Control system and breakdown studies on a small spherical tokamak Gutta.
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Transcript of Control system and breakdown studies on a small spherical tokamak Gutta.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Control system and breakdown studies on a small spherical tokamak Gutta.
G.M. Vorobyov, D.A. Ovsyannikov, A.D. Ovsyannikov, E.V. Suhov, E. I. Veremey, A. P. Zhabko
St. Petersburg State UniversityZubov Institute
of Computational Mathematics and Control Processes,Faculty of Applied Mathematics and Control Processes
AcknowledgementsThis 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
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
OUTLINE
• History and main parameters of Gutta
• Main diagnostics and data acquisition
• Plasma position control systems
• Main experimental results
– ECR breakdown studies
– b/d using reversed current
– Iron core
– Horizontal position control studies
• Conclusions and future plans
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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 1.5plasma current Ip, ka 100
GUTTA, IOFFE, USSR (1980-1986)
GUTTA is now fully operational at St. Petersburg State University, Russia
GUTTA at Ioffe Institute, 1984
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
MAIN DIAGNOSTICS
• Magnetics: 2 Rogowski coils for Ip, Rogowski coils for PF and TF
currents, 2 flux loops at midplane;• Z and R position control, shape control: array of 24 pick-up coils (2
components at one toroidal position), 6 Mirnov coils - toroidal array at
midplane;• Photomultiplier• 94 GHz interferometer• Spectrometer/monochromator with CMOS camera • RF power detector at 900 in toroidal direction at midplane
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
DATA ACQUISITION AND PROCESSING
Measurement channels number 96Input voltage range, В ±1,25Input resistance, Ом 100Sampling interval, μs 2,4,6,8,10,12,14,16Input signals sampling 5461digital capacity 11bit + sign
ADC boards Control and diagnostics complex
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Spectroscopic diagnostics
Spectroscopic diagnostics block-scheme
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Optical diagnostics
pco.1200 hs CMOS detector
Spectrograph SpectraPro SP-2358:
Specifications (1200g/mm Grating):Focal length: 300mmAperture Ratio: f/4Optical Design: Imaging Czerny-Turner with original polished aspheric mirrorsOptical Paths: 90° standard, 180° and multi-port optionalScan Range: 0 to 1400nm mechanical rangeOperating Range: 185nm to the far infrared with available gratings and accessoriesResolution: 0.1nm at 435.8nmDispersion: 2.7nm/mm (nominal)Accuracy: ±0.2nmRepeatability: ±0.05nmDrive Step Size: 0.0025nm (nominal)Focal Plane Size: 27mm wide x 14mm high
Spectrograph SpectraPro SP-2358
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Plasma control systems
Plasma control systems on Gutta consists of:
• Vertical and horizontal position feedback control systems.
• Horizontal plasma position pre-programmed control.
Horizontal control system was build, tested and commissioned
Testing and tuning of vertical control system are in progress.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Horizontal feedback control system
Integrator Comparator Power switch
Diagnostic coils
Displacemet signal
Control signal
Current
Vertival mageticfield
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: 500VCurrent: 400A (1,2 kA in pulse)Frequency: 100 kHz
Capacitor bank:Voltage: 450VCurrent: 39600 µF
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Horizontal program control
Digital controller Power switch
Control signal
Vertical field coil
Plasma column
Start pulseCapacitor bank
Charge and voltage control
system
PC
Settings
Main parameters of horizontal pre-program control system:Power switch:
Voltage: 500VCurrent: 400A (1,2 kA in pulse)Frequency: 100 kHz
Capacitor bank:Voltage: 450VCurrent: 39600 µF
Digital controller:PIC 16F876 Communications: UART
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Vertical feedback control system
Integrator Comparator Power switch
Diagnostic coils
Displacemet signal
Control signal
Current
Vertival mageticfield
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: 1000VCurrent: 200A (400 A in
pulse)Frequency: 100 kHz
Capacitor bank:Voltage: 1000VCurrent: 19800 µF
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR discharge, experiment set-up.
FUNDAMENTAL RESONANCE FOR B0=0.15T
MICROVAWE POWERWAVE LENGTH 30mm
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
0 1 2 3 4 5 6 7 8 90
100
200
300
400
H,
a.u
.
Pressure, x 10-3mm
20 kW 1st peak 20 kW between peaks 10 kW 1st peak 10 kW between peaks
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 dependence of H intensity on pressure to what
observed on START
0 1 2 30
100
200
300
400
b/d
dela
y,
s
Pressure, x 10-3mm
20 kW 10 kW 5 kW
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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
0 2 4 6 80
100
200
300
400
H,
a.u
.
Pressure, x 10-3mm
20 kW 1st peak 10 kW 1st peak 5 kW 1st peak
• H intensity reduces with RF power
• very similar dependence of H intensity on pressure to what observed on START
• no pronounced maximum of H dependence at 5 kW
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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 power 20kW
Gas pressure 1.75*10-4 torr Microwave power 20kW
Top, green – visible light; bottom, yellow – RF power at 900 in toroidal angle
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR Discharge.
Gas pressure 3.75*10-5 torr Microwave power 20kW
Gas pressure 2.5*10-5 torr Microwave power 20kW
At even lower filling pressure breakdown delay increases
Top, green – visible light; bottom, yellow – RF power at 900 in toroidal angle
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR Discharge. UV lamp assisted b/d
Ultra-violet lamp assists breakdown at low pressure
Gas pressure 2*10-5 torr Microwave power 4 kW
Ultra-violet off – no b/d
Gas pressure 2*10-5 torr Microwave power 4 kW
Ultra-violet on – clear b/d
Top, green – visible light; bottom, yellow – RF power at 900 in toroidal angle
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Self-oscillations of light emission – old results
Light emission during ECR discharge in tokamak
Light emission during electrode discharge in linear device
The same processes observed in another devices and even in electrode discharges
B.N. Shustrov, A I. Anisimov, N. Blashenkov. G.Y. Lavrentyev. G.G. Petrov, “Self-organizing in gas discharge”,
Preprint Ioffe Institute, Leningrad,1988
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
1 ms1 ms
5 ms
Top, yellow – visible light; bottom, green – microwave power
Why there is a breakdown delay?Common view is that after microwave power is ON, electron density rises to threshold value, after breakdown occurrence. Delay may depend on gas pressure, microwave power and poloidal fields.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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)
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR preionization
1 ms 4 ms
Top, yellow – visible light; bottom, green – microwave power, red-loop voltage
Standard breakdown order
Breakdown does not occur without microwave power.
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.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR preionization
8 ms 15 ms
30 ms50 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.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
ECR preionization experiments
• Delay in light oscillations 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.
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
Plasma Formation in CTF
Ferrite steel shielding of the central post and ferrite central rod can provide enough flux for breakdown and initial current formation
for use of ferrite steel in JTF-2M see: M Sato, et al., Fusion Eng. Des., 51-52 2000 1073520
Inboard shieldF82H
soft ironCentre pin
GlidcopCentre rod
Stainless steelRod casing
Fe pin radius = 0.18m gives 100 mVsec which is enough to ramp Ipl to 300kA.
• No central solenoid in CTF concept design requires alternative formation schemes
CTF, Culham design with iron pin
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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
G Vorobjev, GUTTA, Chengdu
GUTTA
Saint-Petersbrg
State University
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