6.2.6 TOF

For the Time-Of-Flight section of the NICE setup a modified CODIF (COmposition and DIstribution Function analyzer) as used in the Cluster Ion Spectrometry (CIS) experiment on Cluster II was used (abstract taken from [36]):

The CIS experiment on board the four Cluster spacecraft consists of a comprehensive ionic plasma spectrometry package capable of obtaining full 3D ion distributions with high time resolution (in one spacecraft spin) and mass-per-charge resolution. The broad scientific objectives and the wide dynamic range cannot be covered with a single instrument Consequently, the CIS experiment comprises two different instruments, a Hot Ion Analyzer (HIA) and a time-of-flight ion Composition and Distribution Function analyzer (CODIF). These sensors are controlled by a dual processor based Data Processing System (DPS), which permits extensive on-board processing. Both instruments use symmetrical top-hat analyzers which provide a contiguous, uniform, and well-characterized phase space coverage. The CODIF determines the distribution of the major ion species with energies from spacecraft potential to 40keV/e with an angular resolution of 22.5 \ensuremath{} x 10.25 \ensuremath{} and with two different sensitivities. The HIA does not provide mass measurements, but extends the dynamic range to the highest ion fluxes, and has the necessary angular resolution capability (5.6 \ensuremath{} x 5.6 \ensuremath{}) for ion beam and solar-wind measurements.
The entrance-system of the CODIF was removed for the NICE setup. A special conductive entry plate in front of the time-of-flight section minimized surface charging of the entry section of the TOF. This was necessary because measurements made in autumn 2000 showed that the originally insulating front section of the TOF would charged up and deflected the particles away from the entry slits.

Figure 6.8: The top plate depicts the modified TOF entry plate as used for the measurements in February 2001. Compared to the `old' entry plate shown in the bottom plate, all unused pixels are covered by the entry plate to maximize background suppression. Furthermore diameter of the entry plate was increased to minimize surface charging effects on the insulating outer ring. Of the four remaining pixels only one (A) was used for the measurements.

Figure 6.8 shows a photo of this modified entry plate. All unused pixels (there is a total of 16 pixels, but only 4 of them were used and/or connected to the electronics board) were also covered by the entry plate to minimize background noise.

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