Synchrotron beam profile measurements during
top-up operation

M. J. Boland, et al., from the Australian Synchrotron used the 4 Picos fast gated ICCD camera to observe the profile of the injected beam on a turn-by-turn basis during top-up operation.

Experimental setup of the beam profile measurement using a coronagraph like apparatus.

Optical table configuration of the coronagraph measurement to measure the injected beam profile during top-up operation. The single bunch and single turn resolution is achieved by the fast gated ICCD camera, 4 Picos, which provides a shortest gating time down to 200ps. This figure is reprinted with permission from the Australian Synchrotron.

Beam profile measurements of synchrotron radiation in top-up operation

A coronagraph like experimental setup was constructed by the authors of the present work at the optical diagnostic beamline (ODB) of the Australian Synchrotron. They proved that this approach enables the observation of the injected beam profiles during top-up operation of the synchrotron facility. Top-up is a mode of operation that aims to maintain a steady current in the storage ring of the Australian Synchrotron by periodically injecting small amounts of current. In order to measure the beam profile of the injected beam in the presence of the stored beam requires a imaging device with a dynamic range of more than four orders of magnitude. However, the stored beam was obscured so that the ICCD camera can image the profile of the injected beam.

Experimental setup of the coronagraph like apperatus

The figure on top shows the optical table configuration of the coronagraph measurement including the fast gated ICCD camera, 4 Picos. A coronagraph apparatus used to measure beam halos was adapted to masked the stored beam and used the obsere the injected beam during top-up operation. The mask needed to be wide enough to obscure the stored beam size plus its residual oscillations caused by the injection kickers. These oscillations can be seen in following figure. It shows the superimposed stored beam profiles of 5 turns during the injection kick with a 5mA single bunch and no injected beam. Therefore, a vertical mask was used which allows the injected beam to observed on either side of the mask.

The stored beam of the synchrotron superimposed during 5 turns.

Superposition of 5 turns of stored beam during the injection kick with a 5 mA single bunch and no injected beam. This figure is reprinted with permission from the Australian Synchrotron.

Beam profile measurements of the injected beam in top-up operation

The images below show the injected beam without storage beam (left) and with obscured storage beam by the coronagraph mask (right). On the right figure the turns 1 and 3 of the injected beam can be seen to the left and the right of the masked stored beam. Turn 1 is quite washed out since the ICCD gain had to be reduced to remove some noise from the stored beam. Turn 2 is also masked since the horizontal phase advance places the injected beam almost on the top of the stored beam which can be seen on the image with only the injected beam (left).

Injected beam profile with no stored beam. Injected beam profile with the stored beam obscured by the coronagraph mask.

Left: First 3 turns of single bunch injection with no stored beam. Right: Injected beam turns 1 and 3 observed on either side of the coronagraph mask which blanks the stored beam. In comparison with the left figure the coronagraph mask obscures the stored beam and the second turn of the injected beam. These figures are reprinted with permission from the Australian Synchrotron.

Observation and optimization of the injection process for top-up operation

The authors presented the proof of principle for injected beam profile measurements of synchrotron radiation during top-up operation. They used a coronagraph type apparatus to observe the injected beam in the storage ring on a turn-by-turn basis. The injected beam could be observed despite being three orders of magnitude weaker than the stored beam. The Australian Synchrotron plans to use the data and this setup to observe and optimize the injection process for top-up operation.

Title: Injected beam profile measurement during top-up operation
Author: M.J. Boland, T. Mitsuhashi and K.P. Wootton
Institute: Australian Synchrotron, Clayton, Victoria, Australia