cavity support scheme options thomas jones 1. introduction both cavities will be supported by the...

Cavity support scheme options

Thomas Jones

1

Introduction

• Both cavities will be supported by the fundamental power coupler and a number of blade flexures.

• See 253-meng-fea-013 for a thorough comparison of support options using the RFD cavity.

• It has been proposed that the coupler and blades have individual bellows for penetration through the OVC and that the supports are then held by a common out of vacuum adjustment plate.

2

Analysis - Simplified DQW cavity1. Only coupler 2. Ø4mm Ti Rods

3. Two corner blades (2mm thick) 4. Blades in integration position

Mass ~130Kg

Blade thickness 30mm

3

Analysis Result

• Again blades can significantly improve performance.

• Compromising the blade position can double the deformation due to gravity and reduce vibration modes up to 50Hz.

AnalysisMax Deformation (mm)

Max von-Mises stress (MPa)

Mode 1 Frequency (Hz)




1 1.528 61.4 10.9 11.3 21 59.92 0.081 23.5 14.6 32 33.3 79.63 0.016 8.1 33.1 41.3 57.9 171.44 0.034 10.8 25.7 38.3 42.2 120.5

4

Detailed model - Setup • Model de-featured to improve analysis

efficiency.• Tuner assembly removed at this stage as

exact tuner configuration unknown and complex.

• HOM absorbers and FPC left with antennae to resolve modes with their deflection.

• Material properties applied as appropriate.• Fine mesh used on support components.

OFHC Copper(Work hardened)

316L SS

Grade 2 Ti

316L SS

316L SS

Model fully fixed at base of each ‘foot’.

Niobium

OFHC Copper(Work hardened)

5

Detailed model – Structural Results

6

Detailed model – Modal Results

Mode 1 – 20.3HzSway perpendicular to beam axis.

Mode 2 – 25.2HzSway in line with beam axis.

Mode 3 – 43.1HzTwist about centre of support structure

There are then three modes at 82.1Hz, 82.4Hz and 82.8Hz which are modes of the RF couplers.

Note that the 82.8Hz has both the FPC and HOM oscillating.

7

Structural Result summary







Detailed model 0.049 27.7 20.3 25.2 43.1 82.1

Simplified 0.034 10.8 25.7 38.3 42.2 120.5

• Difficult to compare models due to the much increased complexity.

• Blade thickness of detailed model is 35mm, simplified used 30mm.

• Deflection is increased by introducing the common adjustment plate. The deflection is ~11µm at the flexure.

• The stress values are all well within acceptable limits.

• Due to reduced stiffness of the overall structure the first two vibration modes have reduced.

• The lower 4th mode is due to the introduction of the RF couplers.8

Response spectrumUsing ‘tdl-1165-meng-cal-0010-v3.0 Cavity support transmissibility’ Calculator outputs the following response spectra for each mode.

Maximum amplitude of cavity vibration ~10nm at 43Hz mode.

A rough calculation by G.Burt gives 100nm as the limit for vibration amplitude.

This calculation should be checked, however, we are currently a factor 10 below.

This is based on a ‘worst case’ damping coefficient.

9

Increased top plate thickness







Detailed model 0.049 27.7 20.3 25.2 43.1 82.1

+10% Thickness 0.039 35.4 22.0 27.5 43.9 82.5

10

No significant gain in performance.

Mode 1 has increased x 1.5 due to moving closer to a local peak.

Mode 3 has reduced by a factor of 2.

Conclusion• Several options were considered for the DQW support configuration.

• A flexure blade arrangement again gives significantly improved performance.

• Moving blades from the optimum position (i.e. in the corners) to the integrated position reduces performance by a factor of 5 for deformation and vibration response.

• A detailed model was investigated in ANSYS to find accurate modes with blades in integrated position.

• Note, this was without the tuner assembly which will require a separate study.

• A transmissibility calculator was developed in EXCEL. This can be used to give displacements by combining ground PSD with modal data.

• Displacements appear to be well within specification for the given ground data.

• It is quick to replace this data in Excel therefore we can investigate different vibration scenarios much more efficiently than importing into ANSYS.

11

Appendix

Validation of analysis using RFD

J0 = Mass x r (distance to pivot)2

r 0.322m distance to centre of massm 202kg supported massG 7.50E+10Pa shear modulusd 6.30E-02m coupler diameterl 3.00E-01m coupler lengtht 1.50E-03m coupler wall thickness

jp 2.7E-07mm4 polar area moment of inertiaj0 20.7kg m2 polar mass moment of inertia

kt 6.85E+04 torsional spring constant of coupler

fn 9.1Hz Natural frequency due to torsion

Validation

0.322m

ValidationFEA First mode @ 7.7 Hz Mostly rotation about coupler axis but with some vertical bending.

r 0.322 m distance to centre of massm 202 kg supported massG 7.50E+10 Pa shear modulusd 6.30E-02 m coupler diameterl 3.00E-01 m coupler lengtht 1.50E-03 m coupler wall thickness

jp 2.7E-07 mm4 polar area moment of inertiaj0 20.7 kg m2 polar mass moment of inertia

kt 6.85E+04 torsional spring constant of coupler

fn 9.1Hz Natural frequency due to torsion

Difference of 1.4Hz between calculation and FEA. This is due to the FEA model calculating some bending of the shaft in the vertical orientation, whereas the empirical model is based purely upon rotation/torsion of the shaft.

cavity support scheme options thomas jones 1. introduction both cavities will be supported by the...

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