SNA + MC 2010

1. Environmental adaptability and mutants: exploring new concepts in particle transport for multi-scale simulation Maria GraziaPia INFN Genova, Italy Mauro Augelli1,Marcia Begalli2, Mincheol Han3, Steffen Hauf4, Chan-Hyeung Kim3,Markus Kuster4, Maria Grazia Pia5, Pedro Queiroz6, Lina Quintieri7, Paolo Saracco5, Hee Seo3, Denison Souza Santos6, Georg Weidenspointner8, Andreas Zoglauer9 1 CNES, France – 2 State University Rio de Janeiro, Brazil –3 Hanyang University, Korea 4 MPE and MPI Halbleiterlabor, Germany –5 INFN Sezione di Genova, Italy 6 IRD, Brazil –7 INFN LaboratoriNazionali di Frascati, Italy 8 MPE and MPI Halbleiterlabor, Germany –9 University of California at Berkeley, USA SNA + MC 2010 Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2010

2. Acknowledgments Thanks to: • Zane Bell (ORNL) • Sergio Bertolucci (INFN and CERN) • Simone Giani (CERN) • Vladimir Grichine(Lebedev Inst., Russian Academy of Sciences) • Alessandro Montanari (INFN Bologna) • Andreas Pfeiffer (CERN) for contributions, helpful discussions and advice • CERN Library (TullioBasaglia) for support to the project

3. Collected from the experimental community Object Oriented methods introduced in HEP Background 1994 mid of LEP era GEANT 3successfully used in many experiments • Geant4 R&D phase: RD44 • 1994-1998 (Geant4 0: 15 December 1998) • Designed and built Geant4 • New software technology • GEANT 3 experience + new ideas • Foundation of Geant4: dates back to the mid ’90s • Requirements for core capabilities • Software technology • Evolution: 1999-2010 • Consolidation, validation, extension and refinement of existing capabilities • Support to the experimental community • Proliferation of physics models • Samecore capabilitiesandtechnologyas in themid ’90s The world changes…

4. Courtesy RADMON (M. Moll et al.) Team, CERN, NSS 2006 Conf. Rec. TiO2 nanowires Courtesy A. Montanari et al., INFN Bologna NSS 2006 Conf. Rec. Courtesy eROSITA G. Weidenspointner et al., NSS 2008 Conf. Rec Xenopus XL-177 cell

5. Condensed-random-walkDiscrete simulation • Condensed-random-walk approximation • all general-purpose Monte Carlo codes (EGS, FLUKA, GEANT 3, Geant4, MCNP) • charged particle tracks divided into many steps, several interactions occur in a step • one energy loss and one deflection are calculated for each step • collisions are treated as binary processes • target electrons free and at rest (or binding accounted only in an approximated way) • adequate as long as the discrete energy loss events are » electronic binding energies • Discrete simulation • all collisions are explicitly simulated as single-scattering interactions • prohibitively time-consuming on large scale for charged particles (infrared divergence) • many “track structure” codes documented in literature • single-purpose, not public, maintenance not ensured, lack general functionality

6. Two worlds… Condensed-random-walkOR“discrete” régime Characterizing choice in a Monte Carlo system What does it mean in practice? How does one estimate radiation effects on components exposed to LHC + detector environment? RADMON ATLAS And what about nanotechnology-based detectors for HEP? And tracking in a gaseous detector? And plasma facing material in a fusion reactor? How does one relate dosimetry to radiation biology?

7. Two worlds… • Deterministic methods are widely used in • Reactor physics calculations • Based on the concept of “neutron flux” • Medical physics • Treatment planning • Reactors: series of codes specialized in specific functions • Cumbersome… • Monte Carlo intrinsically more accurate • Model geometry and physics accurately • New trends • Monte Carlo group constant generation for deterministic codes • Conventional deterministic codes not well-suited to complex assembly designs, next generation reactors, advanced MOX technology etc. • Monte Carlo calculations

8. R&D on transport schemes Project launched at INFN (2009) International, multi-disciplinary team R&D = research study, exploration of novel ideas Motivated by concrete experimental requirements Response to current limitations of Geant4 Address experimental use cases by going to the very core of Monte Carlo methods NANO5 R&D on complementary, co-workingtransport methods Condensed-random-walk scheme Discrete scheme Monte Carlo method Deterministic methods

