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Plasma Science, IEEE Transactions on

Issue 5 • Date Oct 1990

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Displaying Results 1 - 12 of 12
  • Demonstration of the frequency upshifting of microwave radiation by rapid plasma creation

    Publication Year: 1990 , Page(s): 814 - 818
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    A technique for frequency-upshifting electromagnetic radiation is demonstrated. By ionizing azulene vapor contained in a resonant cavity using a laser pulse, the frequency of the incident RF wave at 33.3 GHz is upshifted by 5% with greater than 10% efficiency. Maximum frequency upshift of 2.3 times the source frequency is observed. There are two mechanisms thought to be operative in producing the observed frequency upshift: the time-dependent dielectric constant due to increasing plasma density, and rapid Q-switching of the cavity. This technique has the potential of being able to generate tunable and chirped radiation over a very broad (Δf/f≳1) frequency range View full abstract»

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  • Triggered discharges with high arc voltages in a vacuum interrupter

    Publication Year: 1990 , Page(s): 766 - 774
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    Studies of nonsustained disruptive discharges (NSDDs), isolated cases of which can occur in vacuum interrupters, indicate lateral discharges between the cathode and shield, which can initiate a brief discharge between the contacts. To facilitate the study of such discharges, the sample discharges were triggered by a surface discharge induced by a spark gap, built into the side of the cathode, and observed with a high-speed film camera and image-converter camera. The tests showed a cathode spot after igniting. The emitted electrons first charge the shield negatively and then are directed toward the anode. The discharge burns at a high voltage, with current ranging from 10 to 100 A. After a period of up to 400 μs, the current demand increases abruptly; an arc discharge occurs between the contacts and discharges the capacitances near the switch. The contact gap undergoes a rapid dielectric recovery, and the restored voltage is maintained. These types of discharge were also observed with NSDDs; thus it can be assumed that the triggered discharges studied correspond to the NSDD type View full abstract»

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  • An analysis of the folded waveguide: a compact waveguide launcher for ICRF heating

    Publication Year: 1990 , Page(s): 802 - 813
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1016 KB)  

    Theoretical and experimental investigations of the folded waveguide launcher as proposed for use in the ion-cyclotron range of frequencies (ICRF) heating of tokamak plasmas are presented. Theoretical results include an analysis of the folded waveguide using Ritz's method to obtain various field quantities. The cutoff wavenumbers from this analysis are within 10% of those calculated using an unfolded equivalent rectangular waveguide model. Measurements of cavity resonances for a scale-model ICRF-folded waveguide with a cutoff frequency of 2.4 GHz also agree closely with those calculated using an unfolded equivalent model. An unfolded equivalent waveguide model is used to evaluate the properties of an inductive strip placed in the folded waveguide. Applying variational analyses provides upper and lower bounds to the reflection magnitude |S11| that are in good agreement with measured values. Polarizing plates (which have been proposed to increase the on-axis directivity of the radiated power) are modeled using an unfolded equivalent waveguide. A variational analysis is used to determine an upper-bound value of |S11| in air due to a polarizing plate inside a matched folded waveguide. Measured values are found to be within 3% of the calculated values, with |S11|>0.95 for frequencies between 2.5 and 4.5 GHz View full abstract»

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  • Collisional phenomena and current buildup in the electrical breakdown of hydrogen

    Publication Year: 1990 , Page(s): 775 - 783
    Cited by:  Papers (10)
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    The electrical breakdown of hydrogen is examined by means of a two-dimensional mathematical model applied to the case of a 0.50-mm gap at atmospheric pressure. The calculations indicate a very rapid discharge development, characterized by a marked deviation of the axial density profiles from an exponential dependence, but with an approximately exponential variation of the discharge current. The axial-electron and ion-density profiles are similar in form and nearly balanced in magnitude. Notwithstanding the small magnitude of the space-charge field, the radial profiles of the electron and ion density displayed a definite tendency towards constriction, i.e., the incipient formation of a spark-type channel View full abstract»

