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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7503-7509 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The free-electron-laser (FEL) equations are reduced to a set of one-dimensional, normalized equations that allow a universal (dimensional) analysis. In universal parameters, numerical integration of the FEL equations indicates a relatively constant saturated ponderomotive wave amplitude independent of both the normalized wiggler potential amplitude and the injected signal level. The constant ponderomotive wave amplitude and an empirical fit for the universal saturation length as a function of normalized wiggler potential amplitude and gain permits unnormalized design calculations for saturated power and saturated length over a wide parameter range. Tapering is considered by deriving analytical expressions for the intrinsic efficiency and taper length. Design values for a high-gain, high-efficiency, tapered amplifier at 280 and 560 GHz are presented.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1714-1720 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low-frequency velocity-shear instabilities (such as the diocotron mode). This is in contrast to the more familiar unstable behavior in uniform solenoidal magnetic fields. A period-averaged analytic model shows that a PCM-focused beam is stabilized by ponderomotive forces for short PCM periods. Numerical particle simulations for a semi-infinite sheet beam verify this prediction and also indicate diocotron stability for long PCM periods is less constraining than providing for space-charge confinement and trajectory stability in the PCM focusing system. In this article the issue of beam matching and side focusing for sheet beams of finite width is also discussed. A review of past and present theoretical and experimental investigations of sheet-beam transport is presented.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2797-2805 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The shape of the gain curve and physics of interaction between microwave fields and the electron beam for a periodic rectangular grating slow-wave Traveling Wave Tube (TWT) amplifier are investigated. This research focuses on the collective (ωpτ(very-much-greater-than)1) low-voltage (≤10 kV) interaction in the backward wave regime for the Ku-band (12.5–17.5 GHz) range of frequencies. For amplifier experiments, a round "probe" beam (10 kV, 0.25 A, 1 mm diameter) confined by a 1 kG solenoidal focusing magnetic field was utilized. Simultaneous single-pass collective gain and electron-beam velocity spread measurements are performed by means of a Faraday cup repeller energy analyzer configured as the beam collector. Experiments near 13.0 GHz show the maximum normalized single-pass gain to be in agreement with the theoretical prediction for several axial velocity spreads (δv||/v||). Collective single-pass experimental results are presented and compared with theory. The effect of an increased interaction length which is accomplished by partial end reflections on the enhanced convective growth is measured and discussed. Narrowing of the gain curve as a function of beam voltage and frequency is shown to result from critical details of the electron-beam radial current density distribution and is verified experimentally by varying the beam-grating separation. Experimental results for several beam-grating separations and the effect of a nonuniform peaked radial current density on the interaction physics are also discussed. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1664-1670 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating of a variety of ceramic, glass, and polymer materials. An explanation for these controversial observations has eluded researchers for over a decade. This paper describes a series of recent experimental and theoretical investigations that provide an explanation for these intriguing observations in terms of ponderomotive forces acting on mobile ionic species. The ponderomotive phenomenon, like its conventional-plasma analog, can be described in the continuum model limit by combining the continuity, Poisson's, and transport equations. However, the solid-state plasma version typically manifests as a result of gradients in mobile charge mobility (e.g., near physical surfaces or interfaces), whereas the conventional plasma ponderomotive transport is typically a consequence of gradients in the radiation field intensity. Both cases can be captured in a single, general, mathematical articulation developed in terms of the mobile particle fluxes. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2707-2715 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A periodic, rectangular grating slow-wave-structure is considered for forward and backward wave low-voltage (≤10 kV) Ku-band traveling wave tube (TWT) amplifiers. For forward wave operation, it is required that the ratio of groove depth, d, to grating period, p, be large (i.e. d/p≥5) while small values ofd/p allow backward wave operation. For large d/p, skin effect losses in the grating slots are large and can substantially reduce the growth rate produced by the beam-slow wave interaction. Phase and amplitude measurements of the grating structures utilizing a slotted line and a fast Fourier transform (FFT) analysis have been carried out. The results show that the measured dispersion relations for both shallow (d/p= 0.446) and deep groove gratings (d/p= 7.43) agree very well with the theoretical dispersion relations. For amplifier experiments, a round "probe" beam (10 kV, 0.25 A, 1 mm radius) from a Litton Pierce electron gun (model M707) is utilized. The beam is confined by means of a 1 kG focusing solenoidal magnetic field. Tuning curve and single particle backward wave gain measurements are presented and discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3208-3219 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of neutral copper, ground and metastable states, and neutral argon, metastable and resonance states, in an ionized physical vapor deposition plasma. Spectroscopic measurements were carried with a xenon arc lamp as a high intensity, continuum light source, and an optical multichannel detector. Copper radiative transitions in the wavelength range of 324.8–510.6 nm and argon radiative transitions in the 706.7–811.5 nm range were employed. The curve of growth method has been used to calculate the absolute line average densities from fractional absorption data. For a copper–argon plasma of neutral pressure 30 and 10 mTorr copper metastable state densities were found to lie in the range of 1010–1012 cm−3. Comparison of these densities with neutral copper densities derived from independent measurements of neutral copper flux at the substrate indicate gas phase temperatures greater than 1500 K under certain experimental conditions. These values of inferred temperatures indicate the copper metastable state density to be significant in comparison with neutral copper ground state densities at 10 and 30 mTorr with radio frequency heating power of 1 kW. The concentrations of argon 4s sublevels of the first excited state were found to be in the range of 4.5×108–1.5×1011 cm−3 for the experimental conditions studied. The ordering of the relative densities of the argon 4s sublevels and the variation of the lumped first excited state with experimental parameters are discussed. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6313-6322 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerical and theoretical analyses show that stable, two-plane focusing of finite width, elliptical cross section, sheet electron beams with high space charge (low voltage, high current density) can be accomplished using periodically cusped-magnetic (PCM) fields. Magnetic field strength requirements for focusing high-space-charge sheet beams are within technological capabilities of modern permanent magnet technology. Both an offset-pole PCM stack and a PCM stack combined with a periodic quadrupole magnet (PQM) edge array are shown to be effective for two-plane sheet beam confinement. The PCM-PQM hybrid configuration offers inherent advantages for independent adjustment of confinement fields to achieve beam matching (minimum ripple) in both transverse dimensions. The offset-pole configuration offers the advantage of open-side access for applications such as vacuum electronic microwave devices. It is also shown that PCM-focused sheet beam envelope stability obeys criteria equivalent to that previously identified for round-cross-section electron beams in periodic permanent magnet focusing. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3606-3609 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Many experimenters over the past few years have observed rate enhancements when using microwave processing compared to conventional processing. The results have remained somewhat controversial because the driving forces are not constant throughout the experiments and because of the possibility of inaccurate temperature measurement. This paper describes a different experimental approach that avoids the pitfalls of the previous experiments. Specifically, the alternative approach involves fixed driving forces and short duration experiments. Reliable and accurate knowledge of the sample temperature is ensured by restricting the amount of microwave heating to negligible levels and using conventional ohmic heating to control temperature. This approach has allowed us to confirm the presence of a "microwave effect'' on kinetic processes in ionic ceramic materials. With this configuration, many further experiments are possible with different materials and conditions. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1525-1529 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Ionized physical vapor deposition is a technique for sputtering metal into small trenches, by ionizing sputtered metal atoms so that their trajectories can be controlled by electric fields. To this date no one has quantified exactly what fraction of the metal vapor is ionized, although the trends of how ionization varies with input parameters is known. This article describes and demonstrates a new quartz crystal microbalance design, which can be used to measure the ionized metal flux fraction arriving at the substrate location. Instead of using grids to repel ions as similar devices do, this analyzer works by applying a voltage bias to the front surface of the crystal in order to repel ions. A magnetic field adjacent to the face limits electron current to the microbalance, minimizing its perturbation of the plasma. The measurement tool described in this article does not suffer from complications caused by placing grids in front of the monitor and is an attractive method for characterizing ionized physical vapor deposition systems. Ion and neutral metal fluxes as a function of ionizer power are presented for an argon/copper discharge. © 1999 American Institute of Physics.
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2069-2071 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The propagation of a relativistic sheet electron beam through a spatially periodic magnetic field (wiggler) has been studied experimentally. The wiggler serves two purposes; it provides beam focusing as well as the magnetostatic pump for the free-electron laser (FEL) interaction. Experiments conducted to study sheet beam generation and propagation in a short-period (1 cm) planar wiggler are presented. A 500 keV, 7 A sheet electron beam was propagated through a 3.2 mm waveguide with negligible losses due to intercepted current. In addition, the first observation of wiggler-induced radiation was obtained from the sheet beam FEL in a short-period wiggler oscillator configuration.
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