Measurement of groove features and dimensions of the vertical test cathode and the choke joint of the superconducting electron gun cavity of the Energy Recovery LINAC

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A testing program for the superconducting electron gun cavity that has been designed for the Energy Recovery LINAC is being planned. The goal of the testing program is to characterize the RF properties of the gun cavity at superconducting temperatures and, in particular, to study multipacting that is suspected to be occurring in the choke joint of the cavity where the vertical test cathode is inserted. The testing program will seek to understand the nature and cause of this multipacting and attempt to eliminate it, if possible, by supplying sufficient voltage to the cavity. These efforts are motivated by the ... continued below

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Hammons, L. & Ke, M. October 13, 2011.

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Description

A testing program for the superconducting electron gun cavity that has been designed for the Energy Recovery LINAC is being planned. The goal of the testing program is to characterize the RF properties of the gun cavity at superconducting temperatures and, in particular, to study multipacting that is suspected to be occurring in the choke joint of the cavity where the vertical test cathode is inserted. The testing program will seek to understand the nature and cause of this multipacting and attempt to eliminate it, if possible, by supplying sufficient voltage to the cavity. These efforts are motivated by the multipacting issues that have been observed in the processing of the fine-grain niobium gun cavity. This cavity, which is being processed at Thomas Jefferson National Laboratory for Brookhaven, has encountered multipacting at a gradient of approximately 3 MV/m and, to date, has resisted efforts at elimination. Because of this problem, a testing program is being established here in C-AD that will use the large-grain niobium gun cavity that currently resides at Brookhaven and has been used for room-temperature measurements. The large-grain and fine-cavities are identical in every aspect of construction and only differ in niobium grain size. Thus, it is believed that testing and conditioning of the large-grain cavity should yield important insights about the fine-grain cavity. One element of this testing program involves characterizing the physical features of the choke joint of the cavity where the multipacting is believed to be occurring and, in particular the grooves of the joint. The configuration of the cavity and the vertical test cathode is shown in Figure 1. In addition, it is important to characterize the groove of the vertical test cathode. The grooved nature of these two components was specifically designed to prevent multipacting. However, it is suspected that, because of the chemical processing that the fine-grain gun cavity underwent along with the vertical test cathode, the geometry of these grooves was altered, presenting the possibility that multipacting may, in fact, be occurring in this area and contributing to the low gradients that have been observed in the fine-grain cavity. Therefore, the Survey and Alignment group in C-AD engaged in measurements of the cavity joint, shown in Figure 2 and the cathode weldment, shown in Figure 3 for the purpose of characterizing the grooves in both the cavity and the vertical test cathode and comparing the dimensions of the cathode with those of the prints supplied by Advanced Energy Systems (AES), the original designer and manufacturer of both the test cathode and the electron gun cavity, in preparation to have a new one manufactured. The goal was to ensure that the articles as built matched the design prints in preparation for manufacturing a new vertical test cathode. This report describes the data collected by the Survey group in these efforts. The endeavor was challenging for the group given the millimeter-scale dimensions of the grooves and the requirement for high precision.

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  • Report No.: BNL--96439-2011-IR
  • Grant Number: DE-AC02-98CH10886
  • DOI: 10.2172/1032057 | External Link
  • Office of Scientific & Technical Information Report Number: 1032057
  • Archival Resource Key: ark:/67531/metadc837281

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • October 13, 2011

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

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  • Aug. 29, 2016, 8:47 p.m.

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Hammons, L. & Ke, M. Measurement of groove features and dimensions of the vertical test cathode and the choke joint of the superconducting electron gun cavity of the Energy Recovery LINAC, report, October 13, 2011; United States. (digital.library.unt.edu/ark:/67531/metadc837281/: accessed December 14, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.