Electron orbits in the microwave inverse FEL accelerator (MIFELA)

The MIFELA is a new device based on stimulated absorption of microwaves by electrons moving along an undulator. An intense microwave field is used (as = eEsksmc2 = 0.2 as well as a large undulator field (awγ = eBwγkwmc2 = 12) to accelerate electrons emitted at 6 MeV from a rf gun to 15 MeV in 1.5 m. The spiral radius of the electrons in the undulator is 7 mm, in a waveguide of diameter 28 mm, with the undulator period about 10 cm. There is a small guiding field, and the electrons move in type I orbits. We describe three problems connected with the orbital motion of electrons in this structure: (i) injecting the electrons in an increasing undulator field prior to entering the MIFELA; (ii) orbital motion and stability inside the MIFELA; (iii) extraction of electrons from the spiral orbit in the accelerator into an axially-propagating beam, obtaining βw < 0.02 at 15 MeV. These studies have application to a MIFELA which is under construction at Yale University by Omega-P, Inc.