Minutes of the LRFF Task Force
9th meeting on Tuesday 05/06/2012 (09:00-11:00 max, 6-R-018)
LRFF members: Alessandro Bertarelli (AlessandroB), Alexej Grudiev (AG), Benoit Salvant (BS), Elias Metral (EM), Fritz Caspers (FC), Giuseppe Bregliozzi (GB), Hugo Alistair Day (HD), Jose Miguel Jimenez (JMJ), Marco Garlasche (MG), Mike Barnes (MB), Olav Ejner Berrig (OB), Oleksiy Kononenko (OK), Oliver Aberle (OA), Ralph Assmann (RA), Raymond Veness (RV), Rhodri Jones (RJ), Roberto Losito (RL), Sergio Calatroni (SC), Stefano Redaelli (SR), Vincent Baglin (VB), Vittorio Parma (VP), Wim Weterings (WW).
Present/Excused: AlessandroB, AG, BS, EM, FC, GB, HD, JMJ, MG, MB, OB, OK, OA, RA, RV, RJ, RL, SC, SR, VB, VP, WW, Cedric Garion.
1) Comments on the last minutes + Actions
- Reminder from JMJ:
- At the end of this task force, there should be a functional spec written.
- An "RF fingers person" should be nominated.
- A "ferrite person" should be nominated => FC and Christine Vollinger - BE/RF/IS - (after discussion between JMJ and Erk Jensen).
2) New design for RF fingers (Cedric Garion, TE-VSC-EIV): pptx
- This development has been initiated by the CLIC study in particular for the drive beam interconnections in two beam modules.
Why? => 1) very small space available and 2) smoothest transition as possible required. LHC PIMs takes more space and there is also a step there, which is not acceptable for CLIC.
=> Idea to have a deformable RF finger concept => Deformable thin walled sheet (with convolutions like in bellows etc.):
- Both extremities attached to the adjacent chamber,
- Sort of corrugated bellows in free position,
- Almost straight in operation position.
- Comparison between the new RF fingers (deformable body) and old ones (rigid sliding body): electrical resistance, "smoothness", span, mechanical tolerances, reliability. In addition, the new design is much easier to coat (if we coat the part of the contact then the contact might be bad. the coating does not stand where the friction takes place).
- Material choice: presently, CuBe C17200 used for first tests => Reminder: the grade is important when we have bake-out!
- Geometrical parameters (in free position) were then discussed in detail on slide 7: sheet thickness, convolution height, angle alpha0, bending radius, number of convolutions, number of strips and ratio of width strip/gap. Note that the ratio of width strip/gap is also important for vacuum pumping.
- Numerical parameters used:
- Sheet thickness = 0.1 mm (best compromise between fatigue life and robustness).
- Convolution height = 12.5 mm (as a reasonable value to have space for screws, rings etc.).
- Angle alpha0 (in free position) = 60 deg (quite high angle to avoid compressive force).
- Bending radius = 2.5 mm (from fatigue, driven by the plastic strain)
- Mechanical behaviour => Most important slide (10) of this talk:
- Compression => finger in contact.
- Extension => finger ~ straight.
- Limitation of this design => There is a maximum stroke per convolution.
- Alphaoperation is a key parameter for RF but also for mechanics.
- 3D behaviour and misalignment study: elongation, compression, offset.
- Low cycle fatigue: Manson-Coffin equation used to determine the low cycle fatigue.
- Fatigue tests:
- All failures occurred at the crest of the convolutions (predicted by FE analysis) and it fails outward, meaning that there will then be no aperture restriction.
- Reminder: Issue with 2 in 1 collimators when we start to move them as we lose some contacts.
- JMJ said that this design might be used for TCDQ in the future first as we take less risks there.
- Slide 13: left is from literature and right is the conversion for this particular case.
- A 1st prototype has been done in the framework of the TAS (slide 14) => Nice picture on slide 15.
- Next steps:
- Material:
- Define the best copper alloy and heat treatment for mechanical aspects. For him it is not obvious to use Copper Berylium...
- Mechanical tests:
- Fatigue tests on RF finger prototypes with different conditions:
- Temperature: 20 C and high temperature (230 C?),
- Stroke,
- Misalignment.
- Monotonic tests
- Assembly study:
- Define the interface and assembly process between the RF fingers and the copper rings.
- Request from AlessandroB: have fatigue tests with lateral strokes.
- Request from EM: Do we have a prototype on which we could perform some bench impedance measurements (see Action2 below).
- Conclusions:
- A new RF finger concept, presenting some advantages from an RF and mechanical points of view, is under study.
- It is based on deformable thin fingers.
- The design of the RF fingers has been done from a mechanical point of view.
- Preliminary tests on a simplified geometry are promising.
- A first prototype based on two convolutions has been manufactured and a test campaign will start soon.
3) Some pictures of the wake field suppressor in the LHCb VELO (EM)
- EM showed some pictures of the wake field suppressor in the LHCb VELO (after a discussion with Massimiliano Ferro-Luzzi, PH-LBD, who followed this in the past). Massi will come to discuss it in more detail in a forthcoming LRFF meeting on 26/06/2012.
4) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (impedance and equipments teams): We should give Cedric some requests for some (mobile) equipments and he could see, based on his experience, if he can propose some realistic parameters for his new RF fingers design.
- Action 2 (HD and OB): Perform a bench impedance measurement of this new RF finger design prototype with a wire.
5) Miscellaneous
- The next (11th) meeting will take place on 12/06/2012 between 09:00 and 11:00 (max.) in room 6-R-018 => Agenda:
1) Past impedances studies with the RF fingers for some collimators (AG).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 11/06/2012.