On the limiting current of a relativistic electron beam in a vacuum

The results of parameter calculations of high-current tube electron beam, propagating in a vacuum channel in an external longitudinal magnetic field are given. The hydrodynamic model of a beam, the inner radius of which is intended to be constant and equal to the radius of the cathode generating the beam; the outer radius is chosen according to passing current maximum. Magnetic flux in the channel is considered as constant and equal to the external flux. It is shown, that beam propagation is possible, when induction of the external field is above some boundary value Bsub(bound). Calculation dependences of a boundary field and maximum passing current on electron energy as well as inner beam radius ratio and channel radius are presented. The calculation results and the experimental data are compared. During the experiments a coaxial cylindric diode in a homogeneous field and a conic diode placed in the decreased field region were used. Diod coltage was 300-500 kV, magnetic field strength changed from 0 to 80 kgs, passing current was 5-12 kA. Experimental dependences of passing current on a magnetic field had maximum at B approximately Bsub(bound), which well agreed with calculated one, and a sharp drop in field decrease less than Bsub(bound), the steeper the longer transport section was. The inner and external beam radii measured by autographs agree well with calculated ones as well