Pulsed Vacuum Diode Diagnostics at the Texas Tech University High Power Microwave Facility

An axially extracted virtual cathode oscillator has been fabricated. This ultra-high-power microwave generator is powered by the Chundoong intense relativistic electron beam pulser (Max: 600 kV, 88 kA, and 60 ns duration). In this experiment, a solid electron beam with a peak diode current of 21 kA is obtained from the pulser operated at a peak diode voltage of 300 kV. It is found in this experiment that the peak of microwave emission occurred at the moment of the second peak in electron beam current, where the diode voltage V/sub d/ and diode current I/sub d/ are V/sub d/=290 kV and I/sub d/=21 kA, respectively. This observation might be strongly correlated to the inherent oscillations of the electron cloud in time and space originated from both the dynamics of the reflected electron beam due to virtual cathode and oscillations of the virtual cathode itself, from which the peak of high-power microwave can be generated in this experiment. The major operating output frequencies have been measured to be 6.68 GHz/spl les/f/spl les/7.19 GHz based on the waveguide dispersive delayed line method, which is in good agreement with that from MAGIC computational results for an electron beam voltage of 290 kV and a diode current of 21 kA. The maximum microwave output power from the virtual cathode oscillator has been measured to be 200 MW in this experiment. while its power conversion efficiency is approximately 3.3%. The dominant emission mode from the virtual cathode oscillator is shown to be the TM/sub 01/ mode based on the emission pattern of microwave induced air breakdown in this experiment.

In this paper, new high-voltage and current contact probes are proposed as development tools for spark energy measurements. The probes are equipped with active electronic components, namely high-voltage vacuum tubes, unlike the other well-known voltage and current probes containing mostly resistors, capacitors, Zener diodes or spark dischargers. The attenuation of the designed high-voltage probe is variable. Furthermore, the impedance of the current probe can be regulated. The voltage and current probes based on vacuum tubes are tolerant of reverse polarity and are polarity sensitive. They can be applied only to ignition systems with double-ended coils and to other systems equipped with multi-electrode-type spark plugs, which need a positive polarity of the central electrode.

Investigation of material migration and characterization of the film layer on the surfaces of HPM generator structures

A compact high power microwave (HPM) generation system is described in this paper. The main parts of the HPM system are a Marx generator with a pulse forming line and a magnetron with diffraction output. The total weight and length of the system are 250 kg and 120 cm, respectively. The output microwave power of the HPM system at 550 kV of applied voltage and 0.33 T of magnetic field reaches 1 GW at 2.32 GHz of central frequency with 38 ns of pulse duration, 23% of power conversion efficiency, and Gaussian radiation pattern. In the bursts operation, both time and amplitude jitters are less than 4 ns and lower than 1.5 dB, respectively.

The past decade has seen significant advances in the science and technology of high power microwave (HPM) sources (MW-GW) driven by pulsed-power/ high current electron beams. The applications of these high power microwave sources have expanded to defensive measures, including homeland security and countermeasures against improvised explosive devices. In particular, major strides have been made in relativistic magnetrons, with the recirculating planar magnetron (RPM) [1–4], transparent cathodes [5], mode-control cathodes for phase-locking [4], and other innovations. The RPM consists of two, linear, cavity-arrays coupled by recirculating sections. The central-cathode structure supplies much higher current than conventional, cylindrical magnetrons. Recent results from UM's RPM-12a, a 1-GHz, double-coaxial extractor prototype, have demonstrated extracted microwave powers of 140 MW at peak efficiencies of 40%. A 6-extractor design with goals of 400 MW, at 50–60% efficiency is under construction. Simulations show promising results for a multi-frequency RPM in which two, planar slow-wave structures are employed with different resonant frequencies. There have also been important developments in plasma-based techniques for mitigating the effects of HPM pulses on electronic components. Impressive results have been achieved by a consortium of universities in the rapid-cutoff of microwave pulses by plasma-limiters. This presentation will summarize the recent scientific advancements in both HPM source development, as well as techniques to rapidly absorb or reflect these microwave pulses.

Experimental operation of a high power microwave source with a metamaterial (MTM) structure is reported at power levels to 2.9 MW at 2.4 GHz in full 1 μs pulses. The MTM structure is formed by a waveguide that is below cutoff for TM modes. The waveguide is loaded by two axial copper plates machined with complementary split ring resonators, allowing two backward wave modes to propagate in the S-Band. A pulsed electron beam of up to 490 kV, 84 A travels down the center of the waveguide, midway between the plates. The electron beam is generated by a Pierce gun and is focused by a lens into a solenoidal magnetic field. The MTM plates are mechanically identical but are placed in the waveguide with reverse symmetry. Theory indicates that both Cherenkov and Cherenkov-cyclotron beam-wave interactions can occur. High power microwave generation was studied by varying the operating parameters over a wide range, including the electron beam voltage, the lens magnetic field, and the solenoidal field. Frequency tuning with a magnetic field and beam voltage was studied to discriminate between operation in the Cherenkov mode and the Cherenkov-cyclotron mode. Both modes were observed, but pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. A pair of steering coils was installed prior to the interaction space to initiate the cyclotron motion of the electron beam and thus encourage the Cherenkov-cyclotron high power mode. This successfully increased the output power from 2.5 MW to 2.9 MW (450 kV, 74 A, 9% efficiency).

