Undergraduate Research at Jefferson Lab

Automation and Interpretation of a Higher Order Modes Survey and the Separation of Overlapping Modes

Student: Jeffrey G. Stevenson

School: Virginia Polytechnic Institute and State University

Mentored By: Haipeng Wang

A Higher Order Modes (HOM) survey is the process of identifying quality factors of cavities in a cryomodule and is a crucial measure in meeting certain standards of cavities within specification. It serves primarily to prevent beam break-up (BBU) instabilities during accelerator operation. These surveys can be administered in three different areas: the Cryomodule Test Facility (CMTF), the Vertical Test Area (VTA), and the Continuous Electron Beam Accelerator Facility (CEBAF). After the surveys have been performed, a data ambiguity is encountered. Since cryomodule measurement in both the CMTF and the accelerator tunnel contains a string of eight cavities connected together, modes measured from one cavity may actually be resonate sources from adjacent cavities. This could prove to be problematic since it is important to distinguish which cavity may or may not cause BBU. The purpose of this project is to understand the techniques, utility, and efficiency of the HOM surveys and to suggest a practical method of separating modes into their corresponding cavities. It was determined that various portions of the surveys can be further automated in order to save time and needless labor.