Longitudinal and transverse phase space information has been obtained from a statistical analysis of fluctuations in the radiation spectrum of an electron bunch. Uncorrelated shot noise fluctuations in longitudinal beam density result in incoherent radiation with a spectrum that consists of spikes, with width inversely proportional to the bunch length. Measurements were performed at l 620 nm on a 1 -5 ps long, 44 MeV bunch propagating through a wiggler. Bunch length and emittance obtained with this single shot technique agree with independent measurements. [S0031-9007(99)

Experimental studies of the reflection, transmission, and absorption of high-power microwave pulses from a plasma-covered plane conducting boundary are presented. Under optimum conditions, backscattered rf power is attenuated by more than 30 dB over values measured in the absence of the plasma. Measurements of the radial and axial plasma density profiles and the neutral gas pressure near the plane conductor indicate that collisional absorption processes are not the primary source of the observed attenuation in the backscattered microwave signal, and that the plasma density exceeds the critical density over much of the volume nearest the conductor. The effects of a tenfold reduction in the microwave power density on the reflection and absorption characteristics of the system are also reported.

A recent design concept for millimeter-wave free-electron lasers [J. Appl, Phys, 60, 521 (1986) Jwould require the stable propagation of a sheet electron beam through a narrow waveguide channel. Experimental results reported in this article support the feasibility of such a configuration by demonstrating the stable propagation of relativistic sheet electron beams through a narrow waveguide gap (3.2 mm) using focusing by a short-period electromagnet wiggler. 90% of the electron current in a loo-keV sheet electron beam was transmitted through a S-cm-Iong channel with peak wiggler fields of 800 G. Almost 80% of a 400-keV beam was similarly confined with a 16oo-G wiggler field. The data were consistent with single electron trajectory models, indicating that space-charge effects were minimal. No evidence of beam breakup or filamentation instabilities was observed.

The performance characteristics of small-period electromagnet wigglers of novel design are measured and compared with theoretical expectations. Field measurements for wigglers driven by dc, ac, and short-pulse current sources are reported. Fields as high as 1 kG have been readily obtained in a double-sided 3.9-mm-period wiggler. These performance capabilities allow the design of high-power free electron laser oscillators and ‘‘optical klystron’’ amplifiers in the near-millimeter regime using modest electron beam energies in the range 200–400 keV. Oscillator and amplifier designs for operation at 150 and 300 GHz are presented. The generation of 1.2 MW of 150-GHz radiation with >50% efficiency is predicted.

High brightness (∼1010 A/m2 rad2), high power density (∼1010 W/cm2) electron beams have been generated by the mating of a hollow-cathode discharge device operating in the pseudospark regime to the output of a high power pulse line accelerator. Very small diameter (∼1 mm) electron beams with currents in the range 500–1000 A and energies in the range 150–300 keV have been generated with effective emittances estimated to be at or below 170 mm mrad. Such emittances are comparable to those achieved in conventional electron beam sources at current densities several orders of magnitude lower than those observed in these experiments.