def add_collimator(coll)
      raise ArgumentError, "Invalid argument 'coll'. Expected Collimator, got #{coll.class}." unless coll.is_a?(Collimator)
      @collimators << coll unless @associated_collimators[coll.type]
      @associated_collimators[coll.type] = coll
    end
def add_collimator(coll)
      raise ArgumentError, "Invalid argument 'coll'. Expected Collimator, got #{coll.class}." unless coll.is_a?(Collimator)
      @collimators << coll unless @associated_collimators[coll.type]
      @associated_collimators[coll.type] = coll
    end
Adds a Collimator instance to this Beam.

 @param [Collimator] coll a collimator instance to be associated with this beam