CORNELL LABORATORY FOR ACCELERATOR-BASED SCIENCES AND EDUCATION

Cornell ERL Injector Cryomodule

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 [1]. This type of light source promises superior X-ray performance as compared to conventional third generation light sources [2], 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 [3] 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.

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 [4]. Following the successful test of a horizontal test cryomodule [5], the full ERL injector SRF cryomodule has been designed [6] and fabricated [7]. 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 [8].

Table 1: ERL injector cryomodule specifications
Number of 2-cell cavities	5
Accelerating voltage per 2-cell cavity	1 – 3 MV
Fundamental mode frequency	1.3 GHz
R/Q (linac definition) per cavity	222 Ohm
Qext	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

REFERENCES

1. G.H. Hoffstaetter, et al., Progress toward an ERL Extension of CESR, Proc. of PAC’07, pp.107-109 (2007).
2. D. H. Bilderback, Energy Recovery Linac Experimental Challenges; Proceeding of Future Light Sources 2006 meeting in Hamburg, PLT03, p1-6 (2006).
3. I. Bazarov and C. Sinclair, High Brightness, High Current Injector Design for the Cornell ERL Prototype, Proc. of PAC’03, pp. 2062-2064 (2003).
4. V. Shemelin, et al., Dipole-mode-free and kick-free 2-cell Cavity for SC ERL Injector, Proc. of PAC’03, pp. 2059-2061 (2003).
5. R. L. Geng, et al., Fabrication and Performance of Superconducting RF Cavities for the Cornell ERL Injector, Proc. of PAC’07, pp. 2340-2342 (2007).
6. Shemelin et al., Status of the HOM load for the Cornell ERL Injector, Proceedings of EPAC 2006, Edinburgh, Scotland (2006).
7. V. Shemelin, M. Liepe, H. Padamsee, Characterization of Ferrites at Low Temperature and High Frequency, NIM A 557 (2006) 268-271.
8. S. Belomestnykh et al., First Test of the Cornell Single-cavity Horizontal Cryomodule, this conference, paper MOPP117, (2008).
9. M. Liepe et al., Status of the Cornell ERL Injector Cryomodule, Proceedings of the 2007 International Workshop on RF Superconductivity, Beijing, China (2007).
10. M. Liepe et al., Design of the CW Cornell ERL Injector Cryomodule, Proceedings of the 2005 particle Accelerator Conference, Knoxvill, TN, USA (2005).
11. M. Liepe, et al., The Cornell ERL Superconducting 2-cell Injector Cavity String and Test Cryomodule, Proc. of PAC’07, pp. 2572-2574 (2007).
12. E. Chojnacki et al., Design and Fabrication of the Cornell ERL Injector Cryomodule, MOPP123, (2008).
13. S. Belomestnykh et al., Commissioning of the Cornell ERL Injector RF Systems, MOPP116, (2008).