2001 Summer Student Lectures Computing at CERN Lecture 1

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2001 Summer Student LecturesComputing at
CERNLecture 1 Looking AroundTony Cass
Tony.Cass_at_cern.ch
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Acknowledgements

• The choice of material presented here is entirely
  my own. However, I could not have prepared these
  lectures without the help of
• Charles Granieri, Hans Grote, Mats Lindroos,
  Franck Di Maio, Olivier Martin, Pere Mato, Bernd
  Panzer-Steindel, Les Robertson, Stephan
  Russenschuck, Frank Schmidt, Archana Sharma and
  Chip Watson
• who spent time discussing their work with me,
  generously provided material they had prepared,
  or both.
• For their general advice, help, and reviews of
  the slides and lecture notes, I would also like
  to thank
• Marco Cattaneo, Mark Donszelmann, Dirk Düllmann,
  Steve Hancock, Vincenzo Innocente, Alessandro
  Miotto, Les Robertson, Tim Smith and David
  Stickland.

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Some Definitions

• General
• Computing Power
• CERN Unit
• MIPS
• SPECint92, SPECint95
• Networks
• Ethernet
• Normal (10baseT, 10Mb/s)
• Fast (100baseT, 100Mb/s)
• Gigabit (1000Mb/s)
• FDDI
• HiPPI
• bits and Bytes
• 1MB/s 8Mb/s
• Factors
• K1024, K1000

• CERN
• Interactive Systems
• Unix WGS PLUS
• CUTE, SUE, DIANE
• NICE
• Batch Systems
• Unix SHIFT, CSF
• CORE
• PCSF
• Other
• Data Storage, Data Access Filesystems
• AFS, NFS, RFIO, HPSS, Objectivity/DB
• CPUs
• Alpha, MIPS, PA-Risc, PowerPC, Sparc
• Pentium, Pentium II, Merced

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How to start?

• Computing is everywhere at CERN!
• experiment computing facilities, administrative
  computing, central computing, many private
  clusters.
• How should this lecture course be organised?
• From a rigorous academic standpoint?
• From a historical standpoint
• ...
• From a physics based viewpoint

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Weekly use of Interactive Platforms1987-2001
Number of Users each Week
Week
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Computer Usage at IN2P3
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Computing at CERN

• Computing purely for (experimental) physics
  will be the focus of the second two lectures of
  this series. Leaving this area aside, other
  activities at CERN can be considered as falling
  into one of three areas
• administration,
• technical and engineering activities, and
• theoretical physics.
• We will take a brief look at some of the ways in
  which computing is used in these areas in the
  rest of this first lecture.

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Administrative Computing

• As any organisation, CERN has all the usual
  Administrative Data Processing activities such as
• salaries, human resource tracking, planning ...
• Interesting aspects of this work at CERN are
• the extent to which many tasks are automated
• the heterogeneous nature of the platforms used
  when performing administration related tasks.
• The Web is, as in many other cases at CERN,
  becoming the standard interface.

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Technical and Engineering Computing

• Engineers and physicists working at CERN must
• design,
• build, and
• operate
• for experimental physicists to be able to
  collect the data that they need.
• As in many other areas of engineering design,
  computer aided techniques are essential for the
  construction of todays advanced accelerators and
  detectors.

• accelerators and
• detectors

both
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Accelerator design issues

• Oliver Brünings lectures will tell you more
  about accelerators. For the moment, all we need
  to know is that
• particles travelling in bunches around an
  accelerator are bent by dipole magnets and must
  be kept in orbit.
• Of course, they must be accelerated as well(!),
  but we dont consider that here.
• Important studies for LHC are
• magnet design
• how can we build the (superconducting) dipole
  magnets that are needed?
• transverse studies
• will any particles leave orbit? (and hit the
  magnets!)
• longitudinal studies
• how can we build the right particle bunches for
  LHC?

