NEUTRALIZATION OF ION BEAMS
Space charge neutralization for ion beam propulsion system based on time-independent solutions of relevant equations that predict large positive space charge
ION BEAM↗
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Electron beam charging of Space Shuttle thermal protection system tiles
Six space shuttle reusable surface insulation tiles were tested in the NASA Lewis Research Center's electron bombardment test facility. The 30-cm-square specimens were assembled by using the same materials and techniques used to apply the tiles to the space shuttle and were composed to 15-cm- and 20-cm-square tiles and pieces on 0.6-cm-thick aluminum substrates. There were two specimens of each of three thicknesses. One specimen of each thickness had gaps of less than 0.1 cm between tiles, and the other had gaps of approximately 0.15 cm. The specimens were exposed to monoenergetic electron beams (2 to 25 keV) with nominal fluxes of 0.1 and 1 nA/sq. cm. Tests were conducted with both grounded and floating substrates. The data presented include charging rates, equilibrium potentials, and substrate currents. There is evidence that discharging occurred.
Staskus, J. V.↗
Compensation of an ion space charge by electrons in a magnetic field <o kompensatsii ionnogo prostranstvennogo zaryada elektronami v magnitnom pole<
Compensation of ion beam space charge by electrons in high vacuum magnetic field
MAGNETIC FIELD↗
Propagation of charge-neutral beams in space - Modifications when negative ions are present
Two-dimensional (three velocity component) electrostatic simulations are used to investigate the properties of a charge-neutral beam consisting of H(+), H(-), and electrons which will be used in the Beams on Rockets (BEAR) experiment to be launched in late 1987 or early 1988. For cross-field injection and beam densities much greater than the ambient plasma density, the beam splits into two approximately charge-neutral beams: a H(+)-e(-) beam that propagates down the field lines and a H(+)-H(-) beam that propagates at nearly the initial beam velocity on time scales less than the ion gyroperiod. Because of this splitting, space-charge oscillations are induced in the H(+)-H(-) component, which lead to its breakup. At lower beam densities, particularly when the beam electron density is less than about the density of the ambient plasma, the ambient plasma response reduces the space-charge fields as the beam splits and the space-charge oscillations are suppressed.
Winglee, R. M.↗
Spacecraft charging during ion beam emissions in sunlight
During ion beam emissions from the SCATHA satellite, the potential of the negatively charged satellite body shows a sinusoidal oscillation frequency of once-per-spin of the satellite. The minimum occurs when the ion beam is sunward. The processes that may be responsible for the voltage modulation are considered. Neutralization of ion beam space charge by photoelectrons is examined. The photoelectrons are accelerated by the negative potential of the satellite. Effects of electron impact ionization, excitation of metastable states, and photoionization of xenon neutral atoms in the ion beam are studied in detail. Critical ionization velocity interaction is unlikely under the condition considered.
Lai, S. T.↗
Electrostatic ion thruster optics calculations
Calculations have been performed which encompass both a self-consistent ion source extraction plasma sheath and the primary ion optics including sheath and electrode-induced aberrations. Particular attention is given to the effects of beam space charge, accelerator geometry, and properties of the downstream plasma sheath on the position of the electrostatic potential saddle point near the extractor electrode. The electron blocking potential blocking is described as a function of electrode thickness and secondary plasma processes.
Whealton, John H.↗
Ion trajectories in a space-charge wave on a relativistic electron beam
The motion of an ion in a space-charge wave on a strongly magnetized electron beam is investigated. The motions of the ion perpendicular and parallel to the beam direction are coupled by a nonlinear term in the ion Hamiltonian that is proportional to the wave amplitude, and this coupling causes the motion of the ion to deviate significantly from that of a linear harmonic oscillator in certain resonant regions of phase space. A sequence of canonical transformations is employed to investigate the motion of the ion in these regions. It is determined that wave amplitudes that are too small to trap beam electrons are too small to cause these resonances to overlap. When this overlap does not occur, the motion is found not to be discernibly ergodic in any three-dimensional subspace of the energy hypersurface because there exists a third constant of the motion in addition to the total energy and angular momentum. The numerically integrated ion trajectories are studied using surface-of-section techniques in order to verify these findings. It is found that the third constant of the motion constrains an ion initially trapped in a potential well of the wave to remain trapped in this well. It is concluded that ergodic behavior poses no threat at attempts at collective ion acceleration in space-charge waves on an electron beam.
Russell, D. A.↗
Space charge effects during the injection of dense electron beams into space plasmas
One-dimensional electrostatic particle simulations are used to investigate the injection and propagation of intense electron beams and the plasma response to the beam injection. Beam densities greater than about the plasma density are considered. It is shown that if the injection is continuous, most of the beam electrons are drawn back into the spacecraft because of the buildup of positive charge on the spacecraft. Those electrons which are able to propagate away from the spacecraft are emitted periodically because of space charge oscillations induced by electric fields associated with the beam. A substantial increase in the fraction and average energy of electrons which can propagate away can be obtained if the injection is changed to periodic pulses having width and period matched to the induced space charge oscillations.
Winglee, R. M.↗
Phase-space analysis of charged and optical beam transport: Wigner rotation angle
The possibility of using the phase space formalism to establish a correspondence between the dynamical behavior of squeezed states and optical or charged beams, propagating through linear systems, has received a great deal of attention during the last years. In this connection, it has been indicated how optical experiments may be conceived to measure the Wigner rotation angle. In this paper we address the topic within the context of the paraxial propagation of optical or charged beams and suggest a possible experiment for measuring the Wigner angle using an electron beam passing through quadrupoles and drift sections. The analogous optical system is also discussed.
