.

surface formed but no current jump observed What we are interested in The spikes at the beginning of discharges (IP, Ha and ne)

6 2.45 GHz, ~2kW n e dl ( 1 17 m -2 ), L.6m (a) overall light (a.u.

4 ECW startup: experiment Experimental setup and results 2.45 GHz O mode/<1 kw/1 ms ~2 ka I P last for several ms (loaned from SWIP) I P is inversely proportional to B V Closed flux surface formed but no current jump observed What we are interested in The spikes at the beginning of discharges (IP, Ha and ne) The transient process of the plasmas during startup may dominant the efficiency of startup PS: spikes are widely found on STs GHz, ~2kW n e dl ( 1 17 m -2 ), L.6m (a) overall light (a.u.) reflection (%) Ip (ka) (a) (b) (c) (d) (e) (f) 1 st ECR shot (g) (h) time (ms) Typical waveforms of ECW startup on SUNIST (i) H α emission(a.u.) Shot (b) Spikes are found at the beginning of discharges 4

reflected microwave power are found to have connections with

5 ECW startup: experiment (ctd.) B T scanning results H α emission (a.u.) (b) Microwave reflection (a.u.) (a) Bv = 59 G Bv = 37 G Bv = 2 G Bv = 59 G Bv = 37 G 1 Bv = 2 G P rf scanning results B V scanning results H a and the reflected microwave power are found to have connections with these scanning parameters The time and spatial evolution of ne is essential to understand the physics of startup Y Tan, Z Gao and L Wang, Nucl. Fusion 51, 6321(211) SUNIST 5

nk 2 = DDIFF nk DDRIFT nk LVn ( k k ) k ECR t nnp Σnk 1 = t t N Microwave antenna D DRIFT G ECR N 211-11-2 N-1 k+1 k

6 ECW startup: modeling Main processes Ionization by microwaves motion of particles Reflection of microwaves Microwave antenna R (a) Outer wall B T L V Inner wall nk 2 = DDIFF nk DDRIFT nk LB nk + GECRnkn ( k = k ) NP ECR t V D DIFF H nk 2 = DDIFF nk DDRIFT nk LVn ( k k ) k ECR t nnp Σnk 1 = t t N Microwave antenna D DRIFT G ECR N N-1 k+1 k k-1 k ECR 2 SUNIST 1 6 B V (b) Coefficient estimation based on experiments Approximations: optical launch and receive

7 ECW startup: modeling (ctd.) Experimental results One spike Oscillating B T scanning Σn e H α (a.u.) Reflection (a.u.) 1 x (b) 2 1 (a) H α Reflection Reflection (a.u.) Reflection (%) Hα (a.u.) Reflection (%) Σn e shot Reflection Hα 3 (a) (b) (c) x (d) Hα (a.u.) Simulation results Reflection (a.u.) Reflection (a.u.) N e H a (a.u.) Reflection Ratio x (d) (a) (b) R ECR = R - 5 cm R ECR = R + 1 cm R ECR = R + 4 cm R ECR = R + 7 cm (c) 65 G 75 G 85 G 95 G Time (a.u.) Time (us) Y Tan, Z Gao and L Wang, PST 13, 3(211) SUNIST 7

211-11-2 SUNIST Experimental results (left) and theoretical

trend Preliminary results of AW experiments Motivation To

constant (high density at weak field) to verify the theory of

11237) Antenna system four modules in toroidal, two straps in

pairs used with π phasing N =1 ~ 6%, M =1 ~ 15% (no shielding

8 SUNIST Experimental results (left) and theoretical results (right) 8 of the impedances of antenna shows a similar trend Preliminary results of AW experiments Motivation To explore the effective current drive method in high dielectric constant (high density at weak field) to verify the theory of low frequency current drive (Gao, Fisch and Qin, PoP 13, 11237) Antenna system four modules in toroidal, two straps in poloidal for each module BN limiter designed Experimental setup Rf generater: 2 ~ 5 kw,.4 ~ 1 MHz (non-continuous, only two phases stable) Two of four pairs used with π phasing N =1 ~ 6%, M =1 ~ 15% (no shielding yet) Experimental parameters IP:3~5 ka ne:.5 ~ 3 19 m-3 BT:8~12 G Y Tan, Z Gao and Y He, FED 13, 3(29) 天线 antennas

Preliminary results of AW experiments (ctd.

ne (<1E19 m-3) Hard to understand (Noted: the speed of rf

magnitude) Runaway discharges Normal discharges 5 ka,>1e19

9 Preliminary results of AW experiments (ctd.) Runaway discharges are enhanced when: Low IP (~3 ka), low ne (<1E19 m-3) Hard to understand (Noted: the speed of rf phases and the runaway electrons differ by one order of magnitude) Runaway discharges Normal discharges 5 ka,>1e19 m-3 No effects observed The Ohm discharge is not good enough SUNIST 9 Normal discharges

MHD activities: IREs The appearance of IREs strongly depends on the strength of toroidal field IREs widely found on STs IREs and the evolution of MHD activities and

10 MHD activities: IREs The appearance of IREs strongly depends on the strength of toroidal field IREs widely found on STs IREs and the evolution of MHD activities and equilibrium parameters during IREs observed on SUNIST A collapse in pressure profile may correspond to the occurrence of IREs SUNIST 1 L Zeng, Z Gao, Y Tan et al, PST 13, 42(211)

MHD activities: effects of n=1 magnetic field Biased radial magnetic field L: 21 uh, I: 1 ka, BR max: 37 Gauss Suppress the MHD oscillations Change the spatial structures Slightly increase electron

2-37.9ms V 1 12 15 9 1 6.5 3 18 21 33 24 27 3 V 2 12 9 1 6 15.5 3 18 21 33 24 27 3 SUNIST#1142962@37.2-37.9ms V 1 12 15 9 1 6.5 3 18 21 33 24 27 3 12 9 1 6 15.

