Propagation Of Relativistic Electron Beam Research Articles

Experimental study of propagation of intense relativistic electron beams in nonconducting vacuum drift tubes after passage through a localized plasma source

The propagation of intense relativistic electron beams into evacuated nonconducting drift tubes after passage through a localized plasma source has been experimentally studied. Time-integrated photographs of the propagation process have been obtained, as well as quantitative measurements of the propagated beam current and energy.

Computer-simulation studies of electron-beam propagation through plasma into vacuum

A disk model is developed to simulate the propagation of a cylindrical relativistic electron beam through plasma into vacuum via collective acceleration of positive ions from the plasma. Simulation results show dynamic details of electron and ion flow not noticed previously. The high-energy tail in the ion distribution is attributed to motion of the virtual cathode early in time when the ions enter the system. A comparison between the computer simulation and our analytical model published earlier shows good agreement for the time average behavior of the particles.

Interaction of an intense relativistic electron beam with preformed channels

The interaction of an intense relativistic electron beam (REB) with preformed channels in gaseous atmospheres has been analyzed in order to delineate the effects of reduced density, avalanche ionization, preexisting conductivity, and channel currents. The REB for these experiments was produced from a field emission diode driven by the ≈1.4 MV pulse from a pulse forming line. Relativistic electron beam currents up to ≈16 kA with current densities up to ≈2 kA/cm2 were achieved and the REB current was approximately a half sine wave of width 27 nsec (FWHM). Preformed channels in the atmosphere were created using laser-guided electric discharges. Current-carrying reduced density channels were produced by applying a second discharge to the reduced density channel produced by the first discharge. Reduced density (≤ρ0/80), nonconducting channels were produced by the absorption of radiation from a pulsed CO2 laser in ammonia gas at background pressures of ≈40 Torr (ρ0/20). The results show that reduced density had little effect on REB propagation except for a decrease in scattering until the density within the channel had been reduced to such a low level that the dominant mechanism by which conductivity is generated shifted from direct collisional ionization to avalanche ionization. Avalanche ionization in a uniform atmosphere increases the growth of REB instabilities but when it is limited to the reduced density channel region the REB was always repelled or expelled from the channel. Preexisting channel conductivity (σ≥0.1 S/m) also caused the REB to be repelled or expelled from the channel. The presence of a parallel channel current permitted the REB to be readily injected into the channel and guided along it with minimal losses. All of these effects and the thresholds at which they occurred are consistent with the present understanding of the interaction of intense REB’s with gaseous atmospheres.

Spectroscopic studies of an argon plasma produced in a relativistic electron beam gas puff Z pinch

The spectra of argon ions emitted from a plasma created by discharging a 3-TW relativistic electron beam generator through an argon gas column are reported. New lines have been classified for 2s 2pn–2pn+1 transition arrays in Ar XI–XV and energy levels have been derived for lithiumlike argon XVI. The effects of mass motion Doppler shifts on the spectra have been measured and systematic shifts of transition energies with charge state are observed in the data.

Design and performance of a Tesla transformer type relativistic electron beam generator

A relativistic electron beam generator driven by an air core Tesla transformer is described. The Tesla transformer circuit analysis is outlined and computational results are presented for the case when the coaxial water line has finite resistance. The transformer has a coupling coefficient of 0·56 and a step-up ratio of 25. The Tesla transformer can provide 800 kV at the peak of the second half cycle of the secondary output voltage and has been tested up to 600 kV. A 100–200 keV, 15–20 kA electron beam having 150 ns pulse width has been obtained. The beam generator described is being used for the beam injection into a toroidal devicebeta.

Collective ion acceleration and relativistic electron-beam propagation

Experimental results on the collective acceleration of ions using a relativistic electron beam (0.5 MeV, 30 kA, 60 ns) are presented. A gas cloud consisting of either H2, He, or N2 gas was used as the ion source. Ion species, charge state, and energy were measured. Ions were accelerated as derived from the hydrogen and helium gas sources but not from the nitrogen gas source. In almost all shots significant numbers of hydrogen and carbon impurity ions were accelerated. The electron beam exhibited asymmetric propagation characteristics in the region immediately downstream from the anode.

