ARC-EN-CIEL is based on a CW 1.3 GHz superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches at high repetition rate. The ARC-EN-CIEL will be completed in different phases, according to the electron beam energy, the average current and the light sources available for the users.
The beam dynamics has been studied starting from the gun using ASTRA, CSR-Track and TRAFFIC-4 for Phase 1 and 2, and using BETA and BU for Phase 3. The beam parameters taken for the FEL and radiation simulations are presented in Table 1. Better parameters have nevertheless been obtained from the simulations, but conservatice values of table 1 were taken for FEL simulations in order to keep a safety margins. The ERL mode relaxes the constraints with respect to the compression. ARC-EN-CIEL Phase 3 aims at achieving high average currents. Typically, 1 mA can be obtained for a repetition rate of 5 MHz. Two regimes depending on the charge level are envisaged, leading to different values of the emittance and peak current as shown in table 1. Higher average currents can be reached in enhancing the repetition rate up to 100 mA.
| Phase |
1 |
1 |
3, mode 1 |
3, mode 2 |
3 |
| Energy (GeV) |
0.2 |
1 |
1-2 |
1-2 |
3 |
| Rep. rate (kHz) |
1-10 |
1-10 |
103 - 105 |
103 - 105 |
1 |
| Charge (nC) |
1 |
1 |
0.2//1 |
0.2//1 |
0.75 |
| ΔT (fs rms) |
500-600 |
200-300 |
500-600 |
500-600 |
200 |
| <I> (μA) |
1-10 |
1-10 |
103 - 105 |
103 - 105 |
|
| Ipeak (kA) |
0.8 |
1.5 |
0.2 |
1 |
|
| Ipeak, slice (kA) |
1 |
2 |
1 |
1 |
1.5 |
| εtot (π mm mrad) |
2.4 |
1.6 |
2 |
6 |
|
| εslice (π mm mrad) |
1 |
1.2 |
1 |
5 |
1.2 |
| σγ/γtot (%rms) |
0.1 |
0.1 |
0.1 |
0.2 |
|
| σγ/γslice (%rms) |
0.04 |
0.04 |
0.04 |
0.08 |
0.02 |
|
Table 1: ARC-EN-CIEL beam parameters
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ARC-EN-CIEL should provide simultaneous electron beams in the accelerators for feeding the light sources for the users: the 1 kHz high peak current for LEL1 and LEL2 should coexist with the high repetition rate (1-100 MHz) recirculated beam in the ERL loops. Such an operation requires the electron beams to be recombined at low energy at the loop entrance and the beams to be separated at the exit of the accelerating structures thanks to kicker magnets.
The operating mode between the different phases relies on the temporal structure illustrated in figure 1.
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Fig. 1: Simultaneous operation of the electron beams in the different phases of ARC-EN-CIEL
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