CORNELL LABORATORY FOR ACCELERATOR-BASED SCIENCES AND EDUCATION

Suprconducting RF for CESR

The CESR Luminosity Upgrade Plan consists of several consecutive steps, or phases [1-3]. At present time, this program is in Phase III, designed to yield a luminosity of 1.7x10^33 cm^-2 sec^-1 with 45 bunches in each beam for a total current of 1 A . This plan utilizes four superconducting single-cell cavities with an accelerating gradient of 6 to 10 MV/m , which corresponds to a peak accelerating voltage of 1.8 to 3 MV per cell. The power transferred to the beam by each cavity would be 325 kW .

The use of only four SRF cells with stronger damped higher-order modes (HOMs), as compared to the old twenty normal-conducting copper cells, decreases both the broad and narrow band impedances sufficiently to allow stable operation at the high current level [4-5]. Each SRF cavity has its individual cryostat, input coupler and RF window, two ferrite HOM loads, taper transition(s) to the adjacent CESR beam tube, and some other beam-line components.

The name BB1 has been assigned to the Cornell superconducting 500 MHz single-cell cavity shape. Five cavities have been manufactured to date: the first, BB1-1, by Dornier, all others, BB1-2 through BB1-5, by ACCEL . The BB1-1 cavity [6] and prototypes of RF window [7], cryostat [8], HOM loads [10, 19] and beam line components were subjected to a successful beam test in CESR in August 1994 [9-11]. After that necessary changes were made to the design of some components, the new, MARK II cryostat * was designed to meet a rather tight space requirements of the CESR tunnel, and the cavity was equipped with the new ceramic RF window [12, 15-16]. The design and layout of the new RF system was thus completed [13-14].

The first cryomodule has been installed in CESR since September of 1997. Two more cavities were installed in October'98 and February'99 [17] and the final one was installed in September'99. This allows CESR to work with 45 bunches per beam and total average current of 780 mA in two beams at the start of fills for high energy physics and achieve measured peak luminosity of 1.3x10³³cm^-2s^-1 [18]. Along this, not always easy, way of testing and commissioning some progress was made in understanding of gas evolution and multipacting in B-cell cryomodules [20-21].

(saga to be continued)

References

1. D. L. Rubin. CESR Status and Plans. In Proceedings of the 1995 Particle Accelerator Conference, 1, 481-485.
2. D. Rice. CESR: Steps toward a B-factory. In Proceedings of the Fifth European Particle Accelerator Conference, 17-21.
3. S. B. Peck and D. L. Rubin. CESR Performance and Upgrade Status. In Proceedings of the 1999 Particle Accelerator Conference, in print.
4. H. Padamsee, et al. Design Challenges for High Current Storage Rings. Particle Accelerators, 40 , 17-41 (1992).
5. J. Kirchgessner. The Use of Superconducting RF for High Current Applications. Particle Accelerators, 46 , 151-162 (1994).
6. D. Moffat, et al. Preparation and Testing of a Superconducting Cavity for CESR-B. In Proceedings of the 1993 Particle Accelerator Conference, 763-765.
7. D. Metzger, et al. Test Results and Design Considerations for a 500 MHz, 500 kWatt Vacuum Window for CESR-B. In Proceedings of the 1993 Particle Accelerator Conference, 1399-1401.
8. E. Nordberg, et al. Cryostat for a Beam Test with the CESR-B Cavity. In Proceedings of the 1993 Particle Accelerator Conference, 995-997.
9. H. Padamsee, et al. Beam Test of a Superconducting Cavity for the CESR Luminosity Upgrade. In Proceedings of the 1995 Particle Accelerator Conference, 3 , 1515-1517.
10. S. Belomestnykh, et al. Comparison of the Predicted and Measured Loss Factor of the Superconducting Cavity Assembly for the CESR Upgrade. In Proceedings of the 1995 Particle Accelerator Conference, 5 , 3394-3396.
11. S. Belomestnykh, et al. Wake fields and HOMs Studies of a Superconducting Cavity Module with the CESR beam. In Proceedings of the 1995 Particle Accelerator Conference, 5 , 3391-3393.
12. M. Pisharody, et al. High Power Window Tests on a 500 MHz Planar Waveguide Window for the CESR Upgrade. In Proceedings of the 1995 Particle Accelerator Conference, 1720-1722.
13. S. Belomestnykh, et al. Superconducting RF System for the CESR Luminosity Upgrade: Design, Status, and Plans. In Proceedings of the Fifth European Particle Accelerator Conference, 2100-2102 (1996).
14. S. Belomestnykh, et al. Development of Superconducting RF for CESR. In Proceedings of the 1997 Particle Accelerator Conference, 3 , 3075-3077.
15. E. Chojnacki, et al. Design of a High Average Power Waveguide Window. In Proceedings of the 1997 Particle Accelerator Conference, ?-?.
16. E. Chojnacki, et al. Tests and Designs of High-power Waveguide Vacuum Window at Cornell. Particle Accelerators, 61 [309-319]/45-55 (1998).
17. S. Belomestnykh, et al. Commissioning of the Superconducting RF Cavities for the CESR Luminosity Upgrade. In Proceedings of the 1999 Particle Accelerator Conference, in print.
18. S. Belomestnykh. The High Luminosity Performance of CESR with the New Generation Superconducting Cavities. In Proceedings of the 1999 Particle Accelerator Conference, in print.
19. E. Cojnacki, et al. Beamline RF Load Development at Cornell. In Proceedings of the 1999 Particle Accelerator Conference, in print.
20. R. Geng and H. Padamsee. Condensation/Adsorption and Evacuation of Residual Gases in the SRF System for the CESR Luminosity Upgrade. In Proceedings of the 1999 Particle Accelerator Conference, in print.
21. R. Geng and H. Padamsee. Exploring Multipacting Characteristics of a Rectangular Waveguide. In Proceedings of the 1999 Particle Accelerator Conference, in print.
22. E. Cojnacki and J. Sears. Superconducting RF Cavities and Cryogenics for the CESR III Upgrade. In Proceedings of the 1999 Cryogenic Engineering and International Cryogenic Materials Conference, in print.

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• To watch a movie of the MARK II cryostat assembly , download Final_Movie.avi file (49 MB).