Minimum stored energy MRI superconducting magnets: From low to high field

Abstract

The aim of this article is to describe superconducting magnet coil arrangements from low to high field, particularly from 1T to 7T, within the context of the minimum stored energy designs. The findings illustrate that at low field, the maximum peak magnetic fields are located away from the most inner coils of the magnet configuration, whereas in high field designs, the maximum peak magnetic fields are created on coils lying on the inner diameter of the magnet bore. This becomes a critical aspect of any high field design, since there appears to be much less freedom of design at higher fields, due to the inherent limitations posed by peak magnetic fields on superconductors. Our findings also indicate that at low fields, 3T and less, reverse current coils can be used to shorten superconducting magnets, whereas at high field, above 3T, this is not necessarily the case, due to the large peak fields produced between adjacent, alternating current coils.

Conduction cooled magnet design for 1.5 T, 3.0 T and 7.0 T MRI systems

“…The volume of the wire required to design such conduction cooled magnets is also 30% less than that of a MgB 2 magnet. When compared with a conventional helium bath cooled NbTi magnet design by Vegh et al [48], it can be seen that the volume of wire required for such magnets is almost 30% larger than the proposed Nb 3 Sn magnet.…”

“…A good example of NbTi wire is given by Vegh et al [48] where they presented optimized designs for medium to ultrahigh MRI magnets using minimum stored energy optimization. They used the wire properties based on the characteristics provided by Sciver et al [49].…”

“…The factor limiting the use of NbTi superconducting wire is the coil critical current densities at the peak magnetic field within the wire. An optimized shielded 7 T magnet design operating at 4.2 K and with reasonable magnet dimensions proposed by Vegh et al [48] shows that for a NbTi wire of 1 mm 2 crosssectional area the coil operating current density is limited to about 94 A mm −2 due to peak magnetic fields of 9 T on the wire. This limitation on the coil critical current density translates into a bulkier magnet with a larger volume of superconducting wire and also an increased volume of liquid helium as coolant.…”

“…1.5 T and 3.0 T MgB 2 magnet designs compared to NbTi magnet design guidelines. The NbTi wire has a critical current density of 250 A mm −2 at a peak magnetic field strength of 9 T while measured at 4.2 K[48]. Maximum value of J _ op coil for such wire will be less than 250 A mm −2 .…”

A homogeneous superconducting magnet design using a hybrid optimization algorithm

“…The method is very efficient with its few variables, but it is hard to achieve the global optimal results. The second approach is the global optimization method [5][6][7][8][9][10] based on certain global optimization algorithms, such as the genetic algorithm and simulated annealing. The method needs extensive computing power for searching the feasible candidate coils within a broadly wide FCR, but it is very attractive as it can achieve global optimal results.…”