4GLS Phasing Options

Phase 1
Would be low current (good for focus on dynamics expts) and retain some of the combined sources vision. Included is the XUV FEL, the far IR FEL and the spontaneous loop (populated to some level).

There was consensus that completing the HAC loop is a good idea. There are good technical reasons for this relating to the RF. I think it also looks good from a general-project-stance consistency point of view.

Low current in Phase 1 means that fewer IOTs and a smaller cryoplant is needed. Feeling was that we'd buy the rating of IOT and PSUs needed for whole project and use one to power several cavities. When we move to higher power buy more of the units.

A move from three injectors to two injectors was proposed as the spec of the HACL system would cover the requirements of the IR FEL system.

The IR FEL beam would be taken off after Module 1 of the main linac. Need either to schedule operation of spontaneous loop and Far IR FEL at different times or use a kicker of some sort (not felt to be tricky at rep rates condidering).

A move from two upstream arcs to one upstream arc was proposed. There's then a requirement to split the XUV-FEL beam from the HACL beam. At the lower rep rates proposed in Phase 1 this is technically feasble with current technology.

Could phase the development of the XUV FEL, e.g. 6/8-40eV first and then 35-100eV. Might not need to do this.

For the discussion the current in the spontaneous loop was 0.3 mA (4.3MHz at 77pC). There was no real discussion of 13MHz at 200 pC (which of course gives 2.6 mA).

I've tried to capture some of the machine implications on the attached powerpoint file. I've not messed with the HACL though.


Phase 2
Would be high current in the spontaneous loop, the VUV FEL, further IR FEL development, further population of the spontaneous sources.

Need to mesh R&D roadmap with injector development.

More IOTs needed and cryo plant needs uprating.

R&D development on kickers permits a single upstream arc and kicker otherwise a second upstream arc needed. Again need to mesh with the R&D roadmap.

VUV FEL incorporated.

Need a set of milestones for eventual delivery of 100mA


Lia will be producing a document on the global view of R&D needed for ERLs with timeline as an output of ERL07.

Clearly the costing matrix would need to capture phasing of the RF and cryo, have the costs for XUV FELs separate, have the cost for the FAR IR photoinjector and FELs separate.

Hope this is clear, it's not that easy to summarise!