TEST-PARTICLE CALCULATIONS OF PRESSURE PROFILES

AND PUMPING EFFICIENCIES: APPLICATION TO SOME

VACUUM DEVICES OF ITER

R. KersevanVacuum Pumping Group, ITER International Organization,

Route de Vinon, 13165 St. Paul lez Durance, France

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Abstract:- This paper describes the application of the Molflow+ code to the analysis and optimization of some vacuum components envisaged for installation on ITER. Molflow+ is a code written in C/C++ which runs on Windows-based PCs and laptops. It implements the Test-Particle Monte Carlo (TPMC) method [1]. It allows file import from the popular CAD export "STL" file format, allowing the analysis of complex geometries.

- The vacuum system of ITER is composed of a multitude of sub-components, ranging in size and vacuum level, going from the >1000 m3

volume toroidal vacuum chamber in transition flow down to few liters volume components such as RF heating lines under ultra-high vacuum conditions.

- Pumps and pumping manifolds and geometries must be optimized also in view of cost-containment measures.

- Within the Vacuum Pumping Group of the Fuel Cycle Division, the optimization of the design of the ultra-high vacuum system of some subsystems and components has been undertaken.

- The paper will briefly highlight the main features of Molflow+ and then move on to show some applications to ITER.

REFERENCES: [1] R. Kersevan, J-L. Pons, J. Vac. Sci. Technol. A, 27, 1017 (2009).

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AGENDA:

1) ITER on the fly

2) Case Study: ITER’s Pumping Ports

3) Results and Discussion

4) Conclusions

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ITER: a complex vacuum system

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ITER Vacuum Systems

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ITER’s Pumping Ports

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ITER Divertor Geometry

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ITER: tokamak pumping

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- A reduction of the number of TCPs has been

recently proposed in the framework of simplification

and cost-containment of the project.

- Before proceeding to the implementation of such

action a formal “Project Change Request” (PCR) has

been issued.

- A PCR consists of a rather detailed study of the

pros and cons of the proposed change and its overall

impact on the project, and requires formal approval

of all parties before its implementation.

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- The PCR consists of the elimination of the 3 branched

TCPs

- Vacuum-wise, the main impact is a possible reduction of

the pumping speed at divertor level

- In this study, the comparison of the pumping speeds in

molecular flow at the divertor level and inside the vacuum

vessel have been performed using Molflow+

- Prior to that, a modelisation of the latest version

of the TCP has been carried out, and the obtained

results have been compared to previous calculations

made by FZK on a older design

(FZK, EFDA Task, 2007).

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2) Modelization and analysis of the TCP alone:

Drawings for

2007 design

vs

2011 design

- 800 mm ID inlet flange

- 28x 1000 mm x 200 mm charcoal-coated

cryopanels, cooled by 4.5 K SC He

- 11x coaxial 80K thermal shields

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2) Modellisation and analysis of the TCP alone:

TPMC Model for

2007 design

vs

2011 design

(not to same scale!)

Integrated valve: 50 cm stroke

Integrated valve: 47 cm stroke

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Modellisation and analysis of the TCP alone: 2007 results

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STICKING

0.7

0.95

0.95

0.2

1.0

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Modelisation and analysis of the TCP alone: 2011 results

SPEED

m3/s

97.79

70.13

62.39

63.26

35.12

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Modellisation and analysis of the TCP alone: 2011 results

Valve Stroke S(He) m3/s

5 cm 14.6410 cm 30.18

20 cm 49.11

30 cm 57.73

40 cm 61.73

47 cm 63.26

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Modellisation and analysis of the Pumping Port with TCP

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Modelisation and analysis of the Pumping Port with TCP

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Modellisation and analysis of the Pumping Port with TCP

He pumping speed at Vacuum Vessel:

with 2 TCPs = 37.18 m3/s

with 1 TCP = 30.28 m3/s

Net Loss ~7 m3/s (18.6%)

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Conclusions

1) The pumping speed of the ITER Torus Cryopump has been

recalculated and compared to previous calculations, and found higher

than for the 2007 version, probably due to a favorable change in the

geometry in front of the pump’s inlet flange

2) The effective pumping speed in the vacuum vessel and at the

divertor level has been calculated for the direct+branched version

and the PCR-direct-only version of the Lower Port Cryo Pump (LPCP)

3) A substantial reduction of the effective pumping speed has been

obtained for the direct-only version, with a loss of ~19% with

respect to the original direct+branched LPCP version

4) More refined simulations will be run shortly

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Acknowledgments:

Many thanks to M. Dremel, A. Antipenkov and C. Gliss for

helpful discussions and help with CAD drawings, details,

and more.

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