Heterogeneous Distributed Calibration Framework for the High Level Trigger in ALICE

167 Pages·2008·11.51 MB·English

Heterogeneous Distributed
Calibration Framework for the High
Level Trigger in ALICE
Sebastian Robert Bablok
Thesis for the degree of Philosophiae Doctor (PhD)
at the University of Bergen
October 30, 2008
—
Abstract
This thesis focusses on the development of a distributed and re-configurable online
calibration environment for the ALICE (A Large Ion Collider Experiment) HLT
(High Level Trigger). ALICE1 is one of the four major experiments at the new accel-
erator ring (Large Hadron Collider - LHC) at CERN in Geneva (CH). The experiment
is laid out to investigate the properties of strongly interacting matter created in heavy
ion collisions at ultra-relativistic energies. It is assumed that the universe consisted of
such a state of matter shortly after the Big Bang. The HLT is a sub-system of ALICE,
focussing on online event reconstruction and analysis, event selection and data reduc-
tion. These tasks are executed on a large computing farm close to the experiment.
To achieve high accuracy in the analysis, calibration is a major issue for the software
components running in the HLT.
The thesis describes the interfaces and components developed for the HLT cali-
bration framework. These interfaces cover the data exchange with the other ALICE
sub-systems connected to the HLT. Their purpose is to provide calibration and con-
dition settings to the HLT and to send freshly produced calibration objects to the
destined targets. The exchange of data also requires synchronisation with the other
sub-systems and within HLT itself. The interfaces (described in chapter 4.3, 4.4 and
4.5) and their interplay (depicted in chapter 5), as well as the FED-API (Front-End-
Device-API)(specifiedinchapter3)havebeenthemaineffortduringthisPhDproject.
Howwelltheymeettheimposedrequirementsispresentedinthesummaryandoutlook
in chapter 6.
The outline of this thesis is the following: In the first chapter a very brief overview
of the physics goal of the experiment is given. ALICE with its detectors and systems
is presented in chapter two. Chapter three focusses on the FED-API, which deals
with the connection of the ALICE DCS (Detector Control System) to the Front-End-
Electronics (FEE) of the different detectors. The FED-API is (re-)used for the HLT
as well. The different parts constituting the HLT calibration framework, – interfaces
and their related components – are described in detail in chapter four. They are the
maintopicofthethesis. Especiallytheheterogeneityoftheconnectedsystemsandthe
diversity of the used mechanisms are major aspects. Chapter five joins the different
constituents and displays their interaction and synchronisation procedures. Moreover,
examplesfortheusageoftheHLTcalibrationframeworkandbenchmarksfordedicated
1TheALICECollaborationconsistsofmorethan1000membersfrom109Institutesin31Countries
(cf. http://aliceinfo.cern.ch/Public/en/Chapter3/Chap3Collaboration-en.html).
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interfaces are presented. Finally, the results are summarised and an outlook on further
developmentsandenhancementsisgiveninchaptersix. Theappendixcoverstheusage
of the presented interfaces. The calibration framework for the ALICE HLT, as it is
described here, refers to the state of Autumn 2008.
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Introduksjon
Denne doktoravhandlingen baserer seg på utviklingen av et fordelt og rekonfigurerbart
online kalibreringsrammeverk for ALICE (A Large Ion Collider Experiment) HLT
(High Level Trigger). ALICE2 er et av fire hovedeksperimenter ved den nye akseler-
atorringen (LHC - Large Hadron Collider) på CERN i Geneve (CH). Eksperimentet
har til hensikt å studere egenskapene ved materie produsert i kollisjoner mellom tunge
ioner i ultra-relativistiske energiområder. Man antar at universet var i en slik tilstand
i de tidligste fasene etter Big Bang. HLT er et subsystem av ALICE som fokuserer på
online event rekonstruksjon og analyse, event seleksjon og reduksjon av data fra AL-
ICE. Dette arbeidet utføres ved en stor datamaskinfarm lokalisert nær eksperimentet.
For å oppnå høy nøyaktighet i analysen er kalibreringen av komponentene som utfører
HLTs oppgaver særlig viktig.
