Franklin A. Dolezal

An integrated fiber optics/broadband wireless access demonstrator for the next generation Internet (NGI) network extension

We report on the implementation and integration of gigabit fiber networks and a multi-Mbit wireless access NGI network demonstrator. The focus is to merge photonic technology and networking with the broadband wireless access system.

The Hughes low-voltage free electron laser program

Abstract The Hughes Free Electron Laser Program is based upon a previous low voltage oscillator experiment in which a 225-kV electron beam was used to generate 60 kW of 30-GHz radiation in a test model FEL [1]. FEL kinetics, beam propagation and the 4.6% gain require a pulsewidth greater than 2 μs with a pulse flatness greater than 1% for oscillation in the test model FEL to occur. Propagation of the beam through the wiggler is a significant problem. A special “square” wiggler was designed to accomodate beam confinement in both the x and the y direction. The low gain of the system required that a high Q cavity must also be present for oscillation to occur. To this end a distributed-Bragg-reflector resonator was installed, which had a Q greater than 10 000. The results of these tests and previous experiments have led to the design of a second generation low voltage FEL which will be driven at 400 kV and operate between 60 and 100 Ghz. This FEL will be designed to facilitate operation with a second stage 6-MeV electron beam at UCSB to generate 7-μm radiation from a two-stage, two-beam FEL.

PASOTRON high-energy microwave source

The authors describe the operation and performance of a high-energy microwave source called the PASOTRON (plasma-assisted, slow-wave oscillator). The PASOTRON is a unique combination of a novel electron gun, and plasma-filled slow-wave structure which creates a source capable of generating 100- mu s-long RF pulses maintained at power levels of a few megawatts without the use of any magnetic focusing fields. A Hughes hollow-cathode-plasma electron gun is used to produce long, high-power beam pulses from which energy is efficiently extracted and converted into electromagnetic radiation. The authors present results which show that RF output power is in the 1-to-5 MW range, for RF pulse lengths up to 120 mu s from a PASOTRON tube designed to operate in the C-band frequency range. The integrated RF energy per pulse is up to 500 J, and the electron-beam to microwave-radiation power-conversion efficiency is approximately 20%. Instantaneous bandwidth measurements confirm that, for the long RF pulse duration, the PASOTRONs oscillation center frequency is maintained in a narrow line <3 MHz.<<ETX>>

PASOTRON™ high-energy microwave source

A unique, high-energy microwave source, called PASOTRON for Plasma-Assisted Slow-wave Oscillator has been developed. Similar to the Backward Wave Oscillator (BWO), the PASOTRON spontaneously generates microwave radiation by efficiently converting electron beam energy into electromagnetic radiation. The PASOTRON, however, utilizes a novel E-gun and plasma-filled slow-wave structure (SWS) to produce and propagate very long, high-power beam pulses which require no axial magnetic fields for transport. The long electron beam pulses are obtained from a Hughes Hollow-Cathode Plasma (HCP) E-gun, which employs a low-pressure glow discharge to provide a stable, high current-density electron source. Electrons from this source are accelerated through a multi-aperture array to produce a large area, high-current beam consisting initially of many individual beamlets. Since the device is operated in the ion focused regime, the plasma filling the SWS, space-charge neutralizes the beam, and the Bennett self-pinch compresses the beamlets and increases the beams current density. Experimental results from a PASOTRON tube designed to operate in a TM01 mode at C-band frequencies when driven by a 50-to-100-kV, 50-to-250 A electron beam are reported. Results show output power is in the l-to-4 MW range, for rf pulselengths up to 100 μsec, corresponding to an integrated energy per pulse of up to 300 J. Calculations show the E-beam to microwave-radiation power-conversion efficiency is ~20%. Instantaneous bandwidth measurements further reveal that for the duration of the long ripulse the PASOTRONs oscillation center frequency maintains a narrow line <;3MHz.

Access network technology for all-wireless WDM communications system

In this paper, we report design and implementation scenarios for a gigabit-capacity and high-data-rate fixed wireless access technology research demonstrator. The all weather survivable system is based on broadband wireless access concept and implementation techniques utilizing RF/microwave/millimeter-wave as well as free-space optical wireless high speed links. The demonstration platform provides broadband last mile access and networking solutions to Internet users in densely populated areas with homes and businesses (e.g., downtown building-centric and inner city- environment) in need of high bandwidth not served with fiber infrastructure. The focus of this investigation is radio link design, access network architecture, and system integration. Hybrid fiber radio and WDM optical wireless solutions are implemented to interface and complement the existing ATM fiber and satellite core networks in support of all wireless infrastructure for Next Generation Internet (NGI).

Mode Structure Of A Low-Gain Low-Voltage Free-Electron Laser

A test-model free-electron laser, FEL, has been operated at voltages from 120 to 280 kV. The laser has a 2-cm wiggler period and utilizes a linearly polarized wiggler. The resonator is composed of a 1.75-cm-dia circular waveguide coupled to 8.89-cm-dia spherical mirrors. The beam current is about 15 A and the FEL operates at near threshold. The theoretical gain exceeds the measured cavity losses (10 to 30 percent per pass) only for the higher Q modes. The most intense emission occurs at frequencies near the waveguide cutoff of 10.2 GHz, where we estimate the emitted power to be saturated at 10 to 100 kW. Signals have been observed to last for over 10 ps. This lower frequency mode, (which we presume is the backward TE11 FEL wave), dominates. Radiation is reproducibly observed to appear during periods when the voltage corresponds qualitatively to resonator modes; with each mode usually occurring twice during the pulse, e.g. during the rise and fall of the voltage. The rate of change of the voltage affects the gain under these circumstances and the signal is quenched if the change exceeds about 4% per ps. Harmonic frequencies are also observed at frequencies near to, but not on, the forward-wave branch of the FEL-dispersion curve. The intensity of the third harmonic (31 GHz) is on the order of 44 W.