Towards coherent combining of X-band high power microwaves: phase-locked long pulse radiations by a relativistic triaxial klystron amplifier

Abstract

The radio-frequency breakdown due to ultrahigh electric field strength essentially limits power handling capability of an individual high power microwave (HPM) generator, and this issue becomes more challenging for high frequency bands. Coherent power combining therefore provides an alternative approach to achieve an equivalent peak power of the order of ∼100 GW, which consequently provides opportunities to explore microwave related physics at extremes. The triaxial klystron amplifier (TKA) is a promising candidate for coherent power combing in high frequency bands owing to its intrinsic merit of high power capacity, nevertheless phase-locked long pulse radiation from TKA has not yet been obtained experimentally as the coaxial structure of TKA can easily lead to self-excitation of parasitic modes. In this paper, we present investigations into an X-band TKA capable of producing 1.1 GW HPMs with pulse duration of about 103 ns at the frequency of 9.375 GHz in experiment. Furthermore, the shot-to-shot fluctuation standard deviation of the phase shifts between the input and output microwaves is demonstrated to be less than 10°. The reported achievements open up prospects for accomplishing coherent power combining of X-band HPMs in the near future, and might also excite new development interests concerning high frequency TKAs.

Modular Integration of a Compact Ku-Band Relativistic Triaxial Klystron Amplifier Packaged With Permanent Magnets for High-Power Microwave Generation

“…Since the input cavity is the first cavity in a TKA device, the energy stored in it is the lowest among all the cavities. This implies that the input cavity has the lowest fundamental harmonic current modulation ability, and the distance required for electron beams to be sufficiently clustered behind it is also the longest [3,5,27]. Based on the above analysis, enhancing the fundamental harmonic current modulation ability of the input cavity by utilizing the positive feedback coupling of the TEM mode can significantly reduce the axial length of the drift tube after the input cavity.…”

“…To minimize the volume and weight of the permanent magnets, NdFeB-N50M with excellent (BH)max is selected. Its characteristic parameters are as follows [30]: B r > 1.39 T, Hcj > 1114 kA/m, Hcb > 1035 kA/m, (BH)max > 373 kJ/m 3 , and density of 7.55 g/cm 3 .…”

“…Consequently, the equivalent output power density of HPM systems can be rapidly improved by increasing the number of TKA modules. The HPM system of a single TKA module nowadays [3][4][5][6], however, is quite bulky due to the fact that electron modulation and bunching are separated in different regions, and extremely long structures, compared with HPM oscillators [7][8][9], are needed for TKA devices. Besides, the electron beam in TKA devices is constrained by external electromagnetic solenoids.…”

Research on beam‐wave interaction of EIK in THz band

“…With the improvement of design and process level, electric vacuum devices are developing toward high peak power, high frequency, high efficiency, wide frequency band, and compact structure . Electric vacuum devices, such as folded waveguide traveling wave tube, gyrotron, sheet beam klystron, and extended interaction klystron (EIK), have been widely developed in these years.…”

Oversized coaxial output cavity for Ka band relativistic klystron

“…Friedman et al proposed an X band triaxial klystron amplifier (TKA) with a large electron beam diameter for propagating high‐electron beam power and enhancing the power capacity [10]. Based on the TKA structure, simulation and experiments have been conducted to realise a GW‐level microwave output at the X band [11–15]. However, a GW‐level RKA at the Ka band has not been reported because the serious surface electric field breakdown and low electronic efficiency.…”