Lithium Ion Sources for the Investigations of Fast Ion Transport in Magnetized Plasmas. H. Boehmer, Y. Zhang, W. Heidbrink, R. McWilliams, Department of Physics and Astronomy, University of California, Irvine, California 92697 D. Leneman and S. Vincena,
H. Boehmer, Y. Zhang, W. Heidbrink, R. McWilliams, Department of Physics and Astronomy, University of California, Irvine, California 92697
D. Leneman and S. Vincena,
Department of Physics and Astronomy, University of California, Los Angeles, California 90095
In order to study the interaction of ions of intermediate energies
with plasma fluctuations, two plasma immersible Lithium ion
sources of different size, based on solid-state thermionic emitters
(Li-6 Aluminosilicate), were developed. Compared to discharge
based ion sources, they are compact, have zero gas load, small
energy dispersion, and can be operated at any angle with respect to
an ambient magnetic field of magnitude generally found in plasma
experiments. Beam energies range from 400 eV to 2.0 keV with typical
beam current densities in the 1 mA/cm2 range. Because of the low ion
mass of 6 amu, beam velocities of 100 – 300 km/s are in the range of
Alfvén speeds in Helium plasmas. Design considerations
and operation in a high vacuum test chamber as well as in the high density
magnetized plasma of the LArge Plasma Device (LAPD) at UCLA will
The work is supported by DOE.
Diameter: 75 cm; Magnetic field 0.5 – 2 kG
Pulsed at 1 Hz, peak density 2.5x1012 cm-3, Te = 10 eV
Turbulence: Drift waves; Launched and unstable Alfvén Waves
H. Boehmer, et al., “Operation of a 0.2 – 1.1 keV ion source within a magnetized laboratory plasma”. Rev. Sci. Instr. 75, 1013 (2004)
L. Zhao, et al., “Measurement of classical transport of fast ions”. Physics of Plasmas, 12, 052108 (2005)
Y. Zhang, et al., “Lithium ion source for investigation of fast ion transport in magnetized plasmas”. Submitted to Rev. Sci. Instr.
Ion species: Li, K, Cs, Ba.
Size: 3.0” dia., 4.78” long
0.25” dia. Emitter
Fits through 50mm port
Improvement of Performance
Dashed box: Space charge due to
1 mA/cm2, 600 eV beam included.
and errors around grid wires are small
at the useful center section.
(b) 0.25” Emitter with single accelerator
Grid: Fringing fields extend to center of
the beam. Field errors around the 40 lpi
(c) 0.25” Emitter with 90 lpi 1st grid.
Addition of a second accelerator grid
with 40 lpi.
Note: The beam current is
intentionally kept low to avoid
space charge blow-up of beam.
Good beam profile with near
parallel equipotential lines.
(b) 0.25” Emitter.
Blue: Single accelerator grid.
Red: Double accelerator grid.
Improvement of performance.
400 eV, ΔE = 3.7 eV
600 eV, ΔE = 12.3 eV
800 eV, ΔE = 15.0 eV
ΔE/E = 2.0 % = const
Note: The low energy tail of the distribution is probably due to a field error around the grid wires, an effect that becomes more severe with increasing beam voltage.
Lithium Ion Beam Profiles in LAPD
0.6” Emitter with 0.5 cm mask.
(a) Profile 5 cm from gun.
(b) and (c) Profiles at 32 cm
from gun after one cyclotron
orbit; Pitch angle = 280: Profiles
(b) At low plasma density in the
(c) At high density (> 1012 cm-3).
The beam is attenuated and the
centroid is shifted due to energy
loss and/or plasma potential
change: change in cyclotron
(Private communication, E. Wolfrum, Max-Planck-Institut für Plasma Physik, Garching)_
Fast Ion Beam Interaction with Alfv in LAPDén Waves in LAPD
Fig. 2. Picture frame antenna (provided by T. Carter’s group)
Fig. 1. 0.5 cm disk antenna (W Gekelman, S Vincena and D Leneman, Plasma Phys. Control. Fusion 39 (1997) A101–A112.)