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Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 1
ITP-VT
The need to model the ITER high vacuum systemsin transitional flow regime –An engineering perspective
Christian Day
For the Vacuum Pumping Task Force Institute for Technical Physics, Forschungszentrum Karlsruhe, Germany,
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 2
ITP-VT
TD
Hen
2.01 + 3.02 =5.03 AMU
1.01 + 4.00 =5.01 AMU
20% of fusion energy
80% of fusion energy
+17 600 keV
E = mc2
Plasma state
Thermonuclear fusion of deuterium and tritium
First main challenge forITER vacuum systems:Ø Processing of tritium à
availability, safety, accountancy, controlà cryopumps
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 3
ITP-VT
Deuterium storage unit
Tritium separation unit
Turbine-generator
Steam generator
Blanket(Tritium regeneration, heat production)
Plasma(Deuterium-Tritium)
• The energy of the neutrons is converted into heat in the structures (blanket) lining the torus walls
• A circulating coolant removes the heat and, in the heat exchangers, steam will be generated to drive turbines for electricity production
The scheme of a commercial fusion reactor
• In ITER, the fuel tritium will be supplied from external
• In ITER, the fusion energy will be ´wasted´ (not taken out)
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 4
ITP-VT
Current fusion status and the role of ITER
τE, thELMy = 0.0562 × I 0.93 B0.15 P−0.69ne,19
0.41M 0.19 R1.97ε 0.58κ 0.78
Confinement time τ :
Second main challenge for ITER vacuum systemsØ Very big in size à highest pumping speeds !à cryopumps
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 5
ITP-VT
ITER fuelling
Third main challenge for ITER vacuum systemsØ Very high throughputs àØ Comparatively high pressures (in spite of the high
pumping speeds we have) àØ Transitional flow conditions inside the cryopumps
and in the associated pumping ducts
Burn-up fraction only 2%
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 6
ITP-VT
• Role of ITER (=still a R&D project)
– Burning plasma physics
– Integration of physics and technology
– Demonstrate and test fusion power plant technologies and safety features (tritium)
– Demonstrate the technological feasibility of fusion (availability)
The ITER mission
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 7
ITP-VT
ITER is being built in Cadarache, South of France
Tokamak: ?? ?????????? ?????? ? ? ??????? ? ? ????? ????(toroidalnaya kamera, magnitnymi katushkami)
Lev Artsimovich
Andrei Sacharov
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 8
ITP-VT
ITER and its main vacuum systems
Cryostat HV pumping system
Torus exhaust HVpumping system
Neutral Beam HVpumping system
+ Mechanical forepump trains(identical for each of the threehigh vacuum systems)
Cryo-mech cross-over pressure is 10 Pa
3 Large Cryopump systems
Major plasma radius 6.2 m Plasma Volume: 840 m3
Plasma Current: 15 MA Typical Density: 1020 m-3
Typical Temperature: 20 keV Fusion Power: 500 MW
Cryostat:24m high x 28 m dia
Cryostat + Vacuum vessel +
magnets=23 350 t
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 9
ITP-VT
YesYesYesSorbentcoating
Nitrogen, outgassingand leaking gas,
Hydrogen (H2, D2)Hydrogen (all six isotopes), helium, impurities
Depending strongly on theoperation mode (burn& dwell, conditioning, leak detection..)
Gases
Transient pump-down(closed cryostatvolume of 8400 m³) to 10-4 Pa and steady-state pumping of magnet coolant leak helium and outgassingspecies
Dynamic
= maintain the pressureinside the NBI volume(150 m³/H-NBI) at a throughput of
36 Pa·m³/s/H-NBI (protium operation)
Dynamic
= maintain the pressure insidethe VV volume (1350 m³) at a total gas throughput of
(120 Pa·m³/s (fuelling rate) or 60 Pa·m³/s (He case))+
(33 Pa·m³/s (impurities));
Base pressure for hydrogens: 10-5 Pa.
Pumping mode
22 (3) +18# Pumps
CryostatNBITorus
ITER large high vacuum cryopump systems - overview
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 10
ITP-VT
Some ITER areas of concern for transitional flow modelling
1. The divertor system.
2. The torus exhaust pumping duct system.
3. The torus cryopump itself.
4. The neutral beam injector system.
5. The forepumping system.6. …
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 11
ITP-VT
1. Flow modelling of divertor
For correlation of the divertor performance vs. geometry, theB2-EIRENE code is used, which describes the interaction of the plasma and neutral gas.
