The Joint Meeting of 5th IAEA Technical Meeting on Spherical Tori, 16th International Workshop on Spherical Torus (ISTW2011), and 2011 US-Japan Workshop on ST September 27-30, 2011 , National Institute for Fusion Science, Toki, Japan

Recent Progress in the SUNIST Spherical

Yi Tan1, Zhe Gao1, Wenhao Wang1, Lifeng Xie1, Long Zeng1, Huiqiao Xie1, Ou Zhao1, Yangqing Liu1, Yanzheng Jiang1, Song Chai1, Xiaowei Peng1, Kun Yao1, Aihui Zhao1 Chunhuan Feng2, Long Wang2, Xuanzong Yang2 Guixiang Yang3 Email: [email protected] 1) Department of Engineering Physics, Tsinghua University, Beijing, China 2) Institute of Physics, Chinese Academic of Science, Beijing, China 3) College of Nuclear Physics and Technology, Nanhua University, Hengyang, China

This work is supported by the Major State Basic Research Development Program from MOST of China under Grant No. 2008CB717804, 2009GB105002 and 2010GB107002, NSFC under Grant No. 10990214, 10775086 and 11005066. Introduction to SUNIST

• SUNIST: Sino UNIted Spherical Overview of the SUNIST device Tokamak – What are united? • Department of Engineering Physics, Tsinghua University • Institute of Physics, Chinese Academy of Sciences – Major parameters

• R0/a: 0.3/ 0.23m ~ 1.3 • BT0: <0.15 T • IP: ~ 50 kA 19 -3 • ne: ~ 110 m – Major diagnostics • Langmuir probes • Normal ( <100 kHz) / High frequency (~1 MHz) magnetic probes • Visible Spectrometers (250~ 750 nm) • 94 GHz interferometer • 8 mm reflectometer • Fast visible camera

• Ha diode array

Section view of the The vacuum SUNIST device vessel of SUNIST 2011-9-29SUNIST 2 Major Research Interests of SUNIST

• Non-inductive current startup and drive – Startup: by electron cyclotron waves (ECW) • Breakdown the neutral gas and initiate a small plasma current – Drive: by Alfven waves (AW) • Maintain the ohmic plasma current

total IP IP started up IP by ECWs An idealized running scheme for SUNIST IP ramped IP driven up by the by AWs solenoid

O t startup ramp up sustain • Properties of ST plasmas – Edge plasmas • Electrostatic/magnetic fluctuation and anomalous transport characteristics – MHD characters • MHD behaviors and methods to affect or control MHD activities

2011-9-29SUNIST 3 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 4 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 5 Analysis of ECW startup

• Brief experimental results of (a) (b) (c) (d) (e) (f) ECW startup st – 2.45 GHz/100 kW/10 ms (limited) 1 t ECR shot 070930.14 h g i ) l .

1 (g) l u l

– O mode outboard injection . a a r ( e 0 v – ~2 kA I last for several ms o P 100 n o

i (h) ) t

c 50 – I is inversely proportional to B % e

P V ( l f e – Closed flux surface may formed but r 0

) 2 (i) A

no current jump observed k ( 1

p I 0 • What we focused on 6 8 10 12 14 – The spikes at the beginning of time (ms) Typical waveforms of ECW startup on SUNIST discharges (IP,Ha and ne) 2.45 GHz, ~20kW –  The time and spatial evolution of0.9 n dl (1017m-2), L0.6m n is essential to understand the 0.6 e (a) e 0.3

physics of startup 0 2 H emission(a.u.)  Shot 060413.6 –  Investigate the transient 1 (b) process of the plasmas during 0 13 15 17 19 21 23 25 startup ! Time (ms)

– PS: spikes are widely found on STs Spikes are found at the beginning of discharges 6 Effects of BV,BT and Prf on the spikes

Bv = 59 G

) Bv = 37 G . 2 (a) u

. Bv = 20 G a (

n

o 1 i s s i m e

0  H 6.4 6.6 6.8 Time (ms) (b) Bv = 59 G 1 ) . u e . v a 0 Bv = 37 G (

B scanning results a T 1 n w o o i r t c c i 0 e l f M 1 e

r Bv = 20 G 0 6.0 6.5 7.0 7.5 8.0 Time (ms)

