Magnetic quadrupole formation of low-voltage sheet electron beams for high-power microwave devices

Summary form only given. Sheet electron beams have the potential to make possible higher power sources of microwave radiation due to their ability to transport high currents, at reduced current densities, through a single narrow RF interaction circuit. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, grating TWTs, and planar FELs. One difficulty with the experimental investigation and implementation of sheet beams is the lack of a satisfactory source for large aspect-ratio beams. An attractive solution is the use of magnetic quadrupoles to transform an initially round beam from a conventional Pierce gun into a highly eccentric elliptical beam. Both 2-D envelope simulations and 3-D envelope and PIC code simulations indicate that this is a viable method of sheet beam formation, particularly for experimental investigations where flexibility and low-cost fabrication is desired. We are currently constructing a system to experimentally test this method. Features of the experiment include a low-cost commercially available Pierce gun (10 kV, 2 A, r/sub b/=0.3 cm), a four quadrupole sheet beam-forming system (R/sub q/=4 cm, B/sub q//R/sub q/<60 g/cm, L/sub q/=3 cm), and an highly elliptical output beam (a=2.7 cm, b=0.1 cm). Results of the 3-D PIC simulations of the beam and 3-D magnetostatic finite-element simulations of the quadrupole fringe fields will be discussed. Details of the experimental design and initial experimental measurements will be presented.