Commit 6d8a7fa8 authored by Grzegorz Daniluk's avatar Grzegorz Daniluk

papers/ISPCS2012: use common figures

parent 03880d99
all : WhiteRabbit.pdf
.PHONY : all clean
WhiteRabbit.pdf : WhiteRabbit.tex
latex $^
bibtex WhiteRabbit
latex $^
latex $^
dvips WhiteRabbit
ps2pdf -dPDFX -dEmbedAllFonts=true -dSubsetFonts=true -dEPSCrop=true
clean :
# $(MAKE) clean -C fig
rm -f *.eps *.pdf *.dat *.log *.out *.aux *.dvi *.ps *~ *.blg *.bbl
A complete data set gathered from CNGS WR installation analyzed in this paper is
available in the White Rabbit svn repository:
%% bare_conf.tex
%% V1.3
%% 2007/01/11
%% by Michael Shell
%% See:
%% for current contact information.
%% This is a skeleton file demonstrating the use of IEEEtran.cls
%% (requires IEEEtran.cls version 1.7 or later) with an IEEE conference paper.
%% Support sites:
%% and
%% Legal Notice:
%% This code is offered as-is without any warranty either expressed or
%% implied; without even the implied warranty of MERCHANTABILITY or
%% User assumes all risk.
%% In no event shall IEEE or any contributor to this code be liable for
%% any damages or losses, including, but not limited to, incidental,
%% consequential, or any other damages, resulting from the use or misuse
%% of any information contained here.
%% All comments are the opinions of their respective authors and are not
%% necessarily endorsed by the IEEE.
%% This work is distributed under the LaTeX Project Public License (LPPL)
%% ( ) version 1.3, and may be freely used,
%% distributed and modified. A copy of the LPPL, version 1.3, is included
%% in the base LaTeX documentation of all distributions of LaTeX released
%% 2003/12/01 or later.
%% Retain all contribution notices and credits.
%% ** Modified files should be clearly indicated as such, including **
%% ** renaming them and changing author support contact information. **
%% File list of work: IEEEtran.cls, IEEEtran_HOWTO.pdf, bare_adv.tex,
%% bare_conf.tex, bare_jrnl.tex, bare_jrnl_compsoc.tex
\newcommand \todo[1]{\textcolor{red}{\textsl{TODO: }}{\textcolor{black}{#1}}}
\newcommand \modified[1]{{\textcolor{black}{#1}}}
\newcommand \attention[1]{{\textcolor{black}{#1}}}
\hyphenation{op-tical net-works semi-conduc-tor}
\title{Performance results of the first White Rabbit installation for CNGS
\footnote{CERN Neutrinos to Gran Sasso}time transfer }
This paper describes the long-term performance of White Rabbit (WR) based
time and frequency transfer in the systems deployed at CERN and Gran
Sasso National Laboratory. WR is a new technology based on
IEEE 1588-2008 and Synchronous Ethernet which allows for sub-nanosecond
accuracy and picosecond precision of synchronization in
\modified{an Ethernet-based network.}
%the entire WR network.
The first installation of WR is used in the CERN Neutrino
to Gran Sasso (CNGS) project to transfer the Coordinated Universal Time
(UTC) from a Global Positioning System (GPS) receiver to the underground
extraction/detection points. The data collected during the system operation
is used to evaluate its performance. Additionally, the performance
in varying temperature conditions is verified with tests in a climatic chamber.
We evaluate time transfer \modified{by} measuring the offset between the time
reference and the time receiver (WR Node).
% We first provide a short introduction to WR and the underlying
% technologies. Then, we describe the CNGS project focusing on the WR installation
% and measurement setup. Finally we analyze the collected data. We evaluate
% time transfer measuring the standard deviation of the offset between the time
% reference (cesium clock) and the time receiver (WR Node).
The stability of the transfered frequency is evaluated \modified{by} %measuring phase noise and
analyzing the Allan Deviation (ADEV) and the Maximum Time Interval Error (MTIE).
