Theory of relativistic cyclotron masers

Nusinovich, G. S.; Latham, P.E.; Dumbrājs, O.

doi:10.1103/physreve.52.998

Cited by 19 publications

(6 citation statements)

References 36 publications

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“…We should also mention that a cyclotron-Cherenkov instability of an electron beam propagating along a magnetic field is known in the laboratory as a very effective source of the high frequency microwave radio emission (Galuzo et al 1982, Didenko et al 1983, Nusinovich et al 1995. The so called slow-wave electron cyclotron masers (ECM) provides a high efficiency and high power microwave source.…”

Section: Introductionmentioning

confidence: 99%

On the nature of pulsar radio emission

Lyutikov¹,

Blandford²,

Machabeli³

1999

Monthly Notices of the Royal Astronomical Society

100

106

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A B S T R A C TA theory of pulsar radio emission generation, in which the observed waves are produced directly by maser-type plasma instabilities operating at the anomalous cyclotron±Cherenkov resonance q À k k v k q B = g res 0 and the Cherenkov drift resonance q À k k v k À k ' u d 0, is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the interaction of the fast particles from the primary beam and the tail of the distribution with the normal modes of a strongly magnetized one-dimensional electron± positron plasma. The waves emitted at these resonances are vacuum-like, electromagnetic waves that may leave the magnetosphere directly. In this model, the cyclotron±Cherenkov instability is responsible for the core-emission pattern and the Cherenkov drift instability produces conal emission. The conditions for the development of the cyclotron±Cherenkov instability are satis®ed for both typical and millisecond pulsars provided that the streaming energy of the bulk plasma is not very high g p < 10. In a typical pulsar the cyclotron± Cherenkov and Cherenkov drift resonances occur in the outer parts of the magnetosphere at r res < 10 9 cm. This theory can account for various aspects of pulsar phenomenology, including the morphology of the pulses, their polarization properties and their spectral behaviour. We propose several observational tests for the theory. The most prominent prediction is the high altitudes of the emission region and the linear polarization of conal emission in the plane orthogonal to the local osculating plane of the magnetic ®eld.Key words: plasmas ± radiative transfer ± waves ± pulsars: general. I N T R O D U C T I O NMore than 25 years have passed since the discovery of pulsars and there is still no consensus on the basic emission mechanism. At the present time, there are about 12 competing theories, which differ both in the physical effects responsible for the radiation and in the locations where they operate (Melrose 1995). Probably the only point of agreement between all these theories is the association of pulsars with magnetized, rotating neutron stars. By contrast, there is so much observational data available that none of the existing theories can explain all the main observational facts. A useful observational framework for discussing the theory is a description of pulsar radio emission given by Rankin (1990). The main feature of this model is the division of emission into two main classes: core and cone. There may be many cones of emission. In each pulsar the averaged pro®le may be a combination of core and/or cone emissions (Fig. 1).To date, the most widely discussed theory attributes the emission to coherent curvature emission by bunches of particles. Although this theory can explain a broad range of observed pulsar properties by the careful arrangement of the magnetic ®eld geometry and the form and size of bunches, 30 years of theoretical efforts have failed to explain the origin of these bunches (Melrose 1995). This ...

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Section: Introductionmentioning

confidence: 99%

On the nature of pulsar radio emission

Lyutikov¹,

Blandford²,

Machabeli³

1999

Monthly Notices of the Royal Astronomical Society

100

106

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“…The numerical studies of slow‐wave ECM conversion efficiency, including Gaussian beam velocity spread, were presented in Refs. . In Refs.…”

Section: Introductionmentioning

confidence: 99%

A scheme to enhance the conversion efficiency of slow‐wave electron cyclotron masers in the large signal approximation