Dattoli, G.↗
Energy broadening due to space-charge oscillations in high current electron beams
During electron beam accelerator operation on Spacelab I, substantial fluxes of electrons were observed with energies greater than the initial beam energy. Numerical calculations are performed for the emission of an unneutralized, one-dimensional electron beam. These calculations show clearly that space charge oscillations, which are associated with the charge buildup on the emitter, strongly modify the beam and cause the returning beam particles to have a distribution of kinetic energies ranging from half to over twice the initial energy.
Katz, I.↗
The effect of space charge fields due to finite length electron beams in the free-electron laser
The space charge electric field of a finite length electron beam in the free electron laser amplifier with a tapered wiggler is analyzed. In the free drift region between the accelerator and laser, expressions for the increase of energy spread due to the self field are presented. In the FEL interaction region, the general conditions on the importance of the self electric field in the equations of motion is obtained. A numerical example of the FEL experiment at 10.6 microns is given.
Tang, C.-M.↗
Early experiments in charged particle beams from the Space Shuttle
Characteristics of studies on board the Shuttle involving the interaction of particle beams with the atmosphere and the ionosphere, and the effects of the beams on the electrical potential of the platform, are discussed. Noting that the Shuttle allows greater weight and power demands by scientific payloads than previous satellite launches, the OSS-1 Vehicle Charging and Potential experiment and the Spacelab 1 Particle Accelerator and Phenomena Induced by Charged Particle Beams are described. Instrumentation details are provided, including charge and current probes, the Spherical Retarding Potential Analyzer, the Fast Pulse Electron Generator, and digital control and interface units. The SEPAC equipment, which comprises an electron beam accelerator, and MPD plasma jet, and diagnostic units are detailed, and operating procedures and experiment objectives are outlined.
Raitt, W. J.↗
Two-dimensional computer experiments on ion- beam neutralization.
Two-dimensional computer simulation of space charge neutralization of ion beam
NEUTRAL BEAM↗
Ion beams from laser-generated plasmas
The paper describes the space-charge-limited beams produced by the plasma blowoffs generated by 20-MW bursts of 1.06-micron radiation from an active Q-switched Nd:YAG laser. Laser power densities near 10 to the 11th/sq cm on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and electrostatically focused; the spatially defined ion beams are then magnetically analyzed to determine the charge state content in the beams formed from carbon, aluminum, copper, and lead targets. This technique preserves time-of-flight (TOF) information in the plasma drift region, which permits plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.
Hughes, R. H.↗
New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code
We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence, (2) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, and (3) the parallel phase velocity of the whistler wave is smaller than that of the beam mode. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is also involved in the generation of whistler waves.
Nishikawa, Ken-Ichi↗
High-efficiency 20 GHz traveling wave tube development for space communications
A 75 watt CW high efficiency helix TWT operating at 20 GHz was developed for satellite communication systems. The purpose was to extend the performance capabilities of helix TWTs by using recent technology developments. The TWT described is a unique design because high overall efficiency is obtained with a low perveance beam. In the past, low perveance designs resulted in low beam efficiencies. However, due to recent breakthoughs in diamond rod technology and in collector electrode materials, high efficiencies can now be achieved with low perveance beams. The advantage of a low perveance beam is a reduction in space charge within the beam which translates to more efficient collector operation. In addition, this design incorporates textured graphite electrodes which further enhance collector operation by suppressing backstreaming secondaries. The diamond supported helix circuit features low RF losses, high interaction impedance, good thermal handling capability and has been designed to compensate for the low perveance beam. One more discussed tube feature is the use of a velocity taper in the output helix that achieves low signal distortion while maintaining high efficiency.
Aldana, S. L.↗
The theory of Langmuir probes in strong electrostatic potential structures
The operation of collecting and emitting Langmuir probes and double probes within time-stationary strong electrostatic potential structures is analyzed. The cross sections of spherical and cylindrical probes to charged particles within the structures are presented and used to obtain the current-voltage characteristics of idealized probes. The acquisition of plasma parameters from these characteristics is outlined, and the operation of idealized floating double-probe systems is analyzed. Probe surface effects are added to the idealized theory, and some surface effects pertinent to spacecraft probes are quantified. Magnetic field effects on idealized probes are examined, and the time required for floating probes to change their potentials by collecting charge and by emitting photoelectrons is discussed. Calculations on the space-charge effects of probe-perturbed beams and on the space-charge limiting of electron emission are given in an appendix.
Borovsky, J. E.↗
The plasma environment during particle beam injection into space plasmas. I - Electron beams. II - Charge-neutral beams
A realistic electrostatic simulation model is used to investigate the plasma environment in the near vicinity of a spacecraft during the injection of electon beams from the spacecraft. The model is described, and the cases of injection into vacuum and into a low-density plasma are addressed. The relationship of the two-dimensional results to the purely field-aligned one-dimensional simulations is discussed. The dependence of the results on the ambient plasma density is investigated. Then, the properties of a charge-neutral beam and the plasma response are examined for the case where the beam has nonzero velocity components parallel and perpendicular to the magnetic field. The parameters used in the simulation are described, and the properties of the beam injection into the vacuum and in the case where a plasma is present are given.
Pritchett, P. L.↗