Experiments on the beam breakup instability in long-pulse electron beam transport through RF cavity systems

Experiments have been performed to investigate the beam breakup-up (BBU) instability in high current electron beams transported through RF cavity systems. Experiments utilized long-pulse electron beam accelerators operating with the following parameters: energy = 0.3-0.8 MeV, current=0.1-1 kA, and pulselength=0.3-1.5 mu s. The transport system consists of 10 RF cavities separated by tubes which are cut off to the RF. Each cavity has a microwave probe to detect growth of e-beam emission in the TM/sub 110/ mode at 2.5-GHz, corresponding to the BBU. Solenoidal magnetic fields of 0.8-5kG are applied. Experiments show that 40% of the injected current was transported through the cavity system. The growth of the 2.5-GHz RF was found to be 4.4 dB per cavity, which compares well with the theoretical growth of 3.9 dB per cavity.<>