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Title: Experimental and numerical analysis of the electron injection in a Malmberg-Penning trap

Abstract

The injection phase in a Malmberg-Penning trap is investigated both experimentally in the ELTRAP [M. Amoretti et al., Rev. Sci. Instrum. 74, 3991 (2003)] device, and numerically. The resulting plasma density distribution is studied by varying the source parameters, the external magnetic field strength, and the axial position of the external potential barrier. Space charge phenomena dominate the dynamics of the system; formation of hollow plasma columns and three-dimensional structures are observed. The processes are interpreted using a three-dimensional particle-in-cell code which solves the drift-Poisson system.

Authors:
; ; ; ; ;  [1];  [2];  [2]
  1. I.N.F.N. Sezione di Milano and Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133, Milan (Italy)
  2. (Italy)
Publication Date:
OSTI Identifier:
20974916
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2721072; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM-PLASMA SYSTEMS; ELECTRON BEAM INJECTION; ELECTRON BEAMS; MAGNETIC FIELDS; NUMERICAL ANALYSIS; PLASMA; PLASMA DENSITY; PLASMA SIMULATION; POISSON EQUATION; POTENTIALS; SPACE CHARGE; TRAPS

Citation Formats

Bettega, G., Cavaliere, F., Cavenago, M., Illiberi, A., Pozzoli, R., Rome, M., I.N.F.N. Laboratori Nazionali di Legnaro, Viale dell'Universita 2, I-35020 Legnaro, and I.N.F.N. Sezione di Milano and Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133, Milan. Experimental and numerical analysis of the electron injection in a Malmberg-Penning trap. United States: N. p., 2007. Web. doi:10.1063/1.2721072.
Bettega, G., Cavaliere, F., Cavenago, M., Illiberi, A., Pozzoli, R., Rome, M., I.N.F.N. Laboratori Nazionali di Legnaro, Viale dell'Universita 2, I-35020 Legnaro, & I.N.F.N. Sezione di Milano and Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133, Milan. Experimental and numerical analysis of the electron injection in a Malmberg-Penning trap. United States. doi:10.1063/1.2721072.
Bettega, G., Cavaliere, F., Cavenago, M., Illiberi, A., Pozzoli, R., Rome, M., I.N.F.N. Laboratori Nazionali di Legnaro, Viale dell'Universita 2, I-35020 Legnaro, and I.N.F.N. Sezione di Milano and Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133, Milan. Sun . "Experimental and numerical analysis of the electron injection in a Malmberg-Penning trap". United States. doi:10.1063/1.2721072.
@article{osti_20974916,
title = {Experimental and numerical analysis of the electron injection in a Malmberg-Penning trap},
author = {Bettega, G. and Cavaliere, F. and Cavenago, M. and Illiberi, A. and Pozzoli, R. and Rome, M. and I.N.F.N. Laboratori Nazionali di Legnaro, Viale dell'Universita 2, I-35020 Legnaro and I.N.F.N. Sezione di Milano and Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133, Milan},
abstractNote = {The injection phase in a Malmberg-Penning trap is investigated both experimentally in the ELTRAP [M. Amoretti et al., Rev. Sci. Instrum. 74, 3991 (2003)] device, and numerically. The resulting plasma density distribution is studied by varying the source parameters, the external magnetic field strength, and the axial position of the external potential barrier. Space charge phenomena dominate the dynamics of the system; formation of hollow plasma columns and three-dimensional structures are observed. The processes are interpreted using a three-dimensional particle-in-cell code which solves the drift-Poisson system.},
doi = {10.1063/1.2721072},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The phase of injection of the electrons in a Malmberg-Penning trap is investigated both experimentally (in the ELTRAP device) and numerically. The resulting plasma density distribution is studied by varying the source parameters, the external magnetic field strength, the time of injection of the electrons and the axial position of the external potential barrier. The observed processes are interpreted using a three-dimensional particle-in-cell code which solves the drift-Poisson system where kinetic effects in the motion parallel to the magnetic field are taken into account.
  • It is demonstrated using conventional fluid theory that angular momentum can be injected into a single component plasma confined in a Penning{endash}Malmberg trap via an externally generated, oscillating, nonaxisymmetric, electric field. The torque exerted on the plasma by the electric field is a highly nonmonotonic function of the plasma angular rotation velocity. The torque vs angular velocity curve is dominated by sharp resonances at which the angular phase velocity of a particular poloidal harmonic of the external field matches the plasma angular rotation velocity. The torque exerted on the plasma by a given poloidal harmonic is negative when the fieldmore » rotates faster than the plasma, and vice versa. This rather surprising behavior is shown to be entirely consistent with a standard result in hydrodynamic theory, but is generally not observed in present-day experiments. {copyright} {ital 1997 American Institute of Physics.}« less
