To set to components based conversion
cassandra.getPipeLineManager().getLookupTableList().getElementAt(0).getVtkObject().SetVectorModeToComponent()
cassandra.getPipeLineManager().getLookupTableList().getElementAt(0).getVtkObject().SetVectorComponent(1)
To set to a magnitude based conversion
cassandra.getPipeLineManager().getLookupTableList().getElementAt(0).getVtkObject().SetVectorModeToMagnitude()
REMARK: In the current version of Cassandra, the min-max values of the color bar are set on the 1st component be default, and it is generally needed to update them manually.
Julien (Artenum)