1. GOLEM operation based on some results from CASTOR J. Stockel, and the CASTOR team, Association EURATOM / IPP.CR, Czech Republic Several historical picture Tokamak CASTOR/GOLEM Basic tokamak diagnostics Power supplies Basic plasma performance Marianská, 13-16 January 2009

2. Tokamak concept proposed by: Andrei Sacharov and Igor Tamm (both Nobel prize winners) Institute of I.V. Kurchatov in Moscow 1950 History 1

3. Historie doma Ústav fyziky plazmatu založen 1959 Interakce VF záření s plazmatem Interakce elektronových svazků z plazmatem Lineární experimenty ELMAN a VF-1

4. Lev Arcimovich Jeden z otců vodíkové bomby v SSSR na návštěvě v UFP Byl obdarován malorážkou

5. CASTOR tokamak Major radius40 cm Minor radius8,5 cm Toroidal magnetic field< 1,5 T Plasma current5 - 20 kA Pulse length < 50 ms Features: Small tokamak Small ripple (24 TF coils) Routine operation (100 shots/day) Flexible (a good plasma already 1 day after opening)

6. 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.BiblePsalm The Mishnah uses the term for an uncultivated person.Mishnah Similarly, golems are often used today in metaphor as entities serving man under controlled conditions but hostile to him in others. see more at http://en.wikipedia.org/wiki/Golem GOLEM (June 3, 2008) The CASTOR tokamak is now located at the Faculty of Nuclear Physics and Physical Engeneering (Czech Technical University in Prague) located in the proximity of jewish cemetery and baptized as GOLEM.

7. A tokamak (CASTOR/GOLEM) Vacuum and gas handling system Power supplies Basic diagnostics Control and Data acquisition system Hardware required to have tokamak plasma?

8. Preparation of the GOLEM vessel for operation Pumping of the vessel down to 10 -6 mBar (10 -4 Pa) by turbo-molecular pumps is suficient Baking of the vessel to 250 o C (CASTOR) every day before shots Glow discharge cleaning Vessel is filled by Hydrogen gas (~ 1 Pa) Electrode (anode) is inserted into the vessel an biased to ~ +500 V Glow discharge is burning at ~0.5 – 1 Amp Inner wall is bombarded by H ions Molecules are desorbed from the inner surface

9. Toroidal magnetic field Plasma current Loop voltage Position of plasma column in the vessel Plasma density Plasma radiation in visible range (H_alpha, impurity lines, soft x-ray, …..) Basic diagnostics to operate GOLEM

10. Capacitor bank 1 MJ, 2 kV Basic power supplies of CASTOR/Golem - schematically TF COILS Capacitor bank 0.4 MJ, 0.5 kV Grid Rectifier Primary winding of transformer GridRectifier Toroidal magnetic field Breakdown and plasma current

11. Loop voltage The loop voltage is measured by a loop located in the proximity of the plasma column The toroidal electric field E tor = U loop /2  R accelerates charged particles in the toroidal direction (and drives plasma current) d  /dt – magnetic flux Uloop = - d  /dt

12. Toroidal magnetic field Signal of the loop has to be integrated analogue integrator numerical integration

14. ~ density of neutrals ~ density of electons dn e /dt = S ion * n o *n e Plasma is fully ionized I halpha ~ n o *n e ~ dn e /dt Time [ms] Maximum of I halpha is observed when n o = n e

15. Plasma current Plasma current is measured by means of the Rogowski coil (the solenoid of a toroidal shape surrounding the plasma column)

16. Loop voltage [V] Uloop Toroidal current [kA] I_plasma+ I_vessel Plasma density n e [10 19 m -3 ] Start-up phase of a discharge on the CASTOR/GOLEM Time [ms] 02 4 6 I_vessel = I_plasma – Uloop/Rvessel

17. Maximum plasma current - Safety factor q Stability of plasma requires the safety factor at the edge q(a) MIN > 3 Dimensions of a tokamak and the value of the toroidal magnetic field determine the maximum plasma current which can be driven in a tokamak: CASTOR a = 0.085 m, R = 0.40 m, Bt = 1.0 T => Ip Max ~ 0.033 MA JET a = 1.250 m, R = 2.96 m, Bt = 3.45 T => Ip Max ~ 3.2 MA GOLEM Reality ~ 15 kA max

18. Safety factor

19. Temporal evolution of a discharge on the CASTOR tokamak Toroidal mag. field Bt Loop voltage Uloop Plasma current Ip Plasma density n e Time [ms] 0 20 40 -20 Vessel is filled by working gas

20. Plasma radiation Plasma density n e [10 19 m -3 ] Gas puffing H_alpha [a.u.] Recycling H_alpha [a.u.] Impurities CIII line [a.u.] Hard x-ray E>40 keV [a.u.] Additional gas (Hydrogen) is injected into the plasma to keep plasma density at a “constant” value. A piezoelectric valve is used puffs of H2 Photomultipliers equipped by interference filters or scintillators Time [ms]

21. Ohmic heating in tokamaks Plasma – secondary winding of the transformer (a single loop) with a finite conductivity Ohmic power dissipated in the plasma column Electron temperature can be estimated from plasma resistivity (Spitzer formula)

22. Resistivity of plasma column and ohmic power R = U loop /I plasma P oh = U loop *I plasma

23. Global confinement of energy (1)  E Energy confinement time !! globally characterizes losses of energy Balance equation for energy Heating Energy losses  E = W/ P Total kinetic energy in the torus W = 3/2 (n e *T e + n i *T i ) * V = 3 n e T e

24. Electron temperature and confinement time Te ~ R -3/2  e = (n e *T e *V)/ P OH

25. Conclusions GOLEM is the oldest tokamak in the word It will be operational soon (hopefully) Its education potential is huge! Its scientific potential is not definitely exhausted We are looking forward to meeting you in the control room of GOLEM

26. Lavrentev