Proceedings of IBIC2012, Tsukuba, JapanTUPB72INJECTED BEAM PROFILE MEASUREMENT DURING TOP-UP
OPERATION
M.J. Boland, Australian Synchrotron, Clayton, Victoria, Australia
T. Mitsuhashi, KEK, Ibaraki, JapanK.P. Wootton, The University of Melbourne, Victoria, Australia
Abstract

CORONAGRAPH APPARATUS
The beam current injected into the Australian Synchrotron storage ring is ≈1 mA per shot in multi-bunchmode and ≈0.05 mA per shot in single-bunch mode. Thisis a relatively small current compared with the 200 mA ofstored beam. In order to measure the beam proﬁle of theinjected beam in the presence of the stored beam and requires an apparatus with a dynamic range of more thanfour orders of magnitude. However, the stored beam canbe masked so that an ICCD camera on the optical diagnostic beamline is sensitive enough to capture a single bunchinjection. A coronagraph apparatus used to measure beam
halos [1] was adapted to masked the stored beam and used
to observe the injected beam during user mode top-up operation. The mask needed to be wide enough to obscure
the stored beam size plus the residual oscillations causedby the injection kickers but narrow enough to observe theinjected beam. During the ﬁrst few turns the beam at the
optical diagnostic beamline (ODB) source point reaches ahorizontal amplitude of between -5 and 2 mm (see Fig. 4and Ref. [2]) so a vertical mask was used which allows theinjected beam to observed on either side of the mask.

Figure 1: Optical table conﬁguration for the ICCD coronagraph measurement.
mask was then cut to stop the stored beam (shown in Fig. 2)
but allow the injected beam to be observed on either side ofthe mask. Fig. 3 shows the ﬁrst ﬁve turns with only thestored beam and no injected beam. The mask was madelarge enough to obscure this beam motion due to the kicker
imbalance.

Figure 2: One turn of stored beam with a 5 mA single
bunch in the ring.
Figures 2, 3 and 4 show that in principle if the stored
beam including the kicker imbalanced induced motion, ismasked out, the injected beam can be observed during topup injection on turns 1 and 3.

EXPERIMENTAL SETUPRESULTSThe ODB at the Australian Synchrotron [3, 4] was used
to image the visible light from the injected electron beam.
To accommodate this imaging apparatus, the lens in the optical chicane [3] was removed. Instead, the principal focusing optic was positioned on the optical table, as highlighted
in Figure 1 below. A real image of the electron beam photon source was formed close to the ICCD camera [5]. The

The best image captured can be seen in Fig. 5 whereturns 1 and 3 of the injected beam can be seen to the left
and right of the masked stored beam. Turn 2 is also maskedsince the horizontal phase advance places the injected beamalmost on top of the stored beam, as can be seen in the image with only the injected beam in Fig. 4. Turn 1 is quite
washed out in Fig. 5 since the ICCD gain had to be reducedISBN 978-3-95450-119-9

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1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○A coronagraph-like apparatus was constructed on the optical diagnostic beamline on the storage ring to observe theinjected beam during top-up operations. An image was created on an intensiﬁed CCD (ICCD) that can be gated on asingle bunch or on a bunch train for a stronger signal. The
bright central stored beam was obscured so the comparatively faint injected beam could be observed. The injectedbeam comes in at a large enough offset so that it was clearlyvisible above any diffraction or beam halo signals. The
beam proﬁle measured was in good agreement with the observations made of the injected beam only using a telescopeapparatus. The measurements were made during user beam
in top-up operation mode and can be used to optimise theinjection process.

TUPB72

Proceedings of IBIC2012, Tsukuba, Japan

more clearly above the background generated by the stored
beam in the acquisitions before and after the injection.
44x 1083

turn 351

6
turn 1

2420

Figure 3: Superposition of 5 turns of stored beam during
the injection kick with a 5 mA single bunch and no injectedbeam.

−2−4−10−50
510
quisition no. (injection is at 0)c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○123

Figure 4: First 3 turns of single bunch injection with nostored beam.
to remove some of the noise from the stored beam. If theICCD acquisition was synchronistion to the injected beam
bunch offset, the gate could have been tighter and the gainincreased to improve the dynamic range of the measurement.

Figure 5: Injected beam turns 1 and 3 observed on eitherside of the coronagraph mask which blanks the stored beam(compare with Fig. 4 with no stored beam).
Looking at the 1D horizontal projection with background dark ﬁeld subtraction, the injected beam can also
be seen above the stored beam noise. Fig. 6 shows the horizontal projection of ten images before the injection event,the injection event at point 0, followed 10 more imaged after injection. The images are taken at 1 Hz and each image
contains a superposition of three turns. In this representation the ﬁrst and third turns of the injected beam can be seen

0200400600

8001000

1200

1400

horizontal projection (3 turns superimposed per aquisition)

Figure 6: Waterfall plot showing the horizontal projectionof each acquisition, with three turns captured per acquisition. The injection event is at acquisition point 0.

ANALYSIS
Firstly these measurements were taken during user
beamtime, so the storage ring and injection settings could
not be altered; this was as purely parasitic measurement todemonstrate the proof of principle. As a result the ICCD
trigger conditions were not optimal to capture the injected
beam. The gate had to be opened up for several turns since
the absolute timing of the 75 pulse injected bunch train relative to the 300 stored bunches was not known. In principle this can be achieved but the software was not conﬁgured to do so. An improved setup would take the injectedbunch timing offset and adjust the ICCD gate timing accordingly. This would allow the gate to be narrowed down
to the length of the injected bunch train (75 bunches) which
will also reduce the background diffraction caused by thestored beam. In this way the background can be reduced bya factor of 4, since only 75 of the 300 stored bunches will
be captured in the reduce ICCD gating time.

CONCLUSIONS
A proof of principle measurement was performed witha coronagraph type apparatus to observe the injected beamin the storage ring during user beamtime top-up operations.
The injected beam was observed despite being three ordersof magnitude weaker than the stored beam. Several shortcomings of the experimental setup were identiﬁed and will
be improved in future measurements. It is planned to use
the data to observe and optimise the injection process fortop-up operations.

ISBN 978-3-95450-119-92Transverse Profiles, Screens & Wires Monitors

Proceedings of IBIC2012, Tsukuba, JapanTUPB72

REFERENCES[1] T. Mitsuhashi, Proceedings of EPAC 2004, Lucerne, Switzerland, p2655 (2004).
[2] M. J. Boland, et al., These proceedings, MOPB83.
[3] M. J. Boland, et al., Proceedings of EPAC 2006, Edinburgh,UK, THPLS002, June (2006).
[4] M. J. Boland, et al., Proceedings of APAC 2007, Indore, India, WEPMA060, January (2007)[5] Stanford Computer Optics 4Picos ICCD camera<http://www.stanfordcomputeroptics.com>.

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3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 7: Image taken during the tuning of the coronagraph, great care must be taken to eliminate unwanted
diffraction effects.