11 MHD activities: effects of n=1 magnetic field Biased radial magnetic field L: 21 uh, I: 1 ka, BR max: 37 Gauss Suppress the MHD oscillations Change the spatial structures Slightly increase electron density.3 SUNIST# SUNIST# The coils to produce biased magnetic field. U 1 U t(ms) t(ms) I P (ka) Shot , SUNIST# @ ms V V SUNIST# @ ms V The discharge with magnetic field The discharge without magnetic field n e slightly increases when the SUNIST radial magnetic field is applied 11 V 2 Fringes (a.u.) Icoil(KA) by Prof. FC Zhong s group in Donghua U.

12 Outline Recent research progress ECW startup: experiment and modeling Preliminary results of AW experiments MHD activities Recent engineering progress Vacuum chamber Field power supplies Future plans Summary SUNIST 12

13 Device upgrade: dis- and re-assembling Mission: to install AW antenna and new magnetic probe system to open a new manhole window in vessel to erase the Siliconized film deposited inside the VV to check the CS component Completed in early 29 13

14 Device upgrade: vacuum chamber A manhole window opened for convenience of in-vessel components installing and servicing and as an optical /radiant diagnostic window(ccd camera, reflectometer, spectrometer) 14

Device upgrade: field power supplies Ohmic field power supply: double swing operation IGBT switches enable +1 ka -5 ka (+13 ka -13 ka further ) Pulse length of Ohmic discharge is extended to about 1

15 Device upgrade: field power supplies Ohmic field power supply: double swing operation IGBT switches enable +1 ka -5 ka (+13 ka -13 ka further ) Pulse length of Ohmic discharge is extended to about 1 ms (2-3 ms expected further) Vertical field power supply: arbitrarily programmable DSP + IGBT (1.5 ka) solution (in progress) Difficulty: strong coupling between VF and OF Q1 C1 6mF 15V Q2 1 D1 D2 L1 517uH Q3 Q4 2 D3 D4 C4 R1 1uF 1mΩ 1uH 11 C3 5mF 6V Circuit for double swing discharge 4 D5 The 13 ka IGBT switch SUNIST 15

16 Future plans Further investigation of ECW/EBW startup A 5GHz/ 2kW/ 5ms microwave system under construction (expected the end of 211) Further investigation of AWCD experiments Based on Ohmic discharges with longer flat top With BN limiters installed (design completed) Investigation of Alfven eigenmodes excited by AW antenna system Equilibrium and MHD control SUNIST 16

17 Summary Research activities at the SUNIST in recent years are reviewed, mainly on ECW startup, Alfven wave experiments, and MHD behaviors. Progress of the upgrade of the SUNIST device are briefly introduced. Future plans of the SUNIST are also presented. Comments and potential collaborations are welcome SUNIST 17

18 backups SUNIST 18

19 Conjectures from the scanning results Slew rate of the reflected rf power Delay of H α peaks Maximum amplitude of H α Amplitude of the flat top of H α B T + - B V - - P rf - + Conjectured explanations Summary of the scanning results +: positive effects, -: negative effects; : no effects Drift/Formation time of the cut off layer Power ECR Ionization rate and loss rate Microwave frequency SUNIST 19

20 Parameter estimation SUNIST 2

21 ECW 电流启动实验的分析与定量模拟实验结果进一步分析尖峰 ( 等离子体密度电流 ) 的成因多次反射是否也有作用? 多次反射的衡量泄漏的微波功率微波泄露在等离子体产生后迅速减少至微波反射迅速提高多次反射几乎不存在 P Leak t 1 t 2 Shot , P Ref (a.u.), P Leak (a.u.), H α (a.u.) ~ n Cutoff H α P Ref SUNIST 21

22 阿尔芬波实验系统的建立 The triode oscillator with cables connected The coaxial cables connected to resonant circuit The connection between a resonant circuit and a pair of antennas. 22

23 阿尔芬波实验系统的调试 SUNIST Z (m) 在等离子体击穿时, 阿尔芬波天线作为外限制器存在, 但在封闭磁面形成后, 天线隐藏在最外层封闭磁面外 R (m) 23

24 阿尔芬波实验系统的调试 ( 续 ) I p (ka) Io&Iv (A) V l oop (V) VL t (ms) 阿尔芬波天线对欧姆放电影响不大 ( 红线 : 天线安装前, 黑线 : 天线安装后 ) 24

25 V L (V) I P (ka) Ref. (a.u.) B V (ka) Fringes (a.u.) V L (V) Shot , V L (V) I Ref. (a.u.) P (ka) B V (ka) Fringes (a.u.) V L (V) Shot , V L (V) I Ref. (a.u.) P (ka) V L (V) B V (ka) Fringes (a.u.) Shot

26 I (a.u.) Ip (ka) Q (a.u.) Shot , f~28 GHz (n cutoff ~.97E19 m -3 ) Time SUNIST (ms) 26 I (a.u.) Ip (ka) Q (a.u.) Shot 941.1, f~33 GHz (n cutoff ~1.3E19 m -3 ) I (a.u.) Ip (ka) Q (a.u.) Shot , f~37 GHz (n cutoff ~1.7E19 m -3 )

Non-inductive Production of Extremely Overdense Spherical Tokamak Plasma by Electron Bernstein Wave Excited via O-X-B Method in LATE

1 EXW/P4-4 Non-inductive Production of Extremely Overdense Spherical Tokamak Plasma by Electron Bernstein Wave Excited via O-X-B Method in LATE H. Tanaka, M. Uchida, T. Maekawa, K. Kuroda, Y. Nozawa, A.