vacuum technology (in dt fusion devices) -...

KIT – University of the State of Baden-Wuerttemberg and

National Laboratory of the Helmholtz Association

INSTITUTE FOR TECHNICAL PHYSICS, VACUUM DEPARTMENT

www.itep.kit.edu

Vacuum Technology

[email protected]

TIMO © Peter Ginter

(in DT fusion devices)

Chr. Day, ITEP-VAC2 25 January 2011

What is KIT


Institute of Technical Physics -Vacuum Departmentactivities

The whole Institute hasapprox. 170 staff.

The FUSION Programme:~ 220 staff.

KIT Campus North


The people

Vacuum department:In average 16 people, of different disciplines (engineering and physics, junior and senior, growing number of students)with two main working areas:1. Vacuum system design, especially Cryopumping2. Vacuum Gas Dynamics (flow And density distribution simulation).


Outline

General introduction.

A few notes and basics of vacuum.

Fundamentals of cryopumps.

Detailed example: The ITER divertor and torus exhaust cryopumping system

How to calculate a flow under vacuum?

Experimental characterisation of a cryopump

The ITER neutral beam injection cryopumping system.

The other ITER high vacuum systems.

Roughing pumps.

Vacuum technology for DEMO / Fusion Power Plant.

Conclusions.


The Fuel Cycle of a fusion reactor

Roughing

pumps

Fuelling:

-Pellet injection

-Gas injection

-Disruption mitigation

-Pellet pacing

NBI pumping

NBITorus

Tokamak

exhaust

processing

Isotope

separation

Storage

&

delivery

system

Torus pumps

Tritium

extraction

outer part inner part

Removal and recovery of tritium from blanket

Supply fuel to the plasma

Provision of plasma control

Supply fuel-type gases to NBI Exhaust gas cleaning, processing and fuel recovery

Torus exhaust via divertor

Vacuum pumping


Keywords are: Very high pumping speeds (very high throughputs), high

reliability/availability (MTBF), tritium compatibility, high magnetic fields No commercial solution available Dedicated pump developments.

Cryogenic pumping Mechanical pumping Transfer pumping

Why is vacuum pumping an issue?

The inner fuel cycleHIGH VACUUM


Major JET vacuum systems are essentially not tritium compatible (preventive maintenance, exchange upon failure);

Base pressures: similar;

Torus volume: ITER/JET ~10-20;

Pulse lengths:

JET; up to several seconds

ITER: short pulse up to 400 s, long pulse up to 3000 s;

Tritium throughput: the main DT campaign in JET was equivalent to one day of ITER DT operation.

Scale-up JET to ITER

ITER is definitely the most challenging vacuum system of the world and will definitely be first-of-its-kind.


Outline









Roughing pumps.


Conclusions and outlook.


What is vacuum?

Ideal: Vacuum is (a room filled with) nothing.The absence of matter.

Real: Vacuum is the pressure below ambient.

According Standards:(ISO 3529-1, DIN 28400)

p< 300 mbar


Name Pressure range

Rough vacuum 105 Pa (ambient) to 100 Pa

Fine vacuum 100 Pa to 10-1 Pa

High vacuum 10-1 to 10-5 Pa

Ultra high vacuum (UHV) 10-5 Pa to 10-10 Pa

Extreme high vacuum (XHV) < 10-10 Pa

10-12 Pa (outer space)

1 bar = 105 Pa; 1 mbar = 100 PaPressure := Normal force per area: 1 Pa=1 N/m²

Different levels of vacuum

National primary standards:- By force: down to 30 Pa,- By static expansion: down to 10-2 Pa,- By dynamic expansion: down to 10-7 Pa.

Blaise Pascal1623-1662


The gas flow under vacuum is characterised by the dimensionslessKnudsen number:Kn=(mean free path)/characteristic length)(such as the pipe diameter, the channel width..)

The mean free path L is the average distance, a particle has to make before it collides with another one.It holds:

Example: Kn=10 (DN100, Air) p=10-3 Pa @ 300 K, p=10-4 Pa @ 80 K, p=10-5 Pa @ 4 K

constT

Tkp

L

2

The pump-out process is described by the

Knudsen number

Kn=L/d

300K: 10-2....10-3 cm·mbar (Air)

L=64 nm @ 1 atm 6,4 cm @ 10-1 Pa, 64 km @ 10-7 Pa.

64000 km @ 10-10 Pa (~ 1.5 x Diameter of the Earth)


Kn « 1: Viscous or continuum flow(laminar, turbulent, depending on Re)(described with the Navier-Stokes equation) coarse vacuum

Kn » 1: Free mecular flow (Intermolecular collisions are not relevant)(described with Monte Carlo methods) UHV and XHV

Kn ~ 1: Transitional flow(there is no exact solution known (Boltzmann equation)) (empirical approaches vs. hard mathematics) fine vacuum

Flow regimes

Pix: Adixen


1. The gas flow Q (how much is flowing? Usually given in mol/s or kg/s)in vacuum technology is given in volumetric units (as pV-flow Q)(e.g. (mbar·l)/s, (Pa·m³)/s, related to 273.15 K).

