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

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

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

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

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

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

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

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 !

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.

Start of MLC review