9. Topics of research Objective Seamless transition of simulation régime in Geant4 Capability of simulating complex, multi-scale systems • Conceptual and software design challenges • Transport scheme adaptation to the environment • Embedding “mutability” in Monte Carlo physics entities • Pioneering R&D • Capability not yet present in Monte Carlo systems for particle physics Theoretical and mathematical support Software technology Experimental feedback

10. Conceptual investigations PIXE as playground of the interaction of condensed-discrete schemes Mutants How to make them, how to deal with them Side effects in the hadronic sector Radioactive Decay Technological investigation Generic and generative programming techniques applied to a large scale simulation sub-system V&V Self-testing capabilities, cloning, pruning, reproducibility Work in progress

11. Mutants Objects changing their class • Transition of transport scheme addressed by introducing the concept of mutants • Simulation entities capable of adapting to the environment where they operate • Mutants mutate subject to stimuli • Currently investigating the possibility of spontaneous mutations • Reversible mutations • Distinguish stable and mutable parts of simulation entities • Break up physics objects into fine-grained behaviour • Provide the capability of multiple, evolving behaviour • Ideally, without any additional burden to the simulation performance Conceptual investigation Technological R&D

12. Currently working at: Prying eyes State Memento Mediator? Generic programming • Relatively new technology • Aka “programming with templates” • Aka “modern design”: post-Alexandrescu’s book era • C++ is capable of a Turing machine at two levels • Exploit both • Mix and match • Further step: generative programming • Extreme configurability • Bind configurability at compile time • Performance gain relevant to nano-scale simulation • Memory consumption “the hardest of hardcore template programming” Is static polymorphism suitable to runtime mutation? Quantify

13. Candidate technology applied to test environments Pilot projects “track structure” Monte Carlo “conventional” Geant4 electromagnetic physics radioactive decay (hadronic + electromagnetic) On-the-field study of conceptual issues and software solutions Metrics Side benefits Verification, validation, code reviews, documentation, improvement to algorithms, physics refinements etc.

14. Side topics instrumental to the main objectives Physics configurability Needed to implement mutation Relevant to conventional Geant4 use Aspects? Concerns scattered and tangled Not so well supported in C++ as in Java • Geant4 design does not easily support • test processes specific to physics • V&V left to individual developers’ and users’ efforts Built-in physics V&V-ability Epistemic uncertainties in MC: see E3-1 …and more!

15. Software Process R&D at the very heart of Monte Carlo concepts and Geant4 kernel • Iterative-incremental process • To mitigate “waterfall” risk • UP-based, tailored to the project(s) • a/b-releases for testing and application feedback • Risk mitigation strategy • No perturbation to a system currently in production in LHC experiments and many other projects • Develop in parallelto Geant4 kernel • Transition for production use when mature • (if graciously approved by Geant management) Source of risk for experiments relying on Geant4 in production mode Also: optimize the limited resources for high ROI

16. Conclusion NANO5R&D on transport schemes launched in 2009 INFN + international team Requirements from concrete experimental problems Multi-scale simulation in the same environment New concepts being explored for introduction in Monte Carlo kernel Mutability, adaptation to environment Evaluation of software technologies in support to physics issues Publications in http://www.ge.infn.it/geant4/talks Further details in http://www.ge.infn.it/geant4/nano5 …more to follow!

17. Related talks • G3: Information Technology and its Applications II • Physics data management tools: computational evolutions and benchmarks • I1: New Techniques and Applications of Photon-Electron • New techniques in Monte Carlo simulation: experience with a prototype of generic programming application to Geant4 physics processes   • Environmental adaptability and mutants: exploring new concepts in particle transport for multi-scale simulation • I2: Low Energy Electrons and Photons • Design, development and validation of electron ionisation models for nano-scale simulation • Data libraries as a collaborative tool across Monte Carlo codes • Conceptual challenges and computational progress in X-ray simulation • E3: Radiotheraphy (Algorithm and Software) • Epistemic and systematic uncertainties in Monte Carlo simulation: an investigation in proton Bragg peak simulation • F3: Monte Carlo Applications II (Device Damage) • R&