1. 4th IAEA TCM on ST and 14th ISTW Frascati, October 7-10, 2008
Present status and research plan of the SUNIST spherical tokamak*
Zhe Gao,1Yexi He,1 Yi Tan,1 Wenhao Wang,1 Huiqiao Xie,1 Lifeng Xie,1 Long Zeng,1 Liang Zhang,1 Chunhuan Feng,2 Long Wang2 and Xuanzong Yang2
1）Department of Engineering Physics, Tsinghua University, Beijing, China
2）Institute of Physics, Chinese Academic of Science, Beijing, China
Electronic mail:
*This work is supported by the Major State Basic Research Development Program from MOST of China under Grant No. 2008CB717804, NSFC under Grant No , as well as the Foundation for the Author of National Excellent Doctoral Dissertation of PR China under Grant No

2. In memory of Professor Yexi He

3. Progress of ECR startup
OUTLINES
Progress of ECR startup
Plan and progress of Alfven wave current drive
Upgrade plan of the device and present status

4. Experimental system for ECR startup
Microwave source
2.45GHz (nc=7*1016m-3) , <100kW, ~10ms (normal direction injection)
Diagnostics
Rogowski coil (damaged in 2007), Flux loop
8mm interferometer (transferred form SWIP, cannot work in 2006)
Photo diode and Fast camera
Microwave injection
Turbo pump
Cryogenic pump
Fast camera (<20kfps)
Photo diode
Piezo-valve
8 mm interferometer

5. (since low Te and low ionization ratio)
Initial results in 2006
Cut-off density for 2.45GHz
ne is roughly characterized by the emission of visible light
(since low Te and low ionization ratio)
The microwave is not absorbed by plasmas
It is absorbed but no plasma current can be efficiently driven
“The microwave output power has been kept around 20 kW because the plasma current quality could no longer be improved with the higher injected power.”
Y X He, et al. 2006

6. Improved results due to low filling pressure discharges in 2007
Long time discharge conditioning
PH2 ~ 1x10-3 Pa
Bv ~ 15 G
No oscillations
Long delay, 2 kA Ip obtained
PH2 ~ 5x10-3 Pa
Bv ~ 20 G
Oscillation
Short delay, but 0.3kA
1st ECR
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
(n)
launcher
~0.5 ms
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
1st ECR
~2 ms
Tan, ISTW 2007

7. Spiky heads: high filling
Further study in 2008: the light emission signal as a criteria for determining the operation regime
Plasma current is estimated from the change of poloidal flux when Rogowski coil is damaged
Inverse-proportinal relations of Ip to Bv shown
数据表从0开始，气压条件注明
Smooth heads:
low filling
Spiky heads: high filling
Yoshinaga 2006

8. Further study in 2008: analysis of the behavior of spiky
r0=RRES-R0
Delay
Large fraction of microwave power is reflected. The reflection ratio is with respect to the position of ECR layer.
Reflection
Light t
Light (a.u.)
Delay is mainly affected by the power density at the ECR layer .

9. Future Plan on ECR startup
Vacuum Vessel
Limiter
Current antenna
New antenna planned
ECR layer
Change the lauching angle
Plasma density control
New ECR Source
新天线部件图？
Flexibilities for the radial position of the launching face

10. OUTLINES Plan and progress of Alfven wave current drive
Progress of ECR startup
Plan and progress of Alfven wave current drive
Upgrade plan and status of the device

11. Background: AWCD experiments
Low-frequency waves were considered as an attractive mechanism of driving plasma current because of its potential high efficiency, no density limit and the convenience of high power RF sources. But electron trapping dramatically decrease its efficiency
Both experiments shows the CD efficiency obtained is consistent with the Fisch-Carney theory. However, both are in the plateau regime, therefore, the trapped electron (neoclassical) effects cannot be verified.
Wukitch 1995, Intrator 1996 at Phaedrus-T
Ruchko 2002 at TCABR
R0/a(m)
B(T)
ne(1019m-3)
Zeff
Te (keV)
Prf(kW)
frf(MHz)
J/Pd(A/W)
TCABR
0.61/0.18
1.05
0.9~3 4
0.4~0.6 40
4.46
0.1
Phaedrus-T
0.93/0.25
0.67
0.2
1.5~2.3
210 7