3. Vacuum pumps in molecular flow regime do not suck the gas molecules.They can only pump the particles which find their random way in. But not allthese molecules are pumped, as there is a finite probability they are reflectedback and re-emitted. So, pumping speed is the arrival rate of the gasmolecules at the pump inlet (function of T, gas species) times the so-calledcapture probability.

nm TRmVp VptVpTimegasofAmountQ //

Important vacuum terminology

2. The most important property is pumping speed S. Pumping speed denotes the gas throughput (at a reference temperature of 273.15 K), related to the pressure at the inlet of the pump.

pSp

Q

dt

dVS


The pump tree

Sliding Vane

Rotary Pump

Molecular

Drag Pump

Turbomolecular

Pump

Fluid Entrainment

Pump

VACUUM PUMPS

(METHODS)

Reciprocating

Displacement Pump

Gas Transfer

Vacuum Pump

Drag

Pump

Entrapment

Vacuum Pump

Positive Displacement

Vacuum Pump

Kinetic

Vacuum Pump

Rotary

Pump

Diaphragm

Pump

Piston

Pump

Liquid Ring

Pump

Rotary

Piston Pump

Rotary

Plunger Pump

Roots

Pump

Multiple Vane

Rotary Pump

Dry

Pump

Adsorption

Pump

Cryopump

Getter

Pump

Getter Ion

Pump

Sputter Ion

Pump

Evaporation

Ion Pump

Bulk Getter

Pump

Cold TrapIon Transfer

Pump

Gaseous

Ring Pump

Turbine

Pump

Axial Flow

Pump

Radial Flow

Pump

Ejector

Pump

Liquid Jet

Pump

Gas Jet

Pump

Vapor Jet

Pump

Diffusion

Pump

Diffusion

Ejector Pump

Self Purifying

Diffusion Pump

Fractionating

Diffusion Pump

Condenser

Sublimation

Pump

Rough vacuum High vacuum

piston ??Customized cryopumps

(very large is some 1000 m³/s

Turbos < 3 m³/s)

ITER:


ITER´s large high vacuum 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 pumping system(~ 150 m³/s, 8500 m³)

Torus exhaust pumping system(~ 8x80 m³/s, 1400 m³)

Neutral Beam (NBI) pumping system(~ 5000 m³/s, 200 m³)

3 large cryopump systems

+ backing pump trains


OutlineOutline









Roughing pumps.




Definition according to ISO:´……A cryopump is a vacuum pump which captures the gas by surfaces cooled to temperatures below 120 K ….. ´Cryopumps exploit the most elementary form of producing vacuum by lowering the temperature. They are capture pumps which remove gas molecules by sorption or condensation/re-sublimation.4. 2K 20K 27K 77K

LHe LH2 LNe LN2

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E-1 1E+0 1E+1 1E+2 1E+3

Temperature (K)

Sa

tura

tio

n P

ressu

re (

Pa

)

³He

H2

D2

T2

Ne

N2

Ar

CO

O2

CH4

CO2

H2O

He

Cryopumps – How does it work?

(Tailor-made) cryopumps do have the biggest pumping speeds

They are the primary solution when it comes to

a. High throughputs to be pumpedb. Lowest pressures to be achieved


max. T 23 Kor 18-19 K, respectively,for the cold surface of the cryopump to generate vacuum pressures in the orderof 10-7 mbar or10-11 mbar, respectively.

1. Principle - Cryocondensation

Vapor pressure curve indicatesthermodynamic equilibrium Net pumping speed of Zero

In praxi: Gas-oversaturation (rule of thumb: 1-2 Decades in pressure)

e.g. Nitrogen


Hydrogen requires temperatures below the ´normally´ available 4.2 K to produce ultra high vacuum.

Helium can of course not at all be pumped.

Limits of condensation

What to do now?


Pumping of gas via Physisorption on a cold sorbent.The pumping effect is determined by the pore propertiesOf the sorbent (Pore size distribution, up to 3000 m²/g).

Zeolites (Molecular sieves)

Charcoal

Sintered metal

Porous ceramics

Condensed gas itself (Argon frost)

2. Principle – Cryosorption

Charcoal is the Standard material

All three ITER cryopump systems are tailor-made and share the common approach of charcoal-coated modular cryosorption panels. They have been developed for optimum use of the available installationspace (circular for the torus/cryostat pumps, rectangular for the NBI pumps).

- The porous materials are bound to the cold surface (glue, cement, braze). - ITER reference design developed at KIT. - Additional design parameter: Not only p and T, But also surface gas load Saturation effects.


