Minutes BWS Design Review: PSB Beam Wire Scanner -- 19th January 2016 --

Participants: Raymond Veness, Bernd Dehning, William Andreazza, Dmitri Gudkov, Paolo Magagnin, Jose Luis Sirvent, Nicolas Chritin, Jose Antonio Ferreira, Rhodri Jones, Emilien Rigutto, Jan Hansen

Agenda ( https://indico.cern.ch/event/483648/ )

PDF Documents
PDF Version of the Minutes Notes from R.Veness Notes from Bernd Dehning Review Observations and Recommendations from Jan Hansen

1. Review of the PSB Beam Wire Scanner Prototype Design (N.Chritin)

  • Flange and mobile parts Weight: 17kg
  • Vacuum Tank Weight: 23kg
  • Ports CF100 included on vacuum tank for vacuum pump and top viewport
  • Inner diameter of the beam pipe circular 120mm
  • Margin between the tip of the fork and tank: 20mm
  • Margin of 27mm on fork position and the end of the shaft.
  • Question of the small port at the end of the shaft:
    • Requested by Impedance.
    • Rhodri asks if this has been simulated.
    • Dmitry says that they will insert the feedthrough with cylindrical pad inside the shaft axial hole and there is a radial gap of 2 mm between this pad and the shaft internal wall.
    • The configuration was discussed with Fritz Caspers and Christine Vollinger and approved.
    • We should check this with Benoit.
  • Discussion: RF Feedthrough ( See Drawing)
    • Unclear what there will be installed on this Feedthrough: It is required to know the geometry of the device and cabling required.
    • Likely there will be an antenna inside the shaft for RF purposes
    • Study required for mounting-dismounting process
  • Drawings available on line under CDD/EDMS: "PSBBWSRA%"
  • Thin walls of the stepped vacuum chamber:
    • Break and Resolver : 0.3mm
    • Motor/Rotor : Vacuum chamber = 0.4mm, total gap Stator/Rotor = 0.7mm and 80mm long
    • Paolo has done the buckling analysis. The configuration was already ok with t = 0.3 mm. Also the production is easier if the wall thickness is 0.4 mm.
  • Materials for large pieces on both instruments and flanges have been ordered for 6+1 assemblies in December. DN273 flange.
  • Question on the bake out and test procedure for the assembly of the optical system and the window. Is there a sleeve(membrane or glass – body interface)on the window?
  • Maybe errors in Viewport Model : (Jose will send the real Viewport to Nicolas for inspection)
  • Do we need blocking screws?
    • Nicolas has one the main axis screw, but not on smaller screws.
    • We will fix them with a torque wrench.
  • Preparations for scanner mounting/dismounting tool done.
  • Installation - will be close. Should consider an installation jig.
  • Nicolas can expect to get the drawings signed before the end of the month. Emilien says they can look at drawings before they are signed.
  • Tubes for guiding kapton wires after entering on the shaft? (to avoid wires breakage)
  • Stepped vacuum chamber alighning mechanism fixed with 6 screws
  • Significant weight reduction on PSB proto with respect to SPS Proto (from 35kg to 17kg)

2. Beam Wire Scanner Equipment: Motor (Dmitry Gudkov)

  • We need to pass the custom Alxion motor for vacuum test after YETS.

  • Gap size Stator/Rotor measured 0.75mm.
  • Selected Motor Alxion 145STK2M as base line for de BWS Design
  • Alxion performed tests with magnet fixation using shrinking tubes
  • Cleaning of all parts done at CERN
  • Pieces ready for acceptance tests for rotors (Alxion)
  • Inertia of the load recalculated at the final design phase (Now 1.1e-3, Before 8e-4)
  • Alxion baseline model is working at 70% of max torque with the calculated inertia.

3. Beam Wire Scanner Equipment: Forks, Disk and shaft optimization (Paolo Magagnin)

  • Maximum offset on the wire´s edges PSB 16.9um , SPS 20.3um
  • Shaft optimization:
    • Inertia Now 1.1e-3, Before 8e-4
  • Disk Optimization:
    • Inertia 1.7e-4
    • Optimization on the optical disk --> Final disk will contain around 6-7 arms.
    • Disk is optimized to have a retardation in tangential direction less than 10um
    • Decision to make about disk, material, fabrication process.
    • Manufacture of the disc? Turn then mill then EDM the cut-outs? Stress relieve? Not sure. Concerns about the run-out of the disc? Needs to be 0.1 mm. 196 mm external diameter.
    • This would be another good candidate for 3D additive machining with automated form optimisation! (R.Veness)
  • Disk Vibrations simulations would be useful:
    • Simulations with nominal acceleration and small disk mounting imperfections
    • Paolo confirms that vibration simulations are possible.
  • Discussion: Tube inside forks for kapton wire guiding:
    • SPS proto has no tube for Kapton wires.
    • There are a second series of forks with tubes.
  • Discussion: Shaft on titanium.
    • Steel higher elasticity.
    • Difference in terms of inertia, small compared to steel.

