I was just wondering if a beam of whatever charged particles can be compressed in velocity space if you send the beam through a (strong) magnetic field that is parallel to the beam? The charged particles (that are not moving exactly along the field lines) should spiral in the field in my opinion and through magnetobremsstrahlung loose energy and be reduced to moving only in the direction of the field. Is this correct? Is this used to 'cool' ion beams? Is a hideously strong magnetic field needed? Where can I read about this?