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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
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Anomalous losses from relativistic electron rings in decreasing toroidal fields (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 13-16 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalously enhanced fast-electron losses are observed on relativistic E layers in the RECE-Christa device when the applied toroidal magnetic field decreases to zero in times shorter than ring lifetime. These losses consistently occur in a certain region of the field-reversal parameter and the ratio of applied toroidal to axial magnetic fields at the ring position. The critical parameter range is independent of the radial gradient of the applied mirror field, the background gas pressure, and the rate-of-decay of Bθ; however, it depends on the axial length of the rings, and there may be a threshold in dBθ/dt. The observed parameter dependence as well as the absence of any kink or tilt motions point to new orbital resonances as the cause of these losses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865174
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  • 8
    Electronic Resource
    Electronic Resource
    Electron beam tracking in a preformed density channel (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3407-3417 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-current charged particle beams can be guided by reduced density channels. Such guiding occurs when the distribution of plasma currents in the density channel causes a net attractive force to be exerted on the beam. In particular, a relativistic electron beam (REB) injected parallel to a spatially offset, reduced density channel is pulled toward the channel. The force exerted on the beam is predicted to increase as the beam current increases and as the offset between the beam and the channel increases out to offsets equal to the channel radius. An experiment with a 1 MV, ≈10 kA beam was performed that demonstrates this effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860396
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  • 9
    Electronic Resource
    Electronic Resource
    Retarding field energy analyzer for the characterization of negative glow sheet plasmas in a magnetic field (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2818-2825 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A retarding field energy analyzer has been developed for diagnosing 300 μs duration, 60 cm×60 cm negative glow, sheet plasmas immersed in a 150–250 G axial magnetic field. The electron density in these 4.5 kV, 13 A, 120 mTorr discharges in air and other gases, is high enough to reflect X-band microwaves. The presence of the magnetic field makes the suppression of secondary electrons from the Faraday collector surface more difficult. The approach taken here is to bias the entire collection circuit and the amplifiers 90 V positive with respect to the data acquisition room. The differentially pumped analyzer is designed to accept electrons with a large range of perpendicular velocities, and it measures the parallel velocity distribution function of the discharge electrons entering a 0.64-mm-diam hole in the anode plate. It gives valuable information about the energy spectrum of the energetic beam electrons emitted from the cathode, and the effect of energy loss and scattering processes on this propagating beam component. Additionally, since the analyzer sampling hole is offset from the anode-cathode axis, the current density profile can be measured for different bias voltages on the retarding grid, by rotating the linear cathode about the vertical anode-cathode axis. These profiles give the sheet thickness for the beam and plasma components of the negative glow discharge. It also gives useful information about the scattering induced beam spreading and its effects on the plasma sheet thickness and electron density. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147088
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  • 10
    Electronic Resource
    Electronic Resource
    A segmented concentric Faraday cup for measurement of time-dependent relativistic electron beam profiles (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 2895-2903 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multi-element segmented concentric Faraday collector has been developed for measuring the time evolution of the beam half-current radius (a1/2) of an intense relativistic electron beam. Each collector segment measures the total current within its radius. The data analysis procedure fits the data from all five segments at a given time to a prescribed beam profile and calculates a1/2 from the parameters of the fitted curves. The effect of beam centroid offsets on the data analysis was investigated numerically. Beam centroid offsets as large as half the beam radius produce only a 10% error in the experimental measurement of a1/2. The use of a thin graphite overlayer followed by range-thick stainless steel reduces scattering from one collector element to the next. The instrument has been used extensively on the SuperIBEX relativistic electron beam accelerator for measurement of the half-current radius as a function of time. Radius variations in excess of 4:1 have been measured over the duration of the beam pulse for beams with 5-MeV energy, 20-kA peak current and 1-cm final half-current radii.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142178
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