Intra-pulse sub-structure sensing of accelerated electrons

Examination is made of the temporal pattern of 6–15 MeV electrons, specifically at the dose-rates familiar in use of conventional linacs. The observed intra-pulse sub-structure variations are a manifestation of linac power modifications (modulation occurring within the duration of a single accelerator pulse) and inter-bunch electron repulsion. The measurement system, focal in providing sub-μs temporal resolution as well as capability in covering the dose per pulse dynamic range, comprises an in-house fabricated Ge-doped fiber-sensor, a photon-counting circuit, a multi-pixel photon counter (MPPC), and a fast digital oscilloscope. Together with the observed pulse decay-time and magnitude of afterglow, the variations in intra-pulse sub-structure captured by the system can be expected to have influence upon the accuracy of dose deposition. The measurement capability of the optical fiber scintillator system is shown to be sufficient to serve present needs, largely negating a desire for more sophisticated systems offering superior temporal resolution.