Microwave radiation by a relativistic electron beam propagation through low-pressure air

Intense relativistic electron beams fired into air at varying pressures display a wide range of microwave signatures. These experiments held beam current, energy, and pulse length constant while varying gas pressure. Our observing window is 10 to 40 GHz. At low pressures (<10 mTorr) exponential spectra result, consistent with beam reflexing or virtual cathode oscillations. Above 20 mTorr the spectrum flattens and suggests collective emission at the beam-generated plasma frequencies. Power falls linearly with pressure above 20 mTorr, until electron-Neutral collisions damp the emission at a few Torr. However, weak 10 GHz emission appears at full atmospheric pressure.

Pulse power technologies and related new approaches in LIMAY-I.

Technological troubles and new approaches in a pulse-power machine : LIMAYI as a relativistic electron and light ion beam generator are reported. Liquid Fron-113 is successfully tested as insulator of the Marx generator for the first case. We develop a new type of a SF6 spark gap switch for the Marx generator.

Emittance Analysis of Beam Propagation in Low Pressure Air

Relativistic electron beam propagation in a conducting tube filled with low pressure air is investigated. Filling pressures from 20 to 320 mTorr were used. For all of the pressures in this range a significant portion of the beam current was transported over a 1 m tube length. Detailed emittance analysis characterizing beam propagation in the low pressure air is presented.

Propagation of a 3-ns relativistic electron beam in air

Experiments were performed measuring beam current, magnetic field, and energy of a 400-keV relativistic electron beam propagation in air in a 7.6-cm-diam glass guide tube, the same covered with a conducting screen, and in a 3.4-m-diam chamber. Nose-erosion rates, current neutralization, and stability data are given at various pressures. A propagation window exists between pressures of 270–1070 Pa. At the lower pressures, propagation is limited by nose erosion, whereas at higher pressures, propagation is limited by instability of the tail. The conducting screen stabilizes the tail of the beam, extending the high-pressure end of the window to ∼6000 Pa. Rectilinear propagation within 5 mrad occurs in the large chamber at 270–800 Pa.

Pegase: a multifluid code for computational study of high power relativistic electron beam propagation in atmosphere

Pegase: a multifluid code for computational study of high power relativistic electron beam propagation in atmosphere

Propagation of an intense relativistic electron beam through a plasma region into vacuum

An intense relativistic electron beam (IREB) is injected through a narrow plasma region into a vacuum drift tube at current levels far above the space-charge limit of the drift tube. Experiments show that accelerated co-moving positive ions from the plasma enable the beam to propagate to a collector at the end of the 15 cm diameter drift tube. In one set of experiments, the IREB (1 MeV, 27 kA, 30 nsec) passes through a hydrogen gas cloud with an effective width of approximately 2 cm. The net current measured by a 7 cm diameter collector at the end of a 55 cm long drift tube is 70% of the peak injected electron current. In another configuration, the IREB is injected through a laser-produced carbon plasma. A model is proposed linking electron beam propagation with collective ion acceleration which results in the generation of charge- and current-neutral plasmoids capable of free space propagation. Possible implications of this work to astrophysical processes (cosmic ray acceleration) and laser fusion (observation of high-energy positive ions escaping from target plasma) are discussed.

Intense relativistic electron beam propagation in evacuated drift tubes

The propagation of a magnetically confined intense relativistic electron beam (IREB) (1 MeV, 27 kA, 20 ns FWHM) in vacuum drift tubes has been studied experimentally and theoretically. Experimental results for current propagation as a function of uniform applied magnetic field (0–1.2 T) are presented for various drift tube diameters, cathode geometries, and anode aperture sizes. An analytic model of laminar beam flow is presented which predicts the space-charge-limited current of a solid IREB propagating in a grounded drift tube. A steady-state equilibrium is examined and is compared with the experimental results.

