The first experiments on the observation of short pulsed superradiant (SR) emission with the excitation of a surface wave by a relativistic electron bunch moving in an oversized corrugated waveguide ...were performed. Subterahertz SR pulses with a central frequency of 0.14 THz, an ultrashort duration of 150 ps, and an extremely high peak power of 50-70 MW were generated. The experiments were based on a theoretical consideration including the quasioptical approach and direct particle-in-cell simulations.
A new amplification method, weaving the three basic compression techniques, Chirped Pulse Amplification (CPA), Optical Parametric Chirped Pulse Amplification (OPCPA) and Plasma Compression by ...Backward Raman Amplification (BRA) in plasma, is proposed. It is called C
3 for Cascaded Conversion Compression. It has the capability to compress with good efficiency kilojoule to megajoule, nanosecond laser pulses into femtosecond pulses, to produce exawatt-and-beyond peak power. In the future, C
3 could be used at large-scale facilities such as the National Ignition Facility (NIF) or the Laser Megajoule (LMJ) and open the way to zettawatt level pulses. The beam will be focused to a wavelength spot size with a f#1. The very small beam size, i.e. few centimeters, along with the low laser repetition rate laser system will make possible the use of inexpensive, precision, disposable optics. The resulting intensity will approach the Schwinger value, thus opening up new possibilities in fundamental physics.
ABSTRACT We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. ICRF2 ...contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ∼40 as and a directional stability of the frame axes of ∼10 as. A set of 295 new "defining" sources was selected on the basis of positional stability and the lack of extensive intrinsic source structure. The positional stability of these 295 defining sources and their more uniform sky distribution eliminates the two greatest weaknesses of the first realization of the International Celestial Reference Frame (ICRF1). Alignment of ICRF2 with the International Celestial Reference System was made using 138 positionally stable sources common to both ICRF2 and ICRF1. The resulting ICRF2 was adopted by the International Astronomical Union as the new fundamental celestial reference frame, replacing ICRF1 as of 2010 January 1.
Many patients have iliofemoral vessel anatomy unsuitable for conventional transfemoral (TF) transcatheter aortic valve implantation (TAVI). Safe and practical alternatives to the TF approach are, ...therefore, needed. This study compared outcomes of alternative nonfemoral routes, transapical (TA), direct aortic (DA), and subclavian (SC), with standard femoral access. In this retrospective study, data from 3,962 patients in the UK TAVI registry were analyzed. All patients who received TAVI through a femoral, subclavian, TA, or DA approach were eligible for inclusion. The primary outcome measure was survival up to 2 years. Median Logistic EuroSCORE was similar for SC, DA, and TA but significantly lower in the TF cohort (22.1% vs 20.3% vs 21.2% vs 17.0%, respectively, p <0.0001). Estimated 1-year survival rate was similar for TF (84.6 ± 0.7%) and SC (80.5 ± 3%, p = 0.27) but significantly worse for TA (74.7 ± 1.6%, p <0.001) and DA (75.2 ± 3.3%, p <0.001). A Cox proportional hazard model was used to analyze survival up to 2 years. Survival in the SC group was not significantly different from the TF group (hazard ratio HR 1.22, 95% confidence interval CI 0.88 to 1.70, p = 0.24). In contrast, survival in the TA (HR 1.74, 95% CI 1.43 to 2.11; p <0.001) and DA (HR 1.55, 95% CI 1.13 to 2.14; p <0.01) cohorts was significantly reduced compared with TF. In conclusion, TA and DA TAVI were associated with similar survival, both significantly worse than with the TF route. In contrast, subclavian access was not significantly different from TF and may represent the safest nonfemoral access route for TAVI.
A spatially extended planar 75 GHz free-electron maser with a hybrid two-mirror resonator consisting of two-dimensional upstream and traditional one-dimensional downstream Bragg reflectors and driven ...by two parallel-sheet electron beams 0.8 MeV/1 kA has been elaborated. For the highly oversized interaction space (cross section 45×2.5 vacuum wavelengths), the two-dimensional distributed feedback allowed realization of stable narrow-band generation that includes synchronization of emission from both electron beams. As a result, spatially coherent radiation with the output power of 30-50 MW and a pulse duration of ∼100 ns was obtained in each channel.
We report the experimental studies of radiation on fundamental and third cyclotron harmonic from a Ka-band high-current relativistic gyrotron with a maximum output power of 40 MW. Helical electron ...beam is formed by the electron optics system based on using the kicker field for initiation of electrons' gyration and its subsequent pitching in increasing magnetic field. Based on the spectral measurements, we estimate indirectly the radiation power level at the third harmonic of the gyro-frequency as about −30 dB with respect to the first-harmonic radiation level. This estimation is in good agreement with the results of 3-D particle-in-cell (PIC) simulations.
We present the results of simulations and experimental studies of a W-band surface-wave oscillator powered by a ribbon high-current relativistic electron beam produced by SINUKI accelerator (IAP RAS, ...Nizhny Novgorod, 1 kA / 650 keV / 17 ns). Planar geometry of the interaction space facilitates efficient mode selection over wide transverse coordinate by using open waveguide at fairly large oversize factor (the width of the waveguide is ~ 8 wavelengths). Stable oscillation regime is obtained at frequency of 75 GHz with a pulse duration of about 5 ns. The output power measured by the calorimetric method reaches 25 MW.
We propose a variant of a slitted cavity for gyrotrons based on spatial synchronization of TE-type modes with azimuthal indexes equal to multiples of the slit number and close eigenfrequencies. A ...simplified theory of such a cavity is presented demonstrating its basic properties. High selectivity of the novel cavity was confirmed by 3-D PIC simulation of a 0.3-THz gyrotron energized by a helical electron beam with an energy of 500 keV and a current of 2 kA. This simulation demonstrates that, using the slit-type cavity, stable single-frequency operation at TE 6,4 -TE 12,2 mode combined with an output power of more than 80 MW and an efficiency of about 8%. The same arrangement with a conventional solid-wall cavity demonstrates no single-frequency regimes at all.
Based on a quasioptical approach and direct particle-in-cell simulations, we study dynamics of oversized relativistic surface-wave oscillators (SWOs) of the Cherenkov type with 2D periodical ...corrugated structures of cylindrical geometry. Such corrugation allows significant rarefication of the spectrum of modes with different azimuthal indices. As a result, selective excitation of a mode with a given azimuthal index is possible. Azimuthal index of the generated mode depends on the voltage rise time. For short (nanosecond scale) rise time, generation of an azimuthally symmetric mode can be realized. For longer (hundreds nanoseconds to microseconds) rise time, the modes with high azimuthal indexes would be excited. These conclusions are supported by the experiments where Ka-band SWOs with 2D corrugated structures were realized based on the300keV/100A/4μsthermionic accelerator SATURN. For an oversize factor of 16, stable narrow-band generation with output power of 1.5–2 MW was obtained at the frequency of 32.5 GHz corresponding to the mode with an azimuthal index ofm=3. The project of Ka-band subgigawatt power SWOs operating at the azimuthally symmetric mode based on500keV/4kA/20nshigh current explosive-emission accelerator SINUS-6 is under development.
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