Beam Steering
Extraction magnets
The extraction magnets for slow extraction (see here) are:
- electrostatic septum
- magnetic septum (GS06MU3E)
- extraction bends (GS06MU4 and GS06MU5)
The following is a screenshot of SISModi tab in paramodi.
BeamSteering/2019-02-17_17-20-55-693.png "2019-02-17_17-20-55-693.png")
6 paramaters allow to control extraction:
- orbit bump amplitude at electrostatic and change of the amplitude during the spill (delta)
- orbit bump amplitude at magnetic septum and change of the amplitude during the spill (delta)
- a common correction to the angle of extraction dipoles (GS06MU4 and GS06MU5) together with change of the correction during the spill (delta).
For various extraction settings and beam rigidities (below or about 12 T) the correction to extraction dipoles varies. The last one (delta) allows to compensate for the beam movement during the spill. If we do dispersion measurement the delta should be 0.
Beam line sector GTE1
GTE1 is the first section of the beam lines, right after extraction. It is common to all beams extracted from SIS18. Peculiarity of this section is that it does not contain horizontal steering elements, and the two quadrupoles: GTE1QD11 and GTE1QD12 often are necessary for steering, when the GS06MU4 and GS06MU5 have not enough strength to compensate for the angle at which the beam is extracted (what depends on beam rigidity but also orbit and the values of the orbit bump at both septa). Therefore: 1. beam is often seen off-center on screens GS06DFV and GTE1DF, 2. the strength of the two quadrupoles should not be set too low, otherwise the steering is not possible. Traditionally, for high-rigidity beam, the operation keep these values above |k1l|>0.2.
Beam line sector GTH1
For all beam except those going to/via FRS, to HHD and to HHT the steering in TH1 is used. Right after extraction the beam can travel with various angles and therefore various trajectories, still staying within the acceptance of the beam line. The concept of steering along TH is such that, whatever trajectory, the beam should arrive in the centre of GTH1DG2G grid. This grid is a "rear sight" of our cross-hair and GTH1DG4G is a front sight. If the beam arrives in the centre of the GTH1DG4G, then it is well aligned and should go through centres of downstream quadrupoles. The distance between the grids GTH1DG2G and GTH1DG4G is 9.3 meters.