remote operation of the golem tokamak gent university, december 14, 2009 jan stockel institute of...
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Remote operation of the GOLEM tokamak
Gent University, December 14, 2009
Jan StockelInstitute of Plasma Physics, Prague
stockel@ipp.cas.cz
Vojta Svoboda Faculty of Nuclear Sciences and Physical Engineering
Czech Technical University, Prague
svoboda@br.fjfi.cvut.cz
Introduction of the GOLEM tokamak• Basic hardware• Basic plasma diagnostics
Remote operation of GOLEM• Basic plasma performance
Unique feature of the GOLEM tokamak
It is the only tokamak in the world, which can be operated remotely via Internet!
Tokamak - basic principle
Tokamak is composed of
three basic components
• Large transformer
• Plasma ring as secondary winding
• Coils for confinement of plasma ring by magnetic field (toroidal solenoid)
Electric current I generated in the plasma ring by the transformer
• delivers the ohmic power Pohmic = I2Rplasma to plasma (heating)
• generates the poloidal magnetic field in the plasma ring Bpoloidal ~I/2a
REMEMBER! Because of the transformer, tokamak is a pulsed device
The GOLEM tokamak is located at the Faculty of Nuclear Physics and Physical Engeneering (Czech Technical University in Prague) located in the proximity of jewish cemetery.
GOLEM tokamak in Prague
Major radius 0.4 m
Minor radius of the vessel
0.1 m
Minor radius of the limiter
0.085 m
Maximum B-toroidal 0.3 Tesla
Maximum plasma current
8 kAmp
Discharge duration ~ 5 ms
Iron core of the transformer
Toroidal magnetic field coils (28)
Primary winding of the transformer (12 turns)
Diagnostic ports (18)
Front view of GOLEM (schematically)
Engineering scheme of the GOLEM tokamak
Gas handling system
Vacuum pumping
Generation of toroidal magnetic field
Generation of plasma current
Power supplies of GOLEM (schematically)
For generation of toroidal magnetic field
For breakdown of working gas and plasma current drive
Capacitor bank Toroidal Field CoilsGrid Rectifier
Triggeredswitch
Capacitor bank Primary winding of transformerGrid Rectifier
Triggeredswitch
At the moment, we measure:• Toroidal magnetic field (by a pick-up coil)
• Plasma current (by a Rogowski coil)
• Plasma radiation (a photodiode)• Loop voltage
Basic diagnostics of GOLEM
d/dt – magnetic flux
Uloop = - d/dt
The loop voltage is measured by a loop located in the proximity of the plasma column. The toroidal electric field, which accelerates charged particles in the toroidal direction (and drives plasma current) can be easily derived as:
E tor = Uloop/2R
1. Tokamak is pumped down to to the pressure <1 mPa
2. Tokamak vessel is filled by a working gas, typically the pressure of
hydrogen is ~ 30 - 80 mPa
3. Some free electrons are generated in the vessel by means of an a small
electron gun or by a cosmic background (pre-ionization)
4. Power supplies are activated by charging two capacitor banks:
* generation of the current in the toroidal magnetic field coils (0.6-1.2 kV)
* generation of the current in primary winding of the transformer (0.6-1.2 kV)
Sequence of events before a tokamak discharge
1. A trigger pulse is applied to start the data acquisition system
Experimental data a collected
2. A trigger pulse is applied to discharge the capacitor bank UBt to toroidal field coils
Toroidal magnetic field is generated inside the vessel
3. Wait until a reasonable level of the toroidal magnetic field is reached. Typical time delay is 2 - 4 ms
4. A trigger pulse is applied to discharge the capacitor bank Uoh to primary winding of the transformer
Time-dependent current in the primary winding generates the toroidal electric field inside the vessel
Start-up of a tokamak discharge
Sequence of events during a discharge
Toroidal magnetic field
Pressure of Hydrogen
Loop voltage
Uloop is high enough – Breakdown
50 mPa
Time
Delay
Trigger Bt
Trigger Uoh
Electron are accelerated in toroidal direction and ionize the working gas
Fully ionized plasma fills the vessel (in 0.1-10 ms – depending on the size of tokamak)
Density of charged particles increases exponentially in time
Free electron(s) appear in the vessel
Now, we can check the reality
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