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 5 10 15 20 25 30 35 40

Pore Width (Å)

d(V

ads)/

dw

(cm

³/Å

/g)

this work, 3 samples

Belgian Army NBC, 4 samples

Example:Granular type,Ø 1mm

Cryosorption at charcoal

1 mm

13 x 8 Å

Pore size distribution


The efficiency of cryosorption is lower than for condensation (you need more hits before the particle becomes immobilized), but the achievable equilibrium pressures are always lower, e.g. H2: p=10-4 Pa: T~20 K.(whereas condensation would require 4.2 K)

0

5

10

15

20

25

30

1E-04 1E-03 1E-02 1E-01

Pressure (Pa)

Adsorb

ed V

olu

me (

cm

³/g)

10 K

hydrogen on charcoal helium on charcoal

The cryosorption operation point is given by the

sorption isotherm


Baffles + shields, pumping panels, and cryosupply

Tailor-madein-vessel cryopump,4.4 m x 1.5 m LHe @ 4.2 KS=400 m³/s (H2)

Tailor-madeITER Torus cryopump,With integrated valve.Valve DN 800, SCHe (4 bar) @ 4.2 KS=100 m³/s (all gases)

Commercial Refrigerator-Cryopump,Up to about 60 m³/s,DN 1200,Cryogen-free

Elementary Cryopump set-up


.min HQQQQ RadGFtot

)( 4

2

4

111212 TTACQ

211221

122112

)1()1(1

C

1. Solid heat conduction

2. Residual gas heat conduction

12QtQRad

3. Thermal radiation4. Phase change enthalpy

TALQF ·/

Source: Haefer

Cryopump elements given by cryogenics..


Cryopumps can in principle provide the maximum theoretical(´black hole´) pumping speed Sid, if the cold surfaces are installed

directly in the vacuum recipient (i.e. without any conductancelimiting flanges).However, the baffles which are needed due to cryogenic reasonsreduce the pumping speed to the practically achievable value.

The ideal pumping speed is reduced for a real pump- first by the limited transmission probability w of a particle onthe way from the vessel volume on the pumping surface - then by a non 100% sticking probability a of a particle at thepumping surface.

..But this has vacuumtechnical consequences


Classical cryopump design

1. 2. 3. 5.

4.

300K85K

7.

6.

Coated cryopanel (in ITER supplied with 4.35 K)

Thermal shields (in ITER supplied with 80 K) have to reconciletwo contradictory requirements: Minimize thermal radiation onto the panels but still provide sufficient conductance for the particles

Achieves a capture probability of ~ 20% (H2)


Initial hydroformed panel (stainless)

Panel charcoal coated

The reference ITER panel set-up (bare stainless steel panel + bonding agent + charcoal material) coated with the automatic KIT procedure has seen intensive temperature cycling tests (up to 10 000 cycles between 5K to 100 K, and 80 K to 300 K) without any deterioration.

e.g. 1 m long x 0.2 m wide (3 parallel channels)

It was important to demonstrate the series manufacturing process in terms of quality and reproducibility- ITER must not rely on lab scale technology

Modular design of all pump surfaces


Spin-off from fusion technology development:

Where you can find the KIT charcoal know-how

in various pump configurations

http://www.mpg.de/

http://vacuumdetails.oerlikon.com/index.php

http://www.fair-center.de/index.php?id=1&L=1

http://www.gsi.de/portrait/index_print.html

http://www.triumf.ca/


OutlineOutline









Roughing pumps.




Torus cryopump

Scheme of the ITER torus exhaust system

Non-symmetric


The ITER lower port region

Ring with 54 divertor

cassettes

Cryopump1 Divertor

cassette

~ Rectangular pumping

channel

Laminar..........transitional……..…molecularKn~0.01and transitional Kn~500


The vacuum engineering task to solve

recipient

port vacuum pump

Correct description of the process Correct description of the system geometry

1. Process, difficult, input has to come from others.What is the mass flow that the machine defines, and which part of that has to be handled by the vacuum pumping system?

2. System geometry leads to complex flow conditions.What is the maximum possible mass flow through the port?

3. Correct pump choice.What mass flow can be accepted by the pumps?

pR pP


Pumping during burn phase

Maximum fuel throughput (DT) of up to 200 Pa m3/s at divertor pressure between 1 and 10 Pa, on top comes He, impurities etc…

Pumping during dwell phase

The dwell time between the 400 s burn pulses is only 1400 s to pump out the vacuum vessel and ducts (volume of about 1350 m³) at pressures lower than 0.5 mPa.

Extrapolated from JET: Q=3.5 Pam³/s (t/s)-0.73

Other pumping modes

Bakeout, glow discharge cleaning, EC/IC discharge cleaning (dirty)

ultimate pumpdown of the vessel, leak detection

Maximum pumping speed is paramount

Torus pump requirements


Calculation of vacuum flows in a wide range of the

Knudsen number requires to…

1. ….calculate flows in viscous regime, needs FEM modelling effort for ´unusual´ geometries.

2. ….calculate flows in free-molecular regime, needs Monte Carlo modelling effort for ´unusual´ geometries TPMC

3. …..calculate flows in the whole range of Knudsen numbers by the Boltzmann equations for some well defined (simple?) cases. To provide solutions of the Boltzmann equations for additional cases (3D, non-linearized) is ongoing, but a major effort.

