30 μ A beam toroid

A standard commercial toroid modified to operate in the zero flux mode has been applied to the monitoring of the 750 keV polarized proton beam at the Zero Gradient Synchrotron (ZGS). The beam parameters are: rise time - 3 ms, pulse width - 15 ms, current - 30 μA. This beam produces a free space flux of H = 8.2 × 10^-7 oersted at the toroidal core radius. The device has a threshold of 10 μA as determined by system noise and operates with a bandpass of 10 Hz to 2.5 kHz. Ambient electromagnetic interference, predominately 30 Hz, 60 Hz and 200 MHz, was attenuated by use of a cylindrical "zero gauss" chamber. The addition of the magnetic shield introduced a sensitivity to mechanical vibration which was cured by isolation and stiffening.