Proceedings of IBIC2012, Tsukuba, Japan

MOPB77ADJUSTABLE OPTICS FOR A NON-DESTRUCTIVE BEAM PROFILEMONITOR BASED ON SCINTILLATION OF RESIDUAL GAS
V. Kamerdzhiev, A. Pernizki, K. Reimers#, FZ-Jülich, Germany
The scintillation profile monitor (SPM) is being
developed at COSY in addition to the existing ionisation
profile monitor (IPM). Contrary to the IPM it does not
require in-vacuum components, making it a robust andinexpensive instrument. The SPM is suitable for highintensity operation rather than operation with low
intensity polarised beams. A multichannel PMT is used todetect scintillation light. The rate of detectable
scintillation events is about three orders of magnitude
lower compared to the rate of ionisation events. To boost
the photon yield, small amounts of nitrogen are injected
into the SPM vacuum chamber. An adjustable light
focusing system is being built to optimise the SPM
performance for different machine operation modes. The
new system allows using a variety of optical components
ranging from single lenses to high-grade camera
objectives. Cylindrical lenses are considered to further
boost the sensitivity by better fitting the beam image tothe detector geometry. The latest experimental results andthe new design of the optical system are presented.

piezo-electric dosing valve. The vacuum chamber isblackened inside to avoid light reflections. It is equippedwith two DN100 viewports for light extraction and two
DN40 ports for vacuum monitoring and gas injection. A
32-channel photomultiplier (PMT) is used to detect
scintillation light.

INTRODUCTION
The cooler synchrotron COSY is equipped with a low
energy electron cooler and a stochastic cooling system.
While the electron cooler is typically used at injectionenergy stochastic cooling is operated at higher energies. A
2 MeV electron cooler built by BINP is expected to beinstalled in a few months. The new cooler will allow
electron cooling in the entire energy range of COSY [1].
Non-destructive beam diagnostics, in particular profile
monitors are essential for the operation of circular
accelerators with beam cooling. At COSY two profile
monitors are installed. The ionisation profile monitor(IPM) relies on the beam particles ionising residual gas.
The IPM is routinely used and delivers beam profiles withhigh sensitivity down to 1108 protons in the ring at
typical vacuum pressure of 110-9 mbar [1]. It provides
beam profiles in both transverse planes. The IPM becamea very valuable tool for setting up beam cooling.
However, high cost and components prone to aging
triggered a search for alternatives.
The scintillation profile monitor (SPM) detects lightemitted by the residual gas atoms and molecules after
their excitation by the beam particles. This method istypically used in beamlines [3, 4]. The SPM is a robust
and inexpensive instrument aimed at operation at highbeam intensities. At COSY the much lower event ratecompared to the IPM is coped with by creating a local
pressure bump. Nitrogen [5, 6, 7] is injected directly into
the SPM vacuum chamber using a commercially available___________________________________________#k.reimers@fz-juelich.deFigure 1: SPM installation in COSY. Shown is thevacuum chamber with the horizontal vacuum port forlight extraction and the vacuum ports for N2 injection andvacuum measurement.
A housing made of steel seals the electric connections
and the backside of the PMT against incoming light andelectromagnetic fields. All elements of the lens tube areblackened inside to reduce light reflection. The joints aresealed by tape to avoid light from outside of the chamber.
ISBN 978-3-95450-119-9

Transverse Profiles, Screens & Wires Monitors

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Copyright ○ 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)

AbstractMOPB77

Proceedings of IBIC2012, Tsukuba, JapanThe lens is mounted on a sledge inside the lens tube. It
can be moved by about 20 mm. Its position is fixed with
two screws. The whole SPM has an overall height ofabout 450 mm above the flange (see Fig. 1) .
This rigid setup bears disadvantages of mismatched
profile measurement if the beam isn’t crossing the field offocus. Readjusting the optics is time consuming as it has
to be done by hand in the accelerator tunnel.

UpgradeThe newly designed twin drive optical system uses
commercially available components. Each beam profile
monitor has two linear drives. The PMT is placed on theupper, a lens or a lens system is placed on the lower drive.
This setup allows matching the plane of focus to the beam
position. Also, the scale of image can be adjusted toimprove the resolution of the beam profile measurement.
The vacuum chamber was made much shorter than theprevious one. Its length has been reduced from 508 mm to256 mm to fit with the length of the 2MeV cooler beam
pipe. Correspondingly the in-air components have to fit
within the available length.

geometry, approximately 150 mm of beam length can beimaged by the SPM. An optical scaling factor in thecurrent setup is about 0.5 (1/1.837) meaning that only a
14 mm long part of the beam is seen by the detector.
Cylindrical lenses may be useful as they allow different
light focusing along and across the beam axis leading to asignificant boost of light intensity on the detector. The useof two cylindrical lenses oriented as shown in Fig. 3
corresponds to two optical lens systems having the same
overall focal length but different lens positions anddelivering different magnifications to the detector [10].
Beam planeSensor plane

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DrivesFigure 3: Cylindrical lens system for the SPM for one
working distance. The upper lens compresses the beam
image along the beam axis. The lower lens focuses thebeam image across the axis (profile).

