Rad-hard Luminosity Monitoring for the LHC Page: 3 of 3
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Shapers and signal distribution
The shaping amplifier's main function is to reduce the
time occupancy of the preamplifier signal to less than
25ns. The shaper's design has evolved through several
iterations to a two-pole shaper, benefiting from the well
known pole-zero (PZ) cancellation scheme. The zeros
cancel two poles, one associated to the detector
capacitance and the preamplifier's input impedance and
the other associated to the preamplifier's feedback
network. The poles of the shaper implement a pseudo-
gaussian function built using a Sallen-Key low-pass filter
configuration. Proper pole-zero compensation is essential
in order to optimize the return of the signal to the baseline
and each zero is implemented with PZ compensation
capabilities. The shapers will be implemented on a single
board in the final system. The shaped signals from the
quadrants will also be summed in an analog fashion to
provide the total charge measurement and also partial
sums and differences to compute the center of mass
information. Once the signals for the individual
quadrants are processed, they are buffered and distributed
to the digitizers as well as to local diagnostic ports. We
are also sharing such signals with the ZDCs of LHC's
experiments, to cross calibrate our measurements.
The digitization of those analog signals will be
performed using the IBMS board developed by the AB/BI
group at CERN. The IBMS boards have been developed
as mezzanine boards for the DAB64x, a VME64x Data
Acquisition Board developed by TRIUMF for LHC beam
instrumentation . Such board provides a very flexible
platform for signal processing combining a good amount
of on-board memory with the flexibility and processing
power of the Altera Stratix family of FPGAs. Dedicated
firmware running on the DAB64x will be developed to
control the instrument and to process the data from the
Once digitized and processed, the resulting values are
shared and made available to the control room and the
community through the LHC control system.
Due to the demanding requirements of the system, we
completed an R&D program that included testing at
CERN in the SPS, as well as at the ALS.
High speed demonstration
25 ns resolution is a very critical feature that has been
demonstrated using a custom designed this housing and
hard X-rays at a beamline at the ALS. This allowed us to
validate the modeling as well as to demonstrate full signal
processing within the desired 25 ns. Minor pileup still
remains which so we'll have to deconvolve it .
Rad hardness studies
Due to the extreme levels of radiation, we have two
radiation damage tests underway, one at BNL using the
high intensity beam at the RHIC linac, and one at the
CERN ISOLDE ion source facility. The results of these
tests, due later this summer, will guide us towards a final
materials choice for the detector elements.
Taking advantage of the present RHIC run, we have
installed our prototype in the BNL collider, and are
prepared to monitor collisions and compare them with the
results of the nearby Zero Degree Calorimeters. This
provides a test bed for the device in a hadron collider
environment, allowing us to develop an understanding of
the device and its performance in preparation for LHC
The luminosity monitor is under construction and will
be available for LHC operations. Great care has been
taken to ensure the most suitable approach is chosen to
cope with the extreme levels of radiation. While the basic
R&D has demonstrated the feasibility of the system, an
ongoing program continues to allow system development
The list of collaborators across the community is too
long to mention all. Selecting a few, the authors are
particularly grateful for the help of N. Mokhov, who has
provided all MARS modeling and helped us setup our
own system. Similarly we are extremely thankful of N.
Simos of BNL and R Catherall of CERN, who are
independently testing our passive components in their rad
damage test facilities as well as D. Bishop of TRIUMF
for his support of the DABIV environment. The BNL
CAD department has allowed us to install and test our
detector in RHIC; these tests were done under the
leadership of A. Drees.
 "Measurement of the relative luminosity at the LHC" -
LHC-B-ES-0004, Nov. 2003
- N. Mokhov, et al., "Protecting LHC IP1/IP5 Components
Against Radiation Resulting from Colliding Beam Interactions",
FNAL TN -732, and updates at www/cern.ch/tan
 Initial Test results of an ionization chamber shower detector
for an LHC luminosity monitor, P.S. Datte et al. IEEE Trans. on
Nuclear Science Vol 50, 258 (2003)
- "VME64x digital acquisition board for the LHC trajectory
and closed orbit system" - LHC-BP-ES-0002, March 04
 J. Byrd, et al, "High speed measurements of the LHC
luminosity monitor" - Beam Instrumentation Workshop, FNAL,
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Beche, J.F.; Byrd, J.M.; Chow, K.; Denes, P.; Ghiorso, W.; Matis,H.S. et al. Rad-hard Luminosity Monitoring for the LHC, article, June 24, 2007; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc901784/m1/3/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.