• C.E. Mayes, G.H. Hoffstaetter
  CLASSE, Ithaca, New York

Coherent Synchrotron Radiation (CSR) can be a detrimental effect on particle bunches with high charge and short bunch lengths. CSR can contribute to an increase in emittance and energy spread, and can limit the process of bunch compression. It is especially important in Energy Recovery Linacs (ERLs), because any relative energy spread induced at high energy is magnified after deceleration, and any energy lost by the particles is energy that cannot be recovered. Here we present CSR simulation results using the particle tracking code BMAD for the main operation modes in the proposed Cornell ERL, including an additional bunch compression mode. These simulations consider the effect of CSR shielding, as well as CSR propagation between bends.

• C.E. Mayes, G.H. Hoffstaetter
  CLASSE, Ithaca, New York

The current status of the lattice and layout for the proposed Cornell Energy Recovery Linac lightsource is presented. This design is centered about a new hard X-ray user facility to be located on Cornell's campus, and is adapted to the local topography in order to incorporate the existing CESR tunnel and Wilson Laboratory. Nonlinear charged-particle optics for this new machine have been designed and analyzed. The lattice is populated with various components for the appropriate accelerator physics requirements for orbit, bunch length, and emittance growth control, including a vacuum system compatible with rest-gas-scattering limits, a collimation system for halo from effects like Touschek scattering, and correction coils and BPMs for sub-micron beam stabilization. We also show calculations for an additional bunch compression mode, which compresses 19~pC bunches at a 1.3~GHz repetition rate to 25~fs.

• F.A. Laham
  Cornell University, Ithaca, New York
• G.H. Hoffstaetter, C.E. Mayes, J.R. Thompson
  CLASSE, Ithaca, New York

The proposed Cornell Energy Recovery Linac (ERL) is designed for bunches of 77pC and 100mA whose energy is recovered. However, the ERL linac can also be used for larger bunch charges of reduced average current whose energy does not have to be recovered. The proposed Cornell ERL lightsource currently uses a split linac arrangement connected by a turnaround arc. In order to avoid the detrimental effects of Coherent Synchrotron Radiation (CSR) in this arc, a high charge (1nC) bunch must remain relatively long (2ps), and be compressed at high energy (5GeV). An appropriate bunch compressor must take second order effects into account, which adds complications for the large energy spread associated with compression to 100fs or less. We have therefore designed a very simple four dipole bunch compressor at high energy, which uses second order time of flight terms in the turnaround arc rather than in the bunch compressor itself. This design is tested using particle tracking simulations incorporating CSR, as well as magnetic field errors and misalignments.

• M.L. Neubauer, A. Dudas, R. Sah
  Muons, Inc, Batavia
• G.H. Hoffstaetter, M. Liepe, H. Padamsee, V. Shemeli
  CLASSE, Ithaca, New York

Superconducting RF (SRF) systems typically contain unwanted frequencies or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are strategically located, often in the drift tubes adjacent to the SRF cavity. These HOM loads must have broadband microwave loss characteristics and be robust both thermally and mechanically, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on existing work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design will be developed for high-gradient 750 MHz superconducting cavity systems for storage ring and linac radiation sources. This work will build on novel construction techniques to maintain the ferrite in mechanical compression without brazing. 750 MHz RF system designs will be numerically modeled to determine the optimum ferrite load required to meet broadband loss specifications.

• M. Liepe, S.A. Belomestnykh, E.P. Chojnacki, Z.A. Conway, G.H. Hoffstaetter, R.P.K. Kaplan, S.E. Posen, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich
  CLASSE, Ithaca, New York

Cornell University has developed and fabricated a SCRF injector cryomodule for the acceleration of a high current, low emittance beam in the Cornell ERL injector prototype. This cryomodule is based on superconducting rf technology with five 2-cell rf cavities operated in the cw mode, supporting beam currents of up to 100 mA. After a rework of this cryomodule in 2009 to implement several improvements, it is now in beam operation again. In this paper we report on latest results and discuss future test plans.