1. ERL Main-Linac Cryomodule
Why ? and What ?
CW linac R&D
DC-gun R&D
SRF injector R&D
Undulator R&D
Georg H. Hoffstaetter, October 5, 2004

2. Cornell history: The ERL principle
Energy recovery needs continuously fields in the RF structure
Normal conducting high field cavities can get too hot.
Superconducting cavities used to have too low fields.
Georg H. Hoffstaetter, October 5, 2004

3. ERL on Cornell’s campus as extension of CHESS
Cornell
Georg H. Hoffstaetter, October 5, 2004

4. Parameters
Required beam parameters drive MLC choices
5 GeV, 100mA, 8pm emittances, 2ps bunch length

5. From beam parameters to MLC
5 GeV, 100mA, 8pm emittances, 2ps bunch length
8pm: requires small bunch charge and therefore high repetition rate – results in 1.3GHz
Cost optimization: Construction (favors high gradients and small length) + 10 year operation (favors low gradient and small cooling needs) - results in 15MV/m < Eacc < 20MV/m
100mA: By far the largest current in an SRF linac, produces strong Higher Order Modes. To damp these modes, cavities cannot be too long - results in 7-cell cavities with a beam-pipe HOM absorber each.
5GeV and 15MV/m, i.e 312m of acceleration, 7-cells for 1.3GHz – results in 384 cavities
ERL: Optics for two beam requires regular focusing – results in a quadrupole every 10m, and therefore a 10m long cryomodule.
10m MLC for cavities with HOM absorbers – results in 6 cavities per MLC

6. Cornell Energy Recovery Linac Project Design Definition Report (PDDR)
530 pages between conceptual design and engineering design.
Contains considerations for MLC.

7. Beam parameter input to MLC requirements
8pm: Stringent alignment tolerances, obtained by orbit correction simulations
small coupler kick limits obtained by RF and beam dynamics simulations
16MV/m High Q requirements and suitable cryogenic design
100mA: Strong HOM damping requirements, obtained by BBU simulations b)
Georg H. Hoffstaetter, October 5, 2004

8. The right time for an ERL MLC !
Peak DC-gun voltage: 440kV (of 500kV required with beam)
Peak bunched-beam current: 52mA with GaAs / 35mA with CsK2Sb for 8h
Typical bunch length: 2ps (up to spec)
Smallest normalized thermal emittance: 0.25 mm mrad/mm radius
Smallest normalized emittance after injector at 80pC: 0.7 mm mrad
with normalized bunch core emittance : 0.3 mm mrad
For this gun, 0.5 mm mrad is theoretical limit !
This bunch in a 5GeV ERL would produce X-rays brighter than any ring today.
(a 50pmX50pm ERL/USR or a 0.6nmX6pm storage ring)
Cathode research: reduction of the thermal emittance by 2
SRF-cavity: Q of 3.5E10 at 16MV/m without ERL couplers
The injector prototype has already achieved ERL-quality beams.
Now the rest of the accelerator, particularly the MLC has to be prototyped !

9. Charge to the MLC review committee
Review the ERL’s MLC and evaluate whether it’s design is suitable for the ERL’s parameters. Consider the cryogenic and mechanical.
Review the prototype MLC that will be tested individually, and evaluate whether its design and its planned tests will yield sufficient insight of the ERLs MLC.
Write a short report of your findings, if possible before October 14, 2012.

10. Start of MLC review