Velocity selector consisting of rotating Soller-like blades
defining a helically twisted passage.
Geometry is defined by two identical apertures at 12 o'clock position,
The origin is at the ENTRANCE of the selector.
Example: Selector(xmin=-0.015, xmax=0.015, ymin=-0.025, ymax=0.025, length=0.25,
nslit=72,d=0.0004, radius=0.12, alpha=48.298, nu=500)
These are values for the D11@ILL Dornier 'Dolores' Velocity Selector (NVS 023)
Jun 2005: extensive external test, one minor problem
Jan 2006: problem solved (for McStas-1.9.1)
Validated by: K. Lieutenant
for transmission calculation, each neutron is supposed to be in the guide centre
Parameters in boldface are required;
the others are optional.
Lower x bound of entry aperture
Upper x bound of entry aperture
Lower y bound of entry aperture
Upper y bound of entry aperture
Width of entry. Overrides xmin,xmax.
Height of entry. Overrides ymin,ymax.
number of absorbing subdivinding spokes/lamella
width of spokes at beam-center
radius of beam-center
angle of torsion
frequency of rotation, which is ideally 3956*alpha*DEG2RAD/2/PI/lambda/length