High power microwave (HPM) source is attractive in generating gigawatt (GW) class microwaves based on the beam-wave interaction. Generally, HPM source with a high beam-wave conversion efficiency has a higher impedance. To improve the single-tube output power of HPM source, reducing the impedance of the device and increasing its power capacity are necessary. In this paper, a new low-impedance HPM source is proposed and proved to be capable of generating two phase-locked high power microwaves, which makes it promising to realize a higher combined power in a single HPM device.The new low-impedance HPM device consists of a two-cavity TKA (denoting the outer sub-source in the following) and a multiwave Cerenkov generator (referring to the inner sub-source below) inserted in the TKA inner conductor. These two sub-sources are connected in parallel and share a common magnetic field. A dual-concentric annular cathode is used in this microwave source, which is capable of emitting two concentric annular electron beams and driving the internal and external sub-source simultaneously. The advantages of this device are reducing the impedance and improving the injection electric power. When a voltage pulse is applied to the diode, part of microwaves generated in the inner subsource will leak into the outer sub-source (i.e., TKA) through the A-K gap. By amplifying the leakage microwaves, the TKA will be easily locked by the inner sub-source. Considering the fact that the microwave source consists of two sub-sources, the power capacity will also be greatly improved.As a result, particle-in-cell simulation indicates that when the diode voltage is 687 kV and the axial magnetic field is 0.8 T, two microwave beams that have a nearly identical frequency of 9.72 GHz and output powers of 1.20 GW and 2.58 GW respectively, are generated. The corresponding power conversion efficiencies are 28% and 30%, respectively. The frequency difference between these two microwaves fluctuates within 3 MHz and their phase difference is not in excess of 3. When the diode voltage changes from 665 kV to 709 kV, frequency difference between the two sub-sources fluctuates within 3 MHz and their phase difference fluctuation is within 5 in one voltage burst; the phase difference changes 10 in this voltage range. The impedance of this HPM source is as low as 36 .To sum up, the new HPM source proposed in this paper has a lower impedance and higher power capacity. The phase difference between the inner sub-source and the outer sub-source is very stable and favorable for the coherent power combination, which indicates that the new HPM source promises to realize a higher output power in a single-tube device.

A Ku band coaxial high power microwave generator with a low magnetic field was investigated without mode competition in this paper. Mode competition is avoided physically by adopting a two-cavity extractor instead of a three-cavity extractor to eliminate the resonance between the modulation slow wave structure and the extractor slow wave structure at any unexpected frequency except the working frequency. Moreover, the efficiency of the device increases due to the separation process of energy extraction and electron collection by adopting the inner conductor collecting structure. Particle simulation results showed that when the magnetic flux density is 0.6 T, the diode voltage is 560 kV, and the diode current is 8 kA, we get 1.55 GW microwaves with an efficiency of 35% and a frequency of 14.7 GHz. Experimental investigation is carried out based on the physical design and simulation results. 1.0 GW microwaves are obtained, and the frequency is 14.8 GHz in the experiment when the magnetic flux density is 0.64 T, the diode voltage is 590 kV, and the diode current is 8.5 kA. No obvious hint of electron emission or bombardment is observed at the surface of the generator after 10 thousand pulses, and the advantage of this kind of generator working in a low magnetic field is proved.

Overall efficiency of high power microwave generating device depends upon input current in the form of electron beam and currents required for electromagnets. In order to increase the efficiency of device, if electromagnets are replaced by permanent magnets, overall efficiency of device shall increase. So, calculation of exact magnetic field is required. In this paper, the exact relation of magnetic field required in high power microwave generation using Backward Wave Oscillator (BWO) is found. BWO interacts with slow waves and is the most promising device to produce high power microwaves. The interaction involves the beams from high current density and the waveguide mode. An exact relation that specifically relates the various parameters of the waveguide like slow wave structures (SWS) dimensions, input beam voltage and operational frequency with axial magnetic field is derived. The derived equation gives calculation of exact values of magnetic field for focusing of beams. Theoretical and simulated work show good agreement with the previously available experimental data. So, with the derived electromagnetic wave relation exact value of magnetic field is calculated for desired frequency and power regime.

