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

Tokamak concept proposed by:

Andrei Sacharov and Igor Tamm

(both Nobel prize winners)

Institute of I.V. Kurchatov in Moscow 1950

History 1

Historie doma

Ústav fyziky plazmatu založen 1959• Interakce VF záření s plazmatem• Interakce elektronových svazků z plazmatem

Lineární experimentyELMAN a VF-1

Lev Arcimovich

Jeden z otců vodíkové bomby v SSSR na návštěvě v UFP

Byl obdarován malorážkou

CASTOR tokamak

Major radius 40 cmMinor radius 8,5 cmToroidal magnetic field < 1,5 TPlasma current 5 - 20 kAPulse length < 50 ms

Features:Small tokamakSmall ripple (24 TF coils)Routine operation (100 shots/day)Flexible (a good plasma already 1 day after opening)

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

GOLEM (June 3, 2008)

The CASTOR tokamak is now located atthe Faculty of Nuclear Physics and Physical Engeneering (Czech Technical University in Prague) located in the proximity of jewish cemetery and baptized as GOLEM.

• A tokamak (CASTOR/GOLEM)

• Vacuum and gas handling system

• Power supplies

• Basic diagnostics

• Control and Data acquisition system

Hardware required to have tokamak plasma?

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 cleaningVessel is filled by Hydrogen gas (~ 1 Pa)Electrode (anode) is inserted into the vessel an biased to ~ +500 VGlow discharge is burning at ~0.5 – 1 AmpInner wall is bombarded by H ionsMolecules are desorbed from the inner surface

• 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

Capacitor bank1 MJ, 2 kV

Basic power supplies of CASTOR/Golem - schematically

TF COILS

Capacitor bank0.4 MJ, 0.5 kV

Grid Rectifier

Primary windingof transformer

Grid Rectifier

Toroidal magnetic field

Breakdown and plasma current

Loop voltage

The loop voltage is measured by a loop located in the proximityof the plasma column

The toroidal electric field E tor = Uloop/2R accelerates charged

particles in the toroidal direction (and drives plasma current)

d/dt – magnetic flux

Uloop = - d/dt

Toroidal magnetic field

Signal of the loop has to be integrated

• analogue integrator• numerical integration

~ density of neutrals

~ density of electons

dne/dt = Sion * no*ne Plasma is fullyionized

I halpha ~ no*ne ~ dne/dt

Time [ms]

Maximum of I halpha

is observed when

no= ne

Plasma current

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

Loop voltage [V]Uloop

Toroidal current [kA]I_plasma+ I_vessel

Plasma density ne [1019 m-3]

Start-up phase of a discharge on the CASTOR/GOLEM

Time [ms]

0 2 4 6

I_vessel = I_plasma – Uloop/Rvessel

Maximum plasma current - Safety factor q

Stability of plasma requires the safety factor at the edge q(a)MIN > 3

min0

TOR2

POL

TOR

Rq

B2

RB

aBImax

a

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 MAJET a = 1.250 m, R = 2.96 m, Bt = 3.45 T => IpMax ~ 3.2 MA

GOLEM Reality ~ 15 kA max

Safety factor

plasma

TOR

plasma0

TOR2

POL

TOR

I

B100

RI

B2

RB

aBq(a)

a

Temporal evolution of a discharge on the CASTOR tokamak

Toroidalmag. field

Bt

Loop voltageUloop

Plasma currentIp

Plasma densityne

Time [ms]0 20 40-20

Vessel is filledby working gas

Plasma radiation

Plasma density ne [1019 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]

Ohmic heating in tokamaks

Plasma – secondary winding of the transformer (a single loop)with a finite conductivityOhmic power dissipated in the plasma column

loopplasmaOH UIP

2/3/ eplasmaloopplasma TIUR

Electron temperature can be estimated from plasma resistivity (Spitzer formula)

Resistivity of plasma column and ohmic power

R = Uloop/Iplasma

Poh = Uloop*Iplasma

Eτ

WP

dt

dW

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 (ne*Te + ni*Ti) * V = 3 ne Te

Electron temperature and confinement time

Te ~ R-3/2

e = (ne*Te*V)/ POH

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

           

Lavrentev