Measurements of the Total Charge-Changing Cross Sections for Collisions of Fast Ions with Target Gas Using High Current Experiment Page: 4 of 10

                                
It

0.18 A
K+ ion beam

Retarding
Field
Analyzer
k' ~ ~~~ fl ''pcif
MA1         MA2        MA3         MA4
Stabil-Ion          __Faraday
gauge                               Cup

G
s

(a)

Stabil-Ion    , rt          A
gauge                      R FA
=-0.2A. E-1MeV. K*

(b)
Figure 1. Experimental setup for total cross section measurements in the beam transport
section of high current experiment (a) Longitudinal view of the experiment. The
background gas is leaked between quadruple magnets 2 (MA2) and 3 (MA3) and
increases the background pressure from 10-7 Torr to 10-6 Torr. A RFA measures the
amount of expelled ions produced from the K' ion beam interaction with the background
gas concurrently with the measurements of a Stabil-Ion gauge and a Faraday cup. (b)
Transverse view of the experiment showing the Stabil-Ion gauge and RFA positioning
relative to the beam. The contours show simulated electric equipotentials, only ions
expelled within the azimuthal angle cp are able to reach the RFA collector.
After several measurements without gas leak at nominal vacuum conditions, the
total cross section 3.17 x 10-19 m2 was obtained. The Residual Gas Analyzer (RGA)
shows that most of the background gas is water vapor, thus it can be assumed that the
measured cross section is for water vapor.

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