Why Rohacell?

Mass Budget	severe constraint
MVD sensor locations*	loose constraint

Axis Max. Error Max Rotation Error

Z 2.0 mm 1 degree

R 1.3 mm 16 degrees

S 1 degree

Low mass, low Z	machinable piece of air
Good strength to weight ratio	best of any known foam
Coefficient of thermal expansion	unusually low for a plastic material
Excellent fatigue strength

An equivalent cage would be an aluminum shell 0.0006" thick. Such a cage would still need an insulating layer to isolate the silicon detectors.

*Alignment Requirements for the MVD and BB counters,
(PHENIX-MVD-95-6)

Rohacell Support for PHENIX's Multiplicity Vertex Detector, MVD Summary (PHENIX-MVD-94-2)
Mechanical Characterization of the Multiplicity Vertex Detector Truss Structure (PHENIX-MVD-95-2)
Influence of Silicon Wafers on the Expansion and Contraction of Rohacell Cages when Exposed to a Changing Environment (PHENIX-MVD-95-11)
Parylene Conformal Coating for Rohacell (PHENIX-MVD-95-12)
Multiplicity Vertex Detector Subsystem Cage Deflection Studies (PHENIX-MVD-96-2)