1. Fast Wire Scanner Prototype Mechanical Design
Ray Veness
For the FWS Study Group
Particular thanks to Nicolas Chritin for the CAD models, B.Salvant for the RF studies and J.Herranz for the magnetic lock design

2. Contents Overview of mechanical design Components RF and impedance
From schematics to prototype
Integration into SPS and other machines
Components
Magnetic movement lock
Bearings
Motor assembly
RF and impedance
Potential issues
Solutions and studies in progress
Vacuum
Conclusions and Future Work

3. Methodology - Conceptual Design
Vacuum chamber
Optic Fiber
Motor Stator
Optic Disc in vacuum
Resolver
Shaft
Bearings
Fork
Rotor in vacuum
This figure shows the adopted conceptual design for the new wire scanner instrument
This conceptual design has been decided before the beginning of this thesis work
The design provides 2 main advantage respect to the state of the art
(1) no mechanical transmission between the motor and the shaft -> improve accuracy
(2) the position measurement device is located directly in the shaft (in vacuum)
(3) no bellows are required to transmit the moved -> reliability is improved and maintenance work is simplified
Beam
Vacuum pipe
Wire
Slide Courtesy of J.Herranz Alvarez

4. From Schematic to Design
Vacuum chamber
Optic Fiber
Motor Stator
Optic Disc in vacuum
Magnetic lock
Bearings
Resolver
Shaft
Rotor in vacuum
RF screen
Fork
Wire

5. Modulable Design Concept
Machine
Scan aperture (mm)
RF Screen
Bakeout
Space Constraint
PS Booster
146x70 N
Axial, Transverse PS
Axial
SPS
152x83 Y -
LHC
65x65
Transverse
Design is based around the largest aperture scan required (SPS, H & V)
Forks and RF screen can be replaced to produce variants for other machines or locations. Other components will remain unchanged

6. Standard Vacuum Tank Beam
Additional port to access optical system (possibly removed after prototype)
Beam
Ports for vacuum equipment
CONFLAT flanges throughout

7. Installation in Vacuum Tank
Install calibrated scanner module
Beam

8. Integration Issues
LHC has plenty of longitudinal space, but cryo-line limits lateral space on one beam line
PS is limited in longitudinal space

9. Integration Issues
There does not appear to be an integration solution that allows one common vacuum tank to be integrated that can scan all apertures required for machines at CERN
For the moment, integration into the Booster is not considered
A modified design using as many components as possible can be studied at a later date
Booster has 4 lines superposed.

10. Integration in to SPS Prototype is integrated in to the SPS ring.
Advantages:
-LHC-type beams
-No bakeout
-Plenty of space,
-Relatively easy access,
Current Layout
Integration proposal with scanner

11. Magnetic movement locking system conceptual design
Magnetic circuit
(external part)
Permanent
magnet
Magnetic circuit
(in vacuum part)
Shaft
Electric
coil
Vacuum shield
Magnetic blockage of movement system conceptual design
The design will integrate a magnetic blockage of movement in order to avoid undesirable movements of the fork during the transportation or installation tasks and during operation in case of power cut or a failure in the electronic control system.
Uncontrolled movement of the wire toward the beam are not permitted since it could cause the melting of the wire and (in case of LHC) the quenching of the superconducting magnets.
The wire speed due to its own system unbalanced weight would be much slower that the nominal speed required for a safely operation of the scanner.
The conceptual design of the magnetic blockage system is consisting of a magnetic circuit made in two parts, a part located outside of the vacuum where a permanent magnet and an electrical coil are placed, and part inside of the vacuum which consisting of a ferromagnetic piece bounded to the shaft, this latter part has two tips that when aligned with the external magnetic circuit define an equilibrium position that corresponds with the safety fork positions. Thus when the electric coil is energized it cancels the strength of the permanent magnet and the shaft can rotate freely.
The final design is on-going, for the moment the prototype design counts with an allocated place for the tests of this concept.
Conceptual design
Location in the prototype
Courtesy of J.Herranz Alvarez