4. Beam Wire Scanner Equipment: Optical System (Jose Luis Sirvent)

  • Due to the larger disc, we have gained significantly in the number of slits (20’000 to 30’000) so resolution significantly improved (Resolution 314uRad --> 209uRad)
  • Dmitry asks if possible to increase slit spacing to ease manufacture? Jose says probably could if necessary. However, precision of slit position is important and should not decrease (accuracy ~ 25urad).
  • Re-Design of PSB and selection of new lenses system shown.
  • Tests with Stainless Steel 304L and Aluminium Samples with different roughness performed:
    • Laser treatment on samples was OK : In general all tracks were usable by the system (to decide which one shows better characteristics)
    • Surface treatment of samples needs to be improved (light dispersion and optical signal completely lost in many areas of the disk)
  • Next steps to improve the surface finish by diamond machining and/or electro-forming
  • Bernd ask if possible to perform surface treatment with polishing (as done with glasses).
  • Need to aim for Optical standards
    • Ideal Specifications based on high quality optical mirrors: 20-10 Scratch-Dig, flatness lambda /10 @ 1310nm // Parallelism: ≤ 3arcmin // Rotation Run-out: +-100um
    • Check Specifications meaning: http://www.newport.com/Optical-Surfaces/982742/1033/content.aspx

5. Experience of BWS in SPS Maintenance (William Andreazza)

  • Very useful and valuable experience with SPS proto
  • Breakage of glass disk --> Metallic disk selection, type of glass disk fixation and screws used.
  • Plan to use Hybrid bearings with reduced radial gap.
  • Ray asks if the steel cages of the hybrid bearings could seize in place after some use under vacuum. To be looked-at.
  • Fatige tests performed over the SPS BWS operational life showed satisfactory results
  • Accumulation of tolerances lead to friction of one screw with the stepped vacuum chamber (axially), screw type was changed on SPS intervention (Jan 2016).
  • Generally happy with the way it was assembled and works.

6. Discussion:

  • The "Disk Vibration" problem found on the SPS proto was also found in Lab proto (keep in mind for PSB and disk design)
  • Proposed to make Drawings control at the end of January
  • No blocking factors found for production
  • Aiming for 3 Instruments and 2 Vacuum tanks (Offer requested to MME)
  • 1st Goes to installation, 2nd for RF and Vacuum testing, 3rd for laboratory with a holding frame
  • Required planning for PS prototype:
    • Check budget availability for PS and formal request
    • PS installation taken as an option
  • Schedule of Motor tests on test-benches to confirm (Bernd, Jonathan)
  • We need to start design of support system and the integration into the zone.
    • Nicolas will discuss with JM Lacroix.
    • Organization of the ECR for the installation Survey required - invite to another meeting.

7. Design Observations Collected:

  • Think about other processes for reflective surfaces: Material deposition, Surface polishing.
  • Encoder disk fabrication process to avoid deformations must be well studied and defined.
  • What about activation of Cobalt (Rotor magnets)? Ray says does not appear to be an issue, was investigated by student in 2015.
  • Concerns about bake out on viewport and material dilatation
  • Concerns about aligning optical system before and after bake out

8. VSC Requests and recommendations:


  • We would recommend the DN35CF flange foreseen for the RF is changed to a DN35CFQ if this flange has to be opened each time you have to change the wire.
  • The 4 DN16 windows must have direct access for leak detection.
  • The shown window has no membrane, which are important for the installation and in case of bake out.
  • We expect the tank will require damping plates which could be important for the total outgassing. This information is important to calculate the extra pumping speed.
  • Information concerning the central RF unit might also have an effect on the required pumping speed and again important for the vacuum calculation.
  • In the LIU-PSB all new installation concerning vacuum should be send for control 3. In TE/VSC the control 3 for new material is done in a dedicated vacuum design approval meeting where the 3D model and drawings if existing should be presented.


  • To install the FWS an off-set in the big flange might improve the dismantling and reinstallation of the wire scanner.
  • It is important to get the motor vacuum tested as soon as possible (end of YETS 2016)

  • Information about the costs of the extra pumping required will be received on the middle of next week (25-29 January)

9. New Actions:

Action Responsible

Feedthrough Check (Done!)


Bernd / Fritz
Validation of out-gassing of the motor magnets (February) William
Motor Testing on test-benches Jonathan
Vibration simulation and studies on Disk Paolo

First set of drawings for Emilien

Send drawings for approval

Second control at beginning of February


Viewport model and drawing check

New samples tests (Diamond machining and electro-forming)

Jose Luis

Request details about device on RF Flange and cabling

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf 1085_001.pdf r1 manage 92.3 K 2016-01-22 - 09:51 UnknownUser  
PDFpdf 2016_01_19_PSB_Review_Meeting_Minutes.pdf r2 r1 manage 231.3 K 2016-01-22 - 10:02 UnknownUser  
PDFpdf Notes_from_Bernd_Dehning.pdf r1 manage 28.3 K 2016-01-20 - 10:07 UnknownUser  
PDFpdf Notes_from_Raymond_Veness.pdf r1 manage 235.2 K 2016-01-20 - 09:37 UnknownUser  
PDFpdf Review_Requests_and_Recommendations_Jan_Hansen.pdf r1 manage 254.3 K 2016-01-20 - 09:27 UnknownUser  
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