Transcript Task 1 - Golem - tokamak of CTU

Remote tokamak operation
Jan Stockel
Institute of Plasma Physics, Prague, [email protected]
&
Vojtech Svoboda, Ondrej Grover – GOLEM operators
Faculty of Nuclear Physics and Physical Engineering, CTU in Prague
with a local help of
Milos Vlainic (Ghent University)
Aims of this lecture
•
•
Prepare participants for the workshop on
remote operation of GOLEM this afternoon
(necessary technical details)
Explain very basics of tokamak physics
Fusion Days@NS, Novi Sad 2016
Motivation of tokamak research
Tokamak is an experimental facility, which allows to heat the plasma to
temperatures 200 milion Kelvins (20 x higher temperature then in the
core of the Sun) and confine it by the magnetic field for a sufficient
time.
The main goal of the tokamak reseach is to achieve the thermonuclear
fusion for production of electricity
Existing tokamaks
since 1959 =>
ITER (under construction)
2025
DEMO – prototype of fusion reactor (design phase)
2045
Commercial Fusion power plant
2050-2070
However, a lot of research (tokamak physics + technologies) has to be
still performed!!
Tokamak basics
Tokamak is composed of
three basic components
•
•
•
Large transformer with primary winding
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 Pohmic = I2Rplasma to plasma (heating)
•
generates the poloidal magnetic field in the plasma ring Bpoloidal ~I/2pa
Tokamaks ( ~ 175 facilities since 1960)
EURATOM
Germany
France
GB
Italy
Switzerland
Portugal
Czech
JET – the largest tokamak
ASDEX U, TEXTOR 94
TORE – SUPRA
MAST
FT-U
TCV
ISTTOK
COMPASS, GOLEM
USA
Japan
Russia
Canada
China
South Korea
India
Brazil
Iran
Pakistan
D IIID, ALCATOR C-mod, NSTX
JT- 60, …..
T-10, TUMAN 3, FT-2, GLOBUS (spherical), T11-M
STORM-1M
EAST, HT-7, J-TEXT, HL-2A, ….
KSTAR
Aditia, SINP, (SST-1 under construction)
ETE, TCABR
IR-T1
GLAS
Currently ~ 30 operational tokamaks, which differ in:
Major radius 0.4 - 4 m, Magnetic field 0.5 - 4 T, Plasma current 0.01 - 4 MA
Main source: Conventional Tokamaks
Pulse length 0.01 – ~300 sec
from http://tokamak.info/
The GOLEM tokamak in Prague
The GOLEM tokamak is a small and also the "simplest" tokamak
Located in Prague at
the Faculty of Nuclear Physics and Physical Engineering (Czech Technical
University)
Unique feature: Can be operated remotely via Internet
Parameters
Toroidal magnetic field
Plasma current
Plasma density
Electron temperature
<0.5 T
<10 kA
<10^19 m^-3
<100
The oldest tokamak still operational!
Front view of GOLEM (schematically)
Iron core of
the transformer
Toroidal magnetic
field coils (28)
Primary winding of
the transformer (24 turns)
Diagnostic ports
(18)
Any vertical magnetic field is required for equilibrium position of the
plasma column in the horizontal direction in the basic mode of operation
(Iron core, copper shell, low plasma pressure, short pulse,….)
Toroidal magnetic field
28 TF coils - charged by the capacitor bank C = 24.3 mF
Tyristor switch
(always 5 ms after start of DAS)
Signal of the magnetic sensor
Is numerically integrated
Typical temporal evolution of
The toroidal magnetic field
Toroidal electric field
• Toroidal electric field E tor in the "empty" vessel is required for plasma
breakdown
• E tor is generated by by the time varying current in the primary winding
of the tokamak transformer
Etor
M dI prim

