Transcript GolemOperationDAS_HSextrakt

GOLEM operation based on
some results from CASTOR
J. Stockel, and the CASTOR team, Association EURATOM / IPP.CR, Czech Republic
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Several historical picture
Tokamak CASTOR/GOLEM
Basic tokamak diagnostics
Power supplies
Basic plasma performance
Marianská, 13-16 January 2009
CASTOR tokamak
Major radius
Minor radius
Toroidal magnetic field
Plasma current
Pulse length
40 cm
8,5 cm
< 1,5 T
5 - 20 kA
< 50 ms
Features:
Small tokamak
Small ripple (24 TF coils)
Routine operation (100 shots/day)
Flexible (a good plasma already
1 day after opening)
Hardware required to have tokamak plasma?
• A tokamak (CASTOR/GOLEM)
• Vacuum and gas handling system
• Power supplies
• Basic diagnostics
• Control and Data acquisition system
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
Basic diagnostics to operate GOLEM
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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 power supplies of CASTOR/Golem schematically
Grid
Rectifier
Capacitor bank
1 MJ, 2 kV
TF
COILS
Grid
Rectifier
Capacitor bank
0.4 MJ, 0.5 kV
Primary
winding
of transformer
Toroidal
magnetic field
Breakdown and
plasma current
Loop voltage
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 E tor = Uloop/2R accelerates charged
particles in the toroidal direction (and drives plasma current)
Toroidal magnetic field
Signal of the loop has to be integrated
• analogue integrator
• numerical integration
dne/dt = Sion * no*ne
Plasma is fully
ionized
I halpha ~ no*ne ~ dne/dt
~ density of electons
Maximum of I halpha
is observed when
no= ne
~ density of neutrals
Time [ms]
Plasma current
Plasma current is measured by means of the Rogowski coil
(the solenoid of a toroidal shape surrounding the plasma column)
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]
0
2
4
Time [ms]
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
aB
2

a
B
TOR
TOR
Imax


RB

Rq
POL
0
min
2
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
JET
a = 0.085 m, R = 0.40 m, Bt = 1.0 T
a = 1.250 m, R = 2.96 m, Bt = 3.45 T
GOLEM Reality ~ 15 kA max
=> IpMax ~ 0.033 MA
=> IpMax ~ 3.2 MA
Safety factor


2
aB
2
a
B
B
TOR
TO
q(a)

 TOR

100
RB
RI
I
POL
0
plasma
plas
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
-20
0
Time [ms]
20
40
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.]
Impurities
CIII line [a.u.]
Additional gas (Hydrogen) is
injected into the plasma to
keep plasma density at
a “constant” value.
Hard x-ray
E>40 keV [a.u.]
A piezoelectric valve is used
Time [ms]
Ohmic heating in tokamaks
Plasma – secondary winding of the transformer (a single loop)
with a finite conductivity
Ohmic power dissipated in the plasma column
P
Iplasma
U
OH
loop

3
/
2
plasma
loop
plasma
e
R 
U/
I

T
Electron temperature can be estimated from plasma resistivity
(Spitzer formula)
Resistivity of plasma column and ohmic power
R = Uloop/Iplasma
Poh = Uloop*Iplasma
Global confinement of energy (1)
dW
W
P
dt
τE
Heating
Energy
losses
E
Balance equation for energy
E
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
= W/ P
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