1. Options and Recommendations for TL and Dumps
C.Bracco, B. Goddard

2. ERL Test Facility A. Valloni 1 155MeV 80MeV 305MeV 230MeV 455MeV
5 MeV Injector 1
155MeV
80MeV
305MeV
230MeV
455MeV
380 MeV 2
Dump
(5MeV-155MeV-305 MeV-455MeV)
(80MeV-230MeV-380MeV)
Injector
Average current
12.8 mA
Bunch charge
320 pC
Energy
5MeV
rms Emittance
25 mm mrad
Bunch spacing
25 ns
Energy spread
10 keV
Bunch length
3 mm
TL injector  ERL
Space charge effects
Polarity conservation (if need for polarized beams)
Optics and geometric matching
Achromatic lattice
ERL  Dump: momentum acceptance!

3. Operational dump 64 kW (12.8 mA of 5 MeV e-). Two options:
Profit of first vertical dipole (it must be C-shaped) that distributes the different energy beams to the 3 superimposed arcs to bend the 5 MeV beam towards a vertical dump. Recommendations:
Use low Z material dump to limit backscattering and weight
Evaluate effect of back-scattered electrons on circulating beam and if any mitigation is needed (e.g. thin coating of a heavier material on the dump part facing the beam)
Evaluate possible integration issues especially in case of magnet replacement (including activation)
Detailed tracking studies in real 3D field to evaluate fringe field contribution

4. Operational dump 64 kW (12.8 mA of 5 MeV e-). Two options:
The 5 MeV beam is horizontally extracted by one kicker installed in the drift between the end of the linac and the first steerer. A few m long drift follows and ends with a cylindrical dump made of graphite. Recommendations
Use a DC magnet
Add two more kickers after the steerer to correct the trajectories of the high energy beams which could be slightly perturbed by the first one.
Evaluate effect of these three steerers on the optics including edge effects.

5. General recommendations
Evaluate:
Need of cooling for the dump (avoid brazed cooling pipes in vacuum)
Need of shielding around the dump  clearance wrt surrounding equipment
Energy density deposited on the dump  enough a long drift or additional defocusing and/or dilution kickers?
Need a separate vacuum (window) or common with ERL?

6. Setup dumps
During commissioning and setup might be desirable having the possibility to dump the different energy beams.
Easy solution: switch off the first horizontal dipole of the arc corresponding to the wanted energy and let the beam go straight towards a dump.
C-shaped magnet
Y chamber
Need one dump line per beam energy  three superimposed dumps or one big block receiving the three lines?

7. Emergency dump?
In order to limit the energy deposited on the dump an interlock system should stop the injector and pulse all the extraction kickers simultaneously (number of dumped bunches limited to those contained in one arc and one linac)
Need for pulsed kickers with a rise-time of 23 ns (assuming a 25 ns bunch spacing and 2 ns for some jitter)
One extraction system per each energy has to be installed after the vertical spreader when the beams are fully separated
The standard scheme kicker+quad+septum should be used and clearance for the septum blade and the circulating beam have to be considered (integration!).
Kicker waveform flattop to be adapted to the number of dumped bunches

8. Extraction line as test facility
Pulsed magnets to extract only wanted number of bunches at a given energy in the shadow of normal ERL operation (adapt kicker waveform length)
The different energy lines are recombined using a system analogous to the one used at the entrance of the Linacs.
Include steering magnets, a matching section and a triplet to vary beam spot-size and focal point position
Detailed optics studies have to be performed, the dynamic range of the magnets and potential RP issues have to be evaluated.

9. Directions for future study
Study options and make technical choices for operational dump
Finalise layout of setup dumps
Use cases, kickers, septa and optics studies for emergency dump (plus interlock system to limit the number of dumped high energy bunches)
Kicker, steering magnets, RP and optics studies for test facility extraction line