Transcript Gent-Golem
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