Present: Jordi Marcos, Lucia Sabbatini, Alexander Molodozhentsev, Federico Nguyen, Giancarlo Gatti, Sergey Antipov, Ben Shepherd, Evangelos Gazis
Undulator options for EuPRAXIA: 1st site choices (Federico Nguyen)
Federico presented undulator options for the beam driven site. The aim is to have an FEL facility in the water window (beamline AQUA), covering 2-4 nm wavelength and operating in a SASE regime. There is as well an opportunity to provide FEL users with complimentary VUV seeded HGHG FEL, tuneable in 50-180 nm range (beamline ARIA), which is important for chemistry and biology research applications.
- During the choice of technology out-of-vacuum, in-vacuum, cryogenic, and superconducting undulators have been compared. The final selection is to install a string of variable polarization Apple-X out-of-vac permanent magnet undulators (PMUs) followed by a few planar super conducing undulators (SCUs) for the main beamline. This will allow targeting 3-4 nm at 1 GeV beam energy. The SASE beamline will need 10 APPLE-X modules with a short period of 12-20 mm and a total lenght of about 30 m. The physical aperture of the APPLE-X undulators is currently under discussion as it has been noted that detrimental resistive wall effects might become important at small aperture sizes. The NbTi prototype SCUs will be deployed in collaboration with FNAL. An increase of beam energy would be beneficial for reaching shorter wavelengths; increase from 1 to 1.2 GeV is being considered.
- The seeded FEL beamline will used APPLE-II type undulators to produce amplification at 3-11th harmonics.
- The estimated cost is 20 MEuro for the AQUA beamline and 7 MEuro for ARIA.
Sergey inquired about the scalability of the chosen solution to higher energies.
- Federico explained that the beam dynamics is exploring the 1.2 GeV working point; presently it looks feasible. It is tradeoff between the loss of tuning range and the gain in photon energy. The matching quads would work up to 1.5 GeV. Lucia confirmed that the magnet group is working with the assumption of 1.2 GeV beam energy.
Alexander inquired about the cost estimates, in particular how would they change if permanent magnets are used instead of electromagnets in the matching sections.
- Federico replied that, in principle, PMQs could be used for the transfer line, but for the matching intra-undulator gaps, EMQs should be used. Lucia added that the magnet group is also working on the design of the PMQs, as well as phase-shifters and correctors.
Alexander asked why it is the FNAL who will prepare the SCU prototype.
- Federico explained there is a standing collaboration between INFN and FNAL; the prototype will be delivered within the scope of an exchange of equipment between the two labs.
- Sergey asked about the current status of the SCU
- Federico informed that the full conceptual design is complete, but because of budget issues at FNAL further activities are presently stalled.
Evangelos raised the question what is the reason for the relatively expensive vacuum chamber in the cost estimate.
- Federico replied there is no clear answer to that, the details need to be checked.
- After the meeting Federico clarified that the figure includes, in addition to the chamber cost, details such as motors, electronics, and screens, adjusted for an estimated inflation. That estimate is subject to be updated in the forthcoming months.
It is important to emphasize that the ARIA FEL beamline is not yet granted for any funds, and in any case both tables are actually tentative lists, to be taken with a grain of salt.
Magnet design for EuPRAXIA@SPARC_LAB (Lucia Sabbatini)
Lucia is the EuPRAXIA@SPARC_LAB leader of WP17, responsible for magnets and power supplies. She presented an overview of project activites going on at Frascati. Presently, the project is in the TDR phase with the document scheduled for delivery by year-end.
- There used to be a strong manpower issue, but it has been resolved recently.
- Presently, the main issue is that the machine layout is not completely frozen, not all the requirements have been finalized. This forces the design team to pay special attention to the longitudinal size of the magnets. While the general layout of the facility is ready, some variations in the machine layout are still possible.
Lucia described how the design proceeded step-by-step. First, a functional layout has been prepared. The machine is organized in 6 sectors: injector, low energy linac, bunch compressor, high energy linac, plasma cell, and FEL. The functional layout has been converted into 3D elements. The magnet design starget from the most critical components from the infrastructure point of view.
- A dipole that might interfere with civil engineering constraints
- Laser heater chicane and the matching quadrupoles. Mechanical interferences between the magnets led to a compromise between deflection angle and magnetic length
- Currently, the team is working on the spectrometer magnet
In parallel, the group is studying combined function quadrupole and steerer magnets. Two options are being considered: wIth additional coils, as already being done for other experiments, and with independent poles. The later solution complicates PS and controls, and the former one will likely become the final solution. The intra-undulator steerer design has to be a special one due to the tight longitudinal dimensions. A special mechanical support has been invented to save space: the steerer will be mounted on top of the stripline BPM.
Also, the group is upgrading its magnetic measurement laboratory. Rotating coil system designed and built for the dimensions of EuPRAXIA quadrupoles. A stretched wire test stand has been installed. Pulsed wire and Mole Hall probe systems are under development.
Jordi inquired about the design of the stretched wire stand.
- Lucia clarified it is the stand developed at ESRF. ESRF delivered it complete with all the controls, and the group has a positive experience with it.
- The rotating coil stand has been designed in collaboration with CERN who were involved in the electronics design
- As for the pulsed wire stand, INFN could not find any suitable solution available on the market, and developing it themselves.
Sergey raised a question how much additional workload is created by having to fit into the constraints of the existing building
- Lucia explained that because of the long timeline required for the building construction, the design of the building had to be fixed early. This has led to some exotic design choices
later on, and poses a significant challenge to the magnet design team to fit the components into the existing constraint. While there will likely be no significant extra cost on the hardware, the design effort has been made harder. - Lucia is confident that even though it is not if the magnets designs can be reused for the 2nd site, but the design experience gained in the process will be useful.
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