Optimisation of coils for semi-continuous magnetic fields

Abstract

The optimum size, characteristic time, necessary power and energy for magnets for a semi-continuous high field above 40 tesla are strongly dependent on the type of coil-system; several different types can be distinguished. The increase in temperature of the coil is, for a homogeneous coil, about proportional to the square of the maximum field, and nearly independent of all other parameters. The temperature rise and minimum power needed can be reduced considerably by using a two-stage coil-system or a coil system with independently powered sections. Some general properties of these latter types of coil systems will be discussed.

Strength versus conductivity

“…In the power limited case it is efficient to use several nested coils that are energized consecutively [2]. Two different, extreme situations can be distinguished if the total coil assembly is energized from a power-limited supply:…”

“…The outermost coil: The minimum power condition can be calculated analytically or obtained using a graphical method [2] and results in an optimum volume for a coil with a given inner radius, field and wirematerial. Such a coil is normally not stress limited and the best conductor is simply the conductor with the lowest resistivity; in most cases this corresponds to the highest F.…”

“…In this approximation, the action integral of the pulse is taken to be 1.3 times the action integral during the flat top [2].…”

Beyond 60 T; a fruitful staircase to long-pulse 100 T fields

“…The calculations are based on the formulae describing the mechanical behaviour of coils [1] and optimisation of the magnets is based on paper [3].…”

“…(1), where AT is the maximum allowable temperature rise, e.g. 250 K. C .... is the averaged specific heat of the wire, Pv is its averaged resistivity, and Ate is the duration of the constant field [3]: …”