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C. Böhme, Forschungszentrum Jülich, Germany
A. Halama, V. Kamerdzhiev, G. Koch, K. Laihem, K. Reimers
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
Abstract
The High Energy Storage Ring (HESR), within the FAIR
project, will according to current planning, provide antiproton beams for PANDA and heavy ion beams for i.a. theSPARC experiment. Manufacturing for most of the envisaged beam instrumentation devices in vacuum is completed
and testing is well underway. The overall status update of thebeam instrumentation devices is presented, with a focus on
the test-bench results of the BPMs. In addition, the planned
future timeline of the HESR beam instrumentation is briefly
reported.

INTRODUCTION
The HESR, part of the Facility of Antiproton and Ion
Research in Europe (FAIR) in Darmstadt, Germany, isdedicated to the field of antiproton and heavy ion physics.
The envisaged energy range is 0.8 GeV to 14 GeV for
antiprotons and 0.17 GeV/a to 5 GeV/a for heavy ions [1].
The ring will be a racetrack design with a length of 574 m.
The foreseen beam instrumentation within the modularized
start version is:
63
118
2
2
1
1
1
1
5
2

Diagonally Cut Beam Position Monitors (BPM)
Beam Loss Monitors (BLM)
Beam Current Transformers (BCT)
Ionization Beam Profile Monitors (IPM)
In-gap particle measurement
Schottky Pick-up
Phase Pick-up
Dynamical Tune-meter
ViewerScraper

serving through all these devices. But for each configuration a different length of the vacuum chamber, 1585 mm,
1249 mm, or 1180 mm, is needed. In addition, in the straightsections, these restrictions do not apply, therefore a 450 mm
long vacuum chamber is used there. But the BPM pick-ups
itself are identical in each configuration. All these different
length vacuum chamber have to fit on the test stand.

Signal Chain
Within the FAIR project, the standard signal chain consists of the A110 pre-amplifier [4], which features an amplification range of +60 dB to -60 dB. For the readout andcalculation of the beam position the LIBERA Hadron [5]was chosen. It features an extension for orbit control, which
has been adapted to the FAIR magnet control units (ACU).
As an extension to the original plan, the orbit control extension units have been ordered for the HESR as well. As
an addition to the FAIR standard, taking the low expectedsignal for the HESR into account, an additional low-noise
head amplifier of 20 dB, will be used directly on the vacuum feedthroughs in front of the A110 pre-amplifiers. It is
foreseen to use the same head-on amplifiers in other parts of
FAIR with expected low signal, e.g. the high energy beamtransport (HEBT) beamlines.

BPM SYSTEM
The pick-up design is based upon the diagonally cut shoebox design of the COSY BPMs [2]. The design was shownin detail in [3]. While 62 BPMs will have the inner diameterof 89 mm, one is designated to be located closely after the
injection septum, where the beam pipe has a diameter of
150 mm. Therefore, this BPM has to have a larger diameter
to not limit the aperture at this place. This one has still tobe designed and the production is not planned for the near
future.
In the bend sections of the synchrotron, between the
dipole magnets, different configurations of quadrupole, sextupole and steering magnets are foreseen, with at least one
quadrupole magnet but a different secondary magnet being
in place. In order to save as much longitudinal space aspossible, the BPM is build in the single vacuum chamber

Figure 1: Overview of the measured geometric factors ofthe HESR BPMs. Notable spread and outliers result fromthe real statistical characteristic of the individual BPM, systematic errors on the test bench as well as measurement
uncertainties. The standard deviations of the geometricalfactors are 𝑘 𝑥 = 0.55 mm and 𝑘 𝑦 = 0.66 mm.

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CURRENT STATUS OF THE HESR BEAM INSTRUMENTATION

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Figure 2: Overview of the BLM loss rate of the installed HESR BLMs at the COSY synchrotron for testing. The GUI is not
the final GUI for HESR, but only for testing with the FESA explorer.

