CMS LS 2 beam vacuum upgrade Vacuum and

CMS LS 2 beam vacuum upgrade Vacuum and Structural stability Josef Sestak, TE-VSC-BVO 5/19/2021 INDICO event 2

General information • Based on the WP 1065775 (new WP approval ongoing) CMS is going to replace EC, HF, CT 2 and Forward chambers during the LS 2. Forward chamber HF chamber Central chamber CT 2 chamber End Cap chamber TAS VAX area • 18 m Pumping station 16 m bellow CT 2 dish 3 x Ion pump Baseline for material is aluminium EN AW-2219. 5/19/2021 Document reference 3

Proposed IP 5 vacuum layout 5/19/2021 Document reference 4

New LS 2 layout components Central beam pipe – VC 5 C • End cap chamber – VC 5 E • • Chamber with double bellow compensator HF – CT 2 chamber – VC 5 HF-CT • Pumping station on 16 m – VC 5 FP • Forward chamber (to be replaced – LS 3) • VMZAG module (to be replaced – LS 3 • 5/19/2021 Document reference 5

5/19/2021 Document reference 6

New central beam pipe for LS 2 • • • Central chamber is supposed to be redesigned because of the new Pixel detector (LS 3). LS 2 is a good moment to introduce a new central beam pipe in order to avoid an additional features on the end-cap. Full cylindrical ID 43. 4 mm Compatible with LS 3 Be – 3804 mm; Al – 2436 mm 5/19/2021 More about the design afterwards Document reference 7

CMS beam pipe evolution LS 1 – LS 3 LS 1 LS 2 LS 3 5/19/2021 Document reference 8

Detail studies of vacuum and structural stability of CMS beam pipe Josef Sestak 5/19/2021 Document reference 9

Vacuum stability study • Critical beam current is defined as a current at which the gas pressure diverges. Depends on the induced desorption yield and effective pumping speed. • Experimental regions with two beams in a common beam-pipe requires: 2 x 0. 85 A < Ic/2 5/19/2021 Document reference 10

Vacuum stability study NEG pump 400 l·s-1 Ion pump 75 l·s-1 NEG pump 400 l·s-1 -1 Ion pump 75 l·s-1 3 x Ion pump 8 l·s NEG pump 400 l·s-1 Ion pump 75 l·s-1 Full NEG LS 1 LS 2 Full NEG 2 x Ion pump 20 l·s-1 • • Design of a new pumping station on 16 m. EN AW 2219 body with bimetallic flanges and copper RF insert. 5/19/2021 Document reference 11

Critical beam current for CMS No electron cloud even is the NEG is saturated. NEG pump 400 l·s-1 Ion pump 75 l·s-1 +/- 18 m VPIB + VPNCA or VPIXD Full NEG (with saturation effect) +/- 16 m VPIXD 5/19/2021 Document reference 12

Static pressure LS 2 VAX IP New beam-pipe shape and relocation of ion pumps to 16 m will bring small increase of static pressure in IP from 5 e-13 to 1 e-12 mbar (due to change of CH 4 pumping speed). 5/19/2021 Document reference 13

Structural studies • • • Study of VC 5 C – safety against buckling. Study of VC 5 E double bellow – optimisation of number of convolutions and pre-extension. Study of VC 5 E + VC 5 HF-CT – buckling and yielding for different beam pipe configurations. 5/19/2021 Document reference 14

Central chamber in OP regime • • • Position of the supports is the same as now. Critical buckling pressure 17 bars (>4 bar limit) Maximum theoretical sag ≈ 0. 1 mm Study for short Be section 5/19/2021 Document reference 15

VC 5 E double bellow bake-out • • • Maximum allowed bake-out temperature 180°C Compression during the bake-out ≈11 mm Maximum stresses on the convolutions <100 MPa (Re 0. 2 = 130 MPa for 5083 alloy). OP configuration pre-extension 5 mm Simple linear kinematic hardening law considered 5/19/2021 Document reference 16

Forward region chambers Loads - Inertial forces (gravity) – Distributed load - External pressure on shell – 1 Atm - Forces from permanent bake-out installation - Forces from edge welded bellow on 15. 4 m – 1530 N - Thermal loads 230°C as max. during bake-out cycle. 5/19/2021 Thermal expansion ≈ 68 mm Document reference 17

Forward region chambers • Thickness of the chambers optimized for buckling safety factor 6. Numbers of segments to be minimized • Generic weld sizes – 5 types of weld • 5/19/2021 Document reference 18

Buckling in Forward region 5/19/2021 Document reference 19

VC 5 E – VC 5 HF-CT sagging Maximum sag in OP regime ≈ 2 mm (on 8 m) • Maximum sag in Maintenance regime ≈ 50 mm • 10. 6 support released Short time state with no temporary support 5/19/2021 Document reference 20

