Beam Filtering Fingers
The "fingers" are located at the center of the third quadupole of the
RMS and coincide with the momentum focal plane. The beam, which passed
through the target but produced no interactions, is focussed according
to its momentum/charge ratio. The "fingers" are metal rods which can
be moved to coincide with these focii and intercept the beam without
strongly impacting the transmission of the reaction products from
fusion-evaporation reactions. In initial tests, the system has been
shown to work although the performance of the fingers depends strongly on
the spread in momenta caused by the beam passing through the target.
Thus, the thinner the target is, the better. This system should be used
when both beam and reaction products are transmitted beyond the first
electric dipole of the RMS and have different momentum distributions.
This feature has never been used because the targets we use are
typically 0.3 - 1.0 mg/cm2 and the momentum spread is large.
A schematic sketch of the fingers inside Q3 and data taken with a position sensitive detector at the achromatic focal plane. The horizonal spectrum in the middle is the normalized one-dimensional spatial distribution of recoils at the achromatic focus with and without fingers blocking charge state 23+. The normalized count rate spectrum on the right displays the number of recoils reaching the achromat as the position of one finger inside Q3 is changed. Note the dips in this spectrum caused by the fingers intercepting the focussed beam.
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This file last modified Monday January 08, 2007