BPM Testing
Of the 62 envisaged 89 mm BPMs, 47 have been tested,
the so far test results are shown in Fig. 1. An additional 14
recently received from production to be tested in the near
future. That leaves one BPM to be delivered. Every BPM
is tested using a wire test bench to check general electricalfunctionality and determine the linear coefficients and electrical offsets per plane. The test bench is fitted with µ-meter
precision linear drives and optical micrometers for moving
the wire and determining the precise position. In every BPM
two highly precise measured reference markers are added
during manufacturing, which deliver a reference for the wire
positioning. The signals are amplified by head amplifiers
and the A110, before being digitized by a Spectrum 16-bit
250 MHz ADC card. The whole measurement process, including the positioning of the wire, control of the gain of theA110, the ADC signal readout, and writing the measured
values to a file is done with LabView.
The initial concept of performing tests at the test bench
did only include centering the wire using the xy-arrangementof optical micro-meters to determine a suitable homing position. Drifts and mishaps during start up of a measurement
run may ruin an entire measurement cycle, as a permanent
unspecified shift from the geometrical center may occur insuch circumstances. Endeavours to include the optical micrometer readings for the evaluation of the entire measurement
run yielded an increased robustness and the means to mitigate such shifts have been performed. Concerns over someresults lead to a photogrammetric investigation to determine
the optical micro-meters rotation and shifts. It has beenconcluded that the optical micro-meters in the lower box are
rotated by 1.4° for one and 0.5° for the second device andfor the upper box 0.6° and 0.03°. The statistical uncertaintyof these values is estimated around 0.1°. Comparing electrically and optically derived positional wire positions indicate
a tilting behaviour for every position of the meander path ofthe linear drive assembly through the BPM while measuring.
Although the linear drives allow for sub micro-meter motion,
the examinations showed, the actual wire position should
not be taken from raw set-values of the linear drives but the
optical micro-meter readings should be favored.
While the mechanical tolerances for the parts of the BPM
directly involved in the measurement process, such as the
pick-up electrodes, have been specified with tolerances lower
than 2/100 mm, the mechanical deviations have an impact
on both, the electrical zero position in regards to the mechanical zero position, and the geometrical factors used forthe calculation of the position of the particle beam. An additional source for spread of the additive coefficients may
be explained by a large contribution of mechanical deviations in the electrical signal feedthroughs of the BPM because of their varying parasitic capacity. An analysis of
10 feedthroughs and their effects on signal strength against
their individual capacitance indicates strong correlation as
well as a spread in capacitance in the entire tested set thatwould accommodate a good part of the noted distributionof the electrical centers. The expected values for the BPMs
have been presented in [6]. There simulations resulted in
k=73.52 mm and for the offset to 0.7 mm.
Theoretical models have shown a weak but noticeable
coupling between the vertical and horizontal measurement
plane of BPM electrodes. A more realistic approach toconvert the electrical signals to beam position would be to
append a linear term for each decoupled case:𝑥 𝑏𝑒𝑎𝑚 = 𝑥0 + 𝑘 𝑥𝐻 · 𝐷𝑂𝑆 𝐻 + 𝑘 𝑥𝑉 · 𝐷𝑂𝑆𝑉MOP001
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and 𝑦 𝑏𝑒𝑎𝑚 analogous respectively. The terms 𝑘 𝑥𝑉 and 𝑘 𝑦𝐻
are small and could naivly be omitted and even will be for thesimplicity with the Libera Hardron implementation. Yet one
can include a correction calculation within the control system software to transform 𝑥𝑦 𝑏𝑒𝑎𝑚−𝑛𝑎𝑖𝑣 to 𝑥𝑦 𝑐𝑜𝑢 𝑝𝑙𝑒𝑑 using
a predetermined 2x2 matrix for each BPM.

BEAM LOSS MONITOR
For machine commissioning, routine operation and further
beam optimization detailed beam loss data is very valuable.
Unlike other accelerators, the HESR BLM data will not be
used for an automated machine protection, as the stored total
beam energy will not be high enough to damage the machine.
Along the ring 118 BLMs will be used, of which 20 havebeen so far delivered by GSI, mainly for testing purposes.
The BLM consists of a BC-400 plastic scintillator and a
Hamamatsu photomultiplier (PMT). This solution is favored
over e.g. an ion chamber type loss monitor because of thelow expected loss rates. The design was presented in detailat [7]. It was developed by GSI and will be used in otherparts of FAIR as well, e.g. the HEBT.
For the readout of the BLMs a µTCA system will be
used utilizing scaler/counter SIS8800 and RTM discriminator SIS8980 from Struck Innovative Systeme GmbH. Bothcards are connected to each other via the µTCA backplaneand provide 16 channels per card. The BLM PMTs will be
powered individually utilizing a multichannel HV system
in order to be able to compensate for the properties of theindividual BLM detector and the individual location.

FESA Control Test System
In order to have a Front-end Software Architecture (FESA)
control system operational for development and testing, astripped down test system was installed by Cosylab d.d. at
COSY. As a functioning system the control and readout of theBLM system was implemented and can be used in addition
to the COSY BLM system with additional BLMs, with its
GUI shown in Fig. 2. Besides this test setup, the system isalso designed as a reference for further FESA development
and testing.

