[en] Changes of crystal structure induced by high-pressure soaking (hps) up to 9.2 GPa were studied in Ti with 3 to 35 at.% Mo alloys which were in the as-quenched metastable state. The retained structure was analysed by X-ray diffractography and transmission electron microscopy. It was observed that after application of critical pressure, ω phase appears or its quantity increases in all crystal structures that are observed usually in Ti-base alloys and consisting of α',α' + β + ω,β + ω or β phases. Strong diffuse scattering patterns created by short range order in displacement of atomic rows were observed. The β → α' high-pressure transition was observed first in Ti-base alloys. Analysis of the relative stability of all different structures with regard to hps was performed using detailed on Debye temperature, density of electronic states at Fermi level and other parameters. (orig.)

[en] The Moessbauer spectroscopy, X-ray diffraction and electron microscopy were applied to analyse samples of a Ti-3at% Mo-0.13at%⁵⁷Fe alloy in which phase transitions were induced by various treatments. In the as quenched alloy, two martensitic phases were found to be hcp-α' and orthorhombic α''. An amount of about 8-10% ω-phase (in additon to α' and α'') appeared in a quenched sample which was soaked at 92 kbar for 20 h. For a quenched and cold-worked sample, the X-ray and electron microscopy results were not conclusive whereas the Moessbauer spectrum contained an ω-line with a relative spectral area Asub(ω/A)=0.15. In a cold-worked sample that was aged at 350⁰C for 24 h a metastable phase, known as theta, appeared in addition to the ω-phase. The spectrum of a sample aged at 350⁰C for 3.5 h (not cold-rolled) consists of α', α'' and theta lines

[en] Since the first landmark by Bekefi announcing a 900MW relativistic magnetron, substantial improvements accomplished peak power levels of several gigawatts. However, pragmatic considerations emphasized repetitive mode of operation and longer pulse duration (i.e., higher average power) at the expense of peak power. Repetition rate of about 200pps with peak power levels around 600-300MW and pulse lengths 30-70ns (∼) 20J/pulse) were achieved . It seems that pulse duration, at these power density levels, is restrained by universal, not fully understood, mechanisms. At Rafael, we initiated a relativistic magnetron research program aiming for rep- rated generation of 150 - 200ns long pulses with peak power of about 100MW. Our magnetron design (Patent pending) is fundamentally different from those that led to the achievements mentioned above. The cathode is grounded and the positive H.V. pulse is injected to the anode block (essentially, an A6 resonator) through an external cavity, that serves as a buffer cavity between the anode-cathode interaction region and the output waveguide. In this grounded cathode geometry the axial current is eliminated (improving efficiency). For the cathode, we conceived o special scheme of alternating metal/ dielectric disks, employing the principle of triple point plasma initiation . At present, the magnetron is driven by a rep-rated (≥20pps), 120Ω, Marx-PFN generator. Pulse trains of 50MW peak power and 150ns duration at 10Hz were measured with Vgenerator=300kV, Vdiode=180kV, Idiode=kA, and η=28%. At higher charging voltage, improved vacuum conditions, and lower rep-rate, 100MW pulses have been measured with Vgenerator=360kV, Vdiode=180kV, Idiode=1.5kA, and η=37%. However, these pulses tend to be shorter, about 70ns long. We present detailed studies of the emitted pulse shape, the temporal evolution of its spectral power density and diode impedance, which suggest some physical insight to the relativistic magnetron's operation. We also show some preliminary 2-D computer simulations to support our understanding of the power transfer density. (authors)

[en] In this paper experiments are reported on the effects of electron prebunching in a mildly relativistic free electron laser amplifier operating in the collective (Raman) regime. Prebunching is established by injecting a monochromatic wave into a bifilar helical wiggler interaction region. The growth rates are deduced from observations of the radiation intensity as a function of interaction length. Results are presented both in the small signal (linear) and saturated (nonlinear) regimes

[en] The authors discuss two studies of cyclotron autoresonance maser (CARM) amplifiers underway at M.I.T. They differ both in frequency and in the technologies employed. The 35GHz amplifier uses a 1.5MeV,260A,30ns electron beam from a field emission (explosive) cathode energized by a Marx type, Physics International Pulserad accelerator. The entire system is immersed in a uniform, pulsed magnetic field 7kG. Measurements give a small signal gain of 90dB/m, a saturated power output of 10MW and an electronic efficiency of 3%. The 140GH_z amplifier under development will employ a 450-700kV, 30A, 1μs electron beam from a Pierce-type gun driven by a high-voltage, long-pulse modulator. The magnetic field (--25kG) in the CARM interaction region will be produced by a superconducting magnet. Theoretical investigations of CARM efficiency, efficiency enhancement by magnetic field tapering, and amplifier stability are also being carried out