Electron Beam Dynamics Research Articles

Effect of a dc electric field on the trapping dynamics of a cold electron beam

The self-consistent modification of the trapping dynamics of a low density cold electron beam due to the external application of a dc electric field is considered. For dc fields smaller than the peak amplitude of the saturated beam-plasma instability, the beam energy remains clamped while the wave amplitude grows secularly. Large traveling potential wells appear and create strongly focused charge clumps. By considering the role of wave dissipation, an exact dynamic Bernstein–Greene–Kruskal equilibrium is found analytically. It consists of a singular charge clump which propagates through the medium at constant velocity even though a dc field is present. The numerical study of the basic equations shows that the system evolves asymptotically to this singular state. A variety of experimentally relevant properties associated with the trapping dynamics is investigated, including the stability of the dynamic nonlinear equilibrium to sideband growth.

Electron beam dynamics in combined guide and pump magnetic fields for free electron laser applications

The propagation of a cold relativistic electron beam in a free electron laser with an axial guide magnetic field is considered. The possibility of several steady-state helical trajectories for the electrons is shown, and the stability against perturbations and accessibility of such steady states is considered. Necessary and sufficient conditions for the stability are derived and indicate the importance of the transition region at the entrance of the laser. Possible modes of operation of the laser in different steady-state regimes are suggested and illustrated by numerical examples.

The effect of reverse currents on the dynamics of nonthermal electron beams in solar flares and on their emitted X-ray bremsstrahlung

view Abstract Citations (133) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The effect of reverse currents on the dynamics of nonthermal electron beams in solar flares and on their emitted X-ray bremsstrahlung Emslie, A. G. Abstract Recognizing the possible importance of reverse current ohmic energy losses from beams of electrons injected into the solar atmosphere during flares, we solve the equations governing the dynamics of such beams, taking into account energy and momentum losses of the beam particles by both collisional and ohmic heating processes. It is found that for injected fluxes compatible with hard X-ray burst observations of fairly large flares, the inclusion of ohmic terms results in a substantial modification of the variation of electron energy and pitch angle with depth in the target. The chromospheric energy deposition due to the beam, and X-ray bremsstrahlung emitted by the beam, are also evaluated for a variety of empirical flare model atmospheres, and it is found that, although both these quantities decrease as the injected electron flux increases, their ratio is insensitive to the parameters of the problem. Further, the emitted nonthermal X-ray flux is found to be bounded by a limiting value only marginally consistent with observations, thus suggesting that a significant portion of the X-ray flux is thermal in origin. The dependence of the results obtained on the model atmosphere used in the calculations is discussed. Publication: The Astrophysical Journal Pub Date: February 1980 DOI: 10.1086/157709 Bibcode: 1980ApJ...235.1055E Keywords: Bremsstrahlung; Electron Beams; Solar Atmosphere; Solar Flares; Solar Physics; Solar X-Rays; Atmospheric Models; Energy Spectra; X Ray Spectra; Solar Physics full text sources ADS |

Thermal sensitive paper as a diagnostic for intense relativistic electron beam dynamics

Thermal sensitive paper has been used as a diagnostic for an intense relativistic electron beam propagating in a rippled magnetic field. The E(r)xB(z) rotation of the beam has been measured from the exposed pattern on the thermal paper and used to calculate the electrostatic field of the beam E(r), and the corresponding values of electron density and beam current. Exposed strips of thermal paper show longitudinal modulation of the radial electron velocity with a period corresponding to that of a rippled magnetic field; modulation of the radial electron velocity at the cyclotron frequency has also been observed.