% author names and affiliations
% use a multiple column layout for up to three different
% affiliations
% \author{
% %\IEEEauthorblockN{Bunch of Freaks}
% %\IEEEauthorblockA{CERN\\
% %Geneva\\
% %Email:}
% \IEEEauthorblockN{Maciej Lipi\'{n}ski, Tomasz W\l{}ostowski, Javier Serrano, Pablo Alvarez}
% \IEEEauthorblockA{CERN, Geneva\\
% Email: \{maciej.lipinski, tomasz.wlostowski, javier.serrano, pablo.alvarez.sanchez\}}
% }
% conference papers do not typically use \thanks and this command
% is locked out in conference mode. If really needed, such as for
% the acknowledgment of grants, issue a \IEEEoverridecommandlockouts
% after \documentclass
% for over three affiliations, or if they all won't fit within the width
% of the page, use this alternative format:
\author{\IEEEauthorblockN{Maciej Lipinski\IEEEauthorrefmark{1}\IEEEauthorrefmark{2},
Tomasz Wlostowski\IEEEauthorrefmark{2},
Javier Serrano\IEEEauthorrefmark{2},
Pablo Alvarez\IEEEauthorrefmark{2}, \\
Juan David Gonzalez Cobas\IEEEauthorrefmark{2},
Alessandro Rubini\IEEEauthorrefmark{4} and
Pedro Moreira\IEEEauthorrefmark{3}}
\IEEEauthorblockA{\IEEEauthorrefmark{1}Warsaw University of Technology, Warsaw, Poland}
\IEEEauthorblockA{\IEEEauthorrefmark{2}CERN, Geneve, Switzerland}
\IEEEauthorblockA{\IEEEauthorrefmark{3} University College London, London, England}
\IEEEauthorblockA{\IEEEauthorrefmark{4} University of Pavia, Pavia, Italy}
title = "IEEE Standard for a Precision
Clock Synchronization Protocol for Networked Measurement and Control Systems",
organization = "IEEE",
address = "New York",
number = "1588-2008",
year = "2008",
title = "IEEE Standard for
Information Technology--Telecommunications and Information Exchange Between
Systems--Local and Metropolitan Area Networks--Specific Requirements Part 3:
Carrier Sense Multiple Access With Collision Detection (CSMA/CD) Access Method
and Physical Layer Specifications - Section Three",
year = "2008",
organization = "IEEE",
address = "New York",
number = "802.3-2008",
title = "Timing characteristics of a synchronous Ethernet equipment slave clock {(EEC)}",
year = "2007",
number = "G.8262",
organization = "ITU-T",
author = "J.Serrano and P.Alvarez and D.Dominguez, J.Lewis",
title = "Nanosecond Level {UTC} Timng Generation and Stamping in {CERN}'s {LHC}",
booktitle = "Proceedings of ICALEPSC2003",
address = "Gyeongju, Korea",
year = "2003",
author = "T. Fleck and C. Prados and S. Rauch and M. Kreider",
title = "{FAIR} Timing System",
institution = "GSI",
address = "Darmstadt, Germany",
year = "2009",
note = "v1.2",
author = "S. Deghaye and D. Jacquet and I. Kozsar and J. Serrano",
booktitle = "Proceedings of ICALEPCS2003",
address = "Gyeongju, Korea",
year = "2003",
author = "J. Serrano and P. Alvarez and M. Cattin and E. G. Cota and J. H. Lewis, P.
