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  • 1
    Electronic Resource
    Electronic Resource
    Beam-generated plasmas for processing applications : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2558-2564 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of moderate energy electron beams (e-beams) to generate plasma can provide greater control and larger area than existing techniques for processing applications. Kilovolt energy electrons have the ability to efficiently ionize low pressure neutral gas nearly independent of composition. This results in a low-temperature, high-density plasma of nearly controllable composition generated in the beam channel. By confining the electron beam magnetically the plasma generation region can be designated independent of surrounding structures. Particle fluxes to surfaces can then be controlled by the beam and gas parameters, system geometry, and the externally applied rf bias. The Large Area Plasma Processing System (LAPPS) utilizes a 1–5 kV, 2–10 mA/cm2 sheet beam of electrons to generate a 1011–1012 cm−3 density, 1 eV electron temperature plasma. Plasma sheets of up to 60×60 cm2 area have been generated in a variety of molecular and atomic gases using both pulsed and cw e-beam sources. The theoretical basis for the plasma production and decay is presented along with experiments measuring the plasma density, temperature, and potential. Particle fluxes to nearby surfaces are measured along with the effects of radio frequency biasing. The LAPPS source is found to generate large-area plasmas suitable for materials processing. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345506
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  • 2
    Electronic Resource
    Electronic Resource
    Use of an active wire Bθ cell for electron beam conditioning (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4249-4257 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of intense, relativistic electron beams in air is subject to the resistive hose instability. Conditioning the beam prior to injecting it into the air can extend its range by reducing the hose growth rate and by reducing the initial spatial perturbations that seed the hose instability. Experiments have been performed using the SuperIBEX accelerator (Ipeak=10–30 kA, E=4.5 MeV, 40 ns full width at half-maximum) to develop conditioning cells that suppress the hose. This paper describes the performance of an active wire Bθ cell that is used in conjunction with an ion focused regime (IFR) cell. The IFR cell detunes the instability by producing a head-to-tail radius taper on the beam. The wire cell maintains this radius taper while producing an emittance taper that is necessary to suppress the hose growth. In addition, the wire cell reduces the initial beam perturbations through the anharmonic centering force associated with the wire current and its azimuthal magnetic field Bθ. The ability of the Bθ cell to reduce the beam offset with a minimal increase in the beam radius gives it several advantages over the use of a simple, thick scattering foil to perform the radius taper to emittance taper conversion. The SuperIBEX beam propagation distance, in terms of the betatron oscillation scale length, was extended to ∼10λβ using these cells. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363384
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  • 3
    Electronic Resource
    Electronic Resource
    Emittance tailoring of electron beams for propagation in dense gas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4258-4267 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An intense relativistic electron beam injected into dense gas characteristically propagates in a self-pinched mode but is susceptible to the resistive hose instability. This convective instability typically leads to large amplitude beam motion and the disruption of propagation. Theory and computation suggest that, although resistive hose cannot be completely suppressed, its convective growth can be reduced by varying the average betatron oscillation frequency from head to tail in the beam pulse. We report here on experiments designed to implement this variation by tailoring the beam emittance using an ion-focused regime "conditioning'' cell. Conditioning effectiveness is assessed by using measured beam quantities to evaluate a detuning parameter η(t). This information is correlated with beam propagation measurements to determine the optimum conditioning for resistive hose suppression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363385
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  • 4
    Electronic Resource
    Electronic Resource
    Transport and centering of high current electron beams in neutral gas filled cells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3580-3591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conducting tubes filled with neutral gas at pressures between 0.001 and 0.1 Torr can be used to transport, to center, and to reduce the transverse oscillations of high current ((approximately-greater-than)10 kA) electron beams. Electron impact ionization of the gas leads to partial neutralization of the beam space charge allowing self-focused beam transport and phase-mix damping of injected beam oscillations. In addition, the presence of conducting walls helps center the beam in the transport tube. High current beams, transported through a 1.3 m long tube, were centered to within one-tenth of the beam radius and input transverse oscillations were damped to submillimeter values without significant current loss or emittance growth. Beam transport properties are examined as a function of injected current, gas pressure, and cell geometry. Experimental results are compared with a theoretical model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359933
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  • 5
    Electronic Resource
    Electronic Resource
    Foil focusing of electron beams (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5985-5994 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin conducting foils focus charged particle beams through image charges induced on the foils. Such focusing has led to the suggestion that foils be used to transport intense, relativistic electron beams in high-energy accelerators. This paper examines some of the limitations of foil focusing including sensitivity to the beam parameters, emittance growth from anharmonic focusing, and beam stability in multifoil transport. The analysis is based on a thin-lens electrostatic treatment of paraxial beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346932
