Powerful Magnet Built At Everett What may be the largest, high-field superconducting magnet ever built has been turned out by Avco-Everett Research Laboratories for the Argonne National Argonne today, Avco described the device as a 32,800 gauss unit with a 10-inch bore, the largest bore ever developed for a unit of comparable size and strength. It will be used at Argonne in connection with the new 12.5 billion electron volt Zero Gradient Synchrotron, where it will help determine the speed of particles moving into a helium-hydrogen bubble chamber. Physicists using the magnet will compute speeds by measuring the deflection of particles of known mass as they pass through a magnetic field of known strength. Superconducting magnets are capable of tremendous strengths at relatively low cost. They depend on elimination of the resistance found in electrical circuits. This is done by immers.