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AD Phelps

Publications and source records attributed to AD Phelps.

7 recordsLinked to original sources
PubMed2000

High-gain wide-band gyrotron traveling wave amplifier with a helically corrugated waveguide

First bandwidth measurements of a novel gyrotron amplifier are presented. The coupling between the second harmonic cyclotron mode of a gyrating electron beam and the radiation field occurred in the region of near infinite phase velocity over a broad bandwidth by using a cylindrical waveguide with a helical corrugation on its internal surface. With a beam energy of 185 keV, the amplifier achieved a maximum output power of 1.1 MW, saturated gain of 37 dB, linear gain of 47 dB, saturated bandwidth of 8.4 to 10.4 GHz ( 21% relative bandwidth), and an efficiency of 29%, in good agreement with theory.

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PubMed2000

Self-amplification of coherent spontaneous emission in a cherenkov free-electron maser

Ultrashort pulses of microwave radiation have been produced in a dielectric-lined Cherenkov free-electron maser (FEM) amplifier. An intense initial seed pulse, due to coherent spontaneous emission (CSE), arises at the leading edge of the electron pulse. There is evidence to show that 3-4 cycle spikes are produced through the amplification of these seed pulses. A strong dependence of the start-up power on the rise time of the electron pulse has been found. The experimental results are verified by a theoretical analysis. Our study shows that amplification in a FEM amplifier is always initiated by CSE arising from the edge of the electron pulse when the rise time is comparable to the electromagnetic wave period.

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PubMed2000

Effective coupling of cyclotron autoresonance maser and "gyrotron" modes on a phase-synchronized electron beam

For a cyclotron resonance maser (CRM) with a helical axis-encircling electron beam, the possibility of a strong interaction between cutoff (gyrotron) and traveling Doppler-up-shifted (cyclotron autoresonance maser) modes, which are in resonance with the electrons at the same frequency, is demonstrated. This effect can be used in a CRM oscillator of a new type, where the feedback and the mode selectivity for the operating traveling mode are provided due to the excitation of the cutoff mode. According to both the theory and the experiment, such a scheme can provide an effective excitation of the traveling mode with negligibly low losses associated with the cutoff mode.

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PubMed2000

The Rayleigh-like collapse of a conical bubble

Key to the dynamics of the type of bubble collapse which is associated with such phenomena as sonoluminescence and the emission of strong rebound pressures into the liquid is the role of the liquid inertia. Following the initial formulation of the collapse of an empty spherical cavity, such collapses have been termed "Rayleigh-like." Today this type of cavitation is termed "inertial," reflecting the dominant role of the liquid inertia in the early stages of the collapse. While the inertia in models of spherical bubble collapses depends primarily on the liquid, experimental control of the liquid inertia has not readily been achievable without changing the liquid density and, consequently, changing other liquid properties. In this paper, novel experimental apparatus is described whereby the inertia at the early stages of the collapse of a conical bubble can easily be controlled. The collapse is capable of producing luminescence. The similarity between the collapses of spherical and conical bubbles is investigated analytically, and compared with experimental measurements of the gas pressures generated by the collapse, the bubble wall speeds, and the collapse times.

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