Relativistic, intense beam-driven High Power Microwave (HPM) sources emerged as consequence of the development of pulsed power. In this context, pulsed power refers to components of a system following the prime power source, and before the load, which is typically an electron beam diode. Progress in fielding HPM sources on mobile platforms requires developing more compact pulsed power drivers. The Air Force Office of Scientific Research is sponsoring, using resources allocated by DDR&E, a Multidisciplinary University Research Initiative (MURI) program to study basic phenomena and processes that can lead to the design of more compact pulsed power systems. The University of New Mexico is leading a consortium, uniting researchers at Old Dominion University and the University of Nevada-Reno, to study basic phenomena relating to breakdown in solid and liquid dielectrics, high dielectric constant ceramics for use in compact, folded Blumlein transmission lines, gas switches, thermal management in compact pulsed power systems, among other topics. This paper describes the research activities on this program that are being performed in the initial year.

Research is underway on a 6-vane Titan Corp. L-Band relativistic magnetron operating at about 1 GHz. For equal power in both extraction waveguides, the peak microwave power of this device is between 200 MW and 300 MW. Microwave pulse shortening limits pulselengths to the range of 10-100 ns. Two cold cathodes designs were tested: emitting aluminum knob in the vane region with no endcap, and extended cathode with graphite fiber emission region in the vanes and endcap outside the vanes. With no endcap, the cathode exhibited endloss current fraction up to 50% of the total; with one endcap, the cathode reduced the endloss current fraction to as little as 12%. Both cathodes produced peak total- electronic efficiency in the range of 14% to 21%.

We consider a magnetron with diffraction output as the most natural variant of magnetrons for relativistic electron energies because of the unique combination of such favorable properties as high output power, compact design, high resistance to microwave breakdown, the ability to work with extremely high currents, and the possibility to form desirable output radiation patterns. This paper presents preliminary parameters for the design of such a high power microwave generator, and contrasts its features with magnetrons of the traditional design.

Previous studies of crossed-field electron vacuum devices, such as magnetrons and crossed-field amplifiers (CFA), have centered on their initial growth, as an indication of their operating modes. In such an analysis, one assumes a growth rate, and solves the equations for the density profile, the operating frequency, and the growth rate. What one obtains here are the conditions for the initial operation of the device. However, eventually the RF fields will have saturated, and the device then will enter into either a stationary operating regime, or some other mode, which could in general be some non-operating mode. To study this regime of operation, we return to the classical planar magnetron equations and study what the form of the solution will be for these stationary solutions. What we find is that upon saturation, as the growth rate vanishes, its effect is replaced by second-order velocity terms, and in particular, the second-order vertical velocity. What we will do here is to derive and present the magnetron equations when the growth rate vanishes, and discuss the solutions of the RF equations about the resonance points. Lastly, we shall consider what implications these results may have for relativistic and nonrelativistic crossed-field devices.

A novel simulation approach to electromagnetic computations involving large, complex systems is described for studying the effects of high power radio-frequency pulses. The approach uses the electromagnetic topology method. The adoption of the multi-conductor transmission analysis gives the results that are in good agreement with other solution methods. The electromagnetic topology method has been extended to the analysis of buried cables with encouraging results. Tan electromagnetic topology based simulation code provides a useful tool for carrying out EMC and EMI analysis.

The high power microwave program at the Air Force Research Lab (AFRL) includes high power source development in narrow band and wideband technologies. The H2 source is an existing wideband source that was developed at the AFRL. A recent AFRL requirement for a wideband impulse generator to use in materials tests has provided the need to update the H2 source for the current test requirements. The H2 source is composed of a dual resonant transformer that charges a short length of coaxial transmission line. The transmission line is then discharged into an output coaxial transmission line with a self-break Hydrogen switch. The dual resonant transformer is driven by a low inductance primary capacitor bank operating through a sel-break gas switch. The upgrade of the coaxial Hydrogen output switch is the focus of this paper. The Hydrogen output switch was developed through extensive electrical and mechanical simulations. The switch insulator is made of Ultem 2300 and is designed to operate with a mechanical factor of safety equal to 4.0 at 1,000 psi. The design criteria, design data and operational data will be presented.

Photoconductive switching of the stacked Blumlein pulsers, developed at the Univ. of Texas at Dallas (UTD), currently produces high power, nanosecond pulses with risetimes on the order of 200 ps. The device has a compact geometry and is commutated by a single GaAs photoconductive semiconductor switch (PCSS) triggered by a low power laser diode array. Filamentation of the conductivity associated with high gain GaAs switches produces such high current density that the switches are damages near the metal-semiconductor interface and the lifetime is limited. The semiconductor properties of amorphic diamond can be employed to improve the PCSS longevity by coating the switch cathode or anode areas or both. For example if the switch cathode is coated, the tunneling of electrons from amorphic diamond to GaAs during the off-state stage of PCSS operation provides pre-avalanche sites that diffuse conduction current upon switch activation. This report presents the progress toward improving the high gain switch operation and lifetime by advanced treatments with amorphic diamond coatings. A significant improvement in switch lifetime is demonstrated by testing the diamond-coated switch performance in a stacked Blumlein prototype pulser.

