Edgar Mahner 1

First design of a PS2 prototype vacuum chamberEdgar Mahner

thanks to Sebastien Blanchard, Cedric Garion, Giuseppe Foffano

PS2 meeting, 11.06.2009

• Main magnet apertures (baseline)• Vacuum chamber geometry for dipoles

– optimization parameters– geometry, FE model, behavior under vacuum– first prototype fabrication

• Possible bakeout solutions• Conclusions

Edgar Mahner 2

PS2 main magnet apertures

• Proposal for outer dimensions of the vacuum system in the main magnets, now including alignment and heating jackets!– Status 16.04.2009 (MB, PS2 meeting)– Dipoles half sizes: 60 mm horizontal, 40 mm vertical– Quadrupoles half sizes: 65 mm horizontal, 45 mm vertical – First consideration for a PS2 prototype dipole vacuum chamber by C. Garion

PS2 meeting, 11.06.2009

Dipole gap:80 120 mm2

Dipole length: 4.20 m

Installation/alignment:≈1 mm (tbs)

Bakeout system:≈5 mm thick (tbs)

Maximum outer dimensions of the dipole vacuum chamber: ≈68 108 mm2

C. Garion (April 2009)

Edgar Mahner 3

Principle of the vacuum chamber geometry

PS2 meeting, 11.06.2009

34

54

dy

dx

R=5Vertical aperture reduction(or equivalent thickness)

• Objective: vacuum chamber for maximum h/v beam aperture – Shape close to a rectangular (shoe-box type) vacuum chamber with following

main parameters used for calculations:• Thickness, dy, dx

– Main assumptions:• Stainless steel (almost mandatory)• Plane stresses (axial free: required for a baked solution)• No installation pre-stress

C. Garion (April 2009)

Edgar Mahner 4

Parameters

PS2 meeting, 11.06.2009

• Assumption – The aperture is defined by the inner wall of the vacuum

chamber minus a geometrical tolerance, 0.5 mm assumed (tbc)• This tolerance could be, for example, a shape and/or straightness

deviation; under discussion with EN-MME

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.62.9

3

3.1

3.2

3.3

3.4

3.5

3.6

Wall thickness [mm]

Thic

knes

s + d

y +

0.5

The minimum vertical aperture reduction is obtained for a stainless steel wall thickness of 2mm; dy = 0.65 mm; dx = 0.1 mm

C. Garion (April 2009)

Optimization guidelineFind the smallest vacuum chamber thickness to obtain the largest beam aperture but satisfying mechanical stability (stiffness).

Edgar Mahner 5

Geometry, FE model, andMechanical behavior under Vacuum

PS2 meeting, 11.06.2009

Concept: the vacuum chamber is slightly biconvex, under vacuum it becomes almost flat no aperture reduction

Stability checked; equivalent (von Mises) stress under vacuum: 100 MPa

Stainless steels 304L: 175 – 200 MPa; 316L: 200 MPa; 316LN: 300 MPa

– Safety factor with respect to the yield stress? – But: eddy current forces have to be

estimated during the magnet ramp (1.7 T/s) and considered for the design.

Obtained beam apertures– Vertical 62.7 mm– Horizontal 103.8 mm– not including geometrical

tolerances of the vacuum chamber

= 53.9 mm

= 31

.35

mm

2

C. Garion (April 2009)

Edgar Mahner 6

PS2 prototype vacuum chamber – to be coated

PS2 meeting, 11.06.2009

G. Foffano (June 2009)

Three chambers for coating tests (Cu, a-C, TiZrV)316LN st.st. (2 mm wall thickness)3020 108 68 mm3 (with two DN 150 CF)Reduced length fabrication is possible @ CERN

DRAFTunder discussion with EN-MME

Edgar Mahner 7

PS2 prototype vacuum chamber under vacuum

PS2 meeting, 11.06.2009

G. Foffano (June 2009)

Concept: the vacuum chamber is flat, under vacuum it becomes slightly biconcave small aperture reduction

Edgar Mahner 8

Possible bakeout solutions for PS2 dipoles

PS2 meeting, 11.06.2009

S. Blanchard (June 2009)

Blue: dipole vacuum chamberRed: dipole gap (120 80 mm2)

Blue: dipole vacuum chamberRed: dipole gap (120 80 mm2)

• Conclusions – A 5 mm thin bakeout system, which was a first assumption, needs development work to increase its reliability

(problems found in LHC (warm magnets) with 4.3 mm system); a 6.7 mm thin bakeout system is o.k. (good experience, e.g. in LEIR).

– A 1 mm gap between the bakeout equipment and the dipole magnet seems (too) small, risk to damage it during closure of the upper magnet cover.

– Important assumption (agreed with GdR): bolted-type PS2 dipoles and quadrupoles, avoids to slide vacuum chambers with heating elements into magnets, no need to cut/weld flanges (very important in many aspects)

– Next steps: material/dimensions/fabrication methods/tolerances of vacuum chambers, deformation under vacuum as well as bakeout options need more studies to optimize for maximum beam aperture but also to build a (very) reliable system.