Pure electron plasmas are routinely confined within cylindrically symmetric Penning traps. In this paper the static and dynamic properties of plasmas confined in traps with applied electric field asymmetries are investigated. Simple analytical theories are derived and used to predict the shapes of the stable noncircular plasma equilibria observed in experiments. Both analytical and experimental results agree with those of a vortex-in-cell simulation. For an ℓ=1 diocotron mode in a cylindrically symmetric trap, the plasma rotates as a rigid column in a circular orbit. In contrast, plasmas in systems with electric field asymmetries are shown to have an analog to the ℓ=1 mode in which the shape of the plasma changes as it rotates in a noncircular orbit. These bulk plasma features are studied with a Hamiltonian model. It is seen that, for a small plasma, the area enclosed by the orbit of the center of charge is an invariant when electric field perturbations are applied adiabatically. This invariant has been observed experimentally. The breaking of the invariant is also studied. The dynamic Hamiltonian model is also used to predict the shape and frequency of the large amplitude ℓ=1 and ℓ=2 diocotron modes in symmetric traps.

A pure electron plasma, confined within an azimuthally symmetric boundary by a coaxial magnetic field, has an equilibrium shape which is cylindrical. We apply perturbations which break the azimuthal symmetry and deform the plasma into a noncircular shape that is stationary in the laboratory frame. These asymmetric equilibria form a broad new class of stable equilibria. A theoretical model correctly predicts the plasma shapes and explains their stability.

Experimental and computational studies of free-electron lasers operating at high input powers have been undertaken. These studies constitute a novel method of investigating saturation and trapping effects in free-electron lasers.

A theoretical and experimental study of the nonlinear performance of a free electron laser (FEL) amplifier operating in the collective (Raman) regime is reported. The FEL generates up to ∼100 kW of rf power at a frequency of 9.3 GHz and an efficiency of ∼10%. Power saturation, efficiency, and synchrotron oscillations are studied as a function of rf input power, electron beam energy, current, wiggler field amplitude, and axial distance within the helical wiggler. The influences of the nonlinear electron motion in the ponderomotive potential and space-charge waves are studied by measurements of the dependence of gain and efficiency on the initial radiation intensity. Good agreement with a nonlinear theory that takes cognizance of electron trapping in the combined ponderomotive and space-charge potential well is obtained.

Experiments, theory, and simulations are reported on the effects of electron prebunching in a mildly relativistic, low-current (200 kV, 1 A) free-electron laser amplifier operating in the collective (Raman) regime at a frequency of ∼10 GHz. Prebunching is established by injecting an electromagnetic wave into a bifilar helical wiggler and then transporting the bunched beam into a second magnetic wiggler region. The wave growth rate, Γ≡(1/P)(dP/dz), is deduced from measurements of the radiation intensity as a function of interaction length. Observations show that prebunching can increase the radiation growth rate Γ manyfold as compared with a system without prebunching.