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Remote operation of the GOLEM tokamak
Jan Stockel
Vojta Svoboda
Institute of Plasma Physics, Prague
[email protected]
Faculty of Nuclear Sciences and Physical Engineering
Czech Technical University, Prague
[email protected]
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!
Gent University, December 14, 2009
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
= I2Rplasma to plasma (heating)
•
delivers the ohmic power Pohmic
•
generates the poloidal magnetic field in the plasma ring
Bpoloidal ~I/2pa
REMEMBER! Because of the transformer, tokamak is a pulsed device
GOLEM tokamak in Prague
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.
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
Front view of GOLEM (schematically)
Iron core of
the transformer
Toroidal magnetic
field coils (28)
Primary winding of
the transformer (12 turns)
Diagnostic ports
(18)
Engineering scheme of the GOLEM tokamak
Generation of toroidal magnetic field
Generation of plasma current
Vacuum pumping
Gas handling system
Power supplies of GOLEM (schematically)
For generation of toroidal magnetic field
Triggered
switch
Grid
Rectifier Capacitor bank
Toroidal Field Coils
For breakdown of working gas and plasma current drive
Triggered
switch
Grid
Rectifier Capacitor bank
Primary winding of transformer
Basic diagnostics of GOLEM
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
dy/dt – magnetic flux
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/2pR
Uloop = - dy/dt
Sequence of events before a tokamak discharge
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)
Start-up of 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
Sequence of events during a discharge
Pressure of Hydrogen
50 mPa
Toroidal magnetic field
Trigger Bt
Loop voltage
Trigger Uoh
Delay
Uloop is high enough – Breakdown
Time
Electron
Fully ionized
are plasma fills
Density of charged
accelerated
the
vessel
(in
in 0.1-10
toroidal
ms –
Free
electron(s)
particles increases
direction
depending
ionize
the
size
theof
appear and
inon
the
vessel
exponentially in time
working
tokamak)gas
Now, we can check the reality