Today’s high-performance electron beam tools are very sensitive to changing ambient magnetic fields. The fields move the beam causing loss of resolution and measurement accuracy. The SC22 system reduces the ambient AC field and restores the resolution and accuracy. The SC22 is a low-cost, high-performing AC magnetic field cancellation system that replaced the SC12 system which sold over 1,000 units worldwide.
The SC22 system comprises a Magnetic Field Control Unit, an AC Magnetic Field Sensor and three orthogonal multicore cables, which are installed in the room where the field is to be canceled. The SC22 can drive a single loop and double loop room size cables. It also works with Helmholtz cables that are attached to a frame around the column. Each power amplifier in the control unit drives a current through its cable to create a field of the opposite sign to the change in the ambient field. The magnetic field sensor measures the resulting field and real-time negative feedback reduces the ambient field by the loop gain of the system. The system is dynamic, automatically responding to field changes within 100 µs. AC Line fields (50/60 Hz) are reduced by 50x. The SC22 does not cancel DC field changes from sources such as elevators, trains, and traffic. The larger SC24 system is available to cancel both AC and DC fields.