Computing at CERN: Admin, Tech, & Theoretical Physics

1. 2001 Summer Student LecturesComputing at CERNLecture 1 — Looking AroundTony Cass — Tony.Cass@cern.ch

2. 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 Dőnszelmann, Dirk Düllmann, Steve Hancock, Vincenzo Innocente, Alessandro Miotto, Les Robertson, Tim Smith and David Stickland. Tony Cass

3. 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 K=1024, K=1000 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 Some Definitions Tony Cass

4. 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 aphysics based viewpoint Tony Cass

5. Windows 95 Windows NT WGS and PLUS CERNVM VXCERN Weekly use of Interactive Platforms1987-2001 Number of Users each Week Week Tony Cass

6. Computer Usage at IN2P3 Tony Cass

7. 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. Tony Cass

8. 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. Tony Cass

9. Technical and Engineering Computing • accelerators and • detectors • 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 today’s advanced accelerators and detectors. both Tony Cass

10. Accelerator design issues • Oliver Brüning’s 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 don’t 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? Tony Cass

11. LHC Magnet Design 2D field picture for LHC dipole coil 3D representation of dipole coil end with magnetic field vectors Pictures generated with ROXIE. Tony Cass

12. 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. Tony Cass

13. 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 arise—and 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 don’t! Tony Cass

14. 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 can’t 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. Tony Cass

15. Bunch splitting at the PS Tony Cass

16. Accelerator Controls Magnet current trace showing some of the manybeam types the PS can handle for different users. PS Operator Control Windows Tony Cass

17. Detector Design Issues Detector designs also benefit from computer simulations. Tony Cass

18. Detector Design Issues II NA45 TPC with field cage Electric field near the field cage Tony Cass

19. … and some at LEP 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 packages—e.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. Tony Cass

20. 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. Tony Cass

21. 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 costs—one PC is cheap, but managing 200 is not! Tony Cass

22. 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 costs—one PC is cheap, but managing 2000 is not! • And do we have enough space, power and cooling for the LHC equipment? Tony Cass

23. 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 easier—just 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 doesn’t 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… Tony Cass

24. Looking Around—Summary • Computing extends to all areas of work at CERN. • In terms of CERN’s “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. Tony Cass