Acceleration of Electrons by an Electrodynamic Space-Charge Effect
The acceleration method is based on the transfer of the energy of a stream of electrons to the electrons at the front of the stream by virtue of a collective space-charge effect. The apparatus used to demonstrate this effect comprises a cathode at one end of a 214 cm long drift tube, a tubular decelerating electrode at the other end, and solenoidal coils around the grounded drift tube. Under the influence of the magnetic field, produced by these coils, the electrons drawn from the cathode form a cylindrical beam advancing in a screwlike manner towards the electrically insulated decelerator which is negative with respect to the cathode. The increasing magnetic flux and the retarding electric field there stop the arriving electrons. The running on of the succeeding electrons causes the charge density at the front of the beam to grow and the potential to drop until a virtual cathode is formed whose potential is far below that of the decelerator. Electrons ahead of the virtual cathode are accelerated into and through the decelerator. The 2.5 m long instrument, operated with a 20 kV, 350 mA beam, accelerated electrons to energies up to 14 MeV. The energy transfer efficiency was about 1.7 %.
KeywordsFlux Density Magnetic Flux Drift Tube Virtual Cathode Acceleration Method
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