Christopher P J Barty ^1,2,3* J Martin Algots ¹ Alexander J Amador ¹ James C R Barty ¹ Shawn M Betts ¹ Marcelo A Casteñada ¹ Matthew M Chu ¹ Michael E Daley ¹ Ricardo A De Luna Lopez ¹ Derek A Diviak ¹ Haytham H Effarah ^1,2,3 Roberto Feliciano ¹ Adan Garcia ¹ Keith J Grabiel ¹ Alex S Griffin ¹ Frederic V Hartemann ¹ Leslie Heid ^1,2 Yoonwoo Hwang ¹ Gennady Imeshev ¹ Michael Jentschel ¹ Christopher A Johnson ¹ Kenneth W Kinosian ¹ Agnese Lagzda ¹ Russell J Lochrie ¹ Michael W May ¹ Everardo Molina ¹ Christopher L Nagel ¹ Henry J Nagel ¹ Kyle R Peirce ¹ Zachary R Peirce ¹ Mauricio E Quiñonez ¹ Ferenc Raksi ¹ Kelanu Ranganath ¹ Trevor Reutershan ^1,2,3 Jimmie Salazar ¹ Mitchell E Schneider ¹ Michael W L Seggebruch ^1,2 Joy Y Yang ¹ Nathan H Yeung ¹ Collette B Zapata ¹ Luis E Zapata ¹ Eric J Zepeda ¹ Jingyuan Zhang ¹

• ¹ Lumitron Technologies, Inc., Irvine, California, United States
• ² Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, Irvine, California, United States
• ³ Beckman Laser Institute and Medical Clinic, Department of Surgery, School of Medicine, University of California, Irvine, Irvine, California, United States

The design and optimization of laser-Compton x-ray systems based on compact distributed charge accelerator structures can enable micron-scale imaging of disease and the concomitant production of beams of Very High Energy Electrons (VHEEs) capable of producing FLASHrelevant dose rates (∼ 10 Gy in less than 100 ns). The physics of laser-Compton x-ray scattering ensures that the x-rays produced by this process follow exactly the trajectory of the electrons from which the x-rays were produced, thus providing a route to not only compact VHEE radiotherapy but also image-guided, VHEE FLASH radiotherapy. This manuscript will review the compact accelerator architecture considerations that simultaneously optimize the production of laser-Compton x-rays from the collision of energetic laser pulses with high energy electrons and the production of high-bunch-charge VHEEs. The primary keys to this optimization are use of X-band RF accelerator structures which have been demonstrated to operate with over 100 MeV/m 1 Barty et al.acceleration gradients. The operation of these structures in a distributed charge mode in which each radiofrequency (RF) cycle of the drive RF pulse is filled with a low-charge, high-brightness electron bunch is enabled by the illumination of a high-brightness photogun with a train of UV laser pulses synchronized to the frequency of the underlying accelerator system. The UV pulse trains are created by a patented pulse synthesis approach which utilizes the RF clock of the accelerator to phase and amplitude modulate a narrow band continuous wave (CW) seed laser. In this way it is possible to produce up to 10 µA of average beam current from the accelerator. Such high current from a compact accelerator enables production of sufficient x-rays via laser-Compton scattering for clinical imaging and does so from a machine of "clinical" footprint. At the same time, the production of 1000 or greater individual micro-bunches per RF pulse enables > 10 nC of charge to be produced in a macrobunch of < 100 ns. The design, construction, and test of the 100-MeV class prototype system in Irvine, CA is also presented.