Phase-Imposing Initiation of Cherenkov Superradiance Emission by an Ultrashort-Seed Microwave Pulse.

For the first time, we demonstrate experimentally the possibility of Cherenkov superradiant generation with a phase imposed by an ultrashort seed microwave pulse. The phases of seed and initiated Ka-band microwave pulses were correlated with the accuracy of 0.5-0.7 rad for the power ratio down to -35 dB. Characteristics of such a process were determined in the frame of a basic theoretical model that describes both spontaneous and stimulated emission of an electron beam moving in corrugated waveguides. The obtained results open up opportunities of reaching extremely high radiation power density in phased arrays of short-pulse coherently operating microwave generators.

Generation of electromagnetic fields of extremely high intensity by coherent summation of Cherenkov superradiance pulses.

We demonstrate both theoretically and experimentally the possibility of correlating the phase of a Cherenkov superradiance (SR) pulse to the sharp edge of a current pulse, when spontaneous emission of the electron bunch edge serves as the seed for SR processes. By division of the driving voltage pulse across several parallel channels equipped with independent cathodes we can synchronize several SR sources to arrange a two-dimensional array. In the experiments carried out, coherent summation of radiation from four independent 8-mm wavelength band SR generators with peak power 600 MW results in the interference maximum of the directional diagram with an intensity that is equivalent to radiation from a single source with a power of 10 GW.

[The epididymal adipose tissue of mice after nanosecond pulse-periodic microwave irradiation].

The effect of pulse-periodic microwave radiation (PPMR) of the pulse repetition frequency of 8-25 pulseper second, the peak power density of 1500 W/cm2 on the epididymal adipose tissue of micewas investigated. The effect was assessed by the changes in the fat mass and size of the irradiated adipocytes. It was found that the fat mass and size distribution of adipocytes are affected by irradiation. The effects depend on the pulse repetition frequency and intensity of exposure.

[The antioxidant enzyme activity in mouse liver mitochondria after nanosecond pulsed periodic X-ray exposure].

The effect of repetitive pulsed X-ray (4 ns pulse duration, 300 kV accelerating voltage; 2.5 kA electron beam current) on the antioxidant enzyme activity in mouse liver mitochondria has been investigated. The mitochondrial suspension was exposed to single 4000 pulse X-ray radiation with repetition rates ranging between 10 and 22 pps (pulsed dose was 0.3-1.8 x 10(-6) Gy/pulse, the total absorbed dose following a single exposure was 7.2 x 10(-3) Gy). It was shown that a short-time exposure to X-ray radiation changes the antioxidant enzyme activity in mouse liver mitochondria. The greatest effect was observed in the changes of the activity of the metal-containing enzymes: superoxide dismutase and glutathione peroxidase. The effect depends on the pulse repetition frequency and radiation dose.

[DNA double-strand breaks in human lymphocytes after single irradiation by low doses of pulsed X-rays: non-linear dose-response relationship].

Effects of ionizing radiation registered in cells after low dose irradiation are still poorly understood. A pulsed mode of irradiation is even more problematic in terms of predicting the radiation-induced response in cells. Thus, the aim of this paper was to study and analyze the effects of dose and frequency of pulsed X-rays on the frequency of radiation-induced DNA double-strand breaks and their repair kinetics in human peripheral blood lymphocytes in vitro. Analysis of radiation-induced gammaH2AX and 53BP1 repair foci was used to assess the DNA damage in these cells. The dose-response curve of radiation-induced foci of both proteins has shown deviations from linearity to a higher effect in the 12-32 mGy dose range and a lower effect at 72 mGy. The dose-response curve was linear at doses higher than 100 mGy. The number of radiation-induced gammaH2AX and 53BP1 foci depended on the frequency of X-ray pulses: the highest effect was registered at 13 pulses per second. Moreover, slower repair kinetics was observed for those foci induced by very low doses with a nonlinear dose-response relationship.

[Life expectency and fertility of postembrio stage drosophila after the pulse-periodic X-ray irradiation].

The effect of 13 Hz repetition rate X-ray pulses with 3 x 10(-6)-1.5 x 10(-4) Gr per pulse dose during 5 minute on drosophila's larvae and on pupae vas investigated. It was shown that the effect depends on drosophila's age as well as on X-ray dose and manifests itself in variation of life expectancy and fertility.

Gyromagnetic RF source for interdisciplinary research.

We demonstrate a source of high power nanosecond RF pulses based on gyromagnetic nonlinear transmission line. The source is designed to explore the exposure of different biological objects to strong RF fields in an air filled rectangular waveguide loaded onto ethanol RF load. The RF pulse amplitude can be varied by 52 dB, reaching a maximum value of nearly 40 kV/cm and decreasing to tens of V/cm. The RF pulse amplitude is controlled by decreasing the incident pulse amplitude from the high voltage driver. The duration of RF pulses lies in the range from 4 to 25 ns and the frequency from 0.6 to 1.0 GHz.