4. ….calculate flows in the transitional range, needs Monte Carlo modelling effort with intermolecular collissions DSMC, Particle-in-cell

5. For applications most important: A network code for multi-channel systems.


Method Flow regime Validation What calculated Application

examples

MOVAK3D Test Particle

Monte Carlo

Free molecular With MOLFLOW

Fully validated

transmission probability;

Radiation heat load

All ITER cryopumps

ProVac3D Monte Carlo Free molecular,

extended to

collisional flows

With MOVAK3D and

MCGF in free

molecular;

Validation of

collisional flow

against DSMC

ongoing

3D density profiles;

non-isothermal system

with distributed gas

sources; non steady-

state problems

NBI systems

ITERVAC Semi-

Empirical,

Good as

design tool

All flow regimes With experiment

and kinetic theory

Validated for high

L/d; Improvement

currently ongoing

for small L/d

Flow rate

Pressure

Conductance

ITER divertor

DSMC transitional flow With experiment (e.g.

to get accomodation

coefficients right)

All macroscopic

quantities

ITER divertor and

gas injection system

These codes are developed by KIT + CFD for viscous flows

KIT fusion toolbox – Code Overview


How much is the flow to be pumped?

To

Pump

Plasma

Neutrals

Global flow chart of the divertor

ITER map of flows

Competitive pumping


ITERVAC provides the user with all tools to build up 2D networks

and calculates the mass flow through every channel depending on

the pressure of the gas source and inside the pumps.

Idea behind ITERVAC

gas sourcebinding node

channel

pump

Day et al., FEC 2006


Typical rarefied gas channel flow characteristics

1/Kn

Dim

ensio

nsle

ss flo

wra

te

Short circular tube with L/D=1, Nitrogen,ambient T (DSMC solutions by KIT).

Generalized Dimensionless solutions(Kinetic theory solutions by UTH, Greece)

Long channel: Fully developed flow Short channel: Developing flow

Varoutis, Naris, Hauer, Day, Valougeorgis, JVSTA 2009. Varoutis, Hauer, Day, Pantazis, Valougeorgis, in press, FED 2010


Dosing

Dome

Gas flow

Test

channel

Pumping

Dome

Turbo-

molecular

pumps

Experimental facility TRANSFLOW


High Kn numbers Complete failure of CFD

Circular channels

(even for slip flow boundary conditions)


Evolution of the final model by stepwise inclusion

of more and more divertor flow paths

Contains 1428Model ducts of different length and cross-section.

Calculation time is 2-8 h per point and up to 20 h per point in case of poor convergence (higher divertor pressures)

Source:Divertor

Sink:pumps

(55 m³/s per (pump + bellow)

Sink:plasma (black hole at 650 m²)


Input parameter: divertor pressure 1-10 Pa, deuterium (single gas), temperature 420 K

Additional effect of diagnostic cassettes (2008 design):He Conductance ~ 100 m³/s30 % pumped

Competitive pumping: plasma vs. pumps

2006 design: He Conductance ~ 30 m³/s, 2007 design: He Conductance ~ 60 m³/s,Variation of the divertor gaps,40% pumped

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 1 2 3 4 5 6 7 8 9 10

Divertor dome pressure (Pa)

Maxim

um

Th

rou

gh

pu

t (P

a m

³/s) Torus pumps Gap 10mm

Plasma Gap 10mm

Torus pumps Gap 20mm

Plasma Gap 20mm

Torus pumps (2006)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 1 2 3 4 5 6 7 8 9 10


Ma

xim

um

Th

rou

gh

pu

t (P

a m

³/s) Torus pumps

Plasma


0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6 7 8 9 10


Ma

xim

um

Th

rou

gh

pu

t (P

a m

³/s)

H2 torus pumps

H2 plasma

DT torus pumps

DT plasma

He tourus pumps

He plasma

H2

He

DT

Final results of the 2009 divertor pumping


0

50

100

150

200

250

300

0 20 40 60 80 100 120 140

Pumping speed of one pump (m³/s)

Ma

xim

um

Th

rou

gh

pu

t (P

a·m

³/s)

Reference

+ 1 cm

+ 2 cm

+ 3 cm

Protium

@ 2 Pa divertor pressure

Conclusion The design pumping speed

of the individual pump shall be 80 m³/s.

Target pumping speed =

Region 1:Throughput~ Pumping speed

Region 2: Conductance Limitation to Max Value


Requirements revisited

The effective molecular pumping speed of the (2009) divertor system on mass 4 (assumed pumping speed per (pump+bellow) is 55 m³/s) is consequently 1/(1/100)+1(4....8x55)) m³/s = 70....80 m³/s.

For mass 5 (50-50 DT) the values are: 60....70 m³/s.

