1. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Educational and research programme on small tokamak Gutta G.M. Vorobyov, D.A. Ovsyannikov, A.D. Ovsyannikov, E.V. Suhov, E. I. Veremey, A. P. Zhabko St. Petersburg State University Zubov Institute of Computational Mathematics and Control Processes, Faculty of Applied Mathematics and Control Processes Acknowledgements This work was partly funded by the IAEA CRP “Joint Research Using Small Tokamaks” This work is carrying out in the framework of Saint-Petersburg State University project “Innovation educational environment in a classical university

2. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 GUTTA was one of the first attempts to built a spherical tokamak, G.M. Vorobyev et al, Ioffe Institute, 1980-86 Main parameters: major radius R, cm 16 minor radius a, cm 8 aspect ratio A 2 vessel elongation k 2 toroidal field, T 1.5 plasma current I p, ka 100 GUTTA, IOFFE, USSR (1980-1986) GUTTA is now fully operational at St. Petersburg State University, Russia GUTTA at Ioffe Institute, 1984

3. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Scientific scope and Working Plan for the 2nd year of the Project include: Upgrade Data acquisition and processing systems New Plasma diagnostics Plasma control Measuring of plasma characteristics, testing of different control codes, experiments on creating vertical-unstable plasma column and controlling such configuration. Tokamak startup studies Heating of plasma (ECRH), in collaboration with T-10. Education program for undergraduate and postgraduate students. University tokamak “MINI” design studies

4. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Upgrade to the Data acquisition and processing systems: Computer-based data acquisition system was set up, tested and calibrated. It consists of 96 fast ADC. This system allows to collect all experimental data with high time resolution (500kHz).

5. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 New Plasma diagnostics New optical diagnostics, SpectraPro high-resolution spectrometer (SP- 2358i) with attached high-speed detector (CMOS pco.1200hs), has been commissioned. It includes a direct digital grating scan mechanism with full wavelength scanning capabilities. Detector is equipped with 1280х16 pc2 CMOS camera and can process 40000 spectrum measurements per second. Additionally, intensity of fixed spectral line can be measured with photomultiplier attached to the second output of the spectrometer. Experiments with 48-channels electro-magnetic diagnostic for plasma shape reconstruction have started.

6. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Optical diagnostics pco.1200 hs CMOS detector Spectrograph SpectraPro SP-2358: Specifications (1200g/mm Grating): Focal length: 300mm Aperture Ratio: f/4 Optical Design: Imaging Czerny-Turner with original polished aspheric mirrors Optical Paths: 90° standard, 180° and multi-port optional Scan Range: 0 to 1400nm mechanical range Operating Range: 185nm to the far infrared with available gratings and accessories Resolution: 0.1nm at 435.8nm Dispersion: 2.7nm/mm (nominal) Accuracy: ±0.2nm Repeatability: ±0.05nm Drive Step Size: 0.0025nm (nominal) Focal Plane Size: 27mm wide x 14mm high Spectrograph SpectraPro SP-2358

7. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 DATA ACQUISITION AND PROCESSING COMPLEX Measurement channels number 96 Input voltage range, В ±1,25 Input resistance, Ом 100 Sampling interval, μs2,4,6,8,10,12,14,16 Input signals sampling 5461 digital capacity 11bit + sign ADC boards Control and diagnostics complex

8. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Plasma control Plasma parameters required for control purposes were measured. Plasma response time on different control algorithms and vessel influence on control dynamics was measured. Vertical and horizontal feedback control systems were commissioned and tested. An experiment to create vertical-unstable plasma column and to control such configuration was carried out.

9. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Horizontal feedback control system Integrator Comparator Power switch Diagnostic coils Displacemet signal Control signal Current Vertival magetic field Diagnostics Vertical field coil Plasma column Magnetic flux Start pulse Magnetic flux changing Capacitor bank Charge and voltage control system Main parameters of horizontal feedback control system: Power switch Voltage: 500V Current: 400A (1,2 kA in pulse) Frequency: 100 kHz Capacitor bank: Voltage: 450V Current: 39600 µF

10. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Horizontal program control Digital controller Power switch Control signal Vertical field coil Plasma column Start pulse Capacitor bank Charge and voltage control system PC Settings Main parameters of horizontal pre-program control system: Power switch: Voltage: 500V Current: 400A (1,2 kA in pulse) Frequency: 100 kHz Capacitor bank: Voltage: 450V Current: 39600 µF Digital controller: PIC 16F876 Communications: UART

11. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Vertical feedback control system Integrator Comparator Power switch Diagnostic coils Displacemet signal Control signal Current Vertival magetic field Diagnostics Vertical field coil Plasma column Magnetic flux Start pulse Magnetic flux changing Capacitor bank Charge and voltage control system Summation unit Main parameters of vertical control system: Power switch: Voltage: 1000V Current: 200A (400 A in pulse) Frequency: 100 kHz Capacitor bank: Voltage: 1000V Current: 19800 µF

12. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Horizontal control system Green- Magnetic flux through midplane Yellow- Control pulses Red-magnetic flux zero level White-control system threshold value Control feedback system OFF Green- Magnetic flux through midplane Yellow- Control pulses Red-magnetic flux zero level White-control system threshold value Control feedback system ON Flux w/o feedback Flux with feedback f/b input f/b request levelf/b request

13. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Tokamak startup studies Non solenoid startup was investigated: - 300A achieved, duration 0.3ms, using 30kW 9.4GHz ECR. - Dependence of current amplitude on RF power and vertical fields was examined. Scenario with increasing toroidal field to provide constant stability factor (q a (t) = const) during current ramp-up was developed.

14. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR discharge, experiment set-up. FUNDAMENTAL RESONANCE at R = 16cm for B 0 =0.15T MICROVAWE POWER WAVE LENGTH 30mm

15. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR breakdown in pure Toroidal field breakdown delay increases at low pressure no dependence of b/d delay on RF power at 5 - 20 kW H  intensity reduces with RF power very similar results to what observed on START tokamak at Culham b/d delay dependence on filling pressureH  intensity dependence on filling pressure

16. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Comparison of ECR b/d on START and GUTTA START: 2.45GHz ~1.0 kW, 3.5ms TF < 0.2 T, O- and X-mode launch GUTTA: 9.4 GHz, 5 - 20 kW, 0.4 ms TF ~ 0.15 T, O-mode launch H  intensity reduces with RF power very similar dependence of H  intensity on pressure no pronounced maximum of H  dependence at 5 kW – new result

17. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR Discharge. During ECR discharge with constant microwave power and some specific conditions (such as middle gas pressure, high microwave power, not very good conditioned wall) regular self-oscillations of visible light emission appear Gas pressure 1.75*10 -4 torr Microwave power20kW Top, green – visible light; bottom, yellow – RF power at 90 0 in toroidal angle RF probe HH HH

18. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR Discharge. Gas pressure 3.75*10 -5 torr Microwave power20kW Gas pressure 2.5*10 -5 torr Microwave power20kW At even lower filling pressure breakdown delay increases Top, green – visible light; bottom, yellow – RF power at 90 0 in toroidal angle HH RF probe

19. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR Discharge. UV lamp assisted b/d Ultra-violet lamp assists breakdown at low pressure Gas pressure 2*10 -5 torr Microwave power4 kW Ultra-violet off – no b/d Gas pressure 2*10 -5 torr Microwave power4 kW Ultra-violet on – clear b/d Top, green – visible light; bottom, yellow – RF power at 90 0 in toroidal angle HH RF probe

20. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Why there is a breakdown delay? Common view is that when microwave power is ON, electron density rises to threshold value, then breakdown happens. This b/d delay depends on gas pressure, microwave power and poloidal fields. To check, second RF pulse was applied with some delay to the first one No b/d delay was observed during second pulse at same pressure, RF power, magnetic field (even if there was no light emission during 1 st pulse) HH HH RF probe

21. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Reverse current preionization Top, yellow – visible light; bottom, green – Loop voltage Reverse current preionization experiments were carried out. Preionization using plasma current reversal is as effective as ECR preionisation (same light emission level) U loop HH

22. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR preionization with applied U loop 1 ms4 ms Top, yellow – visible light; bottom, green – microwave power, red-loop voltage Standard breakdown order Breakdown does not occur without microwave power at U loop ~15V ECR breakdown not happens, however ohmic field breakdown occurs. Delay between ECR and ohmic field breakdown is increasing up to 1ms. Delay between ECR and ohmic field breakdown is increasing up to 4ms. U loop HH HH

23. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR preionization 8 ms 15 ms 30 ms 50 ms Top, yellow – visible light; bottom, green – microwave power, red-current in TF coils Delay between ECR and ohmic field breakdown is increasing up to 8ms. Delay between ECR and ohmic field breakdown is increasing up to 15ms. Toroidal field between breakdowns is absent. Delay between ECR and ohmic field breakdown is increasing up to 30ms. Toroidal field between breakdowns is absent. Delay between ECR and ohmic field breakdown is increasing up to 50ms. Toroidal field between breakdowns is absent. B tor HH

24. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 ECR preionization experiments Delay in light emission at constant microwave power during ECR discharge, ECR and Ohmic field breakdown depends not only on processes in vacuum chamber, but on vacuum vessel wall conditions Preliminary cleaning methods, ultraviolet radiation before breakdown, ECR preionization (even without breakdown) affects these conditions. Consequence of such influence stay for a long time, which is typical not for charged particles lifetime, but for chemical processes on vacuum vessel walls.

25. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Heating of plasma (ECRH) ECRH experiments, with RF power source with power 30kW and 9.4 GHz were carried out. Experiment with RF power up to 200 kW is now under preparation in collaboration with T-10 team.

26. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Education program for undergraduate and postgraduate students Undergraduate students participated in computation of magnetic configurations, equilibrium and stability conditions and experimental verification of theoretical calculations on GUTTA tokamak and in control and data manipulation software developing. Laboratory work ”Plasma equilibrium control in a tokamak” was prepared and tested. Two graduate students and one post-graduate student participated in the 2 nd JE at T-10

27. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 University tokamak “MINI” design studies Main design features of tokamak “Mini” were chosen. Calculations have been performed to verify these parameters. Major radius, cm 20 Plasma current, kA 200 Minor radius, cm 10 Plasma density, cm -3 3·10 14 Aspect ratio 2 Electron temperature, eV 200 Elongation 3 Ion temperature, eV 150 Toroidal magnetic field, T 2 Energy confinement time,ms 2

28. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Plasma Formation in CTF Inspired by Culham’s new CTF design with the use of Ferritic steel central rod, 1:5 (scale) model of the CTF central post has been installed in GUTTA We plan to use GUTTA tokamak for proof-of-principle demonstration

29. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Plasma Formation in CTF: GUTTA 1:5 model Soft iron rod and Al imitation of TF coil (not shown in photo) Induction coils: 50Hz, 4A x 1000turns Flux measurements have been done with and without TF coil measured flux structure measuring coils z plasma

30. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Plasma Formation in CTF: GUTTA 1:5 model z, cm V Coil signal (flux) vs distance from induction coil: red – without TF coil; black – with TF coil How much flux at midplane can be produced? flux loss by factor of 5 due to iron saturation, some of it can still be used during ramp-up solid TF coil requires radial cuts for flux penetration

31. GUTTA Saint-Petersbrg State University G Vorobjev, GUTTA, 2 nd RCM, Beijin, 2006 Future plans Plasma modeling and control Development and verification of new mathematical models are scheduled. Improvement and adaptation of different control methods under control system capabilities will be performed. Development of control hardware is planned. Reverse current preionization Experiments on preionization with reverse current are scheduled. Dependenses on vertical, toridal, ohmic fields and RF power will be studied. Optical diagnostics Experiments to determine plasma temperature and density with optical diagnostics are scheduled. Outer magnetic surface shape reconstruction Tokamka Gutta is equipped with 48-channel electro-magnetic diagnostic for plasma shape reconstruction. Development, approbation and comparison of different mathematical methods of shape reconstruction are scheduled. Postgraduate students will participate in this activity.