BV scanning results

• Ha and the reflected microwave are found to have connections with these scanning parameters – These two signals are fast enough to be able to catch the details of changes Prf scanning results

2011-9-29SUNIST 7 Conjectures from the scanning results

Summary of the scanning results +: positive effects, -: negative effects; 0: no effects

Slew rate of the Delay Maximum Amplitude

reflected rf of Ha amplitude of of the flat power peaks Ha top of Ha

BT + - 0 0

BV - 0 - 0

Prf 0 - + 0 Drift/Formation Power Ionization Conjectured Microwave time of the cut density rate and loss explanations frequency off layer @ ECR rate

2011-9-29SUNIST 8 The physical image of the initial stage of ECW startup

• Main processes – Ionization by microwaves – Reflection of microwaves – The motion of particles: (1) drift and diffusion across the field lines, (2) parallel motion along field lines • Features of our experimental arrangements – Perpendicular installation of the horn antenna • The antenna acts not only as a launcher of power microwaves but also a receiver of reflected microwaves

2011-9-29SUNIST Tan Y, et al. . 2011;51(6):063021. 9 Estimation of the speeds • For electrons (100 eV)

– Lamor Radius: ~ 0.4 mm (v// = 0, B = 875 G) – v//: ~6E6 m/s ( ) • For hydrogen gas (300 K, 1E-3 Pa) ⊥ – en: ~3E4 1/s (3E9 1/s for 1 torr) – ionization: ~2E4 1/s (2E9 1/s for 1 torr) – ei: ~ 1E3 1/s (ne ~ 1E17) • For SUNIST (R0 =0.3m,B=875G)

– R : ~ 7.6E3 m/s (vertical) ଶ் ଵ – ߘܤ: ~1.1E3 m/s஼ (E = 100 V/m) (radial) × ௤ ோ ஻ ୉ – ܧ ܤ : ~ 1.4E5 m/s (B = 20 G) (vertical) V ୆ z ஻௭ ∥ ஻்

2011-9-29SUNIST 10 Modeling

Cutoff layer

nk W L kECR i  1k2   PP   e nc (5) ECR ik nj    Horn antenna tan2 Wd tan2  Ld kk ANT

2 2  W W L r  REF   tan4  Wd tan4  Ld 2 2 (4)

nk 2       nnGnLnDnD kk ECR)( (1) d t DIFF V NPkECRkBkDRIFTk

nk 2 (2)      nLnDnD  kk ECR )( t DIFF kVkDRIFTk n n 1  kNP (3) t t N • A 1.5 dimension model – To describe the main processes – To simulate the time and spatial evolution of ne, the characters of microwave reflections – Approximations: optical launch and receive, WKB et al.

2011-9-29SUNIST 11 Compare the simulations and the experiments

Due to: Experimental results:

One spike Oscillating BT scanning ) .

shot 060927.6 u Reflection H .

n 40 Reflection 60 a 30 ) (a) ( . o

H i (a) u

 t )

2 ) . (a) n . 40 c

20 a o e

% ( 20 u i l

( . t f 20  R = R - 5 cm c a e ) 10 ECR 0 ( . e H

R l

u 0 R = R + 1 cm f ECR 0 n . 8.0 8.5 9.0 9.5 10.0 e

a 1 o R = R + 4 cm i

( ECR 0 R ) t . 20 (b) 

c R = R + 7 cm u  8 ECR 0 . (b) e ) H a H . l (

f 0 u . e 4 0 a ( R

60 a n o H i 40 (c) 0 t )

6.0 6.5 7.0 7.5 8.0 c e

% 20 l (

Time (ms) f 2.0 2.2 2.4 2.6 12 e 0 x 10 R 2 4 6 8 10 12 14 16 Time (ms) 10 0.04 Time (ms) )

. 12

(b) u x 10 650 G . 11 10 a

( x 10 750 G

) n . e 4 0.04 850 G o u n (c) e i 5 0.02 . 950 G t

 5

(d) a N c 3 0.03 (

e l n e f o n e 2 0.02 i t  R 0 c e l

1 0.01 f

0 0 e o i t 0 0.5 1 1.5 2 R 0 0 a 0.4 R

Time (ms) 0 0.5 1 1.5 2 (d) n o

i 0.3 Time (ms) t c e l

f 0.2 e

R 0.1 0 100 200 300 400 500 600 700 800 900 Time (a.u.) Time (us) Simulation results

