High-harmonic Gyrotrons Research Articles

Mode competition in a high harmonic tunable gyrotron

The nature of the competition between a fundamental mode and a second harmonic mode depends on whether their azimuthal mode numbers are the same or different. If they are the same, the second harmonic may aid the excitation of the fundamental and eventually, at high beam currents, be suppressed by the fundamental, if the azimuthal mode numbers are different, the two modes may grow together.

Study of a high harmonic gyrotron with inner slotted coaxial structure

Abstract The interaction between electron beam and wave field of high harmonic gyrotron with inner slotted coaxial structure is analysed and calculated in this paper. The optimum interaction efficiency is numerically illustrated for the 8th cyclotron harmonic TE81 π-mode atf0 = 35GHz. The influence of electron velocity distribution in cusp-injected system, beam voltage, and length of resonator on the efficiency is taken into consideration in numerical calculation. The results show that the inner slotted coaxial structure is good for an increase in the interaction efficiency.

Slow equations of motion for gyrotron and peniotron interactions

In this paper, a new and more general set of slow equations of motion for computing gyrotron (including high-harmonic gyrotron) and peniotron (including both peniotrons, where the orbit is centered on the axis and gyropeniotrons) interactions is derived. These slow equations are convenient to use and allow the interactions to be investigated numerically. They reduce to the correct expressions in the small-signal limit to yield starting currents. Small-signal and large-signal calculations yield results that agree with those of other workers. The equations are used to investigate the gyropeniotron.

Mode competition in a high harmonic gyrotron

Abstract Non-linear theory is used to examine the limits on the maximum power that might be obtained from a high harmonic gyrotron. In particular, special attention is paid to the situation where the power is limited by mode competition from a nearby fundamental resonance. We find good qualitative agreement between theory and some observations made on a high harmonic gyrotron at Fukui University.

Prebunched high-harmonic gyrotron

A scheme for harmonic wave generation using a prebunched electron beam has been demonstrated. The prebunched electron beam has been used to further increase the efficiency of the authors' axis-encircling high-harmonic gyrotron. The proof-of-principle experiment was performed at the third harmonic with a TE/sub 312/ mode at 27.7 GHz. The conversion power of 6.7 kW was significantly greater than that used in the nonprebunched experiment. Also, mode competition was effectively suppressed. As expected, the unsaturated output power is proportional to the square of the electron beam current and the start of oscillation current is essentially zero. A linear theory, derived by taking into account the spread of the guiding center and the spread of the axial velocity, gives good agreement with the experimental results. >

Theory of high-harmonic gyrotron oscillators with slotted cross-section structure

A linear-theory analysis of gyrotron oscillators with slotted cross section is used to calculate the net change in beam energy. In this formalism, geometric factors are clearly distinguished from the geometry-independent harmonic resonance terms due to the fundamental electron cyclotron maser and peniotron interactions. This separation of the interaction terms from the geometric factors simplifiers the physical analysis, and leads to a very compact form for the net change in beam energy. The theory is applied to slotted rectangular oscillators and to slotted cylindrical oscillators to show that a unified expression can be obtained for the start-oscillation condition. In sample applications of the theory, it is demonstrated that slots lower the start-oscillation condition in both cylindrical and rectangular geometries, and can lead to a decrease in this condition as harmonic number is increased in the rectangular geometry. It is also found that the peniotron interaction, which is easily identified in this formalism, may be very strong in slotted cavities. >

Impact of The High-Energy Product Materials on Magnetic Circuit Design

ABSTRACTMany devices that employ magnetic fields are encumbered by massive solenoids with their equally bulky power supplies or by inefficient permanent-magnet structures designed for use with obsolescent magnet materials. This paper describes how the high-energy product materials are employed in several structures to afford mass and bulk reductions of an order of magnitude or more. Also discussed are novel designs that are not attainable with the older materials such as the alnicos. Substitution of solenoids with permanent magnets also eliminates considerable energy consumption and the attendant problems arising from generation of heat. In many cases, all this is accomplished within leakage-free systems. Among the designs described are: nuclear magnetic resonance imagers; cylindrical solenoidal field structures for klystrons and nonperiodic field TWT's; cylindrical field structures with arbitrary axial gradients for advanced gyrating beam sources; annular field sources for high harmonic gyrotrons; helical transverse field sources for circularly polarized radiation sources; miniature periodic permanent-magnet configurations; and clad permanent-magnet circuits for biasing fields in millimeter-wave filters. Where alternate designs exist, they are compared with regard to performance, bulk, and economy. All of the structures are in various stages of design and construction, and, for completed structures, comparisons are made between theoretical projections and actual performance.

Production of relativistic, rotating electron beams by gyroresonant rf acceleration in a TE111 cavity

The rf acceleration of moderate current (≲1 A) electron beams to 500 keV in a TE111 cylindrical cavity resonator is described. Experimental results are compared with theory. rf to beam energy conversion efficiencies in excess of 50% have been observed. The resultant axis-encircling beam with a large ratio of perpendicular velocity to longitudinal velocity is ideal as a driver for a high-harmonic gyrotron.

Non-linear analysis of a high-harmonic rectangular gyrotron

Abstract Non-linear analysis of a gyrotron using an axially grooved rectangular waveguide operating at the high harmonic l of the cyclotron frequency Ωc is given. We use 120 electrons in the simulation of the electron beam. The growth rate, electric field, relativistic factor γ and phase factor are calculated as functions of the slip parameter χ = lΩ0ωγ0 for the chosen optimized operating parameters of the gyrotron. Efficiency of ∼20% in the electron-beam frame is possible for the sixth harmonic of the cylotron frequency which increases to 58% in the second harmonic.

Theory and Numerical Simulation of a TE/sub 111/ Gyroresonant Accelerator

The production of spiral relativistic electron beams in a TE/sub 111/ gyroresonant accelerator cavity for injection into a compact high-harmonic gyrotron is studied. Parametric studies are performed to determine the effects of variations in the background magnetic field amplitude, the RF amplitude in the cavity, and the initial beam voltage on the output beam.The effects of velocity spread and a finite radial extent of the input beam are also discussed. Power curves for obtaining optimum operating regimes for the TE /sub111/ accelerator are provided.

Enhancement of high-harmonic gyrotron gain by a dielectric rod

A dielectric rod is shown to reduce the energy requirements of the electron beam for high-harmonic gyrotron operation. A large interaction filling factor can occur for moderate-energy electrons (∼80 keV) spiralling around the rod within the evanescent region of a dielectric waveguide mode. Since the magnetic field strength is reduced by an order of magnitude in an interaction at the tenth harmonic of the cyclotron frequency, a submillimeter-wave gyrotron is now truly feasible because the acceleration voltages can be conveniently produced by DC power supplies.