1. Remote operation of the GOLEM tokamak Gent University, December 14, 2009 Jan Stockel Institute 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!

2. 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 P ohmic = I 2 R plasma to plasma (heating) generates the poloidal magnetic field in the plasma ring B poloidal ~I/2  a REMEMBER! Because of the transformer, tokamak is a pulsed device

3. 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 radius0.4 m Minor radius of the vessel0.1 m Minor radius of the limiter0.085 m Maximum B-toroidal0.3 Tesla Maximum plasma current8 kAmp Discharge duration~ 5 ms

4. 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)

5. Engineering scheme of the GOLEM tokamak Gas handling system Vacuum pumping Generation of toroidal magnetic field Generation of plasma current

6. Power supplies of GOLEM ( schematically) For generation of toroidal magnetic field For breakdown of working gas and plasma current drive Capacitor bank Toroidal Field Coils Grid Rectifier Triggered switch Capacitor bank Primary winding of transformer GridRectifier Triggered switch

7. 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 = U loop /2  R

8. 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

9. 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 U Bt 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 U oh 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

10. Sequence of events during a discharge Toroidal magnetic field Pressure of Hydrogen Loop voltage U loop is high enough – Breakdown 50 mPa Time Delay Trigger BtTrigger Uoh

11. 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

12. Now, we can check the reality

13. The word golem is used in the Bible to refer to an embryonic or incomplete substance: Psalm 139:16 uses the word גלמי, meaning my unshaped form. The Mishnah uses the term for an uncultivated person.BiblePsalm Mishnah Similarly, golem is often used today in metaphor as metaphor an entity serving man under controlled conditions but hostile to him in others. Prague GOLEMs