2011-9-29SUNIST Tan Y, et al. Plasma Sci. Tech. 2011;13(1):30. 12 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 13 Principle of Alfven wave current drive

• Diagram of Alfven wave current drive (AWCD) – The peristaltic Tokamak (Wort, 1971) dv B The driving force: m z  eE   z dt z z  v e vf )(

Resonant Vph is slow thus thermal condition： electrons are driven:     vk e 0 v T v

N J Fisch and C F F Karney, 1987 The schema: Vacuum Vessel • Apply AWCD to SUNIST Antennas Plasmas – 4 pairs of strap antennas – 0.15T/ 1E19m-3, resonant frequency: 0.4 ~ 1 MHz Alfven wave antenna design for SUNIST

• Simple design, simple manufacture – Extends in the poloidal direction as much as possible

50 mm bolts bolts

BN plates returning strap main strap Support for BN plates

feeder CF-200 flange 150 mm

2011-9-29SUNIST Tan Y, Gao Z, He Y. Fusion Eng. Des. 2009;84(12):2064-71. 15 Preliminary results of AW experiments

• Antennas antennas – Currently no shielding, no limiters – Two of four pairs used –  phasing – |N|=1 ~ 60%, |M|=1 ~ 15% • The RF generator – Four phases outputs Toroidal arrangement of the antennas(left) and a picture • But only two phases are stable of the antennas along with plasmas (right) – 20 ~ 50 kW, 0.4 ~ 1 MHz (non-continuous) • Experimental parameters

– IP：30~50 kA -3 – ne： 0.5 ~ 319 m

– BT：800~1200 G • Antenna impedances – Have similar trends as 1-d calculations Experimental results (left) and theoretical results (right) of the impedances of antennas

2011-9-29SUNIST 16 The effects of RF waves on IP Runaway discharges • Runaway discharges are enhanced when:

– Low IP (~30 kA), low ne (<1E19 m-3) – Hard to understand • The speed of rf phases and the runaway electrons differ by one order of magnitude -2 • Vc～1.5*10 (2πRn/V)/2 ～ 7 18 -3 Normal discharges 2*10 m/s (for ne～10 m ) • Vph～f2 π R ～ 1.5*106 m/s • Normal discharges – 50 kA，>1E19 m-3 – No effects observed

2011-9-29SUNIST 17 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 18 Internal reconnection events on SUNIST

• Motivations – Internal reconnection events (IREs) are widely found on STs – What mode structures do IREs have? – The evolution of equilibrium parameters during an IRE • Methods

– Magnetic measurements A typical discharge with IREs of SUNIST – EFIT

– SVD analysis 0.5 0.4

0.3

0.2

0.1 )

m 0 ( Magnetic probes (*) and flux Z loops (.) used to study MHD -0.1 activities on SUNIST -0.2

-0.3

-0.4

-0.5 Zoomed in waveforms of IP and magnetic perturbations 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 of an IRE R (m) 2011-9-29SUNIST Zeng L, et al. Plasma Sci. Tech. 2011;13(4):420. 19 IRE analysis • Mode structures and the evolutions of parameters

IREs have a strong dependence on the strength of toroidal field

before during after

The poloidal (upper) and toroidal (lower) modes The evolution of elongation ratio (upper) and before, during and after an IRE on SUNIST poloidal beta (lower) in an IRE on SUNIST 2011-9-29SUNIST 20 The effects of biased electrical field on MHD

• Apparatus – A biased DC voltage is applied to an electrode located at the equatorial plane – Diameter: 3 cm; voltage applied: 200 V • Effects – The biased voltage excites the harmonics

of MHD perturbations !!!??? The electrode – Expected: to suppress MHD (since the Er cross BT shearing effects)

2011-9-29The discharge without biased voltage SUNIST The discharge with biased voltage 21 The effects of biased magnetic field on MHD

• Biased radial magnetic field

– 5 turns, L: 210 uH, I: 1 kA, BR max: 37 Gauss – Suppress the MHD oscillations – Change the spatial structures – Slightly increase electron density The coils to produce a biased SUNIST#110429062 SUNIST#110429061 magnetic field. 0.3 0.3 1 1 0 0 U U