12. Bearings Requirements In-vacuum operation
Low outgassing, so limited or no lubrication
Resistant to bakeout temperatures (for LHC)
Risk of ‘cold welding’
Low (non-systematic) lateral run-out
Low loads – at lower limits of working ranges
Should have no problems of wear or heating…
… but will need to verify slip or run-out
Intermittent operation
Small quantities
Suppliers not interested in R&D

13. Bearing Options Bearing options Lubrication Design
Hybrid bearings: Stainless steel bearing races with Ceramic (Si3N4) balls
Fully-ceramic bearings: Ceramic races and bearings (ZrO2)
Lubrication
Prefer to run ‘dry’ for vacuum reasons, should be possible for these materials
Will test both outgassing and performance
Design
The shaft is designed with an axial pre-load provided by spring washers to minimise run-out
Two different sized bearings are used to allow installation of the shaft sub-assembly into the support
Hybrid
Fully ceramic

14. Motor Assembly Assembly in 3 stages
Mount rotor, along with lock and resolver internal components on the shaft, slide inside the bearings, then tighten screw to load bearings
Insert and tighten ‘stepped vacuum chamber’
Mount the stator, lock and resolver external components
Stepped vacuum chamber
External components
Internal Components

15. Heating Issues in Existing SPS Rotary Scanners
Some existing scanners show signs of heating
3D model of scanner and tank has been re-created to allow analysis and possible modification
Note: No signs of heating observed in 416V, which has a transition added in the chamber

16. Overview of RF Design Permanently installed vacuum chamber
Scanner module (part-view)

17. RF Screens and Forks
Parts of the RF screen remain with the vacuum chamber
Static RF fingers between scanner and vacuum chamber
Part of the screen is inserted along with the scanner

18. Ongoing Simulations
Significant low frequency mode due to the longitudinal gap:
Shunt impedance (longitudinal): 250 kOhm
Quality factor: 2500
Frequency: 140 MHz
Quite worrying as is (for longitudinal coupled bunch instabilities)
Possibility to use ferrites (like in wall current monitor) or mode couplers to damp the mode
Slide courtesy of B.Salvant / CERN

19. Options Studied to Mitigate RF Issues
Ferrites or other absorbers
Studying the sensitivity to the width of the break
High conductivity ‘short-circuit’
Benchmarking against existing designs

20. Vacuum Issues Bakeout Outgassing SPS and PS are not baked
Designed for eventual installation in LHC, fully-baked to 200°C for NEG activation
Structural materials all UHV compatible
Rotor magnets (Sm2Co17) and coils limited, so agreed 150°C bakeout for motor region (differential bakeout with thermocouple control)
Outgassing
Rotor magnets (sintered) under test
Bearings (with/without dry lubricants) under test
Optical components ‘UHV compatible’ but will be tested
Tests of 3D machined forks will be done

21. Project Status and Schedule
‘Laboratory model’
Components required to produce a working scanner are now being manufactured at CERN
Assembly and functional testing at CERN summer/autumn 2013
Vacuum tank and RF screen details being finalised
RF screen could still be modified
Prototype for the SPS
Build a new scanner using feedback from the laboratory tests for installation in the SPS late spring 2014, for operational tests post-LS1
The schedule fall-back solution is to install the ‘laboratory model’ vacuum chamber in the SPS
Series manufacture
Assuming testing in the SPS is successful, a series (with modifications from the prototype) would be manufactured for installation in the PS, SPS and LHC in LS2

22. Conclusions Status Main mechanical design issues for test in the lab
Mechanical design of a scanner is complete and a prototype is in production
It is designed for integration into the SPS, but also with a view to future integration into the PS and LHC
Main mechanical design issues for test in the lab
Assembly and mechanical operation
Bearing operation and tolerances in air and vacuum
Fork displacements
RF testing with baseline screen
Future work (for the SPS prototype)
Correct the design based on test results from the different sub-systems
Design refinements to improve installability, maintainability etc.