Moreira and T. W\l{}ostowski and others",
title = "{The White Rabbit Project}",
booktitle = "Proceedings of ICALEPCS TUC004",
address = "Kobe, Japan",
year = "2009",
author = "E.G. Cota and M. Lipi\'{n}ski and T. W\l{}ostowski and E.V.D. Bij and J. Serrano",
title = "{White Rabbit Specification: Draft for Comments}",
note = "v2.0",
month = "july",
year = "2011",
howpublished = {\url{}}
author = "T. W\l{}ostowski",
title = "Precise time and frequency transfer in a {White} {Rabbit} network",
month = "may",
year = "2011",
school = "Warsaw University of Technology",
howpublished = {\url{}}
author = "Takahide Murakami and Yukio Horiuchi",
title = "{A Master Redundancy Technique in IEEE 1588 Synchronization with a Link Congestion
booktitle = "Proceedings of ISPCS",
year = "2010",
title = "{White Rabbit}",
howpublished = {\url{}}
author = "M. Giampietro",
title = "Hardware joins the open movement",
journal = "CERN Courier",
address = "CERN, Geneva",
year = "2011",
howpublished = {\url{}},
author = "M. Buhler-Broglin and K. Elsener and L.A. Lopez Hernandez and G.R. Stevenson and M. Wilhelmsson",
title = "{General Description of the CERN Project for a Neutrino Beam to Gran Sasso (CNGS)}",
note = "CERN AC Note (200-03)",
year = "2000",
author = "P. Alvarez, J. Serrano",
title = "{Time transfer techniques for the synchronization between CERN and LNGS}",
note = "{CERN BE-CO-HT}",
year = "September 25, 2011",
author = {Adam, T. and others},
title = {Measurement of the neutrino velocity with the OPERA detector in the CNGS beam},
journal = {eprint arXiv:1109.4897},
year = {2011},
archiveprefix = {arXiv},
collaboration = {OPERA Collaboration},
eprint = {1109.4897},
author = "P. Defraigne and others",
title = "{Initial testing of a new GPS receiver, the PolarRx2e, for time and frequency transfer using dual frequency codes and carrier phases}",
journal = "35th Annual Precise Time and Time Interval (PTTI) Meeting",
title = "{PolaRx4/PolaRx4TR: Multi-frequency GNSS Reference Station}",
howpublished = {\url{}}
title = "{Symmetricon frequency standards, Symmetricom, Time and Frequency Systems}",
howpublished = {\url{}},
author = "M. Lipi\'{n}ski and T. W\l{}ostowski and J. Serrano and P. Alvarez",
title = "{White Rabbit: a PTP application for robust sub-nanosecond synchronization}",
journal = "Proceedings of ISPCS",
address = "Munich, Germany",
year = "2011",
author = "Guanghua Gong and Shaomin Chen and Qiang Du and Jianming Li and Yinong Liu",
title = "{Sub-nanosecond Timing System Designed And Developed For LHAASO Project}",
journal = "Proceedings of ICALEPCS",
address = "Grenoble, France",
year = "2011",
author = "P. Moreira and P. Alvarez and J. Serrano and I. Darwezeh and T. Wlostowski",
title = "{Digital Dual Mixer Time Difference for Sub-Nanosecond Time Synchronization in Ethernet}",
journal = "Frequency Control Symposium (FCS), 2010 IEEE International",
address = "London, UK",
year = "2010",
title = "{KM3NeT}",
howpublished = {\url{}}
author = "Jeroen Koelemeij",
title = "{WR TWTFT through long-haul duplexed fiber pairs}",
note = "LaserLaB VU University",
year = "March 2012",
howpublished = {\url{}}
author = "M. Lipi\'{n}ski and J. Serrano and T. W\l{}ostowski and C. Prados",
title = "{Reliability In A White Rabbit Network}",
journal = "Proceedings of ICALEPCS",
address = "Grenoble, France",
year = "2011",
author = "A. Dobrogowski and M. Kasznia",
title = "{Time effective methods of calculation of Maximum Time Interval Error}",
journal = "IEEE Trans. Instrum. Meas., vol.50, No. 3, pp.732-741",
year = "June 2001",
author = "Draka Communications",
title = "{Draka; Single-Mode Optical Fiber (SMF)}",
year = "August 2000",
howpublished = {\url{}}
title = "{Simple PCIe FMC carrier (SPEC)}",
howpublished = {\url{}}
title = "{WRS-3/18; White Rabbit Switch v3; Standalone version with 18 SFP ports}",
howpublished = {\url{}}
title = "{A fine delay generator in FMC format with 1 input and 4 outputs (FMC DEL 1ns 4cha)}",
howpublished = {\url{}}
title = "{Gamma-Ray and Cosmic-Ray experiment HiSCORE-EA at the Tunka-133 Cherenkov EAS-Array.}",
howpublished = {\url{}}
In this paper the first deployment of a ``beta version" of a White Rabbit
system is described. The deployed system includes a WR Network (consisting of switches)
interconnecting WR Nodes.
