Generation of micrometer electron beams from FLASHlab@PITZ

The Photo Injector Test facility at DESY in Zeuthen (PITZ) is developing an R&D platform, FLASHlab@PITZ, for systematically studying the FLASH effect in cancer treatment using its high-brightness 22 MeV electron beam. The facility can provide a uniquely large dose parameter space: for average dose rates from 0.05 Gy/s to 107 Gy/s (averaged in one RF pulse of less than 1 ms, with a peak dose rate of up to 1013 Gy/s). The platform is currently undergoing an upgrade to improve the beam control and quality, highlighted by a 2D sweeping system for generating an arbitrary radiation field by pencil beam scanning. An optional dual-scattering system also allows to generate a wide radiation field. Both systems take advantages of the tightly focused electron beams, which have a sub-mm RMS size for the bunch charge ranging from sub-pC to several nC. Recent simulations on the generation of microbeams showed that electron beams of ultra-low emittance (~0.02 mm mrad) and ultra-low energy spread (<0.001%), which are critical parameters for focusing the beams, can be produced at the bunch charge of a few fC by optimizing our flexible photocathode drive laser. A Kapton window (thickness 7.5 μm) adapted from the SNAKE facility is being considered as an alternative to the existing titanium exit window (thickness 50 μm), which greatly reduces the scattering effects in the window and therefore allows the tiny beam to be delivered to thin samples like cells, tissues and small animals. In this contribution, beam dynamics and Monte-Carlo simulations on the generation and transport of microbeams will be presented.