**4.2. Racetrack and saddle-shaped magnet**

94 Superconductors – Materials, Properties and Applications

connected to an assisting power supply to adjust the operating current. The total superconducting coil set-up should have five high temperature superconducting current leads. The copper adjustment coils 8, 9, and 10 are used to change the operating current to correct the magnetic field distribution in the homogeneous region. The main field distributions are illustrated in Fig.9 (b). For the requirements of IEECAS customers,

superconducting magnets with all kinds of magnetic field distribution are fabricated.

(a) (b)

Magnetic field distribution for various lengths of homogeneous region (b).

theory, we can design all symmetric field distribution magnet system.

**4. Structure and function of magnets** 

and yin-yang coils for different applications.

**4.1. Configuration of solenoid magnet** 

0

**Figure 9.** Superconducting magnet with 10 coils arranged with the same axis: the superconducting coils are installed in the cryostat; the copper coils are located outside of the cryostat and fixed on its flange, where they are cooled by air convection. The superconducting coils are cooled by a GM cryocooler (a),

The desired magnetic field produced by superconducting coils and the shape of field is predetermined by the users and its special application. The magnetic field distribution depends on the size and shape of coils and final system structure. The common shapes of superconducting coils are solenoid, saddle coils, race-track coils, toroid coils, baseball coils

The most efficient and economic coil is the solenoid structure, and normal solenoids are symmetric consisting of a single solenoid or several coaxial solenoids based on the field distribution and homogeneity demands. The solenoid coil is wound layer by layer with round or rectangular cross-section wires on a cylindrical bobbin. The basic parameters for a solenoid are inner radius *rinner*, router radius *router*, the length *L* and the current density *J*. The current density *J = NIop/*[*L(router-rinner)*], where the number of windings and operating current are *N* and *Iop*, respectively. The conductor current density is higher due to the electrical insulation and the eventual mechanical reinforcement. By these parameters, the magnetic field can be calculated by the popular equation (Martin N. Wilson. 1983). By this method, in

1

2

Magnetic field (T)

3

4

4T 250mm 4T 200 mm 1.3T 320mm SC 1.3T 320mm SC+Cu

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Z Axis (m)

The racetrack-shaped coil has two linear segments and two semicircular arc segments. The saddle coil has two linear segments and six small circular segments. The coil structure of racetrack-shaped and saddle coils are shown in Fig. 10. The racetrack-shaped magnet may be used in electrical machinery, magnetic levitation trains, dipole or multipole magnets for an accelerator, wiggler and undulator magnets, large-scale MHD magnets, space detector magnets and in space astronaut radiation shield and accelerator detector magnets, such as the ATLAS magnet at CERN. Sometimes, accelerator magnets, electrical machinery magnets and MHD magnets employ saddle shaped coils. Transverse magnetic field distribution can be produced by combining with the saddle coils and change the current direction. Saddle coils are also used to correcting the magnetic field distribution for magnetic resonance magnets and magnetohydrodynamics.

**Figure 10.** Configurations of a racetrack magnet and a saddle magnet.
