Amorphous NEA Silicon Photocathodes-A Robust RF Gun Electron Source

In radio frequency (RF) guns with a thermionic cathode, electrons are free to leave the cathode at non-optimal phases of the RF field. These electrons can be accelerated backwards and impact the cathode. Such back-bombardment generates an additional heat load on the gun and cathode, which may limit the current available from the cathode. Consequently, thermionic cathode RF guns are not able to supply the high-phase-space densities required for the operation of a short-wavelength free energy laser (FEL). This project will investigate the use of negative-electron-affinity amorphous silicon as a photocathode suitable for RF gun systems. The advantages of amorphous silicon include a high degree of immunity to charged particle flux, low thermal emittance, bandgap tunability when grown in quantum dot form, and low production cost. In Phase I, measurements will be conducted on amorphous silicon to determine the activation procedure, photoresponse, and charged particle (in)sensitivity. Single crystal silicon will be used as a baseline and benchmark, against which the amorphous silicon activation procedure will be compared and contrasted. Commercial Applications And Other Benefits as described by the Applicant: Cw accelerators, such as energy recovery linacs, should find amorphous-silicon-based RF photoinjectors very inviting. Other potential applications include FELs, along with other uses that require the lowest possible source emittance. Finally, reliable, low-cost photocathode-driven RF gun systems could become ready replacements for the diode and triode guns used on medical accelerators for the production of clinical photon beams and therapy electron beams