A gas cell apparatus for measuring charge exchange cross sections with multicharged ions

Abstract

A gas cell apparatus to measure charge exchange cross sections for charge state- and energy-resolved ion beams with neutrals is described. The design features a short well-defined interaction region required for beams of multicharged ions with high cross sections. Our method includes measuring the beam transmission at four different neutral pressures and extracting the cross section from the slope of a beam loss vs pressure plot. The design and procedure were tested for Ar interacting with neutral Ar gas over the incident ion energy range of 1.0-5.0 keV. The charge exchange cross sections agree well with previous complementary measurement techniques.

Charge Exchange Cross Sections for Noble Gas Ions and N2 between 0.2 and 5.0 keV

“…This so-called manipulator-mounted gas cell (MGC) includes two skimmers (1 mm and 2 mm apertures), a front end cap (3 mm aperture), a gas cell body (40 mm length), a back end cap (4 mm aperture), a retarding field analyzer (5 mm aperture), and a suppression electrode (6 mm aperture, −120 V). See [22] for more details. Beams of ions A + (A = He, Ne, Ar, Kr) are produced in an Omicron ISE 10 Sputter Ion Source.…”

“…All experiments were performed in the single collision regime (P < 10 −3 mbar) as determined by observing a strictly linear relationship between ion loss and pressure. We estimated the systematic uncertainty in the cross section at ±17% and observed statistical uncertainties on the order of ±10% (for more details see [22]).…”

“…Not only is this an improvement in our ability to measure the pressure during experiments, the elimination of the narrow tubing of the MGC design results in a significant reduction in the time it takes to pump out the cell, and a reduction by a factor of four in system base pressure (5 × 10 −9 mbar). [22]. Data for the FGC is offset −50 eV for clarity.…”

“…After recording data for a series of beam energies and cell pressures, the analysis was done using Equation (3), the same as with the MGC data. In Figure 3, we can see a comparison of the measurements of the Ar + -Ar cross section in the MGC [22] and preliminary tests using the FGC. For the Ar + -Ar measurements from the MGC [22] in Figure 3, the statistical uncertainties are in the order of ±5%.…”

“…Absolute cross sections are dependent on the ability to measure the ion beam currents and neutral target pressures accurately. The experiments performed herein took place in a gas cell apparatus [22] with the goal of producing absolute cross section measurements. The gas cell was designed with a small effective path length in order to measure charge exchange cross sections with large magnitudes (10 −15 cm 2 ) and mitigate the problem of large angle scattering.…”