The results indicate that a system based on the
White Rabbit technology is capable of providing nanosecond accuracy of synchronization
over large distances (i.e. over 16 km). The measured accuracy of the deployed system
is 0.517~ns and the precision is 0.119~ns. The calculated MTIE is below 1.05~ns
with only 0.0003$\%$ of values exceeding the $\pm$0.5~ns range.
The WR-timebase
guarantees sub-nanosecond accuracy and tens of picoseconds precision of the distributed time
and frequency reference regardless of the changing temperature conditions.
The standard deviation of the skew measured between the time reference (grandmaster) and
the nodes (over a peak-to-peak 45
degrees Celsius temperature range) is 55~ps while the MTIE is below 342~ps.
The temperature tests indicate that the acceptable influence
of the temperature variation of WR devices on the quality of synchronization can be easily
reduced by compensating temperature-induced changes of the hardware delays.
Such a compensation should be considered in future developments of the WR technology.
The high accuracy and precision time transfer over an Ethernet-based WR Network has many potential
applications. Precise time-tagging of the input events using WR-provided timebase is the first to
be realized. Therefore, the described deployment marks an important milestone in the White Rabbit Project --
proof-of-concept technology becomes a working solution. This solution is about to be
commercially available while sustaining its openness (open hardware and open software).
\ No newline at end of file
This diff is collapsed.
%\subsection{White Rabbit}
White Rabbit (WR)~\cite{biblio:whiteRabbit} is a technology based on existing standards, namely
Ethernet (IEEE~802.3) \cite{biblio:IEEE8023}, Synchronous Ethernet (SyncE) \cite{biblio:SynchE}
and IEEE~1588 (PTP)~\cite{biblio:IEEE1588}, which enables sub-nanosecond synchronization of
thousands of devices connected in a network spanning several kilometers. In addition to high-accuracy
timing capabilities, a WR network features low-latency, reliable and deterministic data delivery
Sub-nanosecond accuracy and picosecond precision (jitter) of time distribution in a WR network is
achieved by both extending and hardware-supporting PTP to address its limitations. The WR extension to PTP
is called WRPTP. It is defined in the form of a PTP Profile \cite{biblio:ISPCS2011} and described in the
WR Specification~\cite{biblio:WRPTP}. WRPTP uses SyncE to distribute the common notion of
frequency in the entire network over the physical medium. \modified{By having hardware syntonization}
it casts the problem of timestamping
into a phase detection measurement using Digital Dual Mixer Time Difference (DDMTD)
\cite{biblio:DDMTD}\cite{biblio:WRproject}. The results of these precise measurements are used both during
normal PTP operation and for quantifying physical medium asymmetry during the calibration phase
WR, originally started as a successor of the current control and timing network at
CERN (General Machine Timing)~\cite{biblio:GMT}, is now a multi-laboratory and multi-company
effort with many potential scientific and commercial applications. Apart from the application
for accelerators (i.e.: CERN~\cite{biblio:WRproject}, GSI~\cite{biblio:FAIRtimingSystem}),
WR is also considered a good candidate as a synchronization and acquisition system for
cosmic particle detectors (e.g.:~LHAASO~\cite{biblio:LHAASO}, KM3NeT~\cite{biblio:KM3NeT}) or long distance
time transfer systems \cite{biblio:TWTFT}. Time transfer in the CERN Neutrinos to Gran Sasso (CNGS)
project is the first application for which WR is deployed.
In this paper we describe the CNGS project (Section~\ref{sec:CNGS}) focusing on the
WR installation, monitoring and test setups (Section~\ref{sec:deplAndMeas}).
Then we analyze the collected data in Section~\ref{sec:dataAnalysis} and finish with conclusions
in Section~\ref{sec:conclusions}.