12. Motivation
Low aspect ratio tokamak may be a good platform to study the behavior or contribution of trapped electrons in low frequency wave current drive.
To investigate the possibility of Alfvén wave current drive (or increasing its efficiency) in low aspect ratio toroidal plasmas.
In physics, to evaluate the contribution of nonresonant drive (exist or not? Many previous work suggest “yes” but our recent theoretic work say “No” Gao, Fisch and Qin, 2006, 2007) and to investigate the role of trapped particles ( how the momentum returns from trapped electrons )
Rf coupling physics

13. Experimental system setup: antenna design
Resonant frequency and
impedance calculation
Vacuum
Vessel
Plasma
Straps
Return Limb , , , , , ,
four modules in toroidal direction and two antenna straps in poloidal direction for each module
referenced to the design for the ETE in Ruchko 2004
Test and assembling
Detail in the presentation by Dr Yi Tan，
In Plenary 6, session 3, tomorrow afternoon

14. Experimental system setup: antenna shielding
BN side limiter ?
Metal side limiter?
BN front or BN coating needed?
Sorensen 1996 at Phaedrus-T

15. Experimental system setup: rf generator
Four-phase oscillator (the phase shift between outputs does not depend on the variation of the antenna impedance)
4x100kW / 0.4~1MHz,
Status: four phase output tested for 4x10kW, but still stored in the factory
referenced to
Ruchko 2004 at TCABR

16. OUTLINES Upgrade plan and status of the device Progress of ECR startup
Plan and progress of Alfven wave current drive
Upgrade plan and status of the device

17. Upgrade of diagnostics
New Mirnov probe system
— Equilibrium, excited modes
New Rogowski coil and flux loop
— Equilibrium, plasma current and loop voltage
Electrostatic probe
— density and potential fluctuation, flow
Photo diode and Fast camera
— Equilibrium, temperature
Microwave reflectometer (8~12mm) and interferometer (3mm)
— density and its fluctuation
Radiometer (2~12GHz), Spectrometer ( ICCD, vacuum ultraviolet), X-array
— electron temperature
(Previously Existed; Now ready; budget ready; in application)

18. Upgrade of power supply
Improvement of control of equilibrium field (a set of capacitor bank with 1200V、270mF , IGBT-based control scheme)
rf power: 400kW/<1MHz/30ms
Microwave power: 100 kW/2.45GHz/10ms >40kW/>5GHz/>30ms
(Previously Existed; Now ready; budget ready; in application)

19. Modification of vacuum chamber
A new manhole window is opened for convenience of in-vessel components installing and servicing

20. and start of leak detection
Status of the machine
Mission: to install AW antenna and new magnetic probe system, and to open a new manhole window in vessel
Disassembled
April 17, 2008
Fabrication
May 26, 2008
Before March 27, 2008
expected to be re-assembled before November this year
Vessel reassembled
and start of leak detection
Sep. 25, 2008
Cleaning
Sep 11, 2008

21. Summary
ECR startup improved and analyzed, but limited by poor diagnostics and microwave power (low freq. and short pulse)
AWCD experiment system is preliminarily setuped, but lack of experiences
Diagnostic system and power-supply system will be upgraded in a few years

22. potential areas of collaboration
Any comment is welcome and any help or collaboration is desirable, typically in
Design/improvement of antenna system using more realistic model
Antenna shielding and density control in future AW experiments
The coupling of rf to plasmas
Diagnostic of wave-particle interaction
Theory and simulation of the behaviors of the plasma with ECR/AW injection