↟ Opposite-field superconducting septum magnet
As illustrated in the figure below, fast extraction of charged particle beams from accelerator rings is typically made by a combination of a fast-switched kicker magnet, which gives the beam a small deviation, and a septum magnet, which has two nearby apertures with a large difference in magnetic field, so that trajectories passing through them will be diverging quickly after the magnet. The circulating beam passes through one of the apertures, whereas the kicker will divert the extracted beam into the other aperture.
The current-carrying physical wall between these two apertures must be as thin as possible, so that the strength of the kicker magnets can be reduced and/or the distance between the kicker and the septum magnets can be decreased (leading to a more compact system). On the other hand, the jump of the magnetic field across this wall must be as large as possible so that the circulating and extracted beam diverge quickly downstream of the magnet - giving the possibility to place the next bending magnet of the ring nearby, i.e. for a compact system. These two requirements are, however, often times contradictory. In a typical configuration the septum magnets have zero field in their aperture #1 (for the circulating beam - i.e. the beam trajectory is straight here, and the septum magnet is just a so-called "drift space" in the ring), and a high field in aperture #2 (extracted beam). The large magnetic forces ("magnetic pressure") on the wall (towards the zero-field aperture) require a mechanically stiff system, and thereby sometimes quite thick walls.
An opposite-field septum avoids this problem by providing magnetic fields with opposite direction, but equal magnitude in the two apertures. This results in a zero net force on the wall, making it possible to reduce its thickness. However, in this case the septum magnet has an active effect on the beam, and will be part of the ring lattice (the sequence of beam-manipulating elements), and therefore must fulfil the very strict requirements on terms of field quality (homogeneity), which are typical for accelerators.
Although it was not included in the original HITRIplus proposal, our group aims to construct a proof-of-principle prototype to verify that the concept is realistic and the field quality is satisfying. With respect to the traditional septum magnets, this concept offers a significantly thinner wall for the same separating power, leading to a more compact layout of the ring, which is of primary concern for the HITRI+ project.
The concept proposed in the article at the bottom of this page describes a smart arrangement of superconducting wires, which guarantees a high-quality homogeneous field (2D cross section):
A python code was developed (© Marcell Szakály) to automatically set up a winding scheme and logic, which can be realized (i.e. no crossing of the wire, and sequential winding of the coil), and which generates the 3D path of the entire winding. This coil was then simulated by the RAT software (© Jeroen van Nugteren) to check whether the distortion to the ideal 2D field pattern, introduced by the coil ends, are acceptable in an accelerator ring. This work is summarized in the linked report written by Marcell Szakály. The following illustration is taken from that report.
Another python/VisualBasic code (© Marcell Szakály) automatically generates a CAD model of the so called "formers" (the solid bodies with precisely machined grooves to wind the superconducting wires into) for a given configuration constructed by the previous steps. The video below shows a recording of this software in action, generating one of the end spacers for the coil ends.
The animation below show the winding proces dynamically, illustrating the concept on one hand, and making it possible to visually check the consistency of the winding process, the winding scheme, etc. For a more intense experience, and if you have a virtual reality toolkit connected, click here
Keybindings in first person view: WASD,Space,Shift - Move; Left drag - look around; Scroll - Change movement speed;
- : Two-dimensional conceptual design of a superconducting iron-free opposite field septum magnet. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 959 (2020), 163521 doi:10.1016/j.nima.2020.163521
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