The HiLumi LHC Design Study (a sub-system of HL-LHC) is co-funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement Helium Vessel and Tuning for the UK 4Rod Cavity Thomas Jones, STFC, Daresbury Laboratory

Contents Helium vessel conceptual design Helium vessel conceptual design Vessel manufacture Vessel manufacture Tuning Tuning Pressure vessel analysis Pressure vessel analysis Magnetic shielding Magnetic shielding 2

Helium vessel conceptual design Helium Vessel made from Grade 5 Titanium (Ti-6Al-4V) Helium 2-Phase line Input coupler port Modified Saclay II tuner Stiffening ribs Magnetic shield (Cryoperm) not shown Additional beam tube required for LHC installation Mounting for support system UK 4 Rod Cavity Port for He level probe 3 194mm 550mm 300mm

LOM coupler port Titanium bellows to allow cavity compression when tuning Nb-Ti transitions e-beam welded during cavity manufacture. Naked cavity prior to He vessel installation Rectangular flange to required for tuner. HOM coupler port 4

Sealing technology for beamlines and LHe lines yet to be determined. Currently shown as Conflat flanges. Bent 6mm thick Ti-6Al-4V sheet 40mm deep x 10mm thick Ti-6Al-4V Stiffening ribs 10mm thick Ti-6Al-4V End plates 30mm thick Ti-6Al-4V Mounting blocks for tuner Vessel Manufacture All joints in vessel to be TIG welded 5 420mm

Tuning concepts – RF analysis Longitudinal Tuning 1.1 MHz/mm Vertical Tuning 0.03 MHz/mm Plunger Tuner 0.1 MHz/mm

Tuning - FEA 11kN was applied to try to close the gap between rods. The maximum deformation in the cavity was 0.24mm, however, the movement of the rods was actually a rotation about Point A. The maximum stress it at the room temperature Yield of 75MPa. Coupler ports prevent full cavity deformation, as they are fully fixed to He vessel. 7 11kN A Maximum stress of 73MPa here. Bellows and flanges removed to simplify geometry

The FERMILAB Summary of Niobium material properties states that the acceptable stress limit for Nb at 2K is 137MPa. The danger with using this limit is that if the tuner ‘sticks’ at cryogenic temperatures when the module warms up the yield stress of Nb returns to 75MPa the cavity will be plastically deformed. This, however, may not be a disadvantage as it can be used to permanently tune the cavity. Below is the result of applying 20kN tuning force to the cavity beam pipe. The rods rotate about point A by 0.14°. The deformation perpendicular to the beam direction is 0.36mm (Next slide), the maximum deformation is 0.45mm and the maximum stress has reached 133MPa. Tuning - FEA Von-Mises equivalent stressTotal deformation 8 20kN 0.4mm A

Realistic Tuning – RF analysis Maximum lateral movement is 360 microns with a 130 MPa stress. This is a 0.14° rotation. Frequency tuning was studied in a simplified model. The frequency shift per mm of transverse offset is 0.3 MHz/mm so tuning range with current design is 108 kHz. Tuning in both directions would give +/-108 kHz, so total range of 216kHz. Using a tuner on both sides could give a total range of +/- 250kHz. Further work will be completed to improve the tuning range and also limit the force required by the tuners. This will involve thinning areas to give more deformation, while staying within pressure vessel regulations.

Tuning with Saclay II design Above images ref: Oliver Kugeler, ERL07, Daresbury, May Tuner successfully tested to 7KN, analysis of tuner will be required to ensure 10KN+ operation. Experience with tuner and piezo active tuning system gained on Daresbury International Collaborative Cryomodule project 10 Modified Saclay II tuner installed on DICC module built at Daresbury. Stiffness test of modified Saclay II design at Daresbury.

Tuning with Saclay II design Above images ref: Oliver Kugeler, ERL07, Daresbury, May Tuner successfully tested to 7KN, analysis of tuner will be required to ensure 10KN+ operation. Experience with tuner and piezo active tuning system gained on Daresbury International Collaborative Cryomodule project 11 Modified Saclay II tuner installed on DICC module built at Daresbury. Stiffness test of modified Saclay II design at Daresbury.

