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

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

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

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

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

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

Installation in Vacuum Tank Install calibrated scanner module Beam

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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.