Transient operation of the relativistic S-band magnetron with radial output

Abstract

The influence of the time-varying accelerating voltage and electromagnetic waves reflected from the output window of the antenna on the operation of a relativistic S-band magnetron with radial output is analyzed. It is shown that within the range of radiation frequencies generated by the magnetron, the antenna with the dielectric window and feed waveguide can be considered as a resonant load. Depending on the phase relations between the reflected electromagnetic waves and those traveling in the magnetron, minimal coupling between the magnetron cavities adjacent to the place of microwave extraction can be realized. In this regime, the magnetron represents an open-end chain of coupled cavities and maintains the effective interaction of the electron flow and generated electromagnetic wave at a decreasing voltage. As the drift velocity of electrons decreases and its difference from the electromagnetic wave phase velocity increases, the microwave frequency changes. The changed frequencies do not necessarily belong to and are not limited by the discrete spectrum of closed resonant ring waveguide structures.

Self-Injection-Locked Magnetron as an Active Ring Resonator Side Coupled to a Waveguide With a Delayed Feedback Loop

“…It had been shown 4-8 that ILMs and SILMs are able to fix the operating frequency and phase, and essentially decrease the noise of the radiation. 9,10 show that the efficiency of the relativistic S-band magnetron can be significantly (up to 40%) increased when part of the radiated electromagnetic power is reflected into the magnetron cavity. This effect, to our knowledge, has not yet been discussed.…”

Comparative analysis of radial and axial power output in relativistic magnetron and effect of dielectric side-walls introduced in the resonator on dominant operating mode

“…There is a significant influence of the structural aspect ratio, α in selecting the mode of operation. Generally accepted [13] criteria is that small α devices (α < 1) tend to operate in single mode at π-mode frequency. The tendency to operate in multimode grows at higher α-values, and large-α devices can simultaneously support a number of different modes including π and 2π, etc.…”

S-band microwave radiation by a high-impedance diode with an A6 anode block

“…[11][12][13] Earlier research [14][15][16] of high-impedance (!50 X) RMs with radial microwave power output showed its high microwave power efficiency ($60%). Recently, [17][18][19][20][21] we demonstrated the increase in the microwave pulse duration up to $150 ns with the same high efficiency. However, for long (!100 ns) microwave pulses, RMs have some specific features not typical to conventional magnetrons.…”

“…However, for long (!100 ns) microwave pulses, RMs have some specific features not typical to conventional magnetrons. Namely, the power of the microwave pulses and the frequency vary significantly with very small changes in the reflection coefficient of the microwaves from the load; 19 the microwave generation continues despite a significant decrease (to a half) in the applied voltage and the microwave frequency drifts (by $10%) relative to their value at the beginning of the oscillations. [20][21][22] In addition, in RM experiments 10 with multi-channel microwave output, the power radiated from the open resonant cavities adjacent to closed cavities was found to depend on the direction of the external axial magnetic field.…”

“…19, it was suggested that when the microwave power is obtained from a single open cavity connected with negligible reflections to a linearly expanding waveguide, the high impedance RM can be considered as an open-end chain of cavities with effective interaction of the electron flow and the electromagnetic wave at a lower voltage. In the present paper, we study the same RM 19 and we report direct measurements of the high-frequency magnetic field inside the resonant cavities during the operation of the RM. A Linear Induction Accelerator (LIA) produces output pulses with the duration at a FWHM (Full Width Half Maximum) of s $ 150 ns and voltage and current amplitudes of U 350 kV and I 3 kA, respectively.…”