The Loss-cone Driven Electron-cyclotron Maser

Abstract

Electron-cyclotron instabilities may be classified in two ways depending on whether the relativistic correction to the gyrofrequency is important (class S) or not (class N), and whether the instability mechanism is of a maser type (class M) or due to bunching (class B). Renewed interest in class SM has followed the Wu and Lee application of it to the interpretation of terrestrial kilometric radiation. The maser is assumed to be driven by a one-sided loss-cone distribution of electrons. This mechanism seems particularly favourable for the interpretation of certain planetary, solar and stellar radio emissions.The loss-cone driven SM instability is explored in detail here through numerical calculations of the growth rate and the development of a semi-quantitative theory for the maser mechanism. The numerical calculations are for a hot Maxwellian distribution with a hole in pitch angle IX; the distribution falls off with pitch angle inside the loss cone IX > 1X0 (> tn) as a power of a sine function of 1X-1X0. It is assumed that the dispersive properties of the waves are determined by a cold plasma (with frequency rop) and only emission in the x mode and the 0 mode above their respective cutoff frequencies is considered. The semi-quantitative theory involves the parameters 1X0 and the characteristic range of IIX -lXo lover which the distribution falls off inside the loss cone !!.IX, the energy tmv~ and the number density nH of the energetic electrons, and the ratio rop/Q., with Q. the electron-cyclotron frequency.The maser emission is possible at all harmonics s = 1,2, ... An application of the mechanism to the interpretation of the Jovian decametric radio emissions is outlined.

Ordinary mode auroral kilometric radiation, with harmonics, observed by ISIS 1

“…Similarly, the 2nd and 3rd harmonic noise bands extend on both sides of the stimulated resonances at 2f H and 3f H . The low frequency cutoff of the o-mode AKR near f H , rather than near the o-mode propagation cutoff at fN , is consistent with the theoretical results of Hewitt and Melrose [1983] that radiation near f H is by far the most important and the results of Wu and Lee [1979] and Hewitt et al [1982] that it is mainly directed upward. In each case, the fundamental AKR signal is clearly observed to exist only in the frequency region below the x-mode cutoff fx.…”

Quantum Electrodynamics in Strong Magnetic Fields. III. Electron?Photon Interactions

“…the literature cited by Hewitt et al 1982). Recently it has been pointed out that maser emission of ' Y rays is possible in principle due to pair annihilation (Ramaty.…”

“…After summing over the spin states the resulting expression is independent of the choice of spin eigenfunctions. Using either (1.57) or the form written down by Melrose (1974) + nne n'-n n'-n , (59b) where arguments are omitted.…”

“…Sokolov and Ternov (1968, p.76) indicated an expression for the probability of gyro magnetic emission by an electron in vacuo and then concentrated on the case of synchrotron radiation. Melrose (1974) wrote down a probability in terms of the r function derived using Johnson and Lippmann wavefunctions (see Part I), and when taking the nonrelativistic limit (Melrose and Zheleznyakov 1981) the expected symmetry between electron and positron processes is not apparent.…”

“…It was shown by Melrose (1974) how this synthesis could be achieved in the unmagnetized case. In the present paper we extend the synthesized theory to include the magnetized case.…”