IONIZATION BEAM PROFILE MONITOR
Ionization Beam Profile Monitors (IPM) have been built
and tested in cooperation with the GSI since 2007 [8], becoming a very valuable instrument in beam diagnostics at
COSY and GSI [9]. Based on the experiences, a similar
device is under development for the HESR. Depicted in Fig.
3, it is being designed in a size that would not only fit the
HESR but also in the HEBT. Because of the delicate natureof the microchannel plates and the importance of the system,
2 systems will be installed, providing one backup system
in case of failure. Unlike other systems the side electrodesof the E-field-box are connected individually, thus giving agreater control over the E-field and eliminating the need ofresistors within the vacuum. Parts of that wiring is shown

Figure 3: The ready mounted vacuum part of the IPM. On
top a module with a MCP stack and a phosphor screen will
be mounted. The E-field-box with its 6 field flattening electrodes is visible. On the bottom, covered with a protective
shield during mounting, a fine mesh will be installed, which
flattens the electric field but lets through UV light for calibration purposes. The UV light will be generated by a lamp
mounted outside the vacuum, right behind the vacuum window in the lower CF flange.
in Fig. 3. Within the HESR and HEBT an amount of 17 devices is foreseen, although some of them shall provide only
one plane-measurments.
The first of series device is being build at the ResearchCenter Jülich with the setup being almost complete, somein-vacuum wiring has still to be done. The manufacturingof the vacuum chamber, after facing some delays, has justbeen completed, with vacuum-testing still to be done.

VIEWER
There will be 6 viewers installed in the HESR. One in
the injection beamline. Within the HESR ring, one will be
installed at the beginning and end of each telescope and an
additional one directly after the injection septum magnet.
The ring viewers consist of a scintillation screen mounted
at 45◦ . They will be moved by a pneumatic drive and, asa speciality at the HESR, if the viewer is not used a RF
cage will be moved into its place. This is done in orderto minimize the overall impedance of the ring. If the RF

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cage is in its operational position, a second pneumatic drive
will move RF fingers in their position to ensure an optimal
electrical conduction. Before moving the RF cage out, these
springs will be pulled back. A RF cage before being mounted
onto the system is shown in Fig. 4.

Figure 5: Look into the scraper in the beam plane. The 4
jaws from top, bottom, and the sides are partially moved
in [10].

OUTLOOK
Figure 4: RF cage that is being moved into position if
the vievers are not used. Once in its position the CopperBeyllium springs will be moved outwards to insure a goodelectric conductivity. This is done in order to minimize theoverall impedance of the storage ring.

SCRAPERThe scraper system is shown in Fig. 5. There will be 2
scraper systems installed in the HESR. Each system consistsof 2 vertical and 2 horizontal jaws. Each jaw contains 10
copper rods which are placed in an alternating manner andare each 25 mm in diameter. This layout ensures a particle
will be slowed down by at least 50 mm of material while thestructure will have a minimal effect on the RF impedance
while being in its out position. Each jaw can move in further
than the middle of the beam pipe, in order to allow the
scraping of a non-centered region. In order for the jaws notaccidentally touching each other, they have been placed insuccession. The manufacturing and testing of these devices
is completed.

PHASE PICK-UP
The in-vacuum part of the Phase Pick-Up will be a nonsplit BPM. This is derived from the construction layout of
the regular BPMs and will be manufactured directly after all
regular BPMs have been manufactured. The readout of thePhase Pick-Up still has to be defined.

BEAM CURRENT
For beam current measurements, two commercially available Bergoz transformers will be used. One NPCT and one
FCT have already been delivered and the site acceptance test
was successfully performed.

To the present day, 61 of 63 of the BPM pick-ups havebeen produced and delivered. The measurement of the BPMs
on the test stand is also well underway, as well as the calculation of the individual geometrical factors and offsets,
which has been done for 47 so far. The beam current transformers and the scrapers are completely manufactured andtested. The viewers are partly manufactured, while theirvacuum chamber manufacturing is delayed, and therefore
their overall completion. For the IPM, the first of series isalmost completed, with vacuum tests and about half of thein-vacuum wiring still to be done.
Because of the recent desicions of the FAIR council, thestepwise approach for the completion of FAIR will be pursued [11]. The first step (Early Science: ES) includes theSuper-FRS using beams from the existing SIS18 and will bepossible from 2028, followed by First Science (FS), which
provides beams from the SIS100 for NUSTAR and andatomic physics (APPA) experiments. This will be followedby the First Science Plus (FS+) step, in which beams will be
extracted to the CBM cave. After these steps the rest of theModularized Start Version of FAIR, which includes the antiproton part, the p-bar target, the Collector Ring (CR), andthe HESR, will be realized. Therefore further developmentsof other HESR beam instrumentation, like the measurementof the amount of trapped particles in the injection gap, or
the beam damping, have been postponed.

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[3] C. Böhme et al., “Status Overview of the HESR Beam Instrumentation”, in Proc. IBIC’18, Shanghai, China, Sep. 2018,
pp. 26–28. doi:10.18429/JACoW-IBIC2018-MOPA01

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d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 0 1[4] “Amplifier 110”, Instrumentation Technologies d.o.o.,
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