Mark Rader

A computer model

Summary form only given, as follows. Experiments have demonstrated that a plasma filling of a microwave tube can enhance the efficiency by a factor of 8. The plasma filling can neutralize space charge, cause electron beam focusing by ion space charge, and favourably modify the effective dielectric constant. However, the plasma ions can also exhibit an instability, causing frequency and amplitude jitter, and even termination of the electron beam. However, observations on a steady-state, gas-filled Orbitron Maser have demonstrated stable operation. A suggested stabilization effect is that ions are ejected continuously radically from the system before an instability can grow. Analytical models based on the simplified Budker-Buneman instability show that a slow transverse ion flush greatly reduces the growth rate of the instability. In this report, we present computations based on the computer code MAGIC that support the analytical calculations for the Budker-Buneman model. More advanced calculations for a prototype microwave tube are now in progress.

Observation of closed loops in high-voltage discharges: a possible precursor of magnetic flux trapping

In multimegavolt electrostatic generators, the accidental sparkover discharges change in character as the voltage and stored energy increase. The usual forked, unidirectional discharges are replaced by complex discharges containing numerous closed loops. It is suggested that this is an example of the formation of closed-current loops that generate magnetic fields in astrophysics. >

Plasma-induced frequency shifts in microwave beams

Summary form only given, as follows. Microwave frequency shifts have been investigated by two different processes. In the first, a microwave beam is reflected from a plasma jet produced by a Bostic gun. Frequency upshifts of about 4 MHz are produced on a beam at 3 GHz. The reflected signal at 3 GHz is observed to drop in intensity during this process by about 30 dB. In the second process, microwaves are propagated through a waveguide in which plasma is suddenly created by a pulsed electrical discharge. Since the phase velocity in a plasma is higher than in a vacuum, one might expect the microwaves to be ejected from the plasma, producing a frequency upshift. Experimentally, it is found that a frequency upshift of over 10 MHz in a signal of 2.6 GHz is routinely observed. An interesting observation is that a frequency downshift is observed. This frequency downshift appears only in a system at low gas pressure, less than 10-4 torr, and occurs later in time than the frequency upshift. It is suspected that it is the result of plasma decay and is the inverse of the second process described above

Possible precursors of ball lightning. Observation of closed loops in high voltage discharges

Several hundred photographs of ultrahigh voltage discharges have been obtained that show closed current loops. These closed current loops may be precursors of ball lightning. One feature of these discharges may explain why observations of ball lightning may be infrequent; that is, there is a distinct threshold in voltage and/or current below which the closed loops do not occur. This threshold current fits other experimental data but is well above the usually observed currents in natural lightning. 10 refs., 3 figs.

Steady-State Orbitron Emissions

The Orbitron maser has been operated at a pressure of 2 × 10-6 in the steady state. Electrons are supplied to the device by an oxide-coated tungsten cathode placed inside the cylindrical cavity. The plasma-free emission corresponded to harmonically related steady-state narrow lines. The fundamental (lowest frequency) line corresponds to a resonance in the cavity system, which could be observed with a grid-dip meter.

Microwave frequency shifting using photon acceleration

Using a Bostick Gun as a plasma source, we have been investigating the effects of a moving plasma front on the frequency of an incident R.F. signal. We have been able to measure frequency shifts of 10 MHz frequency with a 2.6 GHz signal. The density is such that the plasma frequency is well above the transmitter frequency 1.3 meters from the plasma source. No magnetic field is used.

Revised derivation of Landau damping

We re-derive Landaus damping equation using an alternative method different from that of the original author. This alternative method results in a factor of two greater damping. This factor of two is a result of inconsistent assumptions by Landau about the nature of the singularity.

Test radar demonstration of the orbitron maser

Summary form only given. The significance of the orbitron maser is in the FEL (free-electron laser) like frequency tunability, which is not achievable by conventional short-wavelength devices. Unlike the FEL, however, the orbitron can readily emit a continuum of wavelengths without a continuous change in beam energy. Using the appropriate bandpass or frequency disperser, this device has been used to construct a frequency-tunable radar. Preliminary test results using a Cassegrain configuration for the transmitter were very favorable. A clear frequency-tunable signal could be received from a 30-meter-distant target over a frequency range from 70 to 90 GHz. It has also been shown to work well in smoke and dust.

A simple and accurate high-pass filter and spectrometer using Huygen's principle

We have developed a new type of high pass filter and a new type of spectrometer. These devices are currently under testing and have yielded good agreement with theory. These devices seem to be easier to use and appear to be more accurate than devices now used.

Recent results on the orbitron maser

Abstract The Orbitron Maser is a device which uses negative mass unstable electrons to produce meter, millimeter, and submillimeter radiation. It can be shown to produce stable steady-state radiation with a glow discharge electron feed, and work without the presence of a two component plasma.