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  • Coaxial configuration of the dielectric Cherenkov maser

    Publication Year: 1990 , Page(s): 831 - 836
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The linearized Lorentz force, continuity equation, and Maxwell's equations are used to calculate the system dispersion relation for a coaxial configuration of the dielectric Cherenkov maser. The system consists of two coaxial conductors lined with dielectric and an annular relativistic electron beam, which propagates between the two liners. The dispersion relation for the beam and dielectric-lined coaxial waveguide structure and the no-beam system that describes the dependence of the generated frequency on the coaxial waveguide parameters are presented. Using the linearized dispersion relation, the growth rate for the beam-TM0n waveguide mode instability is calculated in the strong-coupling tenuous beam limit View full abstract»

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  • Monte Carlo simulation of electron swarms in nitrogen in uniform E×B fields

    Publication Year: 1990 , Page(s): 819 - 825
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The motion of electrons in nitrogen in uniform E× B fields is simulated using the Monte Carlo technique for 240⩽E/N⩽600 Td (1 Td=1×10-17 V cm2) and 0⩽B/N⩽0.45×10-17 T cm3 . The electron-molecule collision cross sections adopted are the same cross sections as those used previously for the numerical solution of the Boltzmann equation. The swarm parameters obtained from the Monte Carlo simulation are compared with the Boltzmann solution and with the experimental data available in the literature. In relation to E×B fields, it is concluded that the Monte Carlo approach provides an independent method of substantiating the validity of the equivalent electric-field approach View full abstract»

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  • Current sheath structure of the plasma focus in the run-down phase

    Publication Year: 1990 , Page(s): 826 - 830
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The current carrying plasma sheath in a 12-kJ plasma focus is studied in the axial run-down phase by means of the Schlieren technique. Subnanosecond ultraviolet light pulses from a preionized, transversely excited, atmospheric nitrogen laser provide sufficiently fine temporal and spatial resolution for such investigation where the propagation speed of the current sheath is of the order of 10 cm/μs. It is observed that the current sheath grows thicker if it is driven at speeds beyond an optimum value of about 8 cm/μs (when the neutron yield is maximum). The thickening of the sheath is seen as an effect of the ratio of the specific heats. At the speed of 11 cm/μs, the effect of the temperature gradient at the electrode surface broadens the sheath further. Slow driving speeds are observed to result in an inefficient and leaky position View full abstract»

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  • On the amplification mechanism of the ion-channel laser

    Publication Year: 1990 , Page(s): 837 - 841
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    The amplification mechanism of the ion-channel laser (ICL) in the low-gain regime is studied. In this concept, a relativistic electron beam is injected into a plasma whose density is comparable to or lower than the beam's density. The head of the electron beam pushes out the plasma electrons, leaving an ion channel. The ion-focusing force causes the electrons to oscillate (betatron oscillations) about the axis and plays a role similar to the magnetic field in a cyclotron autoresonance maser (CARM). Radiation can be produced with wave frequencies from microwaves to X-rays depending on the beam energy and plasma density: ω~2γ3/2ωpe, where γ is the Lorentz factor of the beam and ωpe is the plasma frequency. Transverse (relativistic) bunching and axial (conventional) bunching are the amplification mechanisms in ICLs; only the latter effect operates in free-electron lasers. The competition of these two bunching mechanisms depends on beam velocity ν0z; their dependences on ν0z cancel for the cyclotron autoresonance masers. A linear theory is developed to study the physical mechanisms, and a PIC (particle-in-cell) simulation code is used to verify the theory. The mechanism is examined as a possible explanation for experimentally observed millimeter radiation from relativistic electron beams interacting with plasmas View full abstract»

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  • A review of microelectronic film deposition using direct and remote electron-beam-generated plasmas

    Publication Year: 1990 , Page(s): 753 - 765
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB)  

