Unit 9 - Magnetic design: the role of iron and grading techniques

<!--HTML--><p>This unit belongs to the fourth part of the course, which is focussed on magnet design.</p> <p>Here we will discuss the role of the iron. We will first show how non saturated iron can be treated, for simple geometries, with image current method. We then derive an analytical formula giving the field increase provided by iron for a sector coil. Using the sensitivities developed in Unit 8, we derive the short sample increase that can be expected from iron. We finally deal with the case of saturated iron, that has to be computed through finite element code such as ROXIE.</p> <p>We then introduce the concept of current density grading: higher current densities are used in the outer layer of the coil. This allows either reducing the quantity of conductor for a given short sample field, or to obtain a higher short sample field with the same quantity of conductor. Another flavor of the coil grading concept is using cheaper conductor in regions with lower field, and keeping the same current density.</p>