From: "Dennis Chornay" (chornay@lepdc3.gsfc.nasa.gov)
To: tstephen@du.edu
Subject: Some neutral type conversion experiments.
Date: Fri, 30 Oct 1998 16:21:08 -0500

Dear Tom et al.:

Please find attached the file neutrals.html and associated jpg files, which may be of interest.

In view of the fact that we are not going to Denver for the initial Lena checkout, we performed some experiments to see if we could create a neutral source, albeit molcular oxygen rather than atomic oxygen.

We leak oxygen into our ion gun, and are thus able to create a well defined 500 eV ion beam. This beam passes through a "mask" which has a 5.5mm aperture located in the center. This is located approx. 30cm infront of the detector. The mask/aperture arrangement has two 100lpi grids. Potentials may be applied to the inner grid to prevent the transmission of particles of a particular charge.

The detector is a flight spare imaging detector, sensitive area = 20mmx20mm. It is biased in the usual way to detect electrons. The sensitive area is recessed approx 0.25" from the front surface on which we mounted 3 additional grids.

There are thus a total of 4 grids, 3 of which may be biased as desired,

• Grid 1 = 100lpi = Gnd, infront of MCP
• Grid 2 = 70lpi = Variable usually put -800 v on this to prevent -ve particles getting to the MCP
• Grid 3 = 70lpi = Variable
• Grid 4 = 100lpi = Gnd, outermost grid

Applying a sufficiently large +ve potential on the Mask Grid, we prevent +ve ions from the beam from getting to the detector. The distance from the end of the ions gun lens system to the mask is at least 50cm. A "Neutral" beam approx. 5.5mm in dia may be observed directly, if the detector is moved in to the appropriate position.

Mounted just above and infront of the detector and on the same plate, is a polished 4cm long W surface. The center of this surface coincides with the tilt axis of positioning table. A position reading in these experiments of "Tilt=115.6 Degrees" corresponds to the detector being square to the incident beam. A position reading of "up/down = 53mm" corresponds to the beam hitting the surface (e.g. see fig 6), and a position reading of "up/down = 80mm" corresponds to the beam hitting the detector directly. As mentioned in the conclusions, I'm not sure of the angle of incidence of the beam to the surface, and will measure it next time we vent the system.

Regards Dennis