Beam Breakup in the Jefferson Lab FEL Upgrade

(MO-3-12)

L. Merminga, I. E. Campisi, D. Douglas, B. Yunn  

JEFFERSON LAB

Multibunch beam breakup (BBU) simulations for the 80-200 MeV recirculating linac of the Jefferson Lab FEL Upgrade are presented. The linac uses three superconducting rf cryomodules, two of which consist of 5-cell cavities, the third of 7-cell cavities. The measured values of frequencies and Q's of the Higher Order Modes (HOMs) of the 5-cell cavities are used. The threshold current of the BBU instability is calculated for a range of Q values of the HOMs of the 7-cell cavities. These results are used to derive a specification on the HOM damping requirement for the 7-cell cavities.