Electron Cyclotron Maser

Hirshfield, J. L.; Wachtel, J.

doi:10.1103/physrevlett.12.533

Cited by 198 publications

(48 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hirshfield and Bekefi (1963) pointed out that coherent mechanisms could be at work in planetary magnetospheres such as that of Jupiter when they endeavored to explain the observation of Jovian decametric radiation. Hirshfield and Wachtel (1964) actually demonstrated the emission in a laboratory experiment with relativistic electrons. Non-relativistic versions of electron-cyclotron maser emission had been developed in other papers by Gaponov (1959b), Harris (1959) (who suggested that certain non-thermal electron-velocity distributions favor the emission) and Sagdeev and Shafranov (1960).…”

Section: Historymentioning

confidence: 94%

The electron–cyclotron maser for astrophysical application

Treumann

2006

Astron Astrophys Rev

367

383

View full text Add to dashboard Cite

The electron-cyclotron maser is a process that generates coherent radiation from plasma. In the last two decades, it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural hightemperature magnetized plasmas. Originally proposed as a somewhat exotic idea and subsequently applied to include non-relativistic plasmas, the electroncyclotron maser was considered as an alternative to turbulent though coherent wave-wave interaction which results in radio emission. However, when it was recognized that weak relativistic corrections had to be taken into account in the radiation process, the importance of the electron-cyclotron maser rose to the recognition it deserves. Here we review the theory and application of the electron-cyclotron maser to the directly accessible plasmas in our immediate terrestrial and planetary environments. In situ access to the radiating plasmas has turned out to be crucial in identifying the conditions under which the electron-cyclotron maser mechanism is working. Under extreme astrophysical conditions, radiation from plasmas may provide a major energy loss; however, for generating the powerful radiation in which the electron-cyclotron maser mechanism is capable, the plasma must be in a state where release of susceptible amounts of energy in the form of radiation is favorable. Such conditions are realized when the plasma is unable to digest the available free energy that is imposed from outside and stored in its particle distribution. The lack of dissipative processes is a common property of collisionless plasmas. When, in addition, the plasma density becomes so low that the amount of free energy per particle is large, direct emission becomes favorable. This can be expressed as negative absorption of the plasma which, like in conventional masers, leads to coherent emission even though no quantum correlations are involved. The physical basis of this formal analogy between a quantum maser and the electron-cyclotron maser is that in the electron-cyclotron maser the free-space radiation modes can be amplified directly. Several models have been proposed for such a process. The most famous one is the so-called loss-cone maser. However, as argued in this review, the loss-cone maser is rather inefficient. Available in situ measurements indicate that the loss-cone maser plays only a minor role. Instead, the main source for any strong electron-cyclotron maser is found in the presence of a magnetic-field-aligned electric potential drop which has several effects: (1) it dilutes the local plasma to such an extent that the plasma enters the regime in which the electron-cyclotron maser becomes effective; (2) it generates energetic relativistic electron beams and field-aligned currents; (3) it deforms, together with the magnetic mirror force, the electron distribution function, thereby mimicking a high energy level sufficiently far above the Maxwellian ground state of an equilibrium plasma; (4) it favors emission in the freespace RX mode in a direction roughl...

show abstract

Section: Historymentioning

confidence: 94%

The electron–cyclotron maser for astrophysical application

Treumann

2006

Astron Astrophys Rev

367

383

View full text Add to dashboard Cite

show abstract

“…Any escaping radiation is based on the dynamics of electrons. In the electron equation of motion it is bound to the third time derivative ··· v of the electron velocity v. Gyro and synchrotron radiation is thus weak (providing very weak energy losses only), though it is comparably easy to treat (see, e.g., Jackson, 1975) while, when detected, it maps temperature, magnetic field strength and mean plasma density (see, e.g., Rybicki and Lightman, 1979). Guided by the whistler instability, nonthermal radiation in the free space modes X and O from hot plasmas has early on provoked attempts to base it on thermal anisotropies in the electron distribution (Twiss and Roberts, 1958;Hirshfield and Bekefi, 1963;Melrose, 1976;Melrose and White, 1978).…”

Section: Review and Justificationmentioning

confidence: 99%

Electron cyclotron maser instability (ECMI) in strong magnetic guide field reconnection

Treumann

Baumjohann

2017

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guidefield-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales) electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR) in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects) involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is of particular interest in extended turbulent plasmas where reconnection serves as an integral dissipation mechanism of turbulent energy in myriads of small-scale current filaments.

show abstract

“…The feedback of the radiation, in case of a true laser system is usually secured by a Fabry-Perot type linear resonator arrangement. Besides, already in the sixties of the last century, in the context of cyclotron masers [32] and cavity electrodynamics, more general cavity effects have also been studied [33][34]. In the cyclotron maser the fundamental or low harmonics are generated, on the other hand, in the synchrotron radiation very high harmonics are dominant.…”

Section: Introductionmentioning

confidence: 99%

Interference Phenomena and Whispering-Gallery Modes of Synchrotron Radiation in a Cylindrical Wave-Guide

Varró¹

2012

Free Electron Lasers

View full text Add to dashboard Cite

Electron Cyclotron Maser

Cited by 198 publications

References 8 publications

The electron–cyclotron maser for astrophysical application

The electron–cyclotron maser for astrophysical application

Electron cyclotron maser instability (ECMI) in strong magnetic guide field reconnection

Interference Phenomena and Whispering-Gallery Modes of Synchrotron Radiation in a Cylindrical Wave-Guide

Contact Info

Product

Resources

About