| Magnet Unit(s) | 8017 |
|---|---|
| Typical BDES | < 1.54 kGm |
| Typical Current | < 50 A |
| Typical PS Voltage | < 20 V |
| Nominal Beta X | 80 m |
| Nominal Eta X | 0.0 m |
| Nominal Beta Y | 43 m |
| Nominal Eta Y | 0.0 m |
BM1R is one of four vertical dipole steering magnets (BM2L,BM1L,BM1R,BM2R) which surround the injection septum.
These magnets together with the injection kicker are important for the process of injecting beam onto an already circulating beam (stacking).
These four steering magnets are intended to be used to steer the stored beam's vertical position and angle at the injection septum in a manner which is closed outside the septum region. The magnets are placed strategically about the septum (90 degrees and 180 degrees from the septum) to enable this.
To appreciate the utility of these magnets one must understand the HER injection scheme:
The scheme employed leaves the injected beam with a large betatron oscillation on the first turn with respect to the stored beam. This is termed "off-axis injection".
The beam injected into HER comes in from above and is directed towards the stored beam first by a lambertson type septum magnet. As the incoming beam approaches it is also deflected downward being offset in the QDI magnets (vertically focusing) which are centered on the stored beam axis. Before the current sheet septum the injected beam is above the stored beam and has a large downward angle. This downward angle is then removed by the current sheet septum such that immediately after the septum the two beams are parallel but offset significantly (~ 2 cm.).
This ~ 2cm offset from the design orbit is too large to capture without the injection kicker.
The injection kicker has two magnets equally spaced at 90 degrees from the septum on either side. When the kicker pulses (~200nS FWHM), it bumps the stored beam's position up towards the septum to align it with the incoming injected beam. The second kicker then brings the stored beam back to it's normal trajectory. The injected beam at the second kicker has a large angle due to it's offset 90 degrees earlier at the septum. The second kicker removes much of this angle allowing the injected beam to fit within the ring's dynamic aperture.
The BM magnets are intended to make a DC bump in the stored beam trajectory in a manner that helps the kicker bring the stored beam up towards the injected beam.
It becomes obvious that the BM magnets effect the injected beam in a much different manner than the stored beam. Since the injected beam sees only the second two BM magnets, manipulation of the stored beam's position and angle at the septum leaves the injected beam with a betatron oscillation on the first turn of the ring.
The term "on axis injection" refers to a condition in which the injected beam after the kicker/septum/BM magnets continues onto it's first turn with the same trajectory as the stored beam would have. To achieve this the DC bump magnets are cranked up such that a stored beam would be very close to the injected beam at the septum. The trouble with an on axis setup is that when it comes time to inject another pulse, the kicker fires and the stored beam within the kicker's time duration is kicked up all the way to the septum. In this condition the stored beam would be lost.
So in order to accumulate charge (i.e. not scrape off the stored beam) within the kickers' time duration the injected beam must come in on a different trajectory than the stored beam. This causes the injected beam to have a ~10mm vertical oscillation with respect to the stored beam. This oscillation damps due to the synchrotron radiation process and the injected beam eventually coalesces into the stored beam. This is the process which allows stacking of many injected pulses into the same stored bunch.