An efficient magnetron transmitter for superconducting accelerators

Abstract

Various methods of phase and power control in magnetron RF sources of superconducting accelerators intended for ADS-class projects were recently developed and studied with conventional 2.45 GHz, 1 kW, CW magnetrons operating in pulsed and CW regimes. Magnetron transmitters excited by a resonant (injection-locking) phasemodulated signal can provide phase and power control with the rates required for precise stabilization of phase and amplitude of the accelerating field in Superconducting RF (SRF) cavities of the intensity-frontier accelerators. An innovative technique that can significantly increase the magnetron transmitter efficiency at the widerange power control required for superconducting accelerators was developed and verified with the 2.45 GHz magnetrons operating in CW and pulsed regimes. High efficiency magnetron transmitters of this type can significantly reduce the capital and operation costs of the ADSclass accelerator projects.

Resonant interaction of the electron beam with a synchronous wave in controlled magnetrons for high-current superconducting accelerators

“…To further explore the observed phenomenon, a simplified analytical model has been developed that considers the phase grouping of the Larmor electrons drifting towards the anode. The grouping is caused by the synchronous wave excited in the magnetron [15]. The model substantiated a novel method of power control in magnetrons over a wide range.…”

“…A proof of principle of the novel method providing the highest generation efficiency, low noise, and precise stability was demonstrated in experiments with 2.45 GHz, 1 kW, and CW magnetrons [15]. The method provides a significantly higher average magnetron efficiency at a range of power control up to 10 dB and with wideband phase control.…”

“…Substituting the potential Φ S into Eq. (3) and denoting ϕ 0 ðrÞ ¼ ln r r 1 − 1 2 ð r r S Þ 2 and ϕ 1 ðrÞ ¼ 1 2n ½ð r r 1 Þ n − ð r 1 r Þ n , one can obtain the system of drift equations [17,15] in the frame of the synchronous wave expressed via the relative magnitude of the resonant harmonic of the synchronous wave, ε, taken at the cathode:…”

“…Equation (4) were integrated for a typical model of a commercial magnetron described in Ref. [15] with N ¼ 8,…”

“…Moreover, the acceleration of the lost charge increases the Larmor radius of the rotating electron which may hit the cathode increasing the magnetron cathode losses. For the typical magnetron model [15], the losses of the drifting charge coherently contributing to the synchronous wave are minimized at ε ∼ 0.3 in the main part of the charge drift trajectories. Thus, a sufficient magnitude of the synchronous wave protects from loss of coherency and prevents an increase of the cathode losses even at low magnetron power.…”