Optimization of Higher Order Mode Dampers in the 56MHz SRF Cavity for RHIC

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A 56 MHz superconducting RF cavity was designed for a luminosity upgrade of the Relativistic Heavy Ion Collider (RHIC), including requirements for Higher Order Mode (HOM) damping. In this paper, we describe our optimization of the damper's performance, and modifications made to its original design. We also show the effects of the damper geometry on the cavity's HOM impedance. To reduce the likelihood of magnetic breakdown, we lowered the magnetic field enhancement at the ports to a value less than the highest field in the cavity. We simulated all monopole and dipole HOMs up to 1GHz with their frequencies, mode ... continued below

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Wu, Q. & Ben-Zvi, I. May 23, 2010.

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A 56 MHz superconducting RF cavity was designed for a luminosity upgrade of the Relativistic Heavy Ion Collider (RHIC), including requirements for Higher Order Mode (HOM) damping. In this paper, we describe our optimization of the damper's performance, and modifications made to its original design. We also show the effects of the damper geometry on the cavity's HOM impedance. To reduce the likelihood of magnetic breakdown, we lowered the magnetic field enhancement at the ports to a value less than the highest field in the cavity. We simulated all monopole and dipole HOMs up to 1GHz with their frequencies, mode configurations, R/Qs, and shunt impedances, verifying that all modes are well-damped with the optimized design and configuration. The 56 MHz superconducting RF cavity is a quarterwave resonator designed to have a gap voltage of 2.5 MV. Our plans are to place this beam-driven resonator at a common section of RHIC to provide a storage RF potential for both rings. The large bucket of the cavity will reduce spill due to Intra-Beam Scattering (IBS), and thus increase the luminosity for the detectors. It is very important to damp all the cavity's Higher Order Modes (HOMs) to avoid beam instabilities. The design chosen for the HOM damper is a magnetically coupled loop located at the rear end of the cavity. The loop and its port geometry must be optimized to assure sufficient damping, avoid a large enhancement of the local magnetic field. A high-pass filter is included in the circuit to reduce the power extraction from the fundamental mode. The number of HOM dampers used and their configuration also are important factors for the damping and cooling system. A small loop area will couple out less power from the cavity's fundamental mode, thus reducing the voltage and power dissipation in the damper's filter circuit; however, it might not be sufficient for HOM damping. This problem is resolved by increasing the number of the HOM dampers and carefully choosing their location. Details of the high-pass filter will be discussed in another paper.

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  • First International Particle Accelerator Conference (IPAC) 2010; Kyoto, Japan; 20100523 through 20100528

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  • Report No.: BNL--90769-2010-CP
  • Grant Number: DE-AC02-98CH10886
  • Office of Scientific & Technical Information Report Number: 1013484
  • Archival Resource Key: ark:/67531/metadc834004

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  • May 23, 2010

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

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  • Aug. 29, 2016, 8:57 p.m.

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Wu, Q. & Ben-Zvi, I. Optimization of Higher Order Mode Dampers in the 56MHz SRF Cavity for RHIC, article, May 23, 2010; United States. (digital.library.unt.edu/ark:/67531/metadc834004/: accessed April 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.