Attendees: C. L. Bohn, D. Douglas, E. Feldl, P. Kloeppel, R.
Legg, G. Neil
Purpose: To identify requirements for the design of the beamline
leading to the straight-ahead dump as part of generating first
light from the IRFEL.
Constraints: The power density r in the dump is given as r = I/A x dV/dx, where I is the average current, A is the spot size on the dump face, and dV/dx is the voltage gradient in the dump. The first-light requirement, assuming availability of the 8 kW klystron system, is I = 1.1 mA in the energy range 30 < E(MeV) < 75. Consequently, the total power to be dissipated in the dump is in the range 30 < P(kW) < 80. For copper, the voltage gradient is calculated to be dV/dx = 12.8 MV/cm and is insenstive to beam energy in the range pertaining to generation of first light. The
penetration depth L = E/(dV/dx) is thus in the range 2 < L(cm) < 6. The beamline length needs to be about 5 m to allow for 1-m-thick shielding against neutron production. During high-power operation, the dump will also need to be protected against a system failure that would put the full
average current (nominally 5 mA) on the dump.
Requirements: In view of these considerations, the participants
agreed that the electron beam will have to be rastered to a spot
size A > 50 cm^2. Given the necessary penetration depth, the
dump will need to include a closed water system.
The following dump-line diagnostics are required:
1. energy spread,
2. current (ceramic break),
3. transverse emittance,
4. beam centering,
5. transition-radiation detector,
6. (possibly) pin-hole gamma camera.
Taken together, these requirements are quite similar to those
of the 10 MeV dumps, and the beamline design is likely to be very
similar to that of the 10 MeV dumps.
Douglas -- Design the beamline for the straight-ahead dump per the above requirements.
Bohn -- Have Wiseman identify an engineer to work on the dump design.