Lithium ion sources for investigations of fast ion transport in magnetized plasmas

Abstract

In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters ͑Li aluminosilicate͒ 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 up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mA/ cm 2 range. Because of the low ion mass, beam velocities of 100-300 km/ s are in the range of Alfvén speeds in typical helium plasmas in the large plasma device.

Dependence of fast-ion transport on the nature of the turbulence in the Large Plasma Device

“…The lithium ion gun 22,23 is inserted into the LAPD plasma at port 35 with variable pitch angle to the axial magnetic field. The initial width of the lithium ion beam is limited by the exit aperture of the gun ($5 mm), while the beam energy is set by the biasing voltage between the lithium emitter and the molybdenum grid on the aperture.…”

Measurements of interactions between waves and energetic ions in basic plasma experiments

“…At the LAPD, the source [7,8] uses a ceramic aluminosilicate emitter that is loaded with lithium. The ceramic is heated with ∼80 W to ∼1000…”

Time-of-flight neutral particle analyzer and calibration

“…The flux from a drifting Maxwell-Boltzman distribution with a peak energy of 750 eV and temperature of 83 eV ͑computed by a leastsquares fit͒ is shown in addition to data taken from a biased planar collector. 13 The Maxwell-Boltzman distribution and the collector data have both been transformed to the time domain and convoluted with the aperture function, Eq. ͑2͒, in order to compare with the TOF data.…”

“…13 An ion source with a tunable energy was used to verify that the TOF diagnostic measured the expected energies. The UV calibration method described in Sec.…”

“…III could not be used as a timing reference for this test, since the ion source blocked the UV photon path. Using a 500 V emitter bias for the source, an energy of 460 eV ͑obtained from the ion source calibration 13 ͒ was used to calculate the slot open time and an energy scan was performed.…”