Variable gradient permanent-magnet quadrupole lenses

Rare-earth (RE) permanent-magnet quadrupoles (PMQs) have been used for many applications in particle accelerators. One difficulty associated with PMQs is that the quadrupole gradient is not easily adjusted. Over a certain range, the magnetization of RE magnets is a reversible function of temperature. A scheme has been developed to use this property to make variable gradient PMQs. The field gradient changes required for tuning are typically on the order of a few percent. For many RE magnets, this requires temperature changes of a few tens of degrees centigrade and is accomplished by actively heating or cooling the quadrupoles