% The CNGS Project is introduced shortly below (Section~\ref{sec:CNGS}). The WR installation in
% CERN and Gran Sasso National Laboratory (LNGS) along with the measurement setup are described in
% Section~\ref{sec:deplAndMeas}. Next section analyzes the collected long-term measurement data
% of WR performance. Finally, conclusions are presented in the last section.
\section{CERN Neutrinos to Gran Sasso (CNGS)}
\caption{Schematic of the OPERA timing system at LNGS. Blue delays include elements of the
timestamp distribution. Green delays indicate detector time-response.
Orange boxes refer to elements of the old CNGS-OPERA synchronization system (\cite{biblio:TOF}).
WR Switches, SPECs and PolaRx4e are the elements of the new installation.}
The CNGS project \cite{biblio:CNGS2000} consists of the production of a neutrino beam at CERN and sending
it towards the Gran Sasso National Laboratory (LNGS). The project employs a GPS-based CERN-LNGS
synchronization \cite{biblio:BECOHT_CNGS} to enable discrimination in LNGS detectors between
neutrinos coming from the Sun (or other sources) and those coming from the CNGS beam.
% The very high
% precision (a few nanoseconds) of such synchronization opened the way to meaningful neutrino
% Time Of Flight (TOF) measurements \cite{biblio:TOF} in years 2009, 2010 and 2011.
\modified{The need for} nanosecond accuracy between the GPS receivers located at CERN and LNGS is only a part of the
CERN-LNGS time transfer \modified{challenge. Moreover}, a similar degree of accuracy needs to be
\modified{established} in
calibrating cabling lengths and device delays between the GPS receivers and the points where
the measurements are actually taken.
A common UTC timebase for both remote sites \attention{has} been achieved so far using two identical
systems, composed of a Septentrio PolaRx2e \cite{biblio:PolaRx2e} GPS receiver operating in
``common-view" mode and a Symmetricom Cs4000 \cite{biblio:CS4000} \modified{Cesium (Cs)} atomic clock, installed at
CERN and LNGS. The nanosecond level of accuracy of this setup has been successfully verified by
independent measurements \cite{biblio:TOF}.
The synchronization between the UTC timebase at the GPS receiver and the measurement point \attention{has}
been performed so far using the General Machine Timing at CERN and the detector timing system
(e.g~OPERA's) at LNGS. High accuracy in these systems \attention{is} achieved by hand-evaluating delays introduced
by each element of the timing systems at CERN and LNGS using the methods described in
\cite{biblio:TOF} and \cite{biblio:BECOHT_CNGS}.
\figurename~\ref{fig:operaTiming} depicts the synchronization of the OPERA \cite{biblio:TOF}
detector (orange and blue boxes) and the delays introduced by each of its elements.
Additionally to the system described above and used since 2009, a new WR-based system
(\figurename~\ref{fig:wrLNGStiming}) was installed at CERN and LNGS in May 2012. This new
% enables to unify
\modified{unified} the entire CERN-LNGS time transfer chain
(so far it \modified{had been} identical only from GPS to GPS).
%It is meant to
\modified{Its purpose is to} verify
the performance of the old installation and further enhance the accuracy of the CERN-LNGS
time transfer.
%This WR installation is described in the next section.
% Before White Rabbit installation, the synchronization between UTC time base at GPS receivers and
% measurement points was achieved by hand-evaluating delays introduced by each element of the timing
% systems at CERN and LNGS using methods described in \cite{biblio:TOF} and \cite{biblio:BECOHT_CNGS}.
% \figurename~\ref{fig:operaTiming} depicts synchronization of the OPERA \cite{biblio:TOF} detector
% and delays introduced by each of its elements. Additionally, the new White Rabbit installation
% is presented in the figure to indicate its role in the synchronization. Both systems are running
% in parallel.
% which require high accuracy of the relative time tagging at CERN and
% detectors located at LNGS.
