Solid-State Driven X-band Linac for Electron Microscopy

Current transmission electron microscopes (TEM) accelerate electrons to 200-300 keV using DC electron guns with a nanoamp of current and very low emittance. However at higher voltages these DC sources rapidly grow in size, oftentimes several meters tall for 1 MeV microscopes [1]. Replacing these electron guns with a compact linac powered by solid-state sources could dramatically lower cost while maintaining beam quality, thereby increasing accessibility. Utilizing compact high shunt impedance X-band structures ensures that each RF cycle contains at most a few electrons, preserving beam coherence. CW operation of the RF linac is possible with distributed solid-state architectures [2–4] which power each cavity directly with solid-state amplifiers which can now provide up to 100W of power at X-band frequencies [5]. We present an initial design for a prototype low-cost CW RF linac for high-throughput electron diffraction producing 200 keV electrons with a standing-wave architecture where each cell is individually powered by a solid-state transistor. This design also provides an upgrade path for future compact MeV-scale sources on the order of 1 meter in size.

[1] O. Heid and T. Hughes. Compact Solid State Direct Drive RF Linac Experimental Program. In 25th International Linear Accelerator Conference, page THP068, 2011.

[2] D. Nguyen et al. The Path to Compact, Efficient Solid-State Transistor-Driven Accelerators. In Proc. 9th International Particle Accelerator Conference (IPAC’18), pages 520–523

[3] M. A. K. Othman, et al. Solid-state powered x-band accelerator. Technical report, SLAC National Accelerator Laboratory, 2016.

[4] R. S. Pengelly, et al. A review of gan on sic high electron-mobility power transistors and mmics. IEEE Transactions on Microwave Theory and Techniques, 60(6):1764–1783, 2012.

[5] J. Yang. Mev electron diffraction and microscopy in osaka university. In Workshop on Ultrafast Electron Sources for Diffraction and Microscopy Applications, 2012.