Propagation in Vacuum of an Intense Electron Beam Injected Through a Localized Plasma

Propagation of an intense relativistic electron beam (1 MeV, 27 kA, 30 ns) in vacuum after passage through a localized hydrogen plasma of \ensuremath{\sim} 2-cm width has been observed. A large fraction of the injected current was found to propagate in a vacuum drift tube to a distance in excess of 50 cm downstream of the plasma. A description of the process is proposed which links the electron beam propagation with collective ion acceleration and which relates to cosmic-ray acceleration and laser experiments.

A tabletop relativistic electron beam generator

A compact, tabletop relativistic electron beam generator has been designed and constructed. Electron beam pulses of 1.8 kA, FWHM of 30 ns, and 380 kV were obtained. (AIP)

The Wire Transport Code

The wire transport code is a particle code that follows a single disc of the electron beam through the transport system. It was developed to study the dynamics of relativistic electron beam propagation in a transport tube in which a wire conditioning zone is present. In order for the beam to propagate successfully in the transport section it must be matched onto the wire by focusing elements. The beam must then be controlled by strong lenses as it exits the wire zone. The wire transport code was designed to model this process in substantial detail. It is able to treat axially symmetric problems as well as those in which the beam is transversely displaced from an axis of the transport tube. The focusing effects of foils and various beamline lenses are included in the calculations. After discussing briefly the physics of wire propagation this paper describes the structural and operational aspects of the code.

Propagation of Intense Relativistic Electron Beams through Drift Tubes with Perturbed Walls

High levels of current and energy fluctuation appeared on an intense electron beam traversing a smooth drift tube in which two or more wall perturbations were inserted. The frequency of the fluctuations depended strongly on the geometry of the drift region. Theory and particle simulation showed that wall perturbations drastically altered the motion of the beam causing strong coherent current modulation.

Intense relativistic electron beam injector system for tokamak current drive

We report experimental and theoretical studies of an intense relativistic electron beam (REB) injection system designed for tokamak current drive experiments. The injection system uses a standard high-voltage pulsed REB generator and a magnetically insulated transmission line (MITL) to drive an REB-accelerating diode in plasma. A series of preliminary experiments has been carried out to test the system by injecting REBs into a test chamber with preformed plasma and applied magnetic field. REBs were accelerated from two types of diodes: a conventional vacuum diode with foil anode, and a plasma diode, i.e., an REB cathode immersed in the plasma. REB current was in the range of 50 to 100 kA and REB particle energy ranged from 0.1 to 1.0 MeV. MITL power density exceeded 10 GW/cm2. Performance of the injection system and REB transport properties is documented for plasma densities from 5×1012 to 2×1014 cm−3. Injection system data are compared with numerical calculations of the performance of the coupled system consisting of the generator, MITL, and diode.

Development of a fast risetime pulsed relativistic electron beam generator for the excitation of shorter wavelength lasers

We have developed a compact and simple high current relativistic electron beam (REB) generator for the excitation of lasers in the shorter wavelength region. This REB generator mainly consists of a Tesla transformer-type high-voltage generator, N2 gas insulated Blumlein-type pulse-forming line and cold-cathode electron gun to generate 800 keV, 12 kA pulsed electron beams with 6 ns current duration and approximately 4 ns current risetime. The design and operational characteristics along with discussions of the excitation capabilities of the gas laser media are presented in this paper.

Collective acceleration of protons in relativistic electron beam propagation in evacuated drift tubes

The results are presented of a series of experiments investigating the mechanisms leading to the collective acceleration of protons occurring in electron beam propagation through evacuated drift tubes. Detailed measurements have been made of the electron and ion beam propagation and of the ion energy spectra. The results show that the acceleration cannot occur as a result of a beam head or deep potential well mechanism. It seems likely that the acceleration is due to the self-excitation of a wave on the beam, possibly the electron-ion two-stream instability.