Frequency up-shift for cyclotron-wave instability on a relativistic electron beam

Hirshfield, J. L.; Chu, K. R.; Kainer, S.

doi:10.1063/1.90209

Cited by 35 publications

(6 citation statements)

References 7 publications

(1 reference statement)

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“…This expression for the growth rate is similar to that of the Weibel cyclotron instability, 9 and is independent of the wiggler amplitude 6B. dominating.…”

supporting

confidence: 55%

“…The field given by Eq. (1) can be generated by driving current azimuthally in alternate directions through a periodic assembly of copper rings;1 8 or by making a series of rings from samarium-cobalt' 9 or other magnetic material and magnetizing the rings in the axial direction as is done in systems employing periodic focusing; 20 or the field can be generated by using the technique of magnetic diffusion 2 , 2 2 in a series of copper rings. The field generated by these methods is a multiple-mirror (undulator) field which at a distance r from the axis is approximately given by h _ i[B 0 + 6B I(kr) sin (koz) -r6BII (kr) cos (koz) (2) with I and It being modified Bessel functions.…”

Section: B = _ [B+ 6b Sin (Koz)|mentioning

confidence: 99%

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Stimulated emission from relativistic electrons passing through a spatially periodic longitudinal magnetic field

McMullin

Bekefi

1982

Phys. Rev. A

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Stimulated emission in the high gain regime from a cold, relativistic beam of electrons gyrating in a combined solenoidal and longitudinally polarized, periodic, wiggler magnetic field is considered as a source of short wavelength radiation. The emitted wave frequency is Doppler upshifted in proportion to the wavenumber of the wiggler magnetic field. Amplification is due to a ponderomotive bunching force acting on the electrons in the transverse and axial directions. Expressions for the linear growth rate are obtained; conditions for their validity, and estimates for the saturated efficiency are given.

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“…This expression for the growth rate is similar to that of the Weibel cyclotron instability, 9 and is independent of the wiggler amplitude 6B. dominating.…”

supporting

confidence: 55%

Section: B = _ [B+ 6b Sin (Koz)|mentioning

confidence: 99%

Stimulated emission from relativistic electrons passing through a spatially periodic longitudinal magnetic field

McMullin

Bekefi

1982

Phys. Rev. A

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“…Application of the cooling mechanism to beams for the recently proposed synchrotron-radiation laser may help to make this device practical at millimeter and (perhaps) optical wavelengths. A variant on the mechanism could apply to an electron beam under autoresonance conditions, 8 and might allow reduction in the spread of the quantity (k z v z -Cl 0 /y), where k z and v z are the axial wave number and electron velocity, respectively. Such a cooling interaction could have important consequences for the…”

Section: D\n(y-y)/dt=-ktmentioning

confidence: 99%

Electron-beam cooling by stimulated synchrotron emission and absorption

Hirshfield¹,

Park²

1991

Phys. Rev. Lett.

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It is shown that stimulated synchrotron emission and absorption can act simultaneously on a relativistic electron beam with a narrow energy spread to reduce the spread significantly. This beam "cooling" mechanism acts most effectively for beam energies belonging to a sequence of discrete values, one for each synchrotron harmonic. The discrete energy values are absolute, and are not influenced by external parameters such as magnetic field strength. Application of this mechanism to cool beams for freeelectron lasers, synchrotron-radiation lasers, and slow-wave cyclotron amplifiers is suggested.PACS numbers: 41.80. Ee, 07.77.+p, 41.70.+t In some applications of electron beams for the generation and amplification of electromagnetic radiation it is desirable to have the smallest possible spread in electron energy or axial velocity. Examples of this include the free-electron laser 1 (FEL) and slow-wave gyrotron amplifiers, 2 where a parallel velocity spread of even a few percent has been shown to be highly detrimental to the achievement of high gain, efficiency, and bandwidth. Another example is in the synchrotron-radiation laser 3 (SRL), where high synchrotron harmonic operation is only possible if the fractional energy spread A 7/7 is less than O -1 , where 0 is the interaction transit angle Inflot/y, with n the synchrotron harmonic number, Sl$ the (rest) electron cyclotron frequency, 7 the relativistic energy factor, and t the interaction time. For a typical mm-wavelength SRL, O is of the order of 500, but for an optical wavelength SRL O could be in the range of 10 6 . A requirement for Ay/y< 10 ~6 may well be beyond the realm of known technology.Therefore, considerable interest could attach to a method of reducing the velocity and energy spread in an electron beam. This Letter outlines a novel method for reducing the energy spread on a gyrating relativistic beam in a strong magnetic field B. The method is based on the fact that the sign of the energy flow from electrons to electromagnetic fields in the cyclotron resonance maser interaction 4 depends upon R^coy/nflo, where co is the (radian) frequency of the electromagnetic radiation field, and il^^eB/m for electrons of charge e and rest mass m. If R is greater than unity, energy flows from the electrons to the fields; and when R is less than unity, energy flows from the fields to the electrons. If electrons with a distribution of energies about some mean value 7 are subjected to the radiation fields, with R set equal to unity for the mean energy, i.e., with co^nClo/y, then one can expect the high-energy electrons to lose energy while the low-energy electronics simultaneously gain energy. This could lead to a decrease in the spread of electron energies, or a "cooling" of the energy distribution function. Under conditions to be described below, it will be shown that the time rate of change of electron energy can be given approximately by the following differential equation: d\n(y-y)/dT=-KT 3(1)where T is the normalized time variable, and K is a constant. The solut...

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“…This paper is concerned exclusively with the properties of a CARM as a single pass amplifier. Preliminary studies on this device were reported earlier 2 …”

Section: Introductionmentioning

confidence: 99%

“…This paper describes an experimental and theoretical study of a CARM amplifier operating in the fundamental 1 = 1 mode, with the view of using this or a similar device as a potential driver of the Berkeley-Haimson high gradient acceleration (HGA) test stand 2 4 . The experiments are performed at a radiation frequency of 35 GHz using a mildly relativistic electron beam with an energy of 1.…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical studies of a 35 GHz cyclotron autoresonance maser amplifier

DiRienzo

Bekefi

Chen

et al. 1991

Physics of Fluids B: Plasma Physics

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Experimental and theoretical studies of a cyclotron autoresonance maser (CARM) amplifier are reported. The measurements are carried out at a frequency of 35GHz using a mildly relativistic electron beam (1.5 MeV, 130A, 30 ns) generated by a field emission electron gun followed by an emittance selector that removes the outer, hot electrons. Perpendicular energy is imparted to the electrons by means of a short bifilar helical wiggler. The entire system is immersed in a uniform axial magnetic field of 6-8 kG. With an input power of 17 kW at 35 GHz from a magnetron driver, the saturated power output is 12 MW in the lowest TE 1 1 mode of a circular waveguide, corresponding to an electronic efficiency of 6.3%. The accompanying linear growth rate is 50 dB/m. When the system operates in the superradiant mode (in the absence of the magnetron driver) excitation of multiple waveguide modes is observed. A threedimensional simulation code that has been developed to investigate the self-consistent interaction of the copropagating electromagnetic waveguide mode and the relativistic electron beam is in good agreement with the experimental observations.

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Frequency up-shift for cyclotron-wave instability on a relativistic electron beam

Cited by 35 publications

References 7 publications

Stimulated emission from relativistic electrons passing through a spatially periodic longitudinal magnetic field

Stimulated emission from relativistic electrons passing through a spatially periodic longitudinal magnetic field

Electron-beam cooling by stimulated synchrotron emission and absorption

Experimental and theoretical studies of a 35 GHz cyclotron autoresonance maser amplifier

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