For Helium (Pressure is expected to be between 0.25 Pa and 10 Pa):a) for an under-dome pressure in the range 4 - 10 Pa: throughput up to

120 Pa m³/s b) for an under-dome pressure < 4 Pa: throughput < 120 Pa m³/s and a

minimum pumping speed of 30 m³/s

For D-T (Pressure is expected to be in the range 1-10 Pa): a) for an under-dome pressure in the range 3 - 10 Pa: throughput up to

200 Pa m³/sb) for an under-dome pressure < 3 Pa: throughput < 200 Pa m³/s and

a minimum pumping speed of 50 m³/s


1. Pumping port size is limited Maximize pumping speed / Capture

probability at constant entrance area.

2. Worst case to design the cryosorbent panels reference design shall

include a pure helium/protium shot (which means 100% sorption pumping).

3. The composition of the gas mixture being pumped may vary significantly Minimize the dependency of pumping speed on gas

species.

4. The gas throughput is variable and must be controllable include an

inlet valve for control.

5. Compatibility with the operating conditions Magnetic and electric

fields, seismic, tritium-compatibility, Safety (Hydrogen explosion), Remote handling….

Torus pump design aspects for burn


Staggering interval of 150 s

p some 100 Pa

p = some kPa

p 10 Pa

p 10-6 Pa

p = 10-2 Pa max.

With this trick, we provide to the torus a quasi continuous pumping speed with batch regenerating cryopumps.

Operational scheme of the torus system(long pulse, max throughput)

Cryopump operational pattern is determined by explosion safety considerations, not by saturation effects of the sorbent.


Proper design needs a coherent set of

reliable (i.e. experimentally validated)

input parameters

1. Defined requirements (speeds, gas loads to be pumped, cooling concept).

2. Vacuum technological design: Cryopanel and thermal shield geometry. Optimisation by Monte Carlo calculations.

3. Cryogenic design: Heat loads, regeneration techniques.

4. Thermohydraulic design (cryogen flow pattern, transients, liquid cryogens vs. gaseous helium, pressure losses).

5. Mechanical design, piping, FEM analysis, EM forces, seismic

6. Safety (Hydrogen explosion).

7. Assembly and maintenance aspects.

8. Forepumping.

9. .....

Detailed pump design procedures


Stage I

1990-1995

Qualification of the sorbent

and the panel technique

Stage II

1995-2000

Test of complete

sorbent coated panels

Stage III

1999-2006

Investigation of the

scaled cryopump

Stage IV

2002-2006

Sorbent panels test

under tritium (JET)

1:1 scale prototypes and serial pumps

Development path towards the cryopumps


Heater

Test

Vessel

Process Control

2 KW

Refri-

300 K/450 K GHe

LN-Storage

Model Pump

Gas Dosage80K-System

Valve Box

gerator

80 K GHe

GN

LN

4,5 KSCHe

H

D

He

2

2 He Exhaustsystem

Test bed TIMO-2 @ KIT

TIMO is able to fully replicate ITER-relevant conditions in most aspects (cryogenic flow rates, gaseous flow rates and composition, cycling times) except of tritium.


The cryopump was a model pump (4 m² pumping surface)to investigate all relevant features and to validate in general the cryosorption pumping concept for ITER.

Tests with a model cryopump completed


Successful experiments in JET pumping tritiated gas (during the JET tritium experiment TTE and in a parametric programme in the JET Active Gas Handling System) and for determination of the residual tritium content.

0.4 m2 sorbent

area

Very successful quantitative T2

experience with ITER sorbent.

ITER Cryosorbent R&D

Complementary tritium tests at JET


Performance tests

Pumping speed tests for pure gases and relevant mixtures, at normal (4.5K) and elevated (up to 15K) temperature (relation S – p – Q – Pumped amount - Valve Position)

Capacity tests

(Poisoning) tests after accumulation of air-likes or water-likes (+ hydrocarbons, + radicals)

Cryogenic performance and fast regeneration tests

Safety tests

Sudden venting (LOVA triggered hydrogen release transients)

Water leaks

Mechanical tests

Cycling tests (30 000 full strokes)

Post operational inspection

Main test campaigns in TIMO


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

pin

g s

peed (

m³/

s)

increasing

throughput

100% open

35%

25%

10%

Monte

CarloThe valve gives an additional degree of freedom in operation and allows to decouple the situation upstream the pump from the pumping situation inside.The pump is operated in transitional flow regime

It would be valuable for ITER to have a predictive tool, is doable by DSMC.

Exemplary TIMO results – Interrelation of pumping

speed, valve position and throughput

S = S (gas flow); not constant


Almost insensitive against the type of gas beingpumped, although bigdifferences in stickingcoefficients: a(He)=0.2 vs. a(D2)=0.9,achieved by Monte Carlobased interior design.

