6.2.7 Moving Parts and Electrostatic Shields

The setup took full advantage of the turn table installed in CASYMS. Rotation around the beta axis and translation along the z axis was used to move the setup into the field-of-view of the ion beam. The theta table was mounted overhead and used to rotate the CODIF instrument in order to select one of the several TOF entry slits (pixel). The available pixels were of varying widths and sensitivity. The pixel with the highest gain and the widest entry slit was selected for the measurements. As the width of the pixels was considerably smaller than the width of the exit aperture of the extraction lens, the lens was mounted on a small translation table (x-translation) to allow for scanning the whole exit aperture of the lens. This allowed the verification of the energy resolution of the extraction lens (Figure 6.9).

Figure 6.9: NICE setup with neutralizer and front shielding removed. Neutral particles would travel from the neutralizer along the line of sight to the conversion surface (CS). The x-translation and theta rotation axis are shown in yellow. TOF, EBOX, and DPU are submodules of CODIF. The shown part of the setup is approximately 70 cm in height.

A flexible shielding was built around the extraction lens to make sure that the lens was electrostatically completely shielded regardless of the lens position. For the ion measurements a tunnel made out of copper tape was built to provide a field free path to the grid replacing the conversion surface (Figure 6.10). More shielding was necessary for the neutral measurements because of the conversion surface now being at high voltage. Figure 6.11 shows a view from the outside of the neutralizer and the lens shielding.

Figure 6.10: Additional shielding for ion measurements. Using the original setup (top left) it was impossible to guide low energetic ions to the grid without an arbitrary deflection of the beam. This problem was solved using better shielding (right). The `tunnel' allowed for lens movements relative to the surrounding shielding without opening gaps in the shield.

Figure 6.11: NICE setup inside the CASYMS chamber prepared for neutral measurements. The neutral particle path to the conversion surface is completely shielded to avoid attraction of background ions to the conversion surface.

March 2001 - Martin Wieser, Physikalisches Institut, University of Berne, Switzerland