Hall Effect, Magnetoresistance, and Current Distribution in Quench Heaters

Abstract

Quench heaters are often an essential part of protecting a superconducting accelerator magnet during a quench. Their purpose is to spread the quench throughout the coil as quickly as possible. They are located in areas of high magnetic fields and are thus prone to magnetoresistive phenomena and the Hall effect. Such influences can cause currents to distribute unevenly in the heaters, which results in uneven heating. This can reduce the effectiveness of the heaters and even endanger them due to excessive local heating. Also, the heater geometry itself can be the cause of uneven current density. In this paper we investigate by numerical simulations the importance of the magnetic effects on quench heater performance and whether they should be taken into account in the design. The main interest is in the Hall effect, which was perceived as the most likely source of trouble for the design of quench heaters. We use a simple phenomenological approach for modeling the Hall effect, utilizing values from the literature for the Hall coefficients. Magnetoresistance is also considered and the impact of heater geometry on current distributions is briefly visited. The conclusion of this research is that magnetoresistance plays an insignificant role in the functioning of quench heaters. The Hall effect can clearly be more influential, but nevertheless should not pose any problems in most cases. Current distributions due to heater geometry should be take into consideration in the design phase and, if needed, take measures to equalize the current density by using, for example, copper cladding in appropriate locations.