-0.3 -0.3 Shot 101211009, 101211008 37.5 38 38.5 37.5 38 38.5 18.6 12.7 t(ms) t(ms) ) A k (

6.8 P I 0.9

SUNIST#[email protected] SUNIST#[email protected] 1064

1 1 1 1 ) 90 90 90 90 . u 120 60 120 60 120 60 120 60 . 798 a (

s

0.5 0.5 0.5 0.5 e 532 150 30 150 30 150 30 150 30 g n i r

F 266

1 180 0 2 180 0 1 180 0 2 180 0 V V V V 0.76

) 0.57 210 330 210 330 210 330 210 330 A K ( l

i 0.38 o

240 300 240 300 240 300 240 300 c 270 270 270 270 I 0.19

35 36 37 38 39 40 41 42 Time (ms) The discharge without biased magnetic field The discharge with biased magnetic field ne slightly increases when the radial magnetic field is applied 2011-9-29SUNIST 22 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 23 Upgrade of field power supplies

5 3

Q1 Q3 • Pulse length limits SUNIST’s ability D1 D3 C4 R1 100uF 100mΩ D5 C1 1 L1 1uH • Ohmic field power supply: double 60mF 2 11 1500V 517uH swing operation C3 D2 500mF D4 600V Q2 Q4 – IGBT switches enable +10 kA -5 kA 4 swing (+13 kA  -13 kA further) The circuit for double swing The 13 kA IGBT switch – Pulse length of ohmic discharge has discharge been extended to >10 ms (20 ms Shot 110923040 , 110429061

expected further) ) . 10 u . a

( 0

• Vertical field power supply: B d 40 arbitrarily programmable ) 20 A k

( 0

P – DSP + IGBT (1.5 kA) solution I -20 -40 2 – Adjustments are on going ) V (

0 L

V -2 10 ) A

k 5 (

O 0 B 1.5-5

The assembled circuit )

A 1 k (

V 0.5 B 0 35 40 45 50 The defined waveform (left) and the waveform Time (ms) actually obtained (right) The waveforms of a double swing discharge (blue) and 2011-9-29SUNIST 24 single swing discharge (red) Other upgrades

• SUNIST is wirelessly controlled and monitored – The feasibility of wireless monitoring and control of a tokamak has been verified – Using Zigbee technology (now very popular in the Internet of Things) – Good flexibilities and reliabilities (left) 4 wireless modules installed in the power • A new magnetic diagnostic system supply and the timer; (right) The wireless modem – 13 flux loops / 15 poloidal probes / 6 toroidal probes attached on the remote computer. – Plasma equilibrium reconstruction and MHD analysis can be done based on this system AIO, DIO Remote devices 0.5 ZigBee with high volts, 0.4 Module 0.3 radiation, et al

0.2

0.1 )

m 0 (

Z

-0.1

-0.2 -0.3 Controller ZigBee -0.4

-0.5 Computer RS232 Modem

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 R (m) The diagram of the wireless infrastructure25 for The magnetic probes and flux loops control and monitoring Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary

2011-9-29SUNIST 26 Future plans

• Continue to startup by ECW – The old 2.45 GHz magnetron source is damaged – A 5 GHz/200 kW/50 ms microwave system is under construction (Institute of Electronics, CAS) • Re-try AWCD experiments – Based on ohmic discharges with longer flat top – With BN limiters installed (design completed) • Continue MHD studies – With better abilities of equilibrium control • Alfven eigenmodes investigation – Use the AWCD antenna systems

2011-9-29SUNIST 27 Summary

• The transient of process of ECW startup is analyzed. The process involves particle drifts and microwave reflections. The simulation results of a simple model can reappear the experimental results. • Preliminary results of Alfven wave experiments show that runaway discharges can be enhanced by the low phase speed waves. This is difficult to understood. • Both biased electrical and magnetic field have observable effects on MHD activities. • The ohmic field of SUNIST is now operated in double swing mode. The vertical field can be arbitrarily programmed. • The SUNIST machine is wirelessly controlled and monitored. This brings a lot of flexibilities to us. • Future plans of SUNIST are also presented.

Questions, comments and suggestions are warmly welcome!

2011-9-29SUNIST 28