Hi, sorry if this has been asked before. It is known that two parallel wires carrying electric currents in the same direction attract one another. The force is known as electromagnetic force. My question is whether this has been checked for two pure currents of charges. Specifically, whether there is any experiment in which two parallel electron beams (or positive ions) have been observed to attract one another in vacuum. References to any published experimental work will be much appreciated. I have a very old reference with an experiment done by William Crookes in which he says that the electron beams repelled one another and I would like to double check this. Many thanks.