Tube Section Twisted along z-Axis

A tube section twisted along z-axis can be constructed using C++ or some simple text:

:volu twisted TWISTEDTUBS
 30*degree // angle twisted around z
 10 // inner radius [mm]
 15 // outer radius [mm]
 20 // half z length [mm]
 180*degree // dphi. NOTE: phi0=-dphi/2
 G4_WATER // material

NOTE!

• The default unit of the twist angle here is rad, not degree. We need to explicitly multiply the number with degree if we want to use degree as the unit. This is different from untwisted shapes, where the default unit of an angle is already degree.
• The twist can go beyond 180 degree in code, but note that any shape twisted 180 degree will snap in the middle in reality.
• The twist angle can be negative, which is just a twist clockwise if we see it from above.

The full source code is in tubs.tg, which can be visualized using the macro file tubs.mac, assuming an universal Geant4 application, such as MinGLE or GEARS, is available:

git clone https://github.com/jintonic/geant4
cd geant4/detector/CSG/twisted
# generate animated picture, tubs.gif
./twist.sh
# or launch a UI
gears
# in the UI, run
/control/execute tubs.mac