Pulse compression and intensity enhancement in rotor-propelled molecular beams

Abstract

Modifications to the design of rotors and their gas supply systems can greatly increase the intensity of the outgoing beams while restraining the concomitant deterioration of quality. Discs are for some purposes better than the shafts that have hitherto been used; they offer continuous beams, velocities up to and probably above 1 km s -1 and, for moderately heavy molecules, energies in the 1 ev region with intensities that may exceed 10 18 s -1 and 10 19 sr -1 s -1 ; products of reactive collision could be collected in bulk. Pumping requirements are minimal because most of the input gas is put into the beam, with no carrier gas. At highest intensity, the chance of collision between molecules in opposing beams (relative velocity up to about 2 km s -1 , available energy several electronvolts) may be a few per cent. Spinning shafts can initiate pulses lasting only a few microseconds, repeating several times per millisecond; the available speeds and peak intensities, though not the time-averaged intensities, are higher than for discs. At high beam intensity, the need for intermittent operation to avoid overheating of the tips of shaft rotors is more likely than for discs, and their efficiency of use of input gas is somewhat lower.