Some results on the focussing lightguides. Requirements for the two design options
below were a focal plane perpendicular to the disc and a high degrees/mm dispersion.
* compact focussing lightguide:

*
curvedx2m54x3m09x4m05b.eps: compact focussing lightguide
The black dots are focal points on a particular ray. Ideally they would all lie
on top of one another. The position of a focal point actually does imply the
slope of the focal plane in its vicinity. It only can be changed at the cost
of imperfect focussing. The focal plane was twisted to vertical orientation
to allow photon detectors to be oriented parallel to the magnetic field.
The shorter the focal length, the bigger the focussing imperfections both
absolute (in millimetres) and relative (in degrees or beta). The aim was
here to get the dynamic range of 20degrees (45-25) into less than 50mm range,
so the focal plane could be covered by a standard 50mm or 2" side length PMT.
Focussing polynomial is y= -5.4/60^2*x^2 - 0.9/60^3*x^3 - 0.5/60^4*x^4
the focal plane is at x=77mm, these values can be further optimised.
Focussing imperfections [sigma]:
45deg 0.15mm ; 35deg 0.16mm ; 25deg 0.47mm .
Including an additional mirror surface into the lightguide one can keep the
readout completely upstream or downstream of the disc. It may be easier to
accomodate spacial constraints this way than fighting for extra space.
--
KlausFoehl - 05 May 2006
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DesignItems.