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Benesch, J. F.

Paper Title Page
TPPP016 Beam Physics for the 12 GeV CEBAF Upgrade Project 1482
 
  • L. Merminga, J. F. Benesch, S.A. Bogacz, Y.-C. Chao, A. Freyberger, J.M. Grames, L. Harwood, R. Kazimi, G.A. Krafft, M. Spata, M. Tiefenback, M. Wiseman, B.C. Yunn, Y. Zhang
    Jefferson Lab, Newport News, Virginia
 
  Funding: Work supported by DOE Contract DE-AC05-84ER40150.

Beam physics aspects of the 12 GeV Upgrade of CEBAF are presented. The CEBAF Upgrade to 12 GeV is achieved via 5.5 recirculations through the linacs, and the installation of 10 new high-gradient cryomodules. A new experimental hall, Hall D, is envisioned at the end of North Linac. Simulation results for straight-through and recirculated injectors are summarized and compared. Beam transport designs are discussed and evaluated with respect to matching and beam breakup (BBU) optimization. Effects of synchrotron radiation excitation on the beam properties are calculated. BBU simulations and derived specifications for the damping of higher order modes of the new 7-cell cavities are presented. The energies that provide longitudinal polarization in multiple experimental halls simultaneously are calculated. Finally, a detailed optics design for the Hall D transport line has been obtained.

 
WPAP046 Injection Options for 12 GeV CEBAF Upgrade 2911
 
  • R. Kazimi, J. F. Benesch, Y.-C. Chao, J.M. Grames, G.A. Krafft, M. Tiefenback, B.C. Yunn, Y. Zhang
    Jefferson Lab, Newport News, Virginia
 
  Funding: Work supported by DOE Contract DE-AC05-84ER40150.

Jefferson Lab is planning to upgrade the CEBAF accelerator from 6 to 12 GeV. In order to achieve this, the beam energy at injection into the main accelerator needs to increase from 67 MeV to either 123 or 134 MeV depending on the location of the new experimental hall relative to the accelerator. The present 100 keV electron source and beam formation to 5 MeV will remain unchanged; however, the present accelerating cryomodules in the injector cannot reach the higher injection energies. Consequently, two options for attaining these energies are considered: (1) replacing the present injector cryomodules with new, higher gradient cryomodules, or (2) re-circulating the beam through the existing cryomodules to achieve the necessary energy gain in two passes. In this paper we present simulation results and list the advantages and disadvantages of these two options.

 
FOAA009 SRF Performance of CEBAF After Thermal Cycle to Ambient Temperature 665
 
  • R.A. Rimmer, J. F. Benesch, J.P. Preble, C.E. Reece
    Jefferson Lab, Newport News, Virginia
 
  Funding: This manuscript has been authored by SURA, Inc. under Contract No. DE-AC05-84ER-40150 with the U.S. Department of Energy.

In September 2003, in the wake of Hurricane Isabel, JLab was without power for four days after a tree fell on the main power lines feeding the site. This was long enough to lose insulating vacuum in the cryomodules and cryogenic systems resulting in the whole accelerator warming up and the total loss of the liquid helium inventory. This thermal cycle stressed many of the cryomodule components causing several cavities to become inoperable due to helium to vacuum leaks. At the same time the thermal cycle released years of adsorbed gas from the cold surfaces. Over the next days and weeks this gas was pumped away, the insulating vacuum was restored and the machine was cooled back down and re-commissioned. In a testament to the robustness of SRF technology, only a small loss in energy capability was apparent, although individual cavities had quite different field-emission characteristics compared to before the event. In Summer 2004 a section of the machine was again cycled to room temperature during the long maintenance shutdown. We report on the overall SRF performance of the machine after these major disturbances and on efforts to characterize and optimize the new behavior for high-energy running.