The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV, a circumference of 98 km and beam currents of up to 1.4 A per beam [1]. The high beam currents of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully reconsidered and revisited, including the injection time structure. The FCC-ee injector complex must provide beam for top up injection in the two collider rings supporting a beam lifetime of about 1 hour on Z pole and as low as 12 minutes at high energy. It must also allow for a fairly rapid filling from zero (alternating bootstrapping injection), within at most half an hour. The baseline described in the FCC-ee CDR considers a 6 GeV linac, with at most 2 bunches per pulse, with a repetition rate of up to 200 Hz. In this scheme, portions of the same linac are used for multiple purposes, acceleration of electrons and positrons to the main booster, acceleration of electron bunches for positron production, and acceleration of the produced positrons to the damping-ring at an injection energy of 1.54 GeV.
The entire beam dynamics studies for the full linac, damping ring and transfer lines are major activities of the injector complex design. However, a key point is that any increase of positron production and capture efficiency reduces the cost and complexity of the driver linac, the heat and radiation load of the converter system, and increases the operational margin. Therefore, any progress with R&D on the target and capture systems will have a direct benefit for the injector chain. In this context, the PSI Positron Source (PPS) demonstrator for novel integrated target and capture concepts is also planned at SwissFEL. All these activities are part of a CHART-approved proposal involving a collaboration between PSI and CERN with several external collaborators, such as IJCLab, BINP and LNF/INFN.
The objectives of Injector complex design and PPS project, which aim to contribute to the innovation and development of accelerator concepts beyond existing lepton injector technology are summarized here:
- Concept, design and CDR with cost estimate (CDR+) of a high-average current injector complex with high-end normal conducting RF technology;
- High-yield positron production and capture concept with proof of principle at the PSI;
- Exploitation of experience and know-how from SwissFEL design, construction and operation;
- Exploitation of synergies with PSI activities on light sources.
Reference:
[1] https://fcc-ee.web.cern.ch/content/fcc-ee-lepton-collider
