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Title: Extraction of small-diameter beams from single-component plasmas

Abstract

A nondestructive technique is described to extract small-diameter beams from single-component plasmas confined in a Penning-Malmberg trap following radial compression using a rotating electric field. Pulsed beams with Gaussian radial profiles and diameters as small as 50 {mu}m are extracted from electron plasmas initially 2 mm in diameter. A simple theory for the beam diameter predicts 4{lambda}{sub D} (full width to 1/e), where {lambda}{sub D} is the Debye length, in good agreement with experimental measurements on electron plasmas. Applications and extensions of this technique to create bright, finely focused beams of positrons and other scarce particles are discussed.

Authors:
; ;  [1]
  1. Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States)
Publication Date:
OSTI Identifier:
20971838
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 8; Other Information: DOI: 10.1063/1.2709522; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 43 PARTICLE ACCELERATORS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; DEBYE LENGTH; ELECTRIC FIELDS; ELECTRONS; PLASMA; POSITRON BEAMS; POSITRON SOURCES; POSITRONS

Citation Formats

Danielson, J. R., Weber, T. R., and Surko, C. M.. Extraction of small-diameter beams from single-component plasmas. United States: N. p., 2007. Web. doi:10.1063/1.2709522.
Danielson, J. R., Weber, T. R., & Surko, C. M.. Extraction of small-diameter beams from single-component plasmas. United States. doi:10.1063/1.2709522.
Danielson, J. R., Weber, T. R., and Surko, C. M.. Mon . "Extraction of small-diameter beams from single-component plasmas". United States. doi:10.1063/1.2709522.
@article{osti_20971838,
title = {Extraction of small-diameter beams from single-component plasmas},
author = {Danielson, J. R. and Weber, T. R. and Surko, C. M.},
abstractNote = {A nondestructive technique is described to extract small-diameter beams from single-component plasmas confined in a Penning-Malmberg trap following radial compression using a rotating electric field. Pulsed beams with Gaussian radial profiles and diameters as small as 50 {mu}m are extracted from electron plasmas initially 2 mm in diameter. A simple theory for the beam diameter predicts 4{lambda}{sub D} (full width to 1/e), where {lambda}{sub D} is the Debye length, in good agreement with experimental measurements on electron plasmas. Applications and extensions of this technique to create bright, finely focused beams of positrons and other scarce particles are discussed.},
doi = {10.1063/1.2709522},
journal = {Applied Physics Letters},
number = 8,
volume = 90,
place = {United States},
year = {Mon Feb 19 00:00:00 EST 2007},
month = {Mon Feb 19 00:00:00 EST 2007}
}
  • In a recent communication [Danielson et al., Appl. Phys. Lett. 90, 081503 (2007)], a nondestructive technique was described to create finely focused beams of electron-mass, charged particles (i.e., electrons or positrons) from single-component plasmas confined in a Penning-Malmberg trap. This paper amplifies and expands upon those results, providing a more complete study of this method of beam formation. A simple model for beam extraction is presented, and an expression for a Gaussian beam profile is derived when the number of extracted beam particles is small. This expression gives a minimum beam diameter of four Debye lengths (full width to 1/e)more » and is verified using electron plasmas over a broad range of plasma temperatures and densities. Numerical procedures are outlined to predict the profiles of beams with large numbers of extracted particles. Measured profiles of large beams are found in fair agreement with these predictions. The extraction of over 50% of a trapped plasma into a train of nearly identical beams is demonstrated. Applications and extensions of this technique to create state-of-the-art positron beams are discussed.« less
  • A nondestructive technique was developed recently to create beams of electrons (or positrons) with small transverse spatial extent and high brightness from single-component plasmas confined in a Penning-Malmberg trap [T. R. Weber et al., Phys. Plasmas 90, 123502 (2008)]. A model for beam extraction was developed that successfully predicts the resulting beam profiles. This model is used here to predict the beam amplitudes and the energy distribution of the beams as a function of the exit-gate voltage. The resulting expressions, suitably scaled by the plasma parameters, depend only on the exit-gate voltage and the electrode radius. Predictions of the theorymore » are confirmed using electron plasmas. This technique permits the formation of beams with both small transverse spatial extent and small energy spread. Applications involving antimatter beams (e.g., positrons) are discussed, including bright beams for improved spatial resolution, short pulses for time-resolved studies, and cold beams for improved energy resolution.« less
  • Recently, we developed a non-destructive technique to create narrow beams of electrons (or positrons) of adjustable width and brightness from single-component plasmas confined in a Penning-Malmberg trap [Weber et al., Phys. Plasmas 13, 123502 (2008)]. Here, we review highlights of that work and discuss the distributions in energy of the extracted beams. A simple model for beam extraction predicts Gaussian beam profiles, with transverse spatial widths dependent on the number of particles in the beam. A Maxwellian energy distribution is predicted for small beams. The predictions of the theory are confirmed using electron plasmas. Extraction of over 50% of amore » trapped plasma into a train of nearly identical beams is demonstrated. Finally, the possibility of creating high quality, electrostatic beams by extraction from the confining magnetic field is discussed.« less
  • Tests of a high plasma density high-brightness helicon ion source for nuclear microscopy applications are underway. Experiments were performed with hydrogen, helium, and argon. Different extraction structures of the helicon rf ion source were investigated with an imposed external magnetic field. We present measurements of the extracted current as a function of the extraction voltage and rf power. The source has been diagnosed by a microwave interferometer. Plasma densities in the vicinity of the emission hole of up to 7.2x10{sup 12} cm{sup -3} (for argon), 1.6x10{sup 12} cm{sup -3} (for helium), and 6.0x10{sup 11} cm{sup -3} (for hydrogen) were obtainedmore » for working gas pressure of <5 mTorr and rf power <350 W (f{sub rf}=27.12 MHz). The ion current density was 80 mA/cm{sup 2} with high percentage of protons in the beam ({approx}80%). In the extraction structure, the cathode channel has a 3 mm length and a 0.6 mm diameter. The phase set degradation due to aberrations in the extraction structure of the helicon rf ion source was simulated for a fourth-order approximation in series expansion of the electrostatic potential and third-order approximation in series of the magnetic fields, by the matrizant method. The calculations were performed involving experimental data on ion energy spread, average ion energy, and plasma density of the helicon rf ion source with permanent magnets.« less