Cornell ERL Injector Cryomodule
Figure 1: Layout of the ERL injector prototype.
Cornell University's Laboratory for Accelerator based Sciences and Education (CLASSE) is exploring the potential of an x-ray light source based on the Energy-Recovery-Linac (ERL) principle . This type of light source promises superior X-ray performance as compared to conventional third generation light sources , but several accelerator physics and technology challenges need to be addressed before a full energy ERL light source can be built. These challenges result primarily from the high current, ultra low emittance beam required at the undulator locations beyond.
To study and demonstrate the production and preservation of such an ultra-low emittance beam, a prototype of the ERL injector  is presently under construction and commissioning at Cornell. One of the most challenging and critical components in the injector is its energy booster cryomodule, hosting five superconducting (SC) 2-cell 1.3 GHz cavities. The main challenges facing this cryomodule are (1) the acceleration of a high current beam with up to 500 kW of total power transferred to the beam, (2) significant Higher-Order Mode (HOM) excitation in the SRF cavities up to frequencies of tens of GHz by the high current beam, and (3) the preservation of the ultra-low emittance of the electron beam while it passes through the cryomodule.
Figure 2: Injector cryomodule in the prototype ERL injector.
Solutions to all these challenges have been found, and prototypes of the main beam line components (SRF cavities, HOM loads, and input couplers) have been developed, fabricated and tested . Following the successful test of a horizontal test cryomodule , the full ERL injector SRF cryomodule has been designed  and fabricated . Table 1 lists some key specifications of this cryomodule. Recently, the injector cryomodule has been installed in the Cornell ERL injector prototype, and commissioning has started. Figure 1 shows a layout of the injector. The SRF module is located about four feet downstream of the DC gun; see also Figure 2. The five SRF cavities in the module are powered by individual high power (120 kW) CW klystrons, located on a mezzanine above the injector prototype. The commissioning of the injector RF system is described in detail in .
| Table 1: ERL injector cryomodule specifications
| Number of 2-cell cavities
| Accelerating voltage per 2-cell cavity
|| 1 – 3 MV
| Fundamental mode frequency
|| 1.3 GHz
| R/Q (linac definition) per cavity
|| 222 Ohm
|| 4.6×104 – 4.1×105
| RF power per cavity
|| 100 kW
| Required amplit. / phase stability (rms)
|| 9.5×10-4 / 0.1°
| Maximum beam current
|| 100 mA
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- S. Belomestnykh et al., Commissioning of the Cornell ERL Injector RF Systems, MOPP116, (2008).