Comparative Study of Collectors for High-Power Gridless Inductive Output Tube

Gridless inductive output tube (IOT) amplifiers allow for multi-megawatt power generation, with compact size, moderate gain, and long operational lifetime. The beam collector is at risk of damage and surface erosion when subject to intense electron beams. Beam collectors with small internal surface areas are susceptible to surface plasma effects. Moreover, adequate water cooling is necessary at megawatt power. This article presents a comparative study of IOT collectors, subject to a high-energy 0.1-MeV annular electron beam. Three designs of copper collectors are presented and compared. Namely, a flat beam dump, a tapered conical collector, and a two-stage depressed collector. Surface plasma formation is characterized using the continuous slowing down approximation (CSDA) model for 5-
$\mu$
s device operation. Temperature distributions are obtained using coupled particle–thermal simulations in CST Studio. The heat transfer coefficient is calculated using the Nusselt number for water cooling. Results show that a cylindrical beam dump is generally inefficient under repetitive pulsed operation, with 181 J/g energy dose, and temperatures exceeding 1000
$^\circ$
C at the incident surface. The conical collector shows temperatures below 700
$^\circ$
C, and energy dose below the safe limit of 100 J/g if the surface area is higher than 49.5 cm
$^2$
. Finally, the two-stage depressed collector with 43.3% collector efficiency is simulated with a 20-kV potential at the second stage. It shows the lowest average temperature, remaining below 550
$^\circ$
C, with an electron energy dose of 19 J/g.