Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp

Abstract

The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation.

Conformal Cross-Flow Axis-Encircling Electron Beam for Driving THz Harmonic Gyrotron

“…The electrons are emitted from cathode and helically travel around the z-axis toward the cavity region. In [14], two Busch's theorem [12]- [15] is applied to estimate the parameters of a specified electron trajectory, and given as   …”

“…According to previous studies, using a magnetic cusp gun (MCG) with an axis-symmetrical gradual magnetic reversal is more feasible than other schemes for generating axis-encircling electron beams [5]- [13]. Several factors, including flexible geometry, sensitive electric field, and high magnetic compression ratio, increase the difficulty of suppressing parameter spreads [12]- [13]. This paper proposes a flow-feature compensation principle for building a zero-spread axis-encircling electron beam that is promising for developing high-power high-harmonic terahertz gyrotrons.…”

Numerical Simulation of a Gyro-BWO with a Helically Corrugated Interaction Region, Cusp Electron Gun and Depressed Collector

“…Building on the work of Schmidt et al, continuous efforts and progress have been made through both theoretical analysis and experimental study in the generation of the cusp-based electron beam sources (Destler & Rhee, 1977;Rhee & Destler, 1974). Special attention was paid to methods which can produce an ideal sharp cusp shape by using complex arrays of magnetic coils, magnetic poles and possibly magnetic material inside the cathode (Jeon et al, 2002;Nguyen et al, 1992;Scheitrum et al, 1989;Scheitrum & True, 1981). This culminated in a "state-of-the-art" cusp gun in 2000 by Northrop Grumman (Gallagher et al, 2000) which generated an electron beam of energy 70 kV, current 3.5 A and velocity ratio 1.5 with a small axial velocity spread of 5% at a magnetic field of ∼0.25 T.…”

Experimental verification of low-velocity spread axis-encircling electron beam

“…As stated in previous works, 10 when the gyration of the electron beam before it meets the magnetic cusp is considered, a more general formula expressing the radial position of an electron can be derived. Using it, the axial and perpendicular velocity can be expressed in the region of peak magnetic flux density as a function of parameters describing the intensity of the axial magnetic flux density on the axis, dimensions of the cathode, total beam energy, and the distance between the cathode and the magnetic cusp.…”

“…In the analysis, 10 theoretically, zero percent axial velocity spread could be achieved by choosing an appropriate set of parameters. Based on the theory, a system composed of a Pierce-type 30 kV, 1 A electron gun and a solenoid was designed and a capacitive probe and a pin-hole with a phosphor screen were prepared to measure the velocity ratio ͑perpen-dicular velocity over axial velocity͒ and the axial velocity spread.…”