Avhandlingen beskriver grensesnittet og komponentene utviklet for HLT kalibre-
ringsrammeverket. De dekker utveksling av data mellom HLT og de tilkoblede ALICE
subsystemene. Deres oppgave er å utføre påkrevd kalibrerings- og betingelsesinnstill-
inger i HLT, samt å forsyne nylig produserte kalibreringsobjekter til bestemmelsesst-
edene. Datautvekslingen krever også synkronisering med de andre subsystemene og
innen selve HLT. Grensesnittene (beskrives i kapittel 4.3, 4.4 og 4.5) og deres samspill
(beskrives i kapittel 5), dessuten FED-APIen (Front-End-Device-API) (spesifisert i
kapittel 3) har vært et hovedfokus i denne avhandlingen. Hvor godt de oppfyller
nødvendige betingelser presenteres i kapittel 6.
I første kapittel gis en kort oversikt over fysikken bak ALICE eksperimentene. I
kapittel 2 blir ALICEs detektorer og systemer presentert. Kapittel 3 fokuserer på
FED-APIen som håndterer sammenkoblingen av ALICE DCS (Detektor Kontroll Sys-
tem) og Front-End-Elektronikk (FEE) på de forskjellige detektorene. FED-APIen er
igjen brukt i HLT. Avhandlingens hovedtema, grensesnittene og de tilhørende kompo-
nentene som utgjør HLTs kalibreringsrammeverk, beskrives detaljert i kapittel 4. Spe-
sielt er heterogeniteten av de sammenkoblede systemene og diversiteten i de anvendte
mekanismene satt i fokus. I kapittel 5 bringes de ulike elementene sammen for å belyse
deres samvirke og synkroniseringsprosedyrer. Utover dette presenteres her eksempler
på anvendelsen av HLT kaliberingsrammeverket og målte referanseverdier. Avslut-
ningsvis, i kapittel 6, foretas en oppsummering av resultatene, samt en fremtidsrettet
vurderingavpotensiellvidereutviklingogforbedring. Appendiksetgirenbrukerveiled-
2ALICE Samarbeidet: 31 land, 109 institutt og mer enn 1000 medlemmer
(se http://aliceinfo.cern.ch/Public/en/Chapter3/Chap3Collaboration-en.html).
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ning for de presenterte grensesnittene. Kalibreringsrammeverket for ALICE HLT som
beskrives her, gjelder status per høsten 2008.
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Conventions used in this PhD thesis
This document uses several common typographical conventions.
To emphasise source code or documentation of the tools and applications, they are
written in a monospaced font.
In this thesis several UML (Unified Modelling Language) diagrams are presented.
The design and preparation of these diagrams has been guided by the following book
describing UML 2.0:
M. Jeckle, C. Rupp, J. Hahn, B. Zengler, S. Queins: UML 2 glasklar, Carl Hanser
Verlag, München (Germany), ISBN: 3-446-22575-7, 2004
Trademarks, trade names, services marks and registered names, mentioned in this
dissertation, are protected by international law and national agreements, even if this
is not explicitly marked.
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If at the beginning something looks impossible, start with small steps ...
"Beginne damit, das
Nötige
zu tun.
Dann tue das
Mögliche
und plötzlich tust du das
Unmögliche."
Franz von Assisi (zugeschrieben)
"Start by doing what is
,
necessary
then do what is
,
possible
and suddenly you are doing the
."
impossible
ascribed to St. Francis of Assisi
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Acknowledgements
In the development of the interfaces described within this thesis, I enjoyed very good
cooperation and fruitful exchange of ideas with people of the other ALICE systems. I
would like to say thank you to the involved persons from the ALICE DCS, the ALICE
ECS and the ALICE Offline group. In addition I want to state my regards to the
other people participating in the development of the FED-API.
And, of course, I experienced a perfect collaboration in the whole ALICE HLT
group. Representatively, I would like to name here Prof.Dr.Volker Lindenstruth and
Dr.Timm M.Steinbeck (the complete HLT collaboration is listed in the appendix C).
Moreover, I am thankful to the Norwegian Research Council (NFR) for supporting
this project financially and for the chance of getting experiences abroad.
