Proceedings of IBIC2012, Tsukuba, Japan

MOPA10DIAMOND DETECTORS FOR LHC
Erich Griesmayer, Pavel Kavrigin, CIVIDEC Instrumentation, Vienna, Austria
Bernd Dehning, Ewald Effinger, Tobias Baer, Maria Hempel, Heinz Pernegger, Daniel Dobos,CERN, Geneva, Switzerland

Diamond detectors are installed at the LHC as fast
beam loss monitors. Their excellent time resolution [1]make them a useful beam diagnostic tool for bunch-tobunch beam loss observations [2], which is essential forthe understanding of fast beam loss scenarios at the LHC[3, 4].

INTRODUCTION
Diamond is probably the most versatile, efficient andradiation-tolerant material available for use in beam
detectors. Correspondingly, it has a wide range ofapplications in beam instrumentation and in beamdiagnostics. Currently ten diamond detectors are in use
as fast beam loss monitors at the LHC at CERN. The
nanosecond time response in combination with thesensitivity to single particles makes them ideal for use in
fast beam loss detection. A beam dump caused by a socalled UFO, an “unidentified falling object”, is shown.
UFOs are believed to be dust particles with a typical sizeof a few micrometers, which lead to beam losses, whichlast about ten revolutions of the proton beam.

bit ADC). The installation of the diamond beam loss
monitor in point 7 is shown in Figure 1.

SPACIAL LOSS PROFILE
A beam abort, which was obviously caused by an UFO
event in the injection area in point 4, was recorded on the27th of August 2012 with a diamond beam loss monitor,
which was located in the cleaning area in point 7. Figure
2 shows the spacial loss profile of this event, i.e. therecorded loss amplitude versus the 89 µs turn period ofthe LHC.

Figure 2: Spatial loss profile versus the LHC turn periodof 89 µs. Beam abort event caused by an UFO.
In the following figures, data of the beam abort event,taken with the diamond beam loss monitor, are shown.
Starting with a buffer size of 500 µs, a zoom into thememory in four stages is provided. Each zoom reveals
insights into the loss structure of the LHC.

Figure 1: Installation of a Diamond Beam Loss Monitor
in the LHC tunnel in IP 7.

THE DIAMOND MONITORS
The diamond monitors were provided by CIVIDEC
Instrumentation and installed at TCLA.D6L7.B2. They
are composed of a diamond detector (pCVD diamondmaterial, substrate size 10 mm x 10 mm x 0.5 mm, goldelectrodes 8 mm x 8 mm, operated at 500 V bias voltage),a 4 GHz AD-DC splitter, and a 2 GHz, 40 dB RF
amplifier. A CK50 cable with a length of about 300 m
connects the beam loss monitor the readout
instrumentation. A LeCroy oscilloscope was used for thedigital readout (Waverunner 104MXi, 1 GSPS, 1 GHz, 8The 500 µs Zoom
The Figure 3 shows the loss profile in a time window of
500 µs. The beam losses increase over a period of somemicroseconds and the dump causes a high pulse at the endof the loss pattern. The tree beam abort gaps define therevolution period of the LHC.

ISBN 978-3-95450-119-9
Beam Loss Detection

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Abstract

MOPA10Proceedings of IBIC2012, Tsukuba, Japan

Figure 3: 500 µs zoom; UFO location in Point 4,
recorded in the collimation area in Point 7 with a10x10x0.5 mm3 diamond detector with 40 dB signal
amplification. The length of the loss is about 0.5 ms.
Beam abort gaps are clearly resolved.

The 100 µs Zoomc 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○In Figure 4 the zoom of 100 µs indicates the time
structure of the bunch trains within one turn.

Figure 4: 100 µs zoom; the beam abort gap, and thebunch structure is resolved: a pattern of two 4x36
bunches and one 2x36 bunches are periodically cycling inthe LHC. The losses caused by the beam abort aresynchronous to the beam abort gap.

The 10 µs Zoom
The individual bunch trains can be resolved in Figure 5,which shows a 10 µs zoom of the data. The LHC
injection gap and the SPS injection gaps separate
individual bunch trains.

