Development and optimization of the relativistic klystron amplifier

Serlin, V.; Friedman, M.

doi:10.1109/27.338284

Cited by 34 publications

(10 citation statements)

References 23 publications

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“…Relativistic klystron amplifiers (RKA's) use the self-field of annular intense relativistic electron beams (IREB's) to considerably reduce effects associated with beam stiffness [2,3], but the efficiency is still limited by beam loading, rf breakdown, and the spread in the electron kinetic energies at the gaps.…”

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Efficient Conversion of the Energy of Intense Relativistic Electron Beams into rf Waves

et al. 1995

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A novel relativistic klystron amplifier has achieved 50%%uo energy efficiency, a significant advance over the previous state of the art of 20%%uo. A radially converging structure that was inserted in the output gap reduced the potential energy residing in the electron beam and maximized rf output energy. Electrons that stopped inside the gap were intercepted by this structure and were shunted to ground. This is in contrast to classical klytons in which such electrons would have formed a virtual cathode and/or flow backward, regaining energy from the rf field.PACS numbers: 85.10.Jz, 41.75.Ht A high current "conventional" klystron amplifier has been considered as a candidate for a high power microwave (HPM) source [1]. However, klystrons that operate with high current are inefficient due to space charge effects and the large spread in the electron energy at the output gap. To reduce these effects a high beam voltage is required. But high voltage leads to beam stiffness that can be overcome only by injecting a high rf input power and/or by lengthening the drift region in klystrons.Relativistic klystron amplifiers (RKA's) use the self-field of annular intense relativistic electron beams (IREB's) to considerably reduce effects associated with beam stiffness [2,3], but the efficiency is still limited by beam loading, rf breakdown, and the spread in the electron kinetic energies at the gaps.During the last year, we have developed a new type of RKA [4] that employs cavities with inductively loaded wide gaps. Using these cavities, we eliminated many deleterious effects that plagued the operation of narrow gap RKA's in the past. However, the energy distribution of the electrons at the output gap could not be narrowed down, leading to inefficient operation.The spread in kinetic energy results from the spatial distribution of the potential energy residing in the IREB and from the bunching mechanism. The particle code MASK [5], which successfully simulated the global operation of RKA's [4], was used to obtain microscopic details of the modulated IREB such as density and energy distributions of the electrons [ Fig. 1(a) -1(d)]. To achieve efficient operation of RKA (or any klystronlike devices), the rf voltage across the output gap has to fulfill two conditions that are impossible to satisfy at the same time, especially for a modulated beam with a large energy spread: (1) It has to be low enough to avoid electron reflection that can cause a virtual cathode formation.(2) It has to be high to drain most of the electrons' energy so as to maximize the RF energy output. An energy efficienty of 20% and a power efficiency of 35% were obtained for RKA's at the Naval Research Laboratory [6]; similar efficiencies were obtained at Los Alamos National Laboratory [7] and at Physics International [8].

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Efficient Conversion of the Energy of Intense Relativistic Electron Beams into rf Waves

et al. 1995

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“…[1][2][3][4] However, scaling the RKAs to high frequencies (such as X-band) results in low power and efficiency. The relation between the output power P and the microwave frequency f can be described as P!f À2 (Ref.…”

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confidence: 99%

A non-uniform three-gap buncher cavity with suppression of transverse-electromagnetic mode leakage in the triaxial klystron amplifier

2014

Physics of Plasmas

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The triaxial klystron amplifier is an efficient high power relativistic klystron amplifier operating at high frequencies due to its coaxial structure with large radius. However, the coaxial structures result in coupling problems among the cavities as the TEM mode is not cut-off in the coaxial tube. Therefore, the suppression of the TEM mode leakage, especially the leakage from the buncher cavity to the input cavity, is crucial in the design of a triaxial klystron amplifier. In this paper, a non-uniform three-gap buncher cavity is proposed to suppress the TEM mode leakage. The cold cavity analysis shows that the non-uniform three-gap buncher cavity can significantly suppress the TEM mode generation compared to a uniform three-gap buncher cavity. Particle-in-cell simulation shows that the power leakage to the input cavity is less than 1.5% of the negative power in the buncher cavity and the buncher cavity can efficiently modulate an intense relativistic electron beam free of self-oscillations. A fundamental current modulation depth of 117% is achieved by employing the proposed non-uniform buncher cavity into an X-band triaxial amplifier, which results in the high efficiency generation of high power microwave. V C 2014 AIP Publishing LLC.

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“…[7][8][9][10] However, great challenges still exist in enhancing the efficiency and output power of the traditional RKA devices. [11][12][13] If the cavity gap is too narrow, the RF electric field would exceed the limits for electron emission or breakdown; if the gap is too wide, due to the increasing directcurrent (DC) space-charge potential depression, an electron beam propagating through the empty gap requires a large potential energy and even causes the formation of a virtual cathode. Many promising devices have been proposed to suppress the potential depression, [14][15][16][17] and wide-gap klystron amplifier (WKA) is the most successful one 18,19 which has been studied intensively both in theory and experiment at NRL.…”

Section: Introductionmentioning

confidence: 99%

Design and 3D simulation of a two-cavity wide-gap relativistic klystron amplifier with high power injection

2012

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By using an electromagnetic particle-in-cell (PIC) code, an S-band two-cavity wide-gap klystron amplifier (WKA) loaded with washers/rods structure is designed and investigated for high power injection application. Influences of the washers/rods structure on the high frequency characteristics and the basic operation of the amplifier are presented. Generally, the rod structure has great impacts on the space-charge potential depression and the resonant frequency of the cavities. Nevertheless, if only the resonant frequency is tuned to the desired operation frequency, effects of the rod size on the basic operation of the amplifier are expected to be very weak. The 3-dimension (3-D) PIC simulation results show an output power of 0.98 GW corresponding to an efficiency of 33% for the WKA, with a 594 keV, 5 kA electron beam guided by an external magnetic field of 1.5 Tesla. Moreover, if a conductive plane is placed near the output gap, such as the electron collector, the beam potential energy can be further released, and the RF power can be increased to about 1.07 GW with the conversion efficiency of about 36%. V C 2012 American Institute of Physics.

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Development and optimization of the relativistic klystron amplifier

Cited by 34 publications

References 23 publications

Efficient Conversion of the Energy of Intense Relativistic Electron Beams into rf Waves

Efficient Conversion of the Energy of Intense Relativistic Electron Beams into rf Waves

A non-uniform three-gap buncher cavity with suppression of transverse-electromagnetic mode leakage in the triaxial klystron amplifier

Design and 3D simulation of a two-cavity wide-gap relativistic klystron amplifier with high power injection

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