My notes on the application for CLIC. I have put my own questions in italic. Please, send me your additions, notes or your own questions
The main point of producing very thin NEG coatings is to reduce the total impedance of the accelerator. In the damping rings of CLIC, there is a total budget defined for all effects so reducing the impedance coming from the vacuum chamber could be used to relax tolerances in other elements. We should have an extended discussion with G. Rumolo whose section is in charge of the impedance studies. Roughness and uniformity may also be important, specially for CLIC as bunches get shorter and the impact of impedances at higher frequencies is important.
SEY is ok for application in the DR as it requires around 1.2. Similar requirements are needed for the ILC DR.
The electroforming of small radius vacuum chambers may be useful in CLIC for magnets and elements in the BDS and wigglers in the damping rings (~15 mm gap).
The MBQ magnet at the origin of this technique has a 1mm bore diameter for a length up to ~2m. (http://cds.cern.ch/record/1428908/files/CERN-ATS-2012-021.pdf). Did we ever manufacture/integrated a vacuum pipe in these magnets?
The magnetic gap of the wigglers is 18mm. The design of the wigglers for the DR can be found here: https://indico.cern.ch/event/349171/attachments/689551/947006/SC_wigglers_for_CLIC-Seminar04112014.pdf. In the report the vacuum pipe is not round, can this also be done? Do we have a vacuum pipe design for them?
The achieved roughness of 0.3 microns is also compatible with some RF components and the copper is OFE so this technique could be also suitable for RF applications. The response of these pieces to RF fields remains to be seen but could be tested by manufacturing an electrode for the Fixed Gap System. Igor suggested also its use for "3D printing" the klystron collector around its cooling channels.
Also as most of the pieces have been done to avoid heat cycles, it will be good to test how it behaves after being in a furnace if need will be..
Inverse NEG coating is less interesting for CLIC wigglers in the damping ring as they are superconducting but it could be used in the MBQ. How would you activate the NEG in such small geometry?
The use of SMA flanges to avoid connection was thought to be useful for avoid losses in flanges for the RF system. It works however with a round geometry while the baseline flange in CLIC is rectangular. In te positive side the joint be designed to ensure electric contact between the copper parts by using a conical shape that will add a longitudinal force. A circular flange under design will probably decrease RF loses. As CLIC is not expected to be a high activation area, the remote opening of the joints is not and advantage against traditional methods. Paolo noticed that the real advantage of the system is the low space required when several flanges need to coexist in a small area.
Cedric showed the evolution of the RF bridges firstly developed for drive beam interconnects in CLIC and now being under manufacture for HL-LHC. Did we ever manufacture and test one for the module?
He also presented the concept of cold spray painting. It could be very useful for closing difficult to repair leaks. It can also be used for joining different materials. It was mentioned that this could also be a similar fabrication technique to electroforming but more tests would be needed.
Postponed by lack of time.
C. Rossi mentioned that the help of vacuum group on CLIC facilities is still required and needs to be defined.