Generation of Emissions by Fast Particles in Stochastic Media

Fleishman, Gregory D.

doi:10.1007/3-540-33203-0_4

Cited by 4 publications

(3 citation statements)

References 19 publications

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“…Similarly high brightness temperatures in the radio emission have been found for flare stars (Kuijpers 1985;Benz et al 1998;Stepanov et al 2001), dwarf M stars (Lang et al 1983;Lang 1994), and recently in the bursty radiation of T Tauri stars (Smith et al 2003). In addition, the fine structure of solar type IV radio bursts has often been attributed to maser action [cf., for instance, the reviews by (Aschwanden 1990a,b;Bastian et al 1998;Fleishman et al 2003;Fleishman 2006)]. This might or might not be the case.…”

Section: Exoplanetsmentioning

confidence: 99%

The electron–cyclotron maser for astrophysical application

Treumann

2006

Astron Astrophys Rev

379

383

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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...

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Section: Exoplanetsmentioning

confidence: 99%

The electron–cyclotron maser for astrophysical application

Treumann

2006

Astron Astrophys Rev

379

383

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“…For example, if a turbulent magnetic field is composed of random waves, then the ensemble of these waves results in an incoherent superposition of random Lorentz forces which produces a stochastic electron trajectory quite different from the circular orbit in the regular field. To correctly calculate the emission spectrum in such a case requires not only averaging over the regions of different field strengths and orientations but also over the many possible particle paths (Toptygin and Fleishman 1987;Fleishman 2005), since the microscopic nature of the particle path strongly influences the spectrum, as we have already pointed out when compared synchrotron radiation and bremsstrahlung. This problem is highly nonlinear: in addition to the electron path affecting the nature of the emission, electrons are efficiently mirrored from regions of high magnetic field and thus spend a disproportionate time in the regions of lower field.…”

Section: Diffusive Synchrotron Radiationmentioning

confidence: 99%

“…Here, without derivation, we present expressions valid when either the random field is weaker than the regular magnetic field or the deviation of the particle trajectory from the straight line (due to effect of the regular magnetic field) is small over the correlation length of the random field (Toptygin and Fleishman 1987;Fleishman 2005):…”

Section: Superposition Of Regular and Random Fieldsmentioning

confidence: 99%

Cosmic Electrodynamics

Fleishman

Топтыгин

2013

Astrophysics and Space Science Library

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Computation of Synthetic Spectra From Simulations of Relativistic Shocks

Reville

Kirk

2010

ApJ

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Particle-in-cell (PIC) simulations of relativistic shocks are in principle capable of predicting the spectra of photons that are radiated incoherently by the accelerated particles. The most direct method evaluates the spectrum using the fields given by the Liénard-Wiechart potentials. However, for relativistic particles this procedure is computationally expensive. Here we present an alternative method, that uses the concept of the photon formation length. The algorithm is suitable for evaluating spectra both from particles moving in a specific realization of a turbulent electromagnetic field, or from trajectories given as a finite, discrete time series by a PIC simulation. The main advantage of the method is that it identifies the intrinsic spectral features, and filters out those that are artifacts of the limited time resolution and finite duration of input trajectories.

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Generation of Emissions by Fast Particles in Stochastic Media

Cited by 4 publications

References 19 publications

The electron–cyclotron maser for astrophysical application

The electron–cyclotron maser for astrophysical application

Cosmic Electrodynamics

Computation of Synthetic Spectra From Simulations of Relativistic Shocks

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