Exemplary TIMO results – Gas species

dependency

0

20

40

60

80

1E-3 1E-2 1E-1 1E+0 1E+1

Inlet Pressure (Pa)

Pum

pin

g S

peed

(m

³/s)

D2Base

D2Base/He

D2

He

D2Base

D2Base/He

D2

He

Valve Position 100% open

Valve Position 50% open


4.5 K

1. Helium pumping shows a clear saturation capacity, however beyond the ITER design point.

2. Deuterium is pumped at constant speed until very high pumped gas amounts.

design value

Exemplary TIMO results – Helium saturation

capacity

Result We need a charcoal coated surface of ~ 12 m² per pump for ITER

(Based on the strict regeneration pattern concept)

0

10

20

30

40

50

60

1E+01 1E+02 1E+03 1E+04

Gas load (Pa·m³/m²)

Pu

mp

ing

sp

ee

d (

m³/

s)

Helium

Deuterium

q=0.8 (Pa·m³)/(s·m²)


0

10

20

30

40

50

60

70

80

90

100

40 50 60 70 80 90 100 110

T (K)

Gas r

ele

ase (

% o

f pum

ped G

as)

T2

D2+T2

D2

H2

10 50 90 130 170 210 250 290

Panel Temperature (K)

0

20

40

60

80

100

Re

lea

se

d G

as (

%)

1. Partial regeneration every 600 s 2. Ambient regeneration less frequently

Condensed species evaporate and re-adsorb desorption rules.

Exemplary TIMO results – 3 stage regeneration

Conclude: Go for 90 K regeneration temperature, 100 K supply temperature

3. 470 K regeneration after incidents (e.g. water leaks)


90% D2 + 10% He, 4.5K, always identical (high) flowrate

Pumping speed tests with the cryopanels being pre-loaded with - water- light hydrocarbons (C1,2,3)- heavy hydrocarbons (C6, C8)- aromatics (benzene, xylene,

toluene)- alcohols (butanol)

No significant effect on

pumping speed measured

Exemplary TIMO results – No poisoning

Mixture pump tests after contamination

60

65

70

75

80

0 1000 2000 3000 4000 5000 6000

Gas load (Pa·m³/m²)

S (

m³/

s)

Reference curve

Octane

Hexane

Water


Exemplary TIMO results – LOVA on cryogen

Pressurisation with 50 Pa/s nitrogen, continued cooling,

testing together with CEA Grenoble

LOVA results in an averaged heat flux of 0.5 W/cm² (considerably lower than the ~ 4 W/cm² for non-insulated surfaces).


Exemplary TIMO results – Post-mortem inspection

(first opening after 6 years)

Check, especially of dynamic elements of the integral inlet valve, such as- bearings under vacuum (issue) - Valve and main seal- Spring disks (issue)- BellowsBut also:- Surface - Charcoal coating- etc


Duct double bellows

(compensation of torus

displacement)

Torus cryopump

Valve 80 K shield 4.5 K panels

Exhaust gas

from torus

Actuator

Part of the cryostat

Part of the duct

The pre-production torus cryopump design

8 such pumps on the torus:1:1 scale test in TIMO-2


Outline









Roughing pumps.


Conclusions.


Plasma heating at ITER

Functions of NBI: 1. Heating – 2. Diagnostics – 3. Current drive


NBI cryopumps at JET

As NBI applies very high gas throughputs, the NBI cryopumps in nuclear fusion are the largest worldwide. The JET system provides a pumping speed of 6000 m³/s.


Design process of a customized cryopump

1. Definition of requirements

(e.g. available space).

2. Gas distribution and flow

analysis defines the target

pumping speed.

3. Conceptual design=vacuum

design.

4. Detailed design.

5. Final / build-to-print design.


ITER in-situ NBI cryopump with distributed

sources

Ion Source with accelerator

Neutralizer

Residual Ion Dump

Calorimeter with “improved” water cooling supply

Cryopumps

Main Gas Source=

40 Pam³/s=

Additional Gas Source

5 Pam³/s=

Additional Gas Source

0.5 Pam³/s

=

16.5 MW hydrogen beam input to plasma

3.65m

3.48m

10m P=0.3 Pa

P=0.025 Pa

P=0.001 Pa


The capture coefficient concept

Incoming Gas flux (I)

Pumping of gas particles on cryogenic surfaces (P)

Cry

ogenic

pum

pin

g p

anels

Reflected (R)

Capture coefficientc=P/I

The capture coefficient describes the integral pump property, And can be used for model calculations at a stage where one does not yet know how to do the pump design at all.

AM

TRcScS id

2

A,c


X=0 X=1.6

Main sourceAdditional source Additional source

p1

p2

p3

2 baffles at end of N and RID, with varied capture coefficient

1.00E+17

1.00E+18

1.00E+19

1.00E+20

0 1 2 3 4 5 6 7 8 9 10

Distance X (m)

Den

sity

(1

/m^

3)

c=0.2 c=0.24 c=0.32 c=44

D2

Calculated axial gas profiles for varied c


Requested:

3.5·1018 /m³ = 0.025 Pa

Conclusion from the flow analysis

Conclusion: The cryopump must provide a capture coefficient of approx. 32 % for hydrogen, then the resulting gas profile along the beamline will work.This capture coefficient must be provided at a pressure of ~ 10-4 Pa(typical result of 3D MC radial profile calculations is ~ two orders of magnitude

lower in front of the cryopump)

Now, one can ´forget´ the system as such and concentrate on how to provide the given c in the given volume.


