Three new tutorials are available in the technical library that describe design studies for a hollow-beam, high-power klystron. The documents include material of general interest to anyone interested in high-current electron beam technology.
In the case study, an annular electron beam with kinetic energy 100 keV and power 20 MW power is generated from an immersed cathode in a solenoid field of amplitude 0.1 tesla. The motivation for a hollow beam is to reduce the space-charge potential for a given current, and hence to minimize the longitudinal energy spread. The reduced-energy beam leaving the klystron is captured in a biased collector to recover power.
The following three documents are available in our technical library:
Electron gun design for a hollow-beam klystron using Trak
PerMag design of a focusing magnet for a hollow-beam klystron
Trak design of a single-stage collector for a hollow-beam klystron
Some of the technical issues discussed:
- Design of a hollow-beam gun with no internal anode structure to generate the required current at the operating voltage. Two goals are to minimize 1) the electric field stress on the surface of the focusing electrode and 2) the transverse spread energy of the extracted beam.
- Requirements on magnetic field uniformity for transporting a hollow beam. Determining coil currents in a finite-length solenoid to maximize the field uniformity and the length of the good-field region. Discussion of the role of shielding iron to improve uniformity and to minimize the drive current.
- Review of the energetics of biased collectors in electron beam systems for microwave generation. Concepts for electrostatic collectors in a region of expanding magnetic field. Determining energy efficiency and properties of reflected electrons.
Annular-beam electron run, r-z plot