Extraction of 580 MeV electrons
The septum magnet used for injection into ASTRID is designed to be used as an extraction magnet, too. A current of 1700 A in the 5×5 mm2 copper conductor gives a magnetic field of 0.28 Tesla, which allows deflection of particles with the maximum rigidity by 9.5 degrees into the extraction beam line. The parameters of the septum magnet are given in the table below.
|Maximum current||2000 A|
|Injection angle||14 degrees|
|Extraction angle||9 degrees|
|Orbit-outer septum wall||46 mm|
|Orbit-inner septum wall||35 mm|
|Septum thickness||11 mm|
|Max. Width of extracted beam||16.5 mm|
A new extraction scheme allowing parasitic extraction of 580 MeV electrons
has been devised at ASTRID.
The principle of extraction is shown in the figure below:
The dispersion at the position of the septum magnet is 6 m, for the lattice usually used during electron runs. This means that an electron that has gained more that 0.88 % in energy in a collision with another electron will jump the septum thickness and be extracted. The lifetime of an electron beam in ASTRID is determined by the Touschek effect, that is intrabeam scattering outside the (longitudinal) acceptance of the ring. For a 200 mA beam at 580 MeV with a lifetime of 12 hours, about 4·106 electrons are lost per second, and a fraction of these are extracted into the extraction beam line. The intensity will be proportional to the circulating intensity and inversely proportional to the lifetime. We have observed an intensity of 3·104/sec under these conditions. By reduction of the vertical beam size, and hence of the Touschek lifetime, a corresponding increase in the intensity of the extracted beam is seen. The beam is around 15×0.5 mm2 (H×V) at the septum. The extracted beam is used for tests of detectors for high-energy physics. We emphasize that this extraction is entirely parasitic and delivers a dc beam.
Last Modified 13 June 2009