In a nonequilibrium beam-plasma system, the contribution of the polarization charge to the total force on a relativistic test particle, namely the dynamic polarization force, is calculated to fourth order in the total electromagnetic field for a slowly varying, nearly spatially independent background distribution with no external fields. This relation is useful in calculations of collective radiation processes and the conditions for the occurrence of collective radiative instability in relativistic beam-plasma systems.

The most notable effect in processing dielectrics with micro- and millimeter-waves is volumetric heating of these materials, offering the opportunity of very high heating rates for the samples. In comparison to conventional heating where the heat transfer is diffusive and depends on the thermal conductivity of the material, the microwave field penetrates the sample and acts as an instantaneous heat source at each point of the sample. By this unique property, microwave heating at 2.45 GHz and 915 MHz ISM (Industrial, Medical, Scientific) frequencies is established as an important industrial technology since more than 50 years ago. Successful application of microwaves in industries has been reported e.g. by food processing systems, domestic ovens, rubber industry, vacuum drying etc. The present paper shows some outlines of microwave system development at Forschungszentrum Karlsruhe, IHM by transferring properties from the higher frequency regime (millimeter-waves) to lower frequency applications. Anyway, the need for using higher frequencies like 24 GHz (ISM frequency) for industrial applications has to be carefully verified with respect to special physical/engineering advantages or to limits the standard microwave technology meets for the specific problem.

The use of carbon fiber reinforced composite materials (CFRP) in aerospace industries is consequently increasing due to their unique combination of characteristic features such as light weight, high specific mechanical strength etc. Currently the main obstacle for widespread industrial implementation is high manufacturing costs caused by the necessity of curing at elevated temperatures of 100-200 degree(s)C. Heating the CFRP materials to these temperatures in a conventional furnace is an energy consuming and therefore costly procedure. This paper presents a heating method by means of millimeter waves. Advantages of this method are presented along with theoretical considerations and numerical simulations of the heating process. The results of simulations of the anisotropic thermal and dielectrical material properties are shown and discussed on the basis of experiments.

Influence of dissipation on development of overlimiting electron beam instability caused by aperiodical modulation of beam density in medium with negative dielectric constant is investigated. Fully magnetized beam-plasma waveguide is considered. It is shown that growth rates of dissipative instability of overlimiting electron beam depend on parameter characterizing dissipation more critically as compared with conventional electron beams. The influence of dissipation on space-time evolution of overlimiting beam instability and its gradual transition to that of dissipative type with increase in level of dissipation is investigated in detail.

In this paper the physical mechanism and mathematical description of magnetically self-focusing electron beam are studied.The analysis of electron beam with weak pulsation in drifting tube filled with plasma was given,the beam with strong pulsation under the same condition was also studied accurately.The results show that whether in (alpha) area or in (beta) area both the range and wave length of beam pulsation related to initial condition and plasma parameters although their pulsation properties were different,there exited a optimum plasma density when the other condition was set.The experimental studies are also reported of beam transmission in plasma channel based on Hollow Cathode Plasma(HCP) gun in University of Electronic Science and Technology of China(UESTC).The study shows that efficient transmission of electron beam in plasma channel can be reached by choosing the plasma filling factor and voltage.

The dispersion equation of corrugated waveguide filled with plasma were obtained, the plasma electron redistribution and ion channel were taken into account in the study. The dispersion properties are discussed in detail. The relationship between the wave growth and plasma density is investigated. MAGIC PIC code is used to study the microwave radiation features of corrugated waveguide filled with plasma, 6.4MW output power at 100KV voltage is obtained, and microwave radiation efficiency is about 26.7%.

The paper presents experimental and numerical investigations of the developed one-sectional relativistic Cerenkov generators on the basis of overmoded slow-wave structures with D/(lambda) =4 and a high-current electron beam with the accelerating voltage of 500 kV, current of kA. For numerical analysis a 3D computer code MULTIWAVES-5.2 is used. Discussion and comparison of the obtained results that can be used at development of multisectional multiwave Cerenkov generators were carried out.

The effective charge of a test particle in a nonequilibrium beam-plasma system is the sum of the actual charge and the induced dynamic polarization charge surrounding it. Associated with the latter is the induced dynamic polarization current. Expressions are derived for the induced dynamic polarization charge and current density of a relativistic test particle in a nonequilibrium beam-plasma system. These expressions are useful in the calculation of the nonlinear dynamic polarization force on the test particle.