% The achieved high precision of synchronization (systematic uncertainty at the leve of several
% nanoseconds) between the extraction line at CERN and detector at LNG opened the way to meaningful
% ne
\section{WR deployment, monitoring and test setups}
\subsection{\modified{White Rabbit} in CNGS}
White Rabbit is used to transfer the UTC timebase from the GPS receiver to the
measurement point automatically compensating any cable delays and their variation with temperature.
A~WR setup, both at CERN and LNGS (\figurename~\ref{fig:wrLNGStiming}), consists of WR Switches
and WR Nodes (nodes) connected with single mode fiber (G.652.B type \cite{biblio:Draka}). % TODO: check the type
The node is a Simple PCIe\footnote{Peripheral Component Interconnect Express}
FMC\footnote{Field Programmable Gate Array (FPGA) Mezzanine Card} carrier (SPEC) \cite{biblio:spec}
equipped with a Fine Delay FMC module \cite{biblio:fineDelay} which is used as
a Time-to-Digital Converter (TDC). The TDC time-tags input signals with 28~ps
resolution, 55~ps precision (std. dev) and 300~ps accuracy \cite{biblio:fineDelay}
with reference to the WR-provided UTC timebase.
A~switch connected to an external time reference (i.e. the switch in the WR Room in
\figurename~\ref{fig:wrLNGStiming} connected to PPS and 10~MHz inputs) acts as a
PTP grandmaster. A~switch connected to the grandmaster (directly or through other switches)
acts as a PTP boundary clock (transparent \modified{clocks are not supported} by WRPTP)
and provides a PPS output synchronized to that of the grandmaster (i.e. the switch in LNGS cavern in
A~node is a PTP ordinary clock. The nodes used (SPEC with Fine Delay FMC module)
have the capability of precisely timestamping input signals in the WR-provided UTC domain.
Therefore, an input signal to a SPEC card connected to any switch of the WR network can be
time-tagged with very high accuracy and precision with respect to the
time source connected to the grandmaster switch. This capability is used in the CNGS time transfer.
\caption{White Rabbit based synchronization system in Gran Sasso National Laboratory (LNGS).}
In the new WR installation (\figurename~\ref{fig:operaTiming} and \figurename~\ref{fig:wrLNGStiming}),
a common UTC timebase for both remote sites is achieved using two
identical systems, composed of a Septentrio PolaRx4TR \cite{biblio:PolaRx4e} GPS receiver
operating in ``common-view" mode and a Symmetricom Cs4000 \cite{biblio:CS4000} Cs atomic clock,
installed at CERN and LNGS. The Cs atomic clock is a common part of the new and the old
time transfer systems.
\figurename~\ref{fig:wrLNGStiming} details the WR setup in LNGS. The Septentrio PolaRx4TR
accepts the GPS signal and the high stability CS4000 10~MHz signal to generate a timebase whose
offset with respect to the GPS time can be \modified{derived}
a posteriori with very good accuracy.
The 10~MHz signal of the \modified{Cs atomic} clock (CS4000, installed in the {\it Router Room})
is connected (through a fanout) to the
grandmaster switch. Thus, the timebase of the WR network is that of the \modified{Cs atomic} clock,
which in turn,
can be directly translated to the GPS timebase. The grandmaster in the {\it White Rabbit Room}
is connected through 8.3~km of fiber to the switch installed in the laboratory cavern.
This switch serves as a \modified{fanout}
for the nodes (SPECs) used in different LNGS experiments (i.e. LVD,
OPERA, Borexino and ICARUS) as depicted in \figurename~\ref{fig:wrLNGStiming}.
It is foreseen to extend this very simple network with more switches, possibly
one for each experiment.
%\figurename~\ref{fig:wrCERNtiming} presents a very similar WR setup for CERN installation.
\subsection{Monitoring setup}
The timing performance of the WR installations is carefully monitored.