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  • 6
    Electronic Resource
    Electronic Resource
    Production of large-area plasmas by electron beams : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2137-2143 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis is presented for the production of weakly ionized plasmas by electron beams, with an emphasis on the production of broad, planar plasmas capable of reflecting X-band microwaves. Considered first in the analysis is the ability of weakly ionized plasmas to absorb, emit and reflect electromagnetic radiation. Following that is a determination of the electron beam parameters needed to produce plasmas, based on considerations of beam ionization, range, and stability. The results of the analysis are then compared with a series of experiments performed using a sheet electron beam to produce plasmas up to 0.6 m square by 2 cm thick. The electron beam in the experiments was generated using a long hollow-cathode discharge operating in an enhanced-glow mode. That mode has only recently been recognized, and a brief analysis of it is given for completeness. The conclusion of the study is that electron beams can produce large-area, planar plasmas with high efficiency, minimal gas heating, low electron temperature, high uniformity, and high microwave reflectivity, as compared with plasmas produced by other sources. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872886
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental investigations of the formation of a plasma mirror for high-frequency microwave beam steering (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2532-2538 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Naval Research Laboratory (NRL) has been studying the use of a magnetically confined plasma sheet as a reflector for high-frequency (X-band) microwaves for broadband radar applications [IEEE Trans. Plasma Sci. PS-19, 1228 (1991)]. A planar sheet plasma (50 cm×60 cm×1 cm) is produced using a 2–10 kV fast rise time square wave voltage source and a linear hollow cathode. Reproducible plasma distributions with density ≥1.2×1012 cm−3 have been formed in a low-pressure (100–500 mTorr of air) chamber located inside of a 100–300 G uniform magnetic field. One to ten pulse bursts of 20–1000 μs duration plasma sheets have been produced with pulse repetition frequencies of up to 10 kHz. Turn on and off times of the plasma are less than 10 μs each. The far-field antenna pattern of microwaves reflected off the plasma sheet is similar to that from a metal plate at the same location [IEEE Trans. Plasma Sci PS-20, 1036 (1992)]. Interferometer measurements show the critical surface to remain nearly stationary during the current pulse. Plasma density measurements and optical emissions indicate that the plasma is produced by a flux of energetic electrons formed near the hollow cathode. The sheet appears to be stable to driver voltage and current fluctuations (NRL Memorandum Report No. 7461, 28 March 1994, NTIS Document No. AD-A278758). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871215
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  • 8
    Electronic Resource
    Electronic Resource
    Controlling the resistive hose instability in relativistic electron beams (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4338-4354 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The resistive hose instability has long been recognized as the major impediment to the propagation of intense, relativistic electrons beams in dense gas. However, hose is a convective instability, and therefore its growth is limited by the length of the beam pulse, the local growth rate, and the speed at which the instability convects through the pulse. The convective speed and the growth rate depend on the beam and plasma parameters, and these vary strongly from beam head to tail. In this paper, hose theory is reformulated to incorporate these variations, and the reformulated model is then used to compute the maximum hose growth possible in a given beam pulse. In air, the model predicts that hose grows by many orders of magnitude when the beam current is less than 10 kA or has a rise time more than a few nanoseconds long. But the growth is predicted to be less than a factor of 20 if the current is 50 kA or more, the rise time is subnanosecond, and the beam radius is properly tapered from head to tail. The model is supported by extensive numerical simulations and is in general agreement with available experimental data. Many of the issues discussed here may have application to other instabilities as well. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870989
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  • 9
    Electronic Resource
    Electronic Resource
    Conditioning electron beams in the ion-focused regime (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 4153-4165 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Relativistic electron beams propagating through dense gas are subject to the resistive hose instability, a virulent kink instability that restricts the effective range of high-current beams. Previous studies have shown that the instability can be suppressed by centering the beam and tailoring its emittance prior to injection into the gas. One means of centering and tailoring a beam is to use short "conditioning'' cells that operate in the low-pressure, ion-focused regime. In this paper, analytic models are developed to understand and assess the performance of such cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860322
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of electron-beam tracking in reduced-density channels (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2696-2706 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory is presented for the guiding of relativistic electron beams by rarefied gaseous channels. The analysis is based on analytic computations of the transverse force felt by a rigid-rod beam propagating off axis from a channel of reduced gas density. The density gradients produce an attractive channel force that can be surprisingly robust, even though it develops from relatively subtle gas chemistry properties. Static numerical calculations support the analytic work. Longitudinal beam coupling and effects that degrade channel guidance are discussed as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859981
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