Maximum of stress - Forward chambers Stress concentration – Bottle-neck on HF/CT 2 • Maximum of stress in maintenance position (without support on 10. 6 m and without transfer of load) 80 MPa still well bellow Re 0. 2 (240 MPa) Sfy = 3 • Permanent carbon stiffener sleeve in the bottle-neck will be installed in order to redistribute the stress. 5/19/2021 Document reference 21

Conclusion • Vacuum stability Critical beam current well within the limit. Layout compatible with LS 3 (HL-LHC). • • • Structural stability Central chamber • • • Forward layout • • Local buckling Safety factor 5. 6 Theoretical operational sag 0. 1 mm Local buckling Safety factor 2 (thickness optimised) Theoretical operational sag 2 mm Layout valid for production 5/19/2021 Document reference 22

Thank you for your attention! 5/19/2021 Document reference 23

IP 5 existing vacuum layout 5/19/2021 Document reference 24

New IP 5 vacuum layout proposal 5/19/2021 Document reference 25

New LS 2 layout components • End cap chamber – VC 5 E • Chamber with double bellow compensator • Two length options (issue with bi-metallic flange size) • 7595 mm – existing length; 7395 mm – for DN 160 • ID (IP near side) 43. 4 mm; ID (IP far side) 146. 2 mm Surface 23 000 cm 2 NEG Mass ≈20 kg Volume 61 l ATLAS bi-metallic DN 160 CF Minimized Al-Flange OD 75 mm Aluminium EN AW 5083 – H 112 Convolution design based on ATLAS bellows 5/19/2021 Document reference 26

New LS 2 layout components • HF-CT 2 coupled chamber – VC 5 HF-CT • Coupling between existing HF and CT 2 chamber • CT 2 dish with the pumping instrumentation dropped • Length 4868 mm. ID 63 mm tube - length 1155 mm • ID (IP near side) 146. 2 mm; ID (IP far side) 63 mm Surface 21 800 cm 2 NEG Mass ≈25 kg Volume 86 l ATLAS bi-metallic DN 160 CF ATLAS bi-metallic DN 100 CF Stress concentration Bottle-neck on the transition cone 5/19/2021 Document reference 27

New LS 2 layout components • Forward region (effected by LS 3 VAX) Existing (compatible) edge-welded bellow 316 L New pumping station (aluminium design) • • 2 x Agilent Vac. Ion 20 pump (20 l·s-1 each) • 2 x Passive bake-able Penning gauge VGPB • New fix BP point New BP sliding point • Forward pipe 914 mm long • Warm module with RF bridge type VMZAG 316 L 5/19/2021 Document reference 28

New LS 2 layout components Chambers overview (no spare components) • 1 Be with Al ends chamber (for tender supply) • 8 Al chambers Flanges – ATLAS Bi-metallic Conflat • Bellows – Aluminium (design verified) • • Other components reused or LHC standard 5/19/2021 Document reference 29

Planning for VC 5 C Central chamber After official approval 4 months for Tender • Production time 18 months (to be confirmed) • CERN processes after reception 4 months • Approval (TREX) Q 2 -Q 3 2017 Reception at CERN 18 months Q 1 2017 Tender signed 5/19/2021 Q 3 -Q 4 2019 4 months Q 1 -Q 2 2019 Ready for Installation Document reference 30

Planning for VC 5 E VC 5 HF-CT Place official design request to EN-MME • In-house or outsourcing decision • CERN processes after reception 4 months • Procurement Q 1 -2 2019 Q 2 2017 Approval (TREX) Start of the production 18 months Q 1 2017 Chambers ready for installation Detail design review 5/19/2021 Q 3 2017 4 months Chambers reception at CERN/VSC Q 4 2019 Document reference Inspections, NEG, Acceptance tests 31

VC 5 E double bellow assembly • • Material EN AW 5083 – H 112 External envelope max. 80 mm Thickness 0. 2 mm Number of convolutions 13 5/19/2021 Based on LHCVBX__0029 Pre-extension for CMS 5 mm Document reference 32

Static pressure LS 1 VAX Measured SVT pressure on 18 m 4 e-11 mbar IP 5/19/2021 Document reference 33

VC 5 E double bellow assembly • • Design based on existing shape of ATLAS bellows (str. behaviour, manufacturing verified). Number of convolution and pre-expansion optimised in order to stay out of plastic regime. OP configuration pre-extension 5 mm 5/19/2021 Document reference 34

Central chamber in OP state Max Stress in highest bending moment regions ≈ 4 MPa 5/19/2021 Document reference 35