With big, expensive equipment and closely con- positioned between the poles where all the action
trolled experiment schedules, particle physics has takes place were fabbed out of stainless steel, with
never been a field for the do-it-yourselfer. But that Viton synthetic rubber O-ring seals and an off-the-
didn’t stop Tim Koeth from building two opera- shelf diffusion pump.
tional cyclotrons on his own time and dime. Koeth When the 12-inch cyclotron runs, hydrogen from
began the project as an undergrad physics major an outside tank slowly leaks through a pipe into a
at Rutgers University, soon after learning how the small ceramic cup in the center of the chamber.
machines worked, at least in theory. Koeth and his Inside the cup, a glowing electric filament splits
friend Stuart Hanebuth worked on the atom-smash- the hydrogen ions, a. k. a. protons, away from their
ers for several years and saw their first proton beam electrons. (Don’t try this at home, unless your home
in 1999; now the devices are permanent fixtures in has no oxygen.) Meantime, square-wave AC runs
the physics department and part of Rutgers’ stan- through the electromagnet, producing a shifting field
dard senior lab curriculum. that’s precisely timed using grad-school equations
The cyclotrons are named for the pole diameters to accelerate the ions in an ever-faster spiral out-
of their water-cooled electromagnets: there’s the 9- ward. The much lighter electrons are immediately
inch and the 12-inch. Most of the parts for both were swept far off in the opposite direction and absorbed
scrounged, bought used for cheap, or custom-fab- by the apparatus, which is grounded. In other
ricated at the university machine shop. The 12-inch experiments deuterium replaces hydrogen, and the
cyclotron uses a 2.5-ton magnet that came from magnetic field is timed to accelerate a proton-
Argonne National Laboratory, where it had been the neutron pair rather than a single proton.
steering magnet for a decommissioned accelerator. At the end of its acceleration, the beam is inter-
The vacuum chambers and the cylindrical vessel rupted and detected by instruments inside the
vacuum chamber. Getting the beam to exit would
require an electrostatic projector to peel particles away from their orbits, and a thin Kevlar seal over the port to maintain the vacuum while letting high-energy particles pass through.
Koeth’s success demonstrates that no physics project, no matter how advanced, is beyond the capability of creative and determined college students. Let that be an inspiration, and a warning.
—Paul Spinrad
>>Rutgers University Cyclotron: www.physics.rutgers.edu/cyclotron
References:
Archives