    Soft-vacuum-generated electron beams employed to create a large-area plasma for assisting chemical vapor deposition (CVD) of thin films are reviewed. The electron-beam plasma is used directly, where electron-impact dissociation of feedstock gases plays a dominant role, and indirectly in a downstream afterglow, where electron-impact dissociation of feedstock reactants plays no role. Photodissociation and metastable atom-molecule reactions dominate in the downstream afterglow. The transmitted beam spatial-intensity profiles are quantified from initial generation at a slotted line-shaped cold cathode through acceleration in the cathode sheath and propagation in the ambient gas. The vacuum ultraviolet (VUV) output spectrum and VUV generation efficiency from electron-beam-excited plasmas are measured. The properties of films deposited by direct electron-beam-generated plasma-assisted CVD and downstream afterglow CVD are reviewed and compared to conventional plasma-assisted CVD films View full abstract»

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  • Damping rates of waves in a switched magnetoplasma medium: longitudinal propagation

    Publication Year: 1990 , Page(s): 797 - 801
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The interaction of a circularly polarized electromagnetic wave with a switched-on magnetoplasma medium is considered. A static magnetic field in the direction of propagation is assumed to be present, resulting in longitudinal propagation. The incident wave splits into three waves whose frequencies are different from that of the incident wave. It is shown that these waves ultimately damp out if the plasma is even slightly lossy. The damping of the waves is interpreted in terms of their attenuation with distance and decay with time as they propagate in the lossy plasma. The attenuation-length and decay-time constants of the waves are obtained, and their dependence on the incident-wave frequency and the gyrofrequency is examined. Optimum parameters for an experiment to detect these waves are suggested View full abstract»

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  • Temporal evolution of plasma from a highly ionized helium capillary discharge

    Publication Year: 1990 , Page(s): 784 - 788
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    The generation of a highly ionized helium capillary plasma and the study of its temporal evolution are discussed. A 30-cm-long and 1-mm-diameter helium plasma was created with well-terminated kiloamp current pulses of 90-ns full width at half-maximum (FWHM). Emission spectroscopy was used to study the recombination of totally stripped ions into hydrogenic helium ions and to measure the evolution of the plasma density from the Stark broadening of HeII transitions. A 1.2-kA discharge current pulse was observed to create a plasma density of 8×1016 cm-3 in 1 torr of helium. The maximum intensity of HeII transitions occurs in the afterglow of the discharge pulse, following the collisional recombination of totally stripped ions with plasma electrons when the plasma cools. The study is of interest in relation to the possibility of obtaining amplification in the 164.0-nm line of HeII in a capillary discharge View full abstract»

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  • Electron cooling of high-Z ion beams parallel to a guide magnetic field

    Publication Year: 1990 , Page(s): 789 - 796
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The cooling of high-Z ion beams through collisions with electrons whose temperature parallel to a guide magnetic field is considerably lower than their perpendicular temperature is considered. For initial electron temperatures, magnetic fields, and charged-particle densities, electrons tend to be trapped in the vicinity of their nearest ion neighbor. This results in an energy exchange with the ions that is qualitatively different from conventional models, where electron cooling is described in terms of small angle collisions or within the linearized dielectric response theory. Such models are justified for situations where the potential energy of interactions is small compared to the relevant kinetic energy; e.g. for light ions. For the case of high-Z ions, however, it is the trapping process itself that drives the cooling. Using a variety of parameterizations of the electron shielding of the ions, it is found that resulting steady-state ion temperature parallel to the magnetic field is less than a factor of ten higher than the original parallel electron temperature. The e-folding times of approach to the equilibrium temperature have been found to be on the order of a few milliseconds for Z in the range of 20 and above. This result is encouraging with respect to the production of ultracold beams or even a crystalline heavy-ion state View full abstract»

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IEEE Transactions on Plasma Sciences focuses on plasma science and engineering, including: magnetofluid dynamics and thermionics; plasma dynamics; gaseous electronics and arc technology.

 

 

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