The intensity peaks within a solenoid beam are found in a spiral around the line of the beam itself, while a Bessel beam's intensity rises and falls in peaks and troughs at higher distances from the beam's line.

BBC: Nasa examines 'tractor beams' for sample gathering

Solenoid beams have already proven their "tractor beam" abilities in laboratory tests published in the journal Optics Express, but the pulling power of Bessel beams, presented on the preprint server Arxiv in February, remains to be proved experimentally.

BBC: Nasa examines 'tractor beams' for sample gathering