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/ )

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:

Observations:

• 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.

Recommendation:

• 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: