SRF2011 - List of Authors (Jain, P.)

Paper	Title	Page
THPO041	HOM Identification and Bead Pulling on the Brookhaven ERL	810
	H. Hahn, W. Xu BNL, Upton, Long Island, New York, USA P. Jain, E.C. Johnson Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE and by the DOE grant DE-SC0002496 to Stony Brook University Several past measurements of the Brookhaven ERL at superconducting temperature produced a long list of higher order modes (HOMs). The Niobium 5-cell cavity is terminated with HOM ferrite dampers that successfully reduce the Q-factors to tolerable levels. However, a number of undamped resonances with Q ≈ 10⁶ were found at 4 K and their mode identification remained as a goal for this paper. The approach taken here consists of different measurements on a copper cavity replica of the ERL which can be compared with Microwave Studio computer simulations. Several different S21 transmission measurements are used, including those taken from the fundamental input coupler to the pick-up probe across the cavity, between probes in a single cell, and between beam-position monitor probes in the beam tubes. These measurements are supported by bead pulling with a metallic needle, which is calibrated in the fundamental mode. This paper presents results for the first two dipole bands with the prototypical 958 MHz trapped mode, the high Q quadrupole band, the first beam tube resonances, and other as yet to be identified resonances.

Paper

Title

Page

HOM Identification and Bead Pulling on the Brookhaven ERL

810

H. Hahn, W. Xu
BNL, Upton, Long Island, New York, USA
P. Jain, E.C. Johnson
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE and by the DOE grant DE-SC0002496 to Stony Brook University
Several past measurements of the Brookhaven ERL at superconducting temperature produced a long list of higher order modes (HOMs). The Niobium 5-cell cavity is terminated with HOM ferrite dampers that successfully reduce the Q-factors to tolerable levels. However, a number of undamped resonances with Q ≈ 10⁶ were found at 4 K and their mode identification remained as a goal for this paper. The approach taken here consists of different measurements on a copper cavity replica of the ERL which can be compared with Microwave Studio computer simulations. Several different S21 transmission measurements are used, including those taken from the fundamental input coupler to the pick-up probe across the cavity, between probes in a single cell, and between beam-position monitor probes in the beam tubes. These measurements are supported by bead pulling with a metallic needle, which is calibrated in the fundamental mode. This paper presents results for the first two dipole bands with the prototypical 958 MHz trapped mode, the high Q quadrupole band, the first beam tube resonances, and other as yet to be identified resonances.