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LHC Magnet Design
2D field picture for LHC dipole coil
3D representation of dipole coil end with
magnetic field vectors
Pictures generated with ROXIE.
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Genetic Algorithms for Magnet Design
Original coil design.
Genetic Algorithm convergence plot.
New coil design found usinga genetic
algorithm.This was further developed using
deterministic methodsand replaced the
originaldesign.
The algorithm is designed to come up with a
number of alternative solutions which can then be
further investigated.
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Transverse Studies
These images show how particles in a circulating
bunch move about in a 4 dimensional phase space
X position angle, Y position and angle.
Particles with chaotic trajectories in this phase
space have orbits that are unbounded and so will
hit the walls of the accelerator
eventually. Transverse studies of particle motion
attempt to understand how these instabilities
ariseand how they can be reduced by changes to
the magnets.
Particles that move like this in phase space stay
in the accelerator. Those that move like this
dont!
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Longitudinal Studies

• Not all particles in a bunch have the same
  energy. Studies of energy distribution show
  aspects of bunch shape.
• The energy of a particle affects its arrival time
  at the accelerating cavity which then in turn
  affects the energy.
• Need to measure both energy and arrivaltime, but
  cant measure energy directly.Measuring arrival
  times is easy
• but difficult to interpret successive slices.
• Tomography techniques lead to a completepicture
• like putting together X-ray slices througha
  person.

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Bunch splitting at the PS
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Accelerator Controls
Magnet current trace showing some of the
manybeam types the PS can handle for different
users.
PS Operator Control Windows
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Detector Design Issues
Detector designs also benefit from computer
simulations.
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Detector Design Issues II
NA45 TPC with field cage
Electric field near the field cage
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Computing for Theory
Feynmann diagrams for some LHC processes
Theoretical physicists could not calculate
probabilities for processes represented by
Feynmann diagrams like these without using
symbolic algebra packagese.g. Maple or
Mathematica. These calculations are essential for
two reasons
1 As collision energies increase, and as the
precision of experimental measurements increases
with increasing data volume, more Standard Model
processes contribute to the data that is
collected. 2 Theorists need to calculate how the
effects of theories beyond the standard model,
e.g. SUSY, could affect the data that is
collected today.
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CERN and the World Wide Web

• The World Wide Web started as a project to make
  information more accessible, in particular, to
  help improve information dissemination within an
  experiment.
• These aspects of the Web are widely used at CERN
  today. All experiments have their own web pages
  and there are now web pages dedicated to
  explaining about Particle Physics to the general
  public.
• In a wider sense, the web is being used to
  distribute graphical information on system,
  accelerator and detector status. The release of
  Java has given a big push to these uses.
• Web browsers are also used to provide a common
  interface, e.g.
• currently to the administrative applications, and
• possibly in future as a batch job submission
  interface for PCs.

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1998?1999 What has changed?

• Hardware
• PC hardware has replaced RISC workstations for
  general purpose computing.
• Software
• Future operating system developments clearly
  concentrated on Linux and Windows
• Linux success use of PCs is a positive feedback
  loop!
• Java is coming up fast on the inside lane.
• but C investment is large and C/Java
  interoperability poor.
• Systems Management
• Understand costsone PC is cheap, but managing
  200 is not!

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1999?2000 What has changed?

• Hardware
• PC hardware has replaced RISC workstations.
• Software
• Future operating system developments are clearly
  concentrated on Linux. Windows 2000 will be
  deployed at CERN but is now a distant 3rd choice
  for physics
• Linux success use of PCs is a positive feedback
  loop!
• Java is still coming up fast on the inside lane.
• C investment is still large and C/Java
  interoperability is still poor.
• Systems Management
• Understand costsone PC is cheap, but managing
  2000 is not!
• And do we have enough space, power and cooling
  for the LHC equipment?

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2000?2001 What has changed? I

• Windows 2000 has arrived and Wireless Ethernet is
  arriving.
• Portable PCs replacing desktops.
• Integration of home directory, web files, working
  offline makes things easierjust like AFS and
  IMAP revolutionised my life 8 years ago.
• I now have ADSL at home rather than ISDN.
• I am now outside the CERN firewall when connected
  from home but this doesnt matter so much with
  all my files cached on my portable.
• I just need to bolt on a wireless home network so
  I can work in the garden!
• The number of people connecting from outside the
  firewall will grow
• CERN will probably have to support Virtual
  Private Networks for privileged access
• And users will have to worry about securing their
  home network against hackers

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Looking AroundSummary

• Computing extends to all areas of work at CERN.
• In terms of CERNs job, producing particle
  physics results, computing is essential for
• the design, construction and operation of
  accelerators and detectors, and
• theoretical studies, as well as
• the data reconstruction and analysis phases.
• The major computing facilities at CERN, though,
  are provided for particle physics work and these
  will be the subject of the next two lectures.