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 12
ITP-VT
153Pa.m3/sMaximum throughput during plasma operations
1-10PaTypical divertor pressure during plasma operations
Plasma Operations (pulsewise 400 to 3000 s)
< 5·10-4PaBase pressure
pulses)Dwell Pump-down (in between the
< 10-5PaBase pressure for hydrogen isotopes
~ 2600m²Total surface area for outgassing
~1300m3Vacuum Vessel free volume
Ultimate Pump Down
ValueUnitParameters2. Torus vacuum pumping system – Technical data
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 13
ITP-VT
Conductance modelling of divertor and duct system
Very complex geometry (varying cross-sections, short ducts) àFor design purposes, we have developed a quick, semi-empirical code forflow calculations and a system for network modelling.
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 14
ITP-VT
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140
Pumping speed of one pump (m³/s)
Max
imum
Thr
ough
put (
Pa·
m³/
s)
Reference
+ 1 cm
+ 2 cm
+ 3 cm
Tritium
Requirement:150 Pa·m³/s @ 1-10 Pa divertor pressure,Requires slot increase
Target pumping speed per pump
@ 2 Pa divertor pressureResult à The design pumping speed of the
individual pump shall be 80 m³/s
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 15
ITP-VT
3. The set-up of the torus cryopump
Molecular nominal pumping speeds:Pump + bellows : ~ 55 m³/sPump:~ 75 m³/s
Duct double bellows(compensation of torus displacement)
Torus cryopump
Valve 80 K shield 4.5 K panels
Exhaust gasfrom torus
Actuator
Part of the cryostat
Part of the duct
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 16
ITP-VT
Transitional flow conditions inside the torus cryopump
log (Pressure inside the pump)
molecularflow regime
transitionalflow regime
Kn= =10
Break-Down
mean free path
pump dimension
Generic dependenceS=S(Kn(p))
0
10
20
30
40
50
60
1E-4 1E-3 1E-2 1E-1 1E+0 1E+1
Pressure in pump (Pa) Inlet pressure (Pa)
Pum
ping
spe
ed (
m³/
s) increasingthroughput
100% open
35%
25%
10%
Monte Carlo
Experimental results for a 1:2 scaleITER model pump
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 17
ITP-VT
Extrapolation of pumping speeds?
0
10
20
30
40
50
60
70
1E-4 1E-3 1E-2 1E-1 1E+0 1E+1Pressure in pump (Pa) Inlet pressure (Pa)
Pum
ping
spee
d(m
³/s)
100% open
35%
25%10%
Increasingthroughput
q=42 mbarl/sm²(coated surface)q=149 mbarl/sm² (inlet area)
q=23 mbarl/sm²(coated surface)q=81.4 mbarl/sm² (inlet area)
New requirements(200 Pam³/s total ELM pellet pacing)q=45 mbarl/sm²(coated surface)q=260 mbarl/sm² (inlet area)
Our mid-term goal: Develop a predictive toolto get S=S(throughput), via DSMC?.
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 18
ITP-VT
4. Instantaneous massive gas injection (for disruption mitigation)
Pressure jumps from ~ zero to 100 Pa
How does the pressure(and the speed) evolvein the cryopump?
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 19
ITP-VT
5. Plasma heating at ITER
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 20
ITP-VT
The NBI cryopumping task
P1=0.3 Pa (filling pressure) P2/P1≈0.1 S(av, 1+2)=3800 m³/s
Design case :à H2 (higher flows,
more difficult to pump)
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 21
ITP-VT
Flow and pressure distribution (ITERVAC)
Along the beamline
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 22
ITP-VT
6. Gas dynamics during cryopump regeneration
- 3 regeneration levels:At 100K, 300K, 470 K.
- Evacuation from a few kPa to 10 Paover long lines and varying temperature
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
IUVSTA Gas Dynamics Workshop, Djurönäset, Sweden, July 2007 Transitional flow modelling ITER Chris Day Slide 23
ITP-VT
Conclusions
ü ITER is a very complex, technologically first of its kind device.ü In many areas, the vacuum systems are operated under transitional flow conditions.ü ITER is alive and must be built now:
There will rarely be the situation that the design is frozen and you get the time to do ´nice, accurate and parametric´ calculations.
ü The calculations will in most cases have a design support function to show thatoperational goals can be met.
ü It must reflect aspects such as: manufacturability, versatility, design robustness. ü So: From an academic point of view, this means difficult boundary conditions.
ü But everybody who can imagine working under these conditions isencouraged to come up and do so!
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