Figure 5: 10 µs zoom; the structure of 4x36 bunches isresolved. The LHC injection gap and the SPS injection
gaps separate the bunch trains containing 36 buncheseach.

The 2 µs Zoom
The Figure 6 shows a 2 µs zoom and resolves the 32bunches which are in this bunch train. Also, the 50 nsbunch spacing is visible. All bunches inside a batch
contribute to the beam losses, as it is expected for amacro particle interaction.

Figure 6: 2 µs zoom; the bunches are separated by 50 ns,
36 bunches form a batch. It is remarkable that allbunches inside a batch contribute to the beam losses, asexpected for a macro-particle interaction.

The 200 ns Zoom
In the 100 ns zoom of Figure 7 the single bunches areresolved, the 50 ns bunch separation can clearly beidentified and all pulse parameters can be determined. In
this example the amplitude of the left bunch is 397 mV,
the rms baseline noise is 9.9 mVrms, the rise time is2.34 ns, the pulse width is 6.06 ns and the fall time is10.34 ns.

ISBN 978-3-95450-119-9
2Beam Loss DetectionProceedings of IBIC2012, Tsukuba, Japan

MOPA10second range is demonstrated in this report. These
measurements also proved that beam losses in the LHC
originate almost equally from all bunches. Data wastaken with a digital oscilloscope, but it is foreseen for theend of 2012 to make them available on-line in the LHC
control room.

REFERENCESSIGNAL PROPERTIES
Analogue Bandwidth
The analogue bandwidth BW of the measurement setup
can be estimated via the rise time tr = 2.34 ns as:
𝐵𝑊 =0.35
0.35== 150  MHz𝑡!
2.34  ns[1] H. Frais-Kölbl, E. Griesmayer, H. Pernegger, H.
Kagan, “A fast low-noise charged particle CVD
diamond detector”, IEEE Trans. on Nuclear Science,Vol. 51, No. 6, p. 3833 – 3837, December 2004.
[2] B. Dehning, E. Effinger, D. Dobos, H. Pernegger, E.
Griesmayer, “Diamond detectors as beam monitors”,
CERN-BE-2011-001 BI, March 2011.
[3] E. Griesmayer, B. Dehning, E. Effinger, H.
Pernegger, D. Dobos, H. Frais-Kölbl, “Test of adiamond detector using unbunched beam halo
particles”, CERN-ATS-2010-027, February 2012.
[4] M. Hempel et al., “Bunch-to-bunch beam loss
diagnostics with diamond detectors at the LHC”,
Proceedings of HP 2012, September 2012.

which has to be set into correlation with the cable lengthof about 300 m.

Intrinsic Time Resolution
The intrinsic time resolution (TR) of the monitor isdefined as the ratio of the baseline noise and the slope ofthe signal. In the example in Figure 7 the noise is 9.9 mV
and the slope can be estimated with 170 mV/ns, resultingin:
𝑇𝑅 =𝑛𝑜𝑖𝑠𝑒
9.9  mV== 58  ps𝑠𝑙𝑜𝑝𝑒 170  mV/ns

In this example the intrinsic time resolution is 58 ps.
It should be mentioned that the baseline noise isdetermined by the readout system rather than by thediamond detector. The intrinsic time resolution is limitedby the quantization noise of the 8-bit ADC and by thebandwidth limitation, which is mainly determined byrequired length of the RF cable.

CONCLUSION
Bunch-to-bunch losses were measured at the LHC
accelerator at CERN using diamond detectors. An UFO
event, which occurred in point 4, was recorded with adiamond detector in the IR7 cleaning region. A buffer of
10 ms was filled with data at 1 GSPS data rate. The
excellent amplitude resolution of single particles using a40 dB as well as the excellent time resolution of the nano-ISBN 978-3-95450-119-9
Beam Loss Detection

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 7: 100 ns zoom; single bunches are resolved with arise time of 2.34 ns, a rms baseline noise of 9.9 mV andan amplitude of 397 mV. The corresponding intrinsic
time resolution is 58 ps.