PMT

Operation of SPM
The calibrated optomechanics will allow refocusing
step by step both transverse beam profiles. The horizontal
beam profile will deliver the beam position to focus thevertical one, the vertical beam profile information will be
used for focussing in the horizontal plane.

Lens

RESULTSPMT .
DrivesLens

Vacuumwindows

Particle
beam

Figure 2: New SPM design.
The current data acquisition software written in NI
LabView will be extended to control the linear drives bymeans of a commercially available stepper motorcontroller. The linear drives chosen are made by IGUS
[8].

Cylindrical Lenses
A standard lens system only “translates” an area seen as
an object to an area seen as an image. The sensor is a
PMT with 32 pixels having the dimension of 0.8 mm x7 mm and a pitch of 1 mm [9]. Due to vacuum chamber

A 48-channel picoammeter electronics developed at
iThemba Labs, South Africa [3] is used to read out thePMT. At typical vacuum pressure of 110-9 mbar there is
not enough light to be detected by the PMT. With thepressure bump to about 410-8 mbar and beam intensitiesof 5109 protons reasonable S/N ratio can be achieved.
The local pressure bump doesn’t impact the machine
operation [2].
Figure 4 shows the measured profiles and corresponding
Gaussian fits recorded simultaneously with the SPM andthe IPM. The measurement was carried out with 6109polarized protons circulating in the machine and PMT
voltage set to 750 V. The profiles were observed at thepressure of 810-8 mbar. The horizontal profiles show agood match. As the PMT of the SPM only has 32channels, the profile has lower resolution compared to theprofile taken by the IPM. The IPM uses CCD cameras
with 640 pixels per line.

ISBN 978-3-95450-119-9
2Transverse Profiles, Screens & Wires Monitors

Proceedings of IBIC2012, Tsukuba, Japan

MOPB77and F. Becker for sharing their ideas and experience andF. Klehr for support with mechanical design

Figure 4: Comparison of horizontal profiles of stacked
polarized proton beam taken by SPM and IPM at thesame time. Only during gas injection enough scintillation
events are available for profile measurement by SPM.

SUMMARY
The SPM is robust and inexpensive due to absence ofvacuum parts. Good agreement of horizontal SPM andIPM profiles was achieved with current SPM setup. The
new motorized optomechanical system promises
enhancements in versatility and accuracy of the SPM.
The use of cylindrical lenses is regarded to increase thesensitivity of the SPM by boosting the photon number on
the sensor.

[1] High Voltage Electron Cooler, M. Bryzgunov et al.,RuPAC 2012.
[2] Towards Routine Operation of the Scintillation
Profile Monitor at COSY, V.Kamerdzhiev et al.
IPAC 2012.
[3] Non-destructive Beam Position and Profile
Measurements using Light Emmitted by Residual
Gas in a Cyclotron Beam Line, J. Dietrich et al.,EPAC08.
[4] Beam Induced Fluorescence Monitors, F.Becker,
DIPAC 2011.
[5] N2 and Xe gas scintillation cross-section, spectrum,and lifetime measurements from 50 MeV to 25 GeV
at the CERN PS and Booster, M. A. Plum et al.,Nucl. Instrum. Meth. A 492, p. 74-90, 2002.
[6] Gas Scintillation Beam Profile Monitor at COSY
Jülich, C. Böhme et al., BIW 2010.
[7] Beam Induced Fluorescence Monitor–Spectroscopyin Nitrogen, Helium, Argon, Krypton, and Xenon
Gas, F. Becker et al., BIW 2010.
[8] http://www.igus.de/_Product_Files/
Download/pdf/d_dryline_s.pdf[9] http://sales.hamamatsu.com/assets/pdf/parts_H/
H7260_series.pdf[10] http://www.qioptiq-shop.com/en/Optomechanics/
Mounts-Posts/Mounts-Holders-compatible-to-FLS65/Holder-for-cylindrical-lenses.html

ACKNOWLEDGMENT
The authors would like to thank J. Dietrich andI. Meshkov for initiating the project and valuable
contributions. We are grateful to C. Böhme, L. Conradie

ISBN 978-3-95450-119-9
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REFERENCES