With this PhD thesis, I finally complete my student life. Along this road many
people have accompanied me – during study, work and private life – family, friends,
teachers, fellow students and colleagues (often taking more than one role):
My friends in Germany, who held fast the bonds of friendship. They and others
showed me that distance and friendship are not necessary contradictory: Kerstin &
Marcus Lohr, Frederic Hoffman, Anna Th.Cibis, Christian Kofler, Michael Schaaf,
Larissa Bollinger, Eric S.Conner and Stephan Reichel. With joy I remember your
phone calls, letters, post cards and visits. A special greeting goes to Cornelia "Conny"
Ebitsch, who convinced me to "start doing the necessary". Danke!
In my new home, Bergen, I have felt (and feel) welcome as well. Not only in
science and work aspects, but also in social life activities the Nuclear Physics Group
at the University of Bergen has made (and makes) my living here most comfortable.
In the order they stepped into my life, these are: Ketil Røed, Matthias Richter,
Are S.Martinsen, Kenneth Aamodt, Dag T.Larsen, Dr.Johan Alme, Prof.Dr.Joakim
Nystrand, Prof.Dr.Håvard Helstrup, Prof.Dr.Kristin F.Hetland, Dr.Jens I.Jørdre,
Dr.Hongyan Yang (Xie Xie, especially for the exotic taste discoveries in the Chinese
cuisine), Gaute Øvrebekk (it has been (and is) a great time being office mates), Øys-
tein Djuvsland, Kyrre Skjerdal, Camilla H.Stokkevåg (Tusen takk for alle de hyggelige
og fine kaffepausene, og all norsk-hjelpen), Dominik Fehlker, Øystein S.Haaland,
Dr.Boris Wagner, Hege Erdal, Kristian Ytre-Hauge, Henrik Qvigstad, Dana Huang
and Lijiao Liu. With quite a few of you I share the predicate friends, even after this
relatively short time, and I feel honoured by it.
My very grateful thanks go to Dr.Kalliopi "Kelly" Kanaki, for showing a lot of
patience in explaining to me the ALICE related physics aspects, for the Mediterranean
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flair she brought in our group, for quite some delicious recipes and mainly for the
unappreciative work of proof reading this thesis and for giving a wide array of useful
suggestions for improvements: (cid:15)υχαριστω´ πoλυ´.
Furthermore,IalsoliketoacknowledgeProf.Dr.KjetilUllalandforhisveryfriendly
and straightforward character, his never ending source of new ideas, the jokes during
lunch time and for taking the job of being my co-supervisor. Mange takk!
There are three important persons without them I would have never started work-
ing on a PhD:
– Dr.Randolf Straky, without him I would have never considered the idea of taking
a PhD; – Mein Freund, mögen unsere Abende weiterhin so ergiebig "inspired" sein.
– Prof.Dr.Ralf Keidel, who brought me to the ALICE project and supported me
during my computer science studies and my Diploma thesis. Above all, he encouraged
me in moving to Bergen and taking the PhD-stipend. His support has not stopped
after leaving to Bergen – You deserve my honest thankfulness.
– Prof.Dr.Dieter Röhrich, who offered me the opportunity of working in this
thrilling field of science and writing a PhD-thesis on the presented topic. His re-
laxed and kind manner and his ability of explaining complex physics properties in an
easy and well understandable way has helped me a lot in finding my way through the
relevant physics topics. Moreover, his style has made me interested in a subject, that
does not actually belong to the roots of my studies. In permitting me to travel to the
relevant conferences in India, China and Canada, he allowed me to contribute to the
corresponding community and to experience other countries’s culture as well. I always
enjoyed the amicable atmosphere of him and his wife Dr.Bianca Ross, which reaches
far beyond work life – You both have taken a major part in me feeling at home here.
I will always perceive myself being connected to you in deep gratitude.
Finally, a deep and everlasting gratefulness I feel for my family. I thank my parents
BrigitteandWolfgangBablok(Ihavealwaysfelttheassuranceofyourfatherlyguiding
hand), who supported and encouraged me to all intents and purposes. Your advice
reached and helped me all over the world. Further, I wish to point out that it is
perfectly wonderful having an elder brother: Frank Bablok. He and his family – my
sister-in-law Ursula, my niece Sabine and my nephew Michael – have been at the ready
whenever needed for backup and assistance or for a cheering up.
Bergen in October 2008
Sebastian R. Bablok
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