The TIDE/PSI Instrument Paper

Reference: Moore, T.E., C. R. Chappell, M. O. Chandler, S. A. Fields, C. J. Pollock, D. L. Reasoner, D. T. Young, J. L. Burch, N. Eaker, J. H. Waite, Jr., D. J. McComas, J. E. Nordholt, M. F. Thomsen, J. J. Berthelier, and R. Robson, The Thermal Ion Dynamics Experiment and Plasma Source Instrument, Space Sci. Rev., 1995.

Collimator System

Identical collimator assemblies are installed on each of the seven TIDE polar angle apertures. These collimators consist of two stacks of vanes, one collimating in spacecraft azimuth angle, the other collimating in spacecraft polar angle. The vane stacks are nested with the polar angle stack in the outer position and the azimuth stack in the inner position. The vanes are positioned so as to eliminate all trajectories which would in any case be unacceptable to the mirror/RPA/TOF optics system; that is, all trajectories which lie outside the angular response and effective area of the instrument. This collimator approach is intended to minimize the number of extraneous particles and photons entering the instrument apertures, and particularly to eliminate such particles or photons which would otherwise be incident upon interior surfaces other than the mirror grids. In this way, the susceptibility of the instrument to extraneous particles and photons is minimized.

Collimation of 10 degrees width in spacecraft azimuth is provided by means of parallel vanes which are 0.50 in. deep, 0.005 in. thick, and set on 0.044 in. centers. It should be noted that the M/RPA is designed for a commensurate angular response when its aperture is fully open. When the M/RPA is effectively "stopped down" by choosing a small ratio Vm/VRPA, its angular response is reduced from 10 degrees to as low as approximately 3 degrees.

Collimation of 22.5 degrees in spacecraft polar angle is provided by means of vanes which are set nearly coincident with planes which emanate radially from the instrument symmetry axis. The layout of a single polar angle collimator stack is illustrated in Figure 6. Note that the individual collimator channels each fully illuminate the focal plane (rejection/deflection system entrance aperture), while cutting off rays which would be incident upon the mirror frames or other interior structures. In the figure, "instrument C/L" refers to the symmetry axis of the sensor, around which the individual channels are arranged.

click for larger figure
Figure 6. Geometry for a single TIDE collimator providing 22.5° wide response in polar angle. "Instrument C/L" refers to the symmetry axis of the TIDE sensor, around which the polar angle channels are arranged radially, distributed in polar angle.

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Space Plasma Physics Branch | Space Sciences Laboratory | Marshall Space Flight Center | NASA

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Last Updated: Fri, Mar 8, 1996