Date of Completion


Embargo Period



Accelerator physics, BBU, Beam instability, Beam breakup, CEBAF, Jefferson Lab

Major Advisor

Kyungseon Joo

Associate Advisor

Richard Jones

Associate Advisor

Todd Satogata

Field of Study



Doctor of Philosophy

Open Access

Open Access


Recirculating linear accelerators (linacs) provide a compact and efficient way of accelerating particle beams to medium and high energies by reusing the same linac for multiple passes. In recirculating linacs, maximum current can be limited by multipass beam breakup (BBU), which occurs when an electron beam interacts with the higher order modes (HOMs) of accelerating cavities during multipass recirculations.

The average current of the CEBAF 12 GeV Upgrade accelerator at Jefferson Lab, a 5-pass recirculating linac, may be limited by multipass BBU. This disserta- tion work was performed as part of the 12 GeV Upgrade project at Jefferson Lab to investigate limits on average beam currents from the BBU instability. Exper- imental and simulation studies were carried out, and revealed that the multipass BBU will not be a limiting factor to the average beam current in the 12 GeV Upgrade of the CEBAF accelerator.

This dissertation includes the theoretical calculation for longitudinal BBU, which revealed that the maximum current limit from longitudinal BBU is much higher than the transverse one. Therefore, longitudinal BBU will not become a problem, as long as transverse BBU does not cause instability. A cumulative BBU simulation study for a new injector in the 12 GeV accelerator also was conducted. The results showed that the transient behavior of cumulative BBU in the injector is not problematic.