Experiment on pulse heating and surface degradation of a copper cavity powered by powerful 30 GHz free electron maser

Abstract

Experiments to investigate copper surface fatigue caused by pulsed rf radiation were carried out using the 30 GHz free electron maser. The copper surface of a special test cavity was exposed to 15-20 MW=150-200 ns rf pulses with a repetition rate of 1 Hz, providing a temperature rise of up to 250 C in each pulse. An electron microscope was used to study the copper surface both before and after exposure to 10 4-10 5 rf pulses. An examination of the copper microstructure and cracks which developed during the experiment was made. Dramatic degradation of the copper surface and causes of very frequent breakdown were observed when the total number of rf pulses reaches 6 Â 10 4 .

Peculiarities of the Mode Spectrum in Free-Electron Masers Based on Oversized Bragg Resonators with a Corrugation Phase Step

“…Modeling shows [19,20] that this regime is optimal from the viewpoint of reducing the sensitivity to the parameter spread of relativistic electron beams and, correspondingly, achievement of a high electronic efficiency. This was confirmed in the previous experimental studies of the FEM oscillator [1,2].…”

“…According to condition (2), this corrugation provided an effective Bragg reflection zone for a pair of TE 1,1 ↔ T M 1,1 waves near the frequency 30 GHz. The length of the input section (located on the cathode side) was l 1 = 20 cm, the length of the output (collector) section was l 2 = 15 cm, and the corrugation phase jump at the place of conjugation of the sections amounted to π.…”

“…The Bragg scattering zones for different pairs of partial waves satisfying condition (2) are spaced from each other if the detuning of the chosen pairs of waves with the wave numbers h + and h − from other waves with the wave numbers h i , for which condition (2) is fulfilled, exceeds considerably the corresponding coupling coefficients α i :…”

“…The main requirement to this source of radiation is provision of a high pulse power and stable narrow-band oscillation. To achieve the indicated parameters in the FEM oscillator developed at the JINR and IAP RAS [1,2], the inverse guiding magnetic field regime was used for the first time [3,4]. A Bragg resonator in the form of two sections of a corrugated waveguide with the corrugation phase jump π at the place of their conjunction (the so-called corrugation phase-jump resonator, see Fig.…”

Powerful narrow-band relativistic masers with Bragg resonators operating from mm to sub-mm wavelength band: resent results and prospects

“…The radiation parameters achieved allows JINR-IAP FEM to be used in several applications including testing of components for highgradient accelerators, biology-medical studies, physics of nanoparticles, etc [2]. The aim of present work is development of narrow-band relativistic masers operating up to sub-mm wavelength bands at MW/multi-MW power level for potential applications.…”