80 K

5.5 K Incoming Gas Flux

Transmission

Reflection

Sticking probability at charcoal: H2: 0.7D2: 0.9 - 0.95f (T, pumped amount),Geometry

Transmission probability of a chevron baffle only 0.2…0.25(Louvre not possible, due totoo high direct heat loads)

Classical conceptual cryopump design c = c (a, t)

The capture coefficient has two contributions:- the limited molecular transmission probability t of a particle on the way from the

vessel volume on the pumping surface

- the non 100% sticking probability a of a particle at the pumping surface.


c ~ 18% c ~ 28% c ~ 34%

Cold surfaces (5.5K)

Particle source

Radiation shielding (80K)

The neighbouring

pump unit protects

the cold surfaces

(5.5 K) from direct

radiation

Development of advanced configurationsC from Monte Carlo calculation


Comparison of design variants

Model 3JET like pump

Model 2KIT design

Model 1Classical cryopump

Capture coeff. (H2) 20% 33% 42%

Heat load to 4.5K circuits by thermal radiation related to the pumping surface (stand-by)

3.15 W/m2 3.63 W/m2 8.42 W/m2

Calculated with 3D Monte Carlo simulations


8x1m modules in series

1 module with 4 sections in parallel

1 section

The NBI cryopump so far


Neutral Beam Test Facility

at Padua - Italy

The main risk mitigation measure for resolving NB issues

The heart of the NBI activities will beat in Padova,

site of the MITICA test facility


Current status and outlook:

Detailed design activity programme for ITER / F4E

- We are charged to elaborate the detailed design (up to the level of Build-to-print manufacturing drawings, with CATIA v5) for the PPC and the HNB/MITICA cryopumps. lots of mechanical analysis (ANSYS), welding etc. Manufacturability and cost optimisation.

- These prototype pumps will then be manufactured and tested (the PPC in TIMO-2, the HNB in MITICA).

- Based on the results, we derive the series design.

- Then, the series pumps are built by (European) industry. TIMO-2 isavailable to acceptance check one or more of them.


Outline









Roughing pumps.


Conclusions.


- All of these vacuum systems do see tritium, so they haveto be made tritium compatible. They are categorized intwo classes, depending on permanent or ocassional

exposure to tritium.

- The standard pump type for these systems is aconventional Gifford McMahon based cryocooler cryopump(good compatibility with magnetic and electric fields, highpumping speeds). The compressor stations will probably be centralized.

- However, the pump must be modified towards tritiumsafety (only metal seals).In commercial pumps, the charcoal stages are employingepoxy as bonding agent.This has to be replaced with the ITER reference bonding(inorganic cement) and the ITER reference charcoal (with known behaviour against tritium).

Diagnostics and service vacuum systems


29m dia x 25.5 x 80mm, 304L, 0.5m clearance to bioshield

8500 m³ volume

Part of safety boundary 0.2 MPa internal design pressure.

Sub-assemblies in assembly Hall

Cryostat


It is foreseen to use the torus pump also as cryostat pump(just with closed housing to allow for intra-pump regeneration)!(Confirmative study to be done)

2 pumps in cryostat lower ports

The cryostat high vacuum system

Functional requirements:

Transient pump-down(closed cryostat volume) to 10-4 Pa and steady-state pumping of magnet coolant leak helium and outgassing species (of irradiated epoxy)


Outline









Roughing pumps.


Conclusions.


All high vacuum cryopump systems need a dedicatedforepumping train to provide for ~ 10 Pa cross-over pressure.

Regeneration of Torus Cryopumps (highly tritiated);

Regeneration of NBI Cryopumps (moderately tritiated);

Roughing of Service Vacuum System (slightly tritiated);

Regeneration of Cryostat Cryopumps (non/slightly tritiated);

Trains must discharge to processing systems (Tritium Plant, Vent/Atmosphere detritiation, Release point) appropriate to the tritium concentration in the gas stream;

Complex manifolding and changeover valves needed.

Forevacuum pump requirements (1)


In order to rough down to 10 Pa (cross-over to cryopump operation) :

- the torus within 1 day;- the cryostat within 4 days

(ITER asks for 1 day)- the NBI cryopump (by regeneration) within 8 min

the required maximal pumping speed (typically at ~100 Pa) of the roughing system is 6000 m3/h and for torus cryopumpregeneration within 2.5 min

3000 m3/h

Main clients of the roughing system: Torus (1350 m3) Cryostat (8400 m3) Torus cryopump (7.5…8.5 m3) NBI cryopump (200 m3)

Forevacuum pump requirements (2)

5 Main challenges of a roughing system with mechanical pumps:

Light gases are most difficult to pump (high backstreaming) This is especially complicated at the low pressure side The need to handle water moisture (condensation problems) Tritium compatibility Magnetic fields Very high pumping speeds


Issue of tritium compatibilityRequirements:

1. Secondary containment Enclosure in a glove box.

2. Extreme leak tightness against the outer world 10-9

Pa·m³/s to the outside

3. No elastomer seals allowed (O-rings), only metal seals (impact on sealing surface design, higher forces).

4. No cross-contamination between oil and process gas (tritium destroys the lubricant, and lubricant in tritium leads to increasing inventory due to isotope exchange) 10-7

Pa·m³/s shaft seal tightness (oil-process) no labyrinth

allowed.

