FocussingLightguide

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 .

• compact focussing lightguide with two reflections:
  
• curvedx2m54x3m09x4m05m.eps: compact focussing lightguide with two reflections

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

this page is part of DesignItems.