Four channel high power rf source with beam steering based on gyromagnetic nonlinear transmission lines.

The synchronized operation of four gyromagnetic nonlinear transmission lines (NLTLs) was tested with a pulse repetition frequency up to 1 kHz during 1 s bursts. High voltage pulses with a duration of ∼5 ns from the solid state driver S-500 were split into four 48 Ω channels reaching about -200 kV in each channel with ∼10% variation in the amplitude. The maximum peak voltage at the NLTL output was within 220-235 kV with the maximum modulation depth of decaying oscillations up to 90% at the center frequency near 2.1 GHz. The relative delay between channels reached the half-period of the center frequency of oscillations. The associated beam steering by four element array of conical helical antennas was demonstrated in a horizontal plane at 17°. The effective potential of radiation reached 360 kV at the radiation axis. The effect of ferrite temperature on the shock wave velocity in gyromagnetic NLTL is observed.

Generation of Cherenkov superradiance pulses with a peak power exceeding the power of the driving short electron beam.

Theoretical investigation of a short electron beam (extended bunch) interaction with a backward wave propagating in a slow wave structure demonstrates the possibility of producing ultrashort superradiance pulses with a peak power which exceeds the power of the driving beam (conversion factor K>1). It is shown that a nonuniform slow wave structure with optimized profile is beneficial in order to increase the conversion factor. The results of theoretical analysis are confirmed by the experiments. At X band using the SINUS-150 accelerator (4 ns, 330 kV, 2.6 kA) 0.6-0.8 ns superradiance pulses with a peak power of 1.2 GW and a conversion factor of 1.5 were obtained. Similar experiments at Ka-band based on the RADAN-303 accelerator (1 ns, 290 kV, 2.5 kA) demonstrated production of the superradiance (SR) pulse with duration 200 ps and peak power about 1 GW (conversion factor of 1.4).

[Effect of impulse-intermittent ultrahigh frequency irradiation on synthesis of nucleic acids in tumor cells].

In this work is shown that the repetitive high power microwaves is able to exert an inhibitory influence on the process of DNA and RNA syntheses in tumor cells of P-815 mastocytoma. This effect depends on pulse repetition rate. High power microwave pulses inhibit the process of transcription in tumor cells. No activation of DNA reparation system due to the irradiation of non-proliferating mononuclear blood cells was found. This indicates that the repetitive high power microwaves are not able to initiate single-filament rupture in DNA of tumor cells. The conformation of transcription enzymes is assumed to be changed under the influence of the microwave irradiation that makes for significant inhibition of RNA synthesis.

[Assessment of some metabolic parameters of white rats' liver after exposure to repetitive x-ray or microwave pulses].

Effects of repetitive X-ray and microwave pulses on the rat liver functions were investigated. The action of repetitive nanosecond X-ray is characterized by the metabolic dysfunction of the liver. In particular, it results in a considerable reduction in the ALT activity, augmentation of the AST/ALT ratio and decrease of the total protein content. The most considerable effect is observed at 16 Hz. Microwave pulses render a less significant effect on metabolic functions of the rat liver as compared to X-rays. The effect depends on the frequency of pulses.

High repetition rate multi-channel source of high-power rf-modulated pulses.

This paper presents the results of testing a high voltage pulse generator based on parallel gyromagnetic nonlinear transmission lines filled with saturable ferrite. The generator is capable of producing almost identical stable rf-modulated nanosecond high voltage pulses in each of the two, or four, parallel output channels. The output voltage amplitude in each channel can reach -285 or -180 kV, respectively, with a rf modulation depth of up to 60%. Drive pulses were produced as the packets of duration 1-5 s at a pulse repetition frequency of 800 Hz using a driver equipped with all-solid-state switches. Splitting the driver pulse provided electric field strengths in the channels which were below the breakdown field strength of the transmission lines. As a result, the use of nonlinear transmission lines of reduced diameter made it possible to increase the center frequency of the excited rf oscillations to ∼2 GHz.

Current waveform reconstruction from an explosively emissive cathode at a subnanosecond voltage front.

We describe the methods of registration and reconstruction of an envelope of explosive electron emission current from the edge of a cylindrical cathode, which provides a picosecond time reference of the emitted electron beam with a subnanosecond voltage front applied to the accelerating gap. Variation of the front steepness allows one to determine the beam onset time in the experiments, where a collector-type current probe can be used. The advanced method of dynamic time domain reflectometry provides exact data on electron beam current rise and track changes in the cathode emission from pulse to pulse with a precision of less than 10 ps.