  • This paper summarizes a fast numerical technique for solving Poisson's equation in an axisymmetric Malmberg-Penning trap. The method assumes the charge density qn(r,z) and boundary potentials {phi}(r=R{sub w},z) are specified, and solves for the electrostatic potential {phi}(r,z) within the cylinder. The solution of Poisson's equation is often an important step in the numerical reconstruction of the nonneutral plasma density profile n(r,z) from the axially integrated measurements of the charge density profile, Q(r)=qA{sub h}{integral}dzn(r,z), where q is the charge and A{sub h} is the effective area of the collimator hole.
  • Single species non-neutral plasmas have very robust confinement properties because the conservation of canonical angular momentum in a system with azimuthal symmetry provides a powerful constraint on the allowed radial positions of the particles. If no external torques act on the plasma, the plasma cannot expand radially to the wall. However, collisions with a background neutral gas will exert a torque on the rotating plasma thus allowing the mean-square radius to increase. In the electron diffusion gauge experiment, a pure electron plasma is confined in a Malmberg{endash}Penning trap and the radial density profile is measured as a function of time.more » The base pressure is 5{times}10{sup {minus}10} Torr and purified helium is injected to pressures {ge}5{times}10{sup {minus}9} Torr. The magnetic field is varied between 100 and 600 G. The experimentally measured radial density profile shape is found to match closely the theoretically predicted (expanding) equilibrium profile, where a single free parameter proportional to the electron temperature {ital T} is varied to best fit the experimental data. The best-fit value of the temperature {ital T} is found to stay approximately constant even as the plasma expands and the electrostatic energy decreases. The measured plasma expansion rate is found to scale with magnetic field strength as 1/B{sup 3/2} instead of the expected 1/B{sup 2} scaling. This modification in scaling may be caused by field asymmetries, which are believed to be an important factor in plasma expansion for the pressure ranges examined here. Nevertheless, the expansion rates are observed to increase with increasing background pressure, and the absolute scaling with pressure is consistent with theoretical predictions. {copyright} {ital 1999 American Vacuum Society.}« less
  • The effects of electron-neutral collisions on plasma expansion properties and the evolution of the m=1 diocotron mode are investigated in the Electron Diffusion Gauge (EDG) experiment, a Malmberg-Penning trap with plasma length L{sub p}{approx_equal}15 cm, plasma radius R{sub p}{approx_equal}1.3 cm, and characteristic electron density 5x10{sup 6} cm{sup -3}<n<3x10{sup 7} cm{sup -3}. Essential features of the m=1 diocotron mode dynamics in the absence of electron-neutral collisions are verified to behave as expected. The mode frequency, the growth rate of the resistive-wall instability, and the frequency shift at nonlinearly large amplitudes are all in good agreement with theoretical predictions. When helium gasmore » is injected into the trap, the evolution of the mode amplitude is found to be very sensitive to the background gas pressure down to pressures of 5x10{sup -10} Torr, the lowest base pressure achieved in the EDG device. The characteristic time scale {tau} for nonlinear damping of the m=1 diocotron mode is observed to scale as P{sup -1/2} over two orders-of-magnitude variation in the background gas pressure P. The evolution of the plasma density profile has also been monitored in order to examine the shape of the evolving density profile n(r,t) and to measure the expansion rate. The density profile is observed to expand radially while maintaining a thermal equilibrium profile shape, as predicted theoretically. While the expansion rate is sensitive to background gas pressure at pressures exceeding 10{sup -8} Torr, at lower pressures the cross-field transport appears to be dominated by other processes, e.g., asymmetry-induced transport. Finally, the expansion rate is observed to scale approximately as B{sup -3/2} for confining fields ranging from 100 to 600 G. (c) 2000 American Institute of Physics.« less