Correlation of intense electron beam dynamics with the operation of the relativistic cyclotron maser

The relation between the particle dynamics of an intense relativistic electron beam and its accompanying microwave radiation has been explored. A diagnostic has been developed which makes use of the strong forward directed x-ray radiation pattern of relativistic electrons colliding with a low Z thin target foil, to determine the transverse electron momentum of the beam as it moves along a magnetic field. The transverse momentum of the beam electrons is controlled both by a magnetic undulator, consisting of spaced iron rings similar to those used in previous cyclotron maser experiments, and by a carefully wound electromagnet consisting of alternating dipoles. The effect of relative undulator strength on the beam momentum distribution is determined, together with total microwave power as measured by a calorimeter. The results, which are interpreted with the aid of a numerical model, indicate a positive correlation between perpendicular momentum and radiated power. The spread in perpendicular velocity of the beam electrons was found to depend on the type of undulator used, the relative undulator strength and also influences the amount of radiated power.

Calculation of the Pinch Dynamics in Relativistic Electron Beam Diodes

The pinch dynamics of relativistic electron beams in large aspect ratio diodes are calculated numerically, including both ion and electron currents. The effect of the ions on the pinch phenomenon is demonstrated. The roles of the time scales for ion emission and flow are discussed. Fair agreement with experiment is obtained.

Dynamics of intense relativistic electron beams in toroidal fields: J Benford et al, J Appl Phys, 45 (4), 1974, 1657–1666

Dynamics of intense relativistic electron beams in toroidal fields: J Benford et al, J Appl Phys, 45 (4), 1974, 1657–1666

Dynamics of intense relativistic electron beams in toroidal fields

Intense relativistic electron beams were propagated around a 180° toroidal sector to study beam dynamics in toroidal fields. The major beam drift under conditions for neutralization of self-fields was along - R × B and scaled as γZ/Bt, where Z is the propagated distance, Bt the toroidal field, and γ the relativistic factor. This is indicative of curvature and ∇B drifts. Use of conducting walls caused an additional F × B drift around the chamber due to image current forces. Analysis of the distortion of a propagating rectangular beam shows that beam electrons follow field lines. Preliminary experiments on counterstreaming beams show inefficient reflection of beams from opposing diodes. Application of these results to beam injection and confinement in toroidal magnetic fields is discussed.

Production and Dynamics of High Intensity Electron Beams

High intensity electron beam experiments are in progress at electron energies varying from 100 keV to 2 MeV. The low energy machines are Marx generators, while the high energy one is an electron beam transformer accelerator , home made with some original technical solutions. Its electron energy is 2 MeV, current > 10 kA, pulse length 20 ns at a repetition rate of 10 pps. The purpose is injection in the ANEL - type electron ring accelerators, beam dynamics and plasma - beam interaction investigations. Several models of field emission di odes have been investigated by various diagnostic methods and beam pictures on various materials have been taken.

A Comparision of Theoretical and Actual Beam Performance of a 140 MeV Electron Linear Accelerator at the Universiiy of Saskatchewan

The electron beam optics of the injector and microwave system of a two klystron, four-section linear accelerator with an unloaded beam energy of 140 MeV are discussed. The injector contains a mnicrowave chopper, a nanosecond inflector and a prebunching assembly so that a wide variety of different injection conditions can be presented to the machine. The waveguide sections are of non-uniform impedance design and each is energized by 8.5 megawatts peak r-f power. The design parameters of the waveguide sections are discussed together with the electron beam dynamics for various modes of injector operation, and some comparisons are made with measurements of the electron beam characteristics.

Dynamics of Electron Beams from Magnetically Shielded Guns

The dynamics of electron beams from magnetically shielded guns is examined in detail both experimentally and theoretically. The electron orbits and beam shape variations are investigated with an electron beam analyzer which measures current density variations and transverse velocity. The existence of rings of charge that move through the beam and the gradual reduction in beam scalloping with length are demonstrated. It is shown that simple energy considerations plus an account of the role of transverse thermal velocities is sufficient to account for the experimentally observed features of beam behavior in the limit of negligible space charge. In the presence of space charge the beam behavior is qualitatively unchanged except for some defocusing and precession of the electron orbits provided that the magnetic field is at least several times the Brillouin field.