Generation of high-brightness electron beams with microfabricated field-emitter arrays

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Electron beams were extracted from microfabricated field-emitter arrays (FEA), accelarated up to 6 keV,and propagated over a distance of 1 m. Emittances of both the beam and beamlets were measured. The research concerned the following subjects :1. Study of FEA performance : Characteristics of FEAs (the Spindt cathodes and microtriode arrays) were investigated. The current density on the cathode surface reached 40 A/cm^2 in 1 s regime. Microtriode arrays demonstrated the generation of parallel beam.2. Stabilization and active control of emission current : A field effect transistor, introduced in series with the base of FEA,successfully stabilized and controlled the emission current.3. Long range propagation of the beam : Electron beams extracted from the Spindt cathodea were propagated over 1 m and projected on a fluorescent screen. There a magnified image of the FEA was formed and separate images ofthe tips were observed saparately.4. Emittance measurement : An electrostatic quadrupole lens was utilized to measure the emittance by elongating the image on the screen. Normalized emittances of the order of 10^<-7> m-rad and 2 x 10^<-9> m-rad were obtained for beams from high-current-density model Spindt cathodes and a beamlet therefrom, respectively.5. Beam brightness : FEAs were damaged when the current density exceeded 40 A/cm^2 even in the pulsed mode. For this reason, the effort to increase the beam brightness has been suspended.6. Improvement of FEAs : Collimated beams generated by microtriode arrays suffered from severe deflection due to stray electric fields at the exit. New FEAs, axi-symmetric in electrode configuration, are now being fabricated by our collaborators.