GOLEM operation based on some results from CASTOR

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

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 radius 40 cm Minor radius 8,5 cm Toroidal magnetic field < 1,5 T Plasma current 5 - 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. GOLEM (June 3, 2008) The CASTOR tokamak is nowlocated 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. 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. 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

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

8. Preparation of the GOLEM vessel for operation • Pumping of the vessel down to 10-6mBar (10-4 Pa) by • turbo-molecular pumps is suficient • Baking of the vessel to • 250o 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. Basic diagnostics to operate GOLEM • 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, …..)

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

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

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

14. dne/dt = Sion *no*ne Plasma is fully ionized Ihalpha ~ no*ne ~ dne/dt ~ density of electons Maximum of I halpha is observed when no= ne ~ density of neutrals Time [ms]

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

16. Start-up phase of a discharge on the CASTOR/GOLEM Loop voltage [V] Uloop Toroidal current [kA] I_plasma+ I_vessel Plasma density ne[1019 m-3] 4 0 2 6 Time [ms] 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 => IpMax ~ 0.033 MA JET a = 1.250 m, R = 2.96 m, Bt = 3.45 T => IpMax ~ 3.2 MA GOLEM Reality ~ 15 kA max

18. Safety factor

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

20. Plasma radiation Photomultipliers equipped by interference filters or scintillators puffs of H2 Plasma density ne[1019 m-3] Gas puffing H_alpha[a.u.] Recycling H_alpha[a.u.] Additional gas (Hydrogen) is injected into the plasma to keep plasma density at a “constant” value. A piezoelectric valve is used Impurities CIII line[a.u.] Hard x-ray E>40 keV[a.u.] 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 = Uloop/Iplasma Poh = Uloop*Iplasma

23. Global confinement of energy (1) Balance equation for energy tE Energy confinement time !! globally characterizes losses of energy Total kinetic energy in the torus W = 3/2 (ne*Te+ ni*Ti) * V = 3 ne Te Heating Energy losses tE = W/ P

24. Electron temperature and confinement time Te ~ R-3/2 te = (ne*Te*V)/ POH

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