5. Neglectable permeation rates of tritium through the housing stainless steel (no cast material), or coated surfaces.

Pumping of hydrogen for itself (high vacuum range) is alreadya different task!

Screening of the commercially available solutions


Available (low speed) T2-compatible pumps

Diaphragm pump(Metal bellows)

Scroll(Normetex)

Piston pump(Thales)

Turbopump @ JET(Varian)

These pumps are used as transfer pumps (i.e. not asking for low ultimate pressures) for radioactive gases in nuclear power stations and tritium plants.


There are ´dry´ large speed rotary pumps

…but not in the understanding of fusion

Roots pumpprinciple

Screw pumpprinciple

High amounts of purge gas needed, which increasethe gas load significantly

http://vacuumdetails.oerlikon.com/index.php


Current idea for ITER: Cryogenic forevacuum

The cryopump, after its regeneration, produces a higher pressure than in the case of continuous pumping, so that a (medium-size) tritium-compatible piston pump can be used as single mechanical pump.

Pearce, Baylor et al., SOFE 2009, San Diego, US.


European ITER concept

(pre procurement allocation)

based on mechanical pumping

4200m3/h

Roots

180m3/h Piston1200m3/h

Roots

US/ITER concept based on

cryogenic forevacuum pumping

(adaptation of JET AGHS

concept)

Various concepts on the market


Outline









Roughing pumps.


Conclusions.


An additional challenge..

- many km of welds- feedthroughs and electric breaks

- only very limited accessability

Detect a leak Locate a leak

Water leaks and helium leaks


Perspectives for DEMO

Mission 1 : Burning Plasmas-The development of a tunable torus exhaust vacuum system for plasma control, effective helium removal and disruption mitigation.

Mission 2: Reliability of tokamak operation-High availability of the vacuum pumping system.

Mission 4: Long Pulse and Steady-state Operation-The ITER cryogenic forevacuum pumping system is not an option for continuous operation (no 4 K needed for HTS magnets). Hence, a hybrid vacuum pumping system must be developed, which integrates a full tritium-compatible mechanical pumping solution with low ultimate pressures. This development means significant effort.

The associated R&D programme is in preparation under EFDA.


What do we learn from ITER for DEMO?

ITER pellet injection is slow no deep penetration, most probably not

an option for DEMO

ITER disruption mitigation Will hopefully demonstrate a viable

solution also for DEMO

ITER divertor radiative cooling gas injection We hope to learn from

ITER, but this has to be scaled up.

ITER high vacuum pumping works steady-state but would require

massive multi-cycle regenerations, hence a non-cryogenic solution would be very beneficial (High T superconductors, Helium shortness)

ITER rough vacuum pumping is not an option for DEMO (discontinuously, even more cryo consumption)


Necessary R&D routes towards DEMO

DEMO pellet injection will require deep fuelling compact toroids with

electromagnetic acceleration?

DEMO high vacuum pumping may be more advanced to fit steady-state/long pulse conditions (extend mechanical pumping down to lower ultimate pressures; alternative technologies with direct recyle of the unburnt fuel):

Cold turbopumps

Superpermeable membranes

Cryosorbents @ 20 K

DEMO rough vacuum pumping must be based on a reliable and versatile mechanical solution

DEMO requires real-time monitoring of tritiated substances (e.g. based on spectroscopy)


- We have had a look on the vacuum pumping systems of ITER. They are typical for any DT fusion experiment (where possible proceeding from the lessons learnt at JET).

- The large ITER high vacuum cryopumping systems (torus, cryostat, NBI) share a common modular approach of charcoal coated cryosorption panels, developed by KIT.

- The torus and cryostat vacuum pumping system is in a very advanced stage, testing a prototype and starting serial pump manufacture.

- The NBI vacuum system is in ongoing detailed design phase, but the test bed for the prototype is already under preparation.

- A broad data base for cryopumps has been set up with many parametricexp. data which allow to design customized cryopumps for ´any´application.

- A toolbox has been developed which provides all software means to do a rigorous design (heat loads, capture coefficients, etc…)

- The roughing pumping systems are still in a conceptual phase.

Conclusions

Chr. Day, ITEP-VAC95 25 January 2011 Int. School on Fusion Technologies 2010

- I want to encourage everyone to work in nuclear fusion.

- This holds especially for the vacuum systems field, where many challenging developments are still ongoing.

- The ITER vacuum systems are definitely the most complex in the world.

- Do not hesitate to contact me.

Interesting perspectives....

Our work is supported by EU under the EURATOM-KIT Association contract and F4E:

and the Helmholtz Gemeinschaft Deutscher Forschungszentren

Thank you for your attention!

http://www.efda.org/index.htm

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