1. Crab Cavity support system update
Thomas Jones 11/0316 1

2. [1] Handbook of Accelerator Physics and Engineering, 3rd Edition
Introduction
Following the design review in late 2015 it was suggested that we try to identify simple methods to increase the stiffness of the supporting system and raise the fundamental mode, which was at 12.6Hz.
Previous experience suggest support structures above 15Hz fundamental mode should be sufficiently stiff [1].
From observing the modal shape it became apparent that the fundamental mode was oscillation about the single support foot.
STFC suggested creating a 5 point mount to prevent rotation and increase the mode.
[1] Handbook of Accelerator Physics and Engineering, 3rd Edition 2

3. Previous Modal result
Mode 1
Mode 2
Mode 3 3

4. New model
Plate still 20mm thick
360mm
Ø20mm x 20mm long

5. Mode increased from 12.6Hz to 19.1Hz
Improved model result
Mode increased from 12.6Hz to 19.1Hz

6. SPS Ground data
Tuner rotation is now ‘mode 1’
Integrated RMS displacement for this lateral swinging mode has been reduced from 26nm to 15nm

7. Comments No significant change to results for other load conditions.
Still have tuner rotation mode at 14Hz
Increasing top plate thickness will have a very limited effect now. Deformation is minimal now we have introduced blocking nuts.
I would like to run a random vibration analysis in ANSYS to find combined RMS deformation of the cavity. I can also compare to the transmission calculation for validation.