The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
We present an experimental and computational study to investigate the feasibility of microwave radar for non-invasively and accurately estimating fruit yields in cranberry beds prior to harvesting and within agricultural research plots. Dielectric measurements of the fruit and leaves show a significant contrast in the 0.5–7.5 GHz range. Full-wave computational electromagnetics simulations of microwave...
High power, high frequency vacuum electronic devices require high brightness, low emittance electron beams to operate [1]. To meet these demands, thermionic cathodes encounter challenges with rapid turn-on, lifetime, rapid emission gating, and the system inefficiency of the heater power requirement. Field-emission cathodes can provide sufficient current for hundreds of hours but typically produce...
Many applications demand high-brightness, low-emittance electron beams, including vacuum electronic devices and high-power microwave sources [1]. For this reason, we have constructed an experimental system around a field emission microscope and pepper-pot anode to study the field emission characteristics and emittance of novel cathodes and geometries.
Observations of rapidly formed (<50–300 ns) distributed plasma discharges using X-band microwaves in neon and Ne(Ar) mixture gases are presented. A stainless steel cylindrical discharge test chamber, which is enclosed with polycarbonate windows on both ends, is used to observe microwave breakdown in noble gases including Penning discharge Ne(Ar) and Ne(Kr) mixes from 10 to 760 torr. The chamber...
Observations of rapidly formed (<50–300 ns) distributed plasma discharges using X-band microwaves in neon with 1 mTorr residual air are presented. A stainless steel cylindrical discharge test chamber, which is enclosed with polycarbonate windows on both ends, is used to observe microwave breakdown in neon gas from 10 to 760 torr. The chamber is illuminated by the output of 25 kW, 0.8 µs pulse-width,...
Observations of rapidly formed (<50−400 ns) distributed plasma discharges using X-band microwaves in Neon with 1 mTorr residual air are presented. A stainless steel cylindrical discharge test chamber is used to observe microwave breakdown at 10 to 760 torr pressures. The chamber is enclosed with polycarbonate windows on both ends and has two side ports. The magnetron illuminates the chamber using...
Preliminary observations of rapidly formed (<50 ns) distributed plasma discharges using X-band microwaves are presented. The following setup establishes the conditions necessary to study complex microwave discharges. The microwave discharge test chamber is an L-band brass rectangular waveguide with polycarbonate windows. The chamber is illuminated by the output of 25 kW, 0.8 µs pulse-width,...
Summary form only given. A recent resurgence of interest in new, more powerful, coherent sources of terahertz (THz) radiation (0.3-3.0 × 1012 Hz) has been driven by advances in fabrication and device physics modeling, emergence of new security threats, and application potential in high data rate communications, concealed weapon or threat detection, remote high resolution imaging, chemical spectroscopy,...
The development of new terahertz power amplifiers at 0.67, 0.85 and 1.03 THz presents significant challenges in both design and fabrication. This paper describes the design challenges and methodology, an outline design of the new device and an analysis of fabrication techniques considered.
Summary form only given. Extended Interaction Klystrons have been demonstrated at frequencies up to 218 GHz CW and 229 GHz pulsed. Modern design, fabrication, and measurement technologies show promise of extending their operation into the THz regime. This paper describes the challenges and some novel approaches to the development of EIKs operating terahertz frequencies, while simultaneously meeting...
Summary form only given. Field emission from cold copper knife-edge cathodes was experimentally studied by measuring emission currents on the Madison cathode experiment (MACX) in UHV with a base pressure of 10-10 Torr. The cathode was machined first using EDM to produce raised ridges or knife-edges of 0.13 mm width and 0.75 mm depth. The knife-edge width was further reduced by chemically etching it...
We report the experimental study of field emission from cold cathodes having a raised ridge or knife-edge structure and analyses using a Transfer Matrix Method (TMM) model used to extract the cathode parameters. Local emission current measurements were done on a copper cathode, which was fabricated using electric discharge machining (EDM) and chemical etching yielding ridges of thickness 15 mum. Measurements...
The structure of eukaryotic cells is maintained by a network of filamentous actin anchored subjacently to the plasma membrane. This structure is referred to as the actin cortex. We present a locally constrained surface tension model for electroporation in order to address the influence of plasmalemmal-cortical anchoring on electropore dynamics. This model predicts that stable electropores are possible...
Calabazas Creek Research, Inc. (CCR) and the University of Wisconsin, Madison (UW) are developing a 650 GHz traveling wave tube amplifier (TWTA). Simulations predict 360 mW peak output power with a 2-10% duty cycle. This paper summarizes the design and fabrication of the TWT. Testing is expected in November, 2008.
Summary form only given. We report the measurements and analysis of metal cold field emission cathodes utilizing an advanced cathode test facility and a TMM (transfer matrix method) model. The facility is designed to measure the field emission currents from cathodes on the micro- and macroscale. Measurements are obtained under UHV (10-10 torr) conditions. The vacuum chamber is a stainless steel six-way...
This paper reports on measurements and analyses of field emission from both copper and aluminium cathodes. To analyze the data, a numerical model of electron emission was developed using a transfer matrix function method. The work function and effective field enhancement factor of the cathodes were obtained.
Results are reported for numerical modeling of concepts for non-circular beam formation for near-THz frequency TWTpsilas. Several methods for beam compression were examined, and one method appears promising for producing a 12 kV, 8 mA beam with a cross section 70 times 160 microns, while keeping the cathode loading to about 59 A/cm2. This would be suitable for a 650 GHz TWT. The beam loading is significantly...
Calabazas Creek Research, Inc (CCR) and the University of Wisconsin (UW) used advanced simulation tools to design a 95 GHz TWT providing approximately 1 kW of average power. This output power would be extremely challenging if not impossible using a conventional TWT design because of limitations imposed by the interaction circuit with respect to beam current density and thermal-mechanical stability...
We report measurements and analyses of field emission from both copper and aluminum cathodes. To analyze the data, we have developed a numerical model of electron emission. We note that localized heating of high current density field emission cathodes can provide regime where thermionic as well as field emission effects must be considered. Our analysis of experimental data fitting in both the thermionic...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.