Monitoring the ambience's condition is emerging as one of the most important issues in mobile robots. While we need to detect and process the condition quickly and efficiently using sensors, they (sensors) introduce extra complexity to the systems. Therefore this paper aims to develop a new method to simplify the sensing process. It describes an experimental process for monitoring path conditions of a power wheel chair inside and outside of the lab. The monitoring method triggers impedance via transduction matrix of the DC motors which run the wheelchair. The matrix is based on the relationship between electrical and mechanical impedance of the motors. A voltage probe and a current probe are used to monitor the changes of voltage and current supplied to the two DC motors of the system while the wheel chair is moving and the signals are recorded by a Digital Signal Analyzer (DSA). The recorded data are processed by MATLAB and the graphs representing various conditions are plotted. The relationship between the conditions of the path and the changes of voltage, current, and impedance of the motors are listed. The use of the method is justified but miniaturization of the voltage and current probes is necessary for real-life implementation of the system.

The XVth International Conference on Calorimetry in High Energy Physics, CALOR2012, was held in Santa Fe, New Mexico from 4–8 June 2012. The series of conferences on calorimetry started in 1990 at Fermilab, and they have been the premier event for calorimeter aficionados, a trend that CALOR2012 upheld. This year, several presentations focused on the status of the major calorimeter systems, especially at the LHC. Discussions on new and developing techniques in calorimetry took a full day. Excellent updates on uses of calorimeters or about ideas that are deeply rooted in particle physics calorimetry in astrophysics and neutrino physics were followed by talks on algorithms and special triggers that rely on calorimeters. Finally, discussions of promising current developments and ongoing R&D work for future calorimeters capped the conference. The field of calorimetry is alive and well, as evidenced by the more than 100 attendees and the excellent quality of over 80 presentations. You will find the written contributions in this volume. The presentations can be found at calor2012.ttu.edu.

A multifunctional, long-lifetime, compact, and coaxial high-voltage (HV) vacuum insulator for Tesla-type generators is proposed for high-power microwave (HPM) generation. This vacuum insulator has two features. First, it is multifunctional since it can not only support the two conductors of the transmission line (TL), supply a vacuum environment for load, but also can eliminate a prepulse from the main pulse, which is realized via a grounded inductor. Second, it has a long lifetime. This feature is realized by optimizing the grounded inductor on the switch side and by grooving on the vacuum side. A 50-cm 700-kV compact coaxial HV vacuum insulator of such kind was designed, which was applied to a 1-MV Tesla-type generator to drive the relativistic backward-wave oscillator (RBWO) for HPM generation. Significantly, it has operated for a lifetime longer than 3 00 000 pulses at a repetition rate of 50 Hz without failure, which verifies the design.

Summary form only given, as follows. To broaden our knowledge in radio frequency (RF) and a high power microwave (HPM) generation, it is useful to energize our advanced RF& HPM source with a driver that has low internal impedance. It is useful to find out if our source also suffers from limitation known as shortening. This means that by increasing the radiative power, the length of the pulse becomes shorter. Hence, there is a limitation in the energy radiated in a single shot. This paper describes a compact six stage-Marx generator. It is built using the concept of pulsed-forming networks. The capacitance per stage is 0.500 F and the charging voltage is organized to vary from 25 to 100 kV. With the matching (dummy) load of 7.5 ohms; used, the maximum output voltage should be 300 kV and the maximum output current 40 kA. The stored energy in the system is 15 kJ and the peak power supplied to the load of 7.5 Ohms is 12 GW. Without crowbaring, the pulse width is 0.82 ns. When the crowbar switch is added, the pulse width can vary from 100 to 500 ns in a predictable manner.

The aim of this work is to design a novel metamaterial slow wave structure (SWS) for high power microwave (HPM) generation using a short pulse relativistic electron beam. The structure provides around 15% efficiency with 250 MW output power at 1.4 GHz frequency. It generates backward wave generation and beam-wave interaction with a TE 21 -like mode.

6H-SiC photoconductive semiconductor switches (PCSS) are new alternative of high power microwave (HPM) or RF generators with the special potential of compactness, tunable frequency and pulse width due to the superior material properties. For PCSS behavior investigation including on-resistance and transient, optical absorption, carrier process, and circuit elements are commonly important issues. This brief builds the major physics framework from the expressions of these influence factors considering simplicity and reliability. According to the basic physics models, a scalable, general model of vanadium compensated, semi-insulating (VCSI), vertical 6H-SiC PCSS is constructed in PSpice. The experiments are performed to verify this circuit model. Consequently, the correspondence between the measured results and simulation results proves its applicability.