Saclay II design integration Piezo units Tuner width increased to suit He Vessel geometry Eccentric cam Stepper motor in its own magnetic shield Ribs support He vessel under tuning loads Use of an additional tuner on this side would increase tuning range, and give symmetric deformation, but will bring additional costs, practibility and synchronisation issues. 12

Pressure vessel analysis – Mesh, Load and Boundary conditions Fully fixed point Point fixed in upwards and lateral direction. Free in longitudinal Point only fixed in upwards direction. Outer He vessel modelled as Grade 5 Titanium Young’s modulus 113GPa Poisson’s ratio Cavity modelled as Niobium Reactor grade Type 1, UNS R Young’s modulus 100GPa, Poisson’s Ratio MPa applied to all internal surfaces, to simulate a 2 Bar internal pressure test. 13

Pressure vessel analysis – Results Max stress in Niobium 60MPa which is below allowable 70MPa calculated by Yield Stress/1.05. Ref: BS EN :2002, Part 3. Max stress in model 76MPa but in Ti-6Al-4V tank which has a Yield Strength of 820MPa. Largest deformation 0.58mm (shown in red) Vessel as designed is suitable for 2 Bar gauge internal pressure test. Note: If beam tube is evacuated during test gauge pressure of 1 Bar should be used as this means 2 Bar absolute pressure on cavity. Ref: BS EN :2002 +A11:2006 Unfired pressure vessel Part 3: Design 14 Bellows and flanges removed to simplify geometry. Bellows purchased will be rated for 2 bar internal gauge pressure and 1 bar external pressure.

Pressure vessel analysis – Validation DL FEA CERN FEA Same load of 0.2MPa applied to all surfaces as used by CERN in their structural assessment of the cavity. This was calculated by multiplying the relief valve pressure of 1.5 Bar by the relevant safety co-efficient of 1.43/1.1 (=1.3). Ref: CERN Strength assessment and design review of the CRAB/LHC superconducting Nb cavities. Shown below is an FEA of the naked cavity model by the Daresbury Laboratory compared to the CERN model. The results are within 5% error and therefore validate each other. 1.37mm Deformation1.33mm Deformation 15

Magnetic Shielding 16 1 layer of 2mm thick Mu Metal 1 layer of 1mm thick Cryoperm Analysis by Magnetic Shields LTD Shielding shown gives 36x attenuation of the external magnetic fields. Considering the Earths magnetic field only this gives a <14mG resultant field at the cavity.

Conclusions and Further work Concept for UK 4 Rod cavity He vessel has been designed. Concept for UK 4 Rod cavity He vessel has been designed. The concept uses a TIG welded Ti-6Al-4V tank with Nb-Ti transition pieces e-beam welded to the cavity. The concept uses a TIG welded Ti-6Al-4V tank with Nb-Ti transition pieces e-beam welded to the cavity. Analysis of tuning the cavity has been performed. Using the current design a tuning range of +/-250kHz could be achieved, but may be impractical. Analysis of tuning the cavity has been performed. Using the current design a tuning range of +/-250kHz could be achieved, but may be impractical. Further work will be performed to reduce the tuning force required on the cavities and to improve the range of tuning. Further work will be performed to reduce the tuning force required on the cavities and to improve the range of tuning. The viability of using a Saclay II tuner has been investigated. The viability of using a Saclay II tuner has been investigated. Finite Element analysis has been used to ensure the He vessel meets the British Standard for pressure vessels. Finite Element analysis has been used to ensure the He vessel meets the British Standard for pressure vessels. A scheme for the magnetic shielding has been devised, however, a 3D conceptual model of the shielding around the He Vessel is required. A scheme for the magnetic shielding has been devised, however, a 3D conceptual model of the shielding around the He Vessel is required. 17