Magnetic field

The magnetic field directly affects the pumping speed. Above 85 °C, the pumping speed of an ion pump declines with temperature. Ion pumps have difficulty maintaining operation above 250 °C because of magnetic field loss. The ceramic magnets used exhibit reversible field loss of 0.2 % per degree Celsius and an irreversible field loss of 7 % at 350 °C. This loss is non-cumulative (subsequent bakeouts to 350 °C do not cause an additional irreversible loss).