Fred Dyer

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

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.

Plasma antennas for lowering co-site interference among closely spaced antennas

Summary form only given. Plasma antennas were built and tested to operate at frequencies between 30 MHz and 1500 MHz. Vertical antennas were tested with RF coupling to each antennas by a capacitive sleeve located near the lower end of the glass discharge tube. At frequencies below 500 MHz, a DC current is used to ionize and maintain the plasma discharge. Above 500 MHz, the DC current required for operation as an antenna causes excessive heating of the glass envelope and electrodes. To solve this problem, current is pulsed to several Amperes for about 5 microseconds; with a repetition rate of 1500 Hz. Therefore the average current is greatly reduced to less than 20 mA. Ion density, however, decays slowly after the fast pulse ends, and plasma frequency is relatively constant and remains higher than the antenna operating frequency. Unlike a conventional metal antenna, the frequency of plasma antenna for optimum efficiency can be tuned by varying discharge current. As an example, our plasma antenna operating at 50 MHz is much less susceptible (by 40 dB) to co-site interference from a nearby antenna transmitting at 170 MHz. Another way to lower co-site interference is to place a plasma shield around an antenna to reflect interference from a nearby antenna transmitting at lower frequencies. Our plasma shield consists of an array of plasma discharge tubes placed side by side around the antenna. Plasma discharge current is set at an appropriate value to assure that desirable signals pass unimpeded through the shield, but lower frequency interfering signals are reflected away by the shield. We have built plasma shields, using pulsed discharge current, that reflect signals with frequencies up to 24 GHz.

A Simple High-Voltage Opening Switch Using Spoiled Electrostatic Confinement

We have initiated and sustained a plasma discharge at pressures well below the Paschen minimum by trapping electrons in orbits around a positively charged wire. Spoiling the trapping process terminates the discharge and opens the circuit in spite of high voltage applied.

Increasing the Efficiency of Light Emission from a Plasma by Electrostatic Confinement

Electrostatic confinement has been used to increase the efficiency of light emission from a plasma discharge. Biasing the wall negatively increases efficiency by a factor 2.5 over the floating wail case. High energy electrons are confimed, thereby increasing excitation. The average electron confinement, however, is not increased.

Plasma antenna VSWR and co-site and parasitic interference reduction or elimination

Plasma antennas use partially or fully ionized gas as a conductor instead of metal. Plasma antennas can perform as metal antennas do but with reconfiguration, lower thermal noise at the higher frequencies, and lower side lobes in some experiments. At the higher frequencies, plasma antennas have lower thermal noise than metal antennas and the thermal noise of plasma antennas decreases with the operating frequency of the plasma antenna making them ideal for satellite antennas Plasma reflector antennas, plasma FM/AM radio antennas, various plasma transmitting antennas, high power plasma antennas, plasma frequency selective surfaces, plasma waveguides, plasma co-axial cables, and smart plasma antennas have been built. Alexeff and Anderson and [1]-[2] Anderson and Alexeff [3] have done theory, experiments, and have built prototype plasma antennas. Anderson [4] wrote a comprehensive book on plasma antennas. S. Sakai [5] et al have shown that a plasma antenna is a type of metamaterial.

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.

Experimental Observations of Ion-Acoustic Wave Reflection from Discharge-Tube Walls

We have experimentally observed the reflection of ion-acoustic waves from the walls of a discharge tube by a very simple technique. We first excite intense spontaneous oscillations, then rapidly switch to a quiescent mode of operation. The ion-acoustic waves are observed to persist after the transition, but damp away with time.

Magnetic momentum probe for plasma studies with application to high pressure plasmas

Summary form only given. A magnetic momentum probe1 is investigated. This diagnostic device appears similar to a Langmuir probe, but interacts with particles by magnetic field rather than (or in addition to) an electric field. The probe is a bare wire loop immersed in the plasma. When a DC current flows through the wire, it is surrounded by a magnetic field which diverts charged particles. In this way, the momentum of plasma particles can be measured. The Langmuir probe in contrast measures particle energy.The Langmuir probe has the disadvantage of not working well at high pressure because of the high density of electrically charged particles. A magnetic field penetrates through the charged particles to allow interaction with particles farther from the probe. The magnetic field also suppresses secondary electron emission from the probe. The momentum probe allows a mass analysis of the various ionic species in the plasma. An electrostatic potential has been introduced to the magnetic momentum probe to add some of the characteristics of a Langmuir probe.

Recent advances in orbitron microwave development

Summary form only given, as follows. By using a low-impedance Mylar line for pulsed power feed at low voltages (5 kV) and a special power feed to avoid electron ejection by magnetic forces, about 1 kW of microwave power has been produced in the 10-cm band. This orbitron is gas filled to provide electrons by ionization. The second orbitron advance was to use a split cathode coupled to a resonant circuit. This provides a resonant system for the orbiting electrons to couple to, generating more power in a narrow, fixed frequency range. This orbitron uses a tungsten heated cathode for electron injection. The device operates well, producing a narrow line at 145 MHz at a power level of -20 dBm (0.01 mW) as picked up by an external antenna. The coupling has not been optimized