Zhang

Wang

et al. 2018

Contributions to Plasma Physics

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Based on the anomalous Doppler effect, we propose a scheme to improve the practicability of slow-wave electron cyclotron masers in the large signal approximation. This scheme simultaneously contains the tapered guiding magnetic field and tapered refractive index. Numerical calculations show that this scheme enables the conversion efficiency to reach a higher value within a shorter time than previous schemes. Besides, this scheme also works well in the cases of THz wave band and beam axial-velocity spread. KEYWORDSconversion efficiency, electron cyclotron maser, tapered guiding magnetic field, tapered refractive index INTRODUCTIONThe electron cyclotron maser (ECM), which is based on the stimulated cyclotron emission process involving energetic electrons in gyrational motion, has undergone a remarkably successful evolution from theoretical research to device implementation. Nowadays, ECM-based devices are important, coherent, high-power microwave sources, which have numerous applications in plasma diagnostics, particle accelerators, advanced radars, and industrial processing. [1][2][3][4][5][6][7][8] The resonance condition of the ECM is = k z v z + sΩ, in which , k z , v z , s and Ω = eB/m 0 c are the microwave angular frequency, axial wave number, axial velocity of electron, harmonic numbers, and relativistic electron cyclotron frequency, respectively. For the gyro-devices, resonance occurs at positive cyclotron harmonics (s > 0) in the normal Doppler effect. The gyrating electrons interact with a fast wave in the presence of a strong guiding magnetic field. The coherent radiation is produced by decelerating the rotational component of the electron beam velocity. It is applied to the coherent microwave or millimetre wave radiation sources. [9][10][11][12] Contrarily, for the resonance occurring at negative cyclotron harmonics (s < 0) in the anomalous Doppler effect, the axial velocity of the electrons exceeds the wave phase velocity, and the radiation is produced by decelerating the axial component of the electrons velocity. Due to this interaction mechanism, the slow-wave ECM has some distinctive advantages. Firstly, the initially rectilinear straight beam operated in the slow-wave ECM can be easily generated by a Pierce electron gun with a high-quality beam, as has been confirmed by the experiments. Secondly, there is no need for a strong guiding magnetic field, and the tolerance of the beam velocity spread is better than gyro-devices. Besides these reasons, the slow-wave ECM has the potential to induce a large frequency upshift with a moderate arrangement of the initial axial velocity of the beam and the guiding magnetic field, so the broadband width is attainable. The studies on the slow-wave ECM are highlighted. As the equations that describe the interaction between electrons and electromagnetic field are too complicated to be solved exactly, the large signal approximation method is applied. In this approximation method, the amplitude of the electric field in the electromagnetic wave is assumed to be large, ...

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“…When an EM wave of large amplitude and electrons of relativistic initial energy interact, the electron cyclotron frequency can vary significantly in the process, which may lead to the overlapping of cyclotron resonances at different harmonics [3]. The current study shows that this resonance overlap, which is similar to one known in the theory of dynamic systems as Chirikov criterion [I], may cause electrons to exhibit stochastic trajectories.…”

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confidence: 74%

The design of space-charge limited MIGs with control grids for gyroklystron applications

Lawson

Raghunathan

The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts.

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At the University of Maryland we have been investigating the designs of Space-charge-limited (SCL) Magnetron Injection Guns (MIGs) as potential replacements for temperature-limited (TL) MIGs, which can suffer from non-uniform azimuthal current density dismbutions due to thermal and work-function variations. Preliminary designs indicate that the same beam-quality can he achieved with only a slight cost in terms of required peak electric fields and cathode loading densities.['I One objection to these devices has been that you lose some control of the beam current which is available with TL MIGs. In this paper we address this issue, in part with parameter studies of the SCL MIG designs, and in part with the design of SCL MlGs with control grids.Two different designs with non-intercepting control grids are presented. The first design has small grids with low capacitance that can be adjusted hy a few percent of the main beam voltage to adjust the current by +/-20%. The second design has larger control grids that can be biased sufficiently to actually cut off the beam flow even when the full beam voltage is applied.For many applications of relativistic gyro-devices the ultimate goal is to achieve the highest possible coherent electromagnetic (EM) power from the interaction of gyrating electrons with EM waves. When an EM wave of large amplitude and electrons of relativistic initial energy interact, the electron cyclotron frequency can vary significantly in the process, which may lead to the overlapping of cyclotron resonances at different harmonics [3]. The current study shows that this resonance overlap, which is similar to one known in the theory of dynamic systems as Chirikov criterion [I], may cause electrons to exhibit stochastic trajectories. In this work, the particular case of electrons interacting with an initial resonant second harmonic field is considered. The study shows that depending on whether electrons lose or gain energy in the process of interacting with the large magnitude EM field their cyclotron frequency shifts from being close to the second harmonic towards fundamental or third resonant harmonic. Therefore, these particles can interact with the field at several harmonics simultaneously. It is shown that in the process of this interaction, electrons can exhihit stochastic orbits. This might explain why previous studies [2,4] which were focused on isolated cyclotron resonance failed to observe this effect.A number of parametric studies are presented, all with the basic goal of achieving a 500 kV, 500A beam for our Ku-Band frequency-doubling gyroklystron experiment for accelerator applications.[I] W. Lawson, H. Raghunathan, and M. Esteban, to he published June 2004 in IEEE Trans. Plasma Sci. This work is supported by the Division of High Energy Physics at the US depaltment of Energy.1.

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Theory of relativistic cyclotron masers

Cited by 19 publications

References 36 publications

On the nature of pulsar radio emission

On the nature of pulsar radio emission

A scheme to enhance the conversion efficiency of slow‐wave electron cyclotron masers in the large signal approximation

The design of space-charge limited MIGs with control grids for gyroklystron applications

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