Proton Synchrotron Division
Proton Synchrotron Division
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DC magnetic septa are continiously powered with a high electric current.
Generally the coil is constructed as a multi turn coil, as to reduce the current needed to power the magnet. The coil and the magnet yoke can be split in two, an upper and a lower part, to allow the magnet to be 'clamped' over the vacuum chamber of the extraction line.
These magnets are typically used as part of a slow extraction installation in a synchrotron, where the magnetic field doesn't have to be changed.
Rarely these magnets are sitting in a vacuum tank, but are usually operated at atmospheric pressure.
No displacement system is used to allign the magnet with the beam.
The most important feature of septa magnets is to have a homogeneous field in the magnet gap, and an as low as possible fringe field next to the magnet, as not to affect the circulating beam. This is achieved by using a conductor at the outer side of the magnet gap, called septum conductor, which separates the gap field from the low fringe field. The thickness of this septum conductor is of great importance. The goal is to construct a magnet with a septum conductor as thin as possible, to 'ease' as much as possible the task of preceding ejection elements as kickers or electrostatic septa. Due to the considerable current in these magnets lots of power is dissipated in the coil. Therefore a generous cooling circuit is embedded in the coil to keep the magnet coil at reasonable temperatures. In the individual turns of the coil are electrically put in series, but their respective cooling circuits are put in parallel as to increase cooling capacity.
In the figure above a cross section of a magnetic septum is shown.
The coil constisting of the septum and return conductors is marked in red. Each of the coil turns has to be insulated from the others, thus preventing a homogenious current density distribution in the septum conductor. Therefore an electromagnetic screen needs to be added next to the septum conductor to reduce the fringe field next to the septum magnet.
To minimise as much as possible the heat generated in the coil, the section of the rear conductor is increased to reduce the electrical resistance.
Since the magnet works outside vacuum, the vacuum chamber for the extracted beam is sitting in the septum magnet gap. For installation or repair purposes the magnet yoke and the coil are each made up of two halves to allow the magnet to be manipulated, without the need to remove the vacuum chambers.