*
2πR
dt
M –mutual inductance between
primary winding and the plasma ring
R – major radius of the torus
Primary winding is charged by a condenser bank
Toroidal electric field at the breakdown should be as low as possible!!!!
Toroidal current
Toroidal current is measured
inductively by means of Rogowski coil
(a toroidal solenoid surrounding the
tokamak vessel form outside)
Again, the output signal of the RC has
to numerically integrated!
Note: The RC measures the total toroidal current Itotal = Ivessel + Iplasma
The vessel current must be subtracted to get plasma current
Ivessel = Uloop/Rvessel
Rvessel = 10 mOhm
Evolution of a vacuum shot – no plasma
No working gas in the tokamak vessel
Voltage Vloop is induced along the torus
The GOLEM vessel is the stainlesssteel torus without any insulating
break
=> the loop voltage induces the current
in the tokamak vessel
Time delay between Btor and Etor
Time delay can be selected
A proper time delay is selected to optimize breakdown of the working gas
Poloidal Limiter & pre-ionization
A circular diaphragm is installed inside to reduce
interaction of plasma with the inner surface
a = 85 mm
Some free electrons have to exist inside the vessel –
pre-ionization of the working gas by an electron gun (hot filament) is used
But background cosmic radiation can be also exploited
Pumping and gas handling system
b = 0.1 m
R0 =0.4 m
Pressure of working gas is adjusted according your request!
GOLEM
Basic engineering
scheme
Available at the remote control room of GOLEM
http://golem.fjfi.cvut.cz/current/index.html
http://golem.fjfi.cvut.cz/NoviSad
To summarize the remote operation
We need only five “buttons” to operate the GOLEM tokamak
We have to select:
•
Pressure of the working gas
Recommended range 5 – 30 mPa
•
Preionization of the working gas – ON (Top electron gun) or OFF
•
Charging voltage of the condenser bank of the toroidal magnetic field
Recommended range 100 – 1400 V
•
Charging voltage of the condenser bank to generate the toroidal
electric field (current in primary winding)
Recommended range 300 – 1000 V
•
Time delay between triggers switching the toroidal magnetic field and
the toroidal electric field (the loop voltage) –
Recommended range 0 – 10 000 ms
TOP view of
the tokamak
Electron
Fully ionized
are plasma fills
Density of charged
accelerated
the
vessel
(in
in 0.1-10
toroidal
ms –
Free
electron(s)
particles increases
direction
depending
ionize
the
size
theof
appear and
inon
the
vessel
exponentially in time
working
tokamak)gas
Conditioning of the tokamak vessel
• Inductive heating of the vessel to 150 - 250o C (after opening the vessel to
atmospheric pressure
• Glow discharge cleaning
Diagnostics available for the remote workshop
1.
Toroidal magnetic field in Tesla
2.
Total toroidal current (vessel & plasma) in Amps
3.
Plasma current in Amps
4.
Loop voltage in Volts
5.
Intensity of HXR radiation measured by a proportional detector
6.
Interferometer
7.
Rake of 16 Langmuir probes
8.
Mirnov coils
9.
Visible camera
Organization of the workshop
Participants will convene in the computer room (here)
Participants are divided in five experimental groups
Each group is supervised by:
1. Ana Kostić
2. Jordan Cavalier
3. Ondřej Kudláček
4. Branka Vanovac
5. Ondřej Ficker
NOTE: Even though two
mentors are Serbian, the
official language of the
Workshop is English – thus
students will be pursued to
communicate in English ;)
Requirements from participants
• Each student is asked to occupy one PC with internet connection
(hopefully there will be enough of them)
• Each student is asked to use an available software to process and plot
experimental data from GOLEM database (EXCEL, ORIGIN, MatLab,
Python…)
Active participation is highly required!!!!!
• AFTER THE WORKSHOP
– each student will write a report (A rough template will be given, while details
what to write in report will be given by your mentors. Tip: Do not make tables of
data!!!)
– PRICE: 2 best will go to COMASS training next summer!!!
GOLEM tokamak – long story
The GOLEM tokamak is the oldest tokamak in the word which is still
operational with a long term history!!
Built by the godfather of tokamak research, Lev Artsimovich in Kurchatov
Institute, Moscow around 1960 as TM-1
The first real tokamak plasma was achieved (simultaneously with the T-2
tokamak!)
Moved to Institute of Plasma Physics Prague and baptised as CASTOR in
1977
Replaced by COMPASS tokamak 2007
Moved to Czech Technical University and baptised again as GOLEM
Prague GOLEM
The word golem is used in the Bible to
refer to an embryonic or incomplete
substance
Similarly, golem is often used today in
metaphor as
an entity serving man under controlled
conditions but hostile to him in others.
Prague GOLEM was created by Rabbi Loew, who is buried at Jewish cemetery,
Just 50 meters from the Faculty of Nuclear Physics and Physical Engineering
THE END
(there are some additional slides with simple tasks
if somebody wants to play more)
Task 1: Produce the highest Te
Measured loop voltage has resistive and inductive component
U loop  I p R p  L p
dI p
dt
The inductance of
the plasma ring
on GOLEM is
L p  1 μH
The inductive component can be neglected, if the loop voltage is measured,
when the plasma current is maximum =>
U
Rp 
I
loop
max
p
The (Maxwellian) plasma resistivity is linked to the electron temperature.
A rough estimate for GOLEM
 I max

p

Te  32.5
U 
 loop 
2/3
eV, kA, V
Task 2: Produce the lowest Ubreak
Breakdown voltage
Ubreak ~ 6.5 V
Power supply of the primary winding has a relatively high resistance
Resistance of the secondary winding without plasma is the vessel – 10 Ohm
Plasma column represents an additional resistance in parallel to the vessel
resistance => the total resistance of the secondary winding is reduced
Task 3: Produce the highest q(a)
Extremely important quantity, which characterize stability of the plasma ring
It denotes the number of turns a magnetic field line goes
around a torus toroidally to finalize a single poloidal turn
a Btor
q(a) 
R B pol
Poloidal magnetic field is a function of the plasma current
m0 I p
B pol (a) 
2pa 2
=>
In practical units
Btor
q(a)  90.3
Ip
[T, kA]
2pa 2 Btor
q(a) 
m0 R I p
Task 4: Investigate the role of glow discharge
Plasma should be as clean as possible!!! Where ‘clean’ means that
there is no atoms different than the working gas.
Z eff  
j
njZ j
2
njZ j

j
njZ j
2
ne
Zeff donates the effective ion charge of the plasma. Perfectly
clean hydrogen, deuterium or tritium plasma would have Zeff=1.
Artsimovich at 1st IAEA Fusion Energy Conference in Salzburg (1961):
Braams and Stott ''Nuclear Fusion: Half a Century of Magnetic Confinement Fusion Research" (2002), p. 164
Task 5: Measurements with Langmuir Probes
Theory: see lecture of Jordan Cavalier :D
Experiments: Jordan has many ideas . . .
- floating potential
- profiles of electic field
- H vs He (old shots)
- correlations (very advanced)
Is somebody interested looking
into the old data?
#16312
#16346
Runaway electrons (lecture by Žana Popović)
A fraction of electrons in tokamak plasma is accelerated by the toroidal
electric field to very high velocities.
These electrons are usually called runaway electrons.
If the runaway electron hits a material
surface (the limiter, the vacuum
vessel), the high-energy photon(s) is
generated.
High energy photons are registered by a proportional detector
Task 6: Find the most energetic HXR photon
A signature of runaway electrons
Individual spikes are HXR photons resulting
from impact of a high energy on the limiter
Amplitudes of spikes are proportional to
energy of HXR photons (calibrated by
radiosotop Cs)
Energy [keV] = Amplitude [V]* 492