Dust trajectory sensor schematics. Four planes carry 16 electrode wires, each equipped with a charge-sensitive amplifier. Two shield grids are placed in front and behind the charge sensing wires. A dust particle enters the sensor from the top and crosses all planes. The bottom carries an impact detector, which releases the trigger signal (not shown).
Trajectory sensor signals, recorded in the dust laboratory, from two planes of 16 wires each, are displayed in arbitrary units. From an independent measurement of the particle charge of 6.7 fC we estimate a sensitivity of 143 units per fC. The rms noise level was . Notice (1) the two high peaks indicating that the charged particle passed very close to a wire, (2) the coincident dips in signals next to the high peaks, and (3) the distortion of the signals by noise.
The COULOMB sensor model used for this work is depicted without the front walls. It consists of a cubic box containing three planes with seven electrode wires per plane and a minute sphere representing the dust particle.
The 21 signals from the three planes (at , 0, and 40) of seven wires per plane for a trajectory from 2,6, to 2,6,80, at normal incidence . They are offset in the abscissa for clarity. Notice the peaks and dips at the position of each plane when .
Responses from the seven wires of the middle plane to a charged particle moving along the axis from ,0,0 to 80,0,0. For clarity, only the tall portion of each signal is displayed (at ). The remaining signal portions, where the particle is at a greater distance from the wire, have been deleted. Notice that the seven signals look almost identical. Only the left flank of the first signal and the right flank of the seventh signal (when the particle is near a wall) are different.
The 21 signals from the three wire planes for an oblique trajectory, entering the sensor at ,, and exiting at 78,53,80, at angles of incidence and . Notice that the signals reach their peaks either before or after the position of a plane when , .
Signals from the seven wires of the middle plane for a trajectory at a very large angle of incidence . Notice that when the particle dwells at ,10,0, i.e., in the middle between wires ,,0 and ,,0, the amplitudes of the signals from both of these wires are 0.244, as expected from Table II for . Also notice the very high peak of the signal from the wire ,,0 at .
Charge induced in the center wire as a function of the particle’s position on the axis for wire diameters , 0.4, 1, and 2 mm and according to the formula given in Eq. (2). Notice how the signal magnitudes at the midpoint increase with increasing wire diameter (see also Table III).
The positions of the 21 wire electrodes (all dimensions in millimeter).
Largest signal amplitudes, and , and ratio as functions of (or ), which is the distance between and the wire that produced the largest amplitude, .
Midpoint signal amplitude and wire capacitance vs wire diameter per Eq. (2), the derivation of which was based on the assumption that (Ref. 4).
Midpoint signal amplitude and wire capacitance vs plane distance .
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