Discussion
Undulator options:
- Reaching higher photon energies becomes a lot easier at higher beam energy. There is a substantial difference between 7 GeV and 8 GeV. Therefore an upgrade to 8 GeV should be a main focus of Porthos. (Paolo to check C-band and X-band options.)
- In the context of the choice of undulator parameters it is agreed that 3 mm should be considered the minimal acceptable gap for the Porthos undulators. This is an important input when evaluating different undulator concepts.
- Instead of two undulator lines, one providing full polarization control for photon energies up to 12 keV and a second one providing high photon flux at high energies (up to 20 keV or 25 keV), it may be more efficient to use one undulator type to cover all requirements, e.g. an Athos-type APPLE-X with 15 mm period would fit the bill at 8 GeV. Not clear if and how it is feasible (in-vacuum? gap? foil?) This would go in the direction of a cryogenic in-vacuum APPLE device, as pursued at Soleil. Still at an R&D stage but seems closer to operational viability than an HTS undulator.
- An alternative would be to generate circularly polarized light (without control) and then modify the polarization of (a part of) the light with an afterburner. This afterburner could operate at very low K, since it does not have to perform bunching.
Linac upgrade:
- To be evaluated C-band or X-band option. For X-band the klystrons are about a factor 2.5 more expensive. Paolo will investigate and report back.
- The klystron gallery will have to be on the roof of OSFA (extra cost).
- Probably not enough space for an upgrade of linac-3, unless we accelerate the beam between kicker and septum (off-axis acceleration - to be investigated).
- Possible energy upgrade before BC1 (SINSB05/06). (But this can be done independent of Porthos.)
- Increase of C-band accelerating gradient in principle possible, in practice the radiation levels become to high (DRPS alarm).
Kicker options:
- A kicker upgrade is strongly preferred over schemes accommodating the current kicker design (56 period), which inevitably leads to either stability issues (zero crossing) or inacceptable loss of RF power.
- Between the two possible technological options (faster kicker with 21 ns half-period and kicker modulation providing an inflection point at zero-crossing, making possible a 14 ns bunch spacing), it is not clear which one is to be preferred. Martin will pursue both for the moment. The question can be left open for some time, as long as we are convinced there is a solution to the problem.
- Martin points out that going from 28 ns to 21 ns will be easier to digest for most system rather than the radical step to 14 ns.
- The laser systems can live with a 21 ns bunch spacing as long as not all lasers must be capable of feeding all beam lines.
Action items
- Marco S. will clarify the exact requirements with respect to polarization control with Gabriel and the photon science community (this week's PSAC provides an excellent opportunity for this). This has a huge impact on the design choices.
- Marco C. will investigate the possibilities regarding new undulator designs: circular polarization at small period, cryogenic in-vacuum APPLE, afterburner options...
- Beam dynamics (Eduard, Sven, Eugenio) will think about designs involving afterburner for polarization (degree of polarization, pulse energy etc.)
- Paolo will investigate options with regard to linac upgrade: increase of C-band gradient, Porthos C-band linac, Porthos X-band linac. Performance and cost evalulation.
- Thomas will start a survey collecting pros and cons for 14 ns and 21 ns bunch spacing.
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