Generation of a cold, intense relativistic electron beam using a magnetized foilless diode

Abstract

An annular electron beam with less than 30 mrad of angular velocity spread, a radius of 1 cm, and a current density exceeding 0.4 MA/cm2 has been generated with a magnetized foilless diode. The diode current loss is limited to less than a few percent by careful design of the tapered transition region connecting a self-magnetically insulated vacuum transmission line to the externally magnetized foilless diode. Details of the transition section design and operating characteristics of the electron beam generator are given.

Current loss of magnetically insulated coaxial diode with cathode negative ion

“…Consequently, there was no such reverse current loss as described in Refs. [7], [11], and [12]. The outer radius of the annular graphite cathode R c was 2.8 cm with a blade width of 0.15 cm.…”

“…[9,10] Some researchers found that the reverse electron current could cross the diode anode and cathode gap (A-C gap) and be absorbed by the anode in the diode transition region, resulting in the reverse current loss. [7,11,12] The others considered that the extra electron emission occurred on the external ring of a shield hoop, which leads to a parasitic current loss especially when the reverse current flows on the shield hoop. [13] The above current losses all appearance with the diode impedance collapsing.…”

Thomson Backscattering from an Intense Relativistic Electron Beam as a Diagnostic for a Free Electron Laser

“…(1 KA/cm-^ )is dense enough , while the energy spread from all sources (Section I-D) should be held to a value below 2 %. (McDermott, 1978;Sheffield et al, 1982) or by aperturing (Jackson, 1983). We want to know if the beam thereby generated has adequate quality for a Raman FEL.…”

Simulative research on reverse current in magnetically insulated coaxial diode

“…The reverse electrons phenomenon is unavoidable for MICDs in the transition region before the uniform axial magnetic field, namely, a portion of electrons which stem from the stray emission on the cathode move in cycloidal orbits following a magnetic force line in a direction opposite to the downstream primary electron flow. [1][2][3][4] Apart from energy loss in some cases, 5 it would cause issues concerning surface flashover once the reverse electrons bombard the insulator, which leads to the decline of the insulator longevity and the vacuum contamination. 1,6,7 Thus a shield hoop is introduced to protect the insulator from this bombardment.…”