The PPS output
of the grandmaster's time source is timestamped by two SPECs
(\figurename~\ref{fig:wrLNGStiming}). One of the
SPECs (called \textit{local SPEC}) is connected (through a short fiber) directly to the grandmaster switch (in WR Room),
thus time-tagging the time source's PPS in
the time referenced to the grandmaster. The second SPEC (called \textit{loopback SPEC})
is connected through 8.3~km of fiber to the
second switch (located in the cavern), thus time-tagging the time source's PPS in the time
referenced to the first-layer switch (boundary clock). This SPEC acts as a system loopback which
provides an estimate of the quality of the time transfer to the SPECs used to time-tag
the input signals in each experiment. The total distance of the loopback is over 16~km
(\modified{grandmaster $\rightarrow$ boundary clock $\rightarrow$ SPEC}).
% Additionally, the 10MHz clock outputs of both
% monitoring SPECs and the cesium clock are analyzed with Agilent E5052B signal source analyzer to
% measure the phase noise, L(f), and estimate the rms jitter.
% In order to compare and monitor differences between the new and the old systems, a PPS signal
% generated by the old system is time-tagged (SPEC (2) in \figurename~\ref{fig:operaTiming}).
The temperature in the WR Room (in which the SPECs and the grandmaster switch are installed) as well
as the temperatures of the SPECs and Fine Delay modules are monitored.
% The WR installation at CERN features additionally a roll of
% fiber exposed to varying external condition (i.e. temperature)\footnote{Data from this setup not available at the time of writing.}. The variation of temperature
% is logged. The SPEC node, connected to this fiber roll, time-stamps the PPS output of the
% cesium clock while the 10MHz output of the SPEC is also analyzed with the Agilent device.
\subsection{Temperature test setup}
%Additionally to
\modified{Aside from} monitoring the performance and parameters of the deployed system,
a similar setup was tested in a CTS Climatic Chamber (Type T-40/500) to determine influence
of the temperature variation on the %system's
\modified{synchronization} performance. In this setup, a switch acting as a
free running grandmaster was connected through 11~km of fiber to another switch acting as
a boundary clock. One SPEC (called \textit{local}) was connected through 10~m of fiber to
the grandmaster switch. Another SPEC (called \textit{loopback}) was connected to the boundary clock
switch through 5~km of fiber. \modified{The boundary clock was connected to the grandmaster switch through 11~km
of fiber.} The skews between the clock of the grandmaster switch and that of
the boundary clock switch, the \textit{local} SPEC and the \textit{loopback} SPEC were measured using
LeCroy WavePro 7300A oscilloscope. Monitoring the skew of the recovered clocks
(unlike \mbox{timestamping} the PPS reference) allows to evaluate the performance of the WR-timebase without
additional jitter or inaccuracy introduced by a system using the WR-timebase
(i.e. TDC on the Fine Delay).
Different elements of the described setup were placed in the climatic chamber while the rest
of the setup was placed in a reasonably stable conditions of the laboratory (ambient temperature
of 26$\pm$1.5 degrees Celsius).
A temperature cycle consisted of ramping the temperature from 20 to 50 degrees, stabilizing
at 50 degrees, ramping down to 0 degrees, stabilizing at 0 degrees and ramping up back to 20 degrees.
% \begin{figure}[!t]
% \centering
% \includegraphics[height=2.0in]{fig/}
% \caption{TODO}
% \label{fig:wrCERNtiming}
% \end{figure}
The synchronization between UTC time base at GPS receiver and measurement point is performed
using two independent systems (running in parallel):
\item General Machine Timing at CERN and detectors' timing system (e.g OPERA's) at LNGS.
\item White Rabbit at CERN and LNGS.
\figurename~\ref{fig:operaTiming} depicts synchronization of the OPERA \cite{biblio:TOF}
detector and delays introduced by each of its elements. Additionally, the new White Rabbit
installation is presented in the figure to indicate its role in the synchronization.
The former systems (1) have been in operation for CNGS time transfer since 2010.
Their accuracy is achieved by hand-evaluating delays introduced by each element of the timing
systems at CERN and LNGS using methods described in
\cite{biblio:BECOHT_CNGS} and \cite{biblio:TOF}.
The latter system, White Rabbit, has been installed at CERN and LNGS very recently.
It enables to transfer the common UTC time base from the GPS
receiver to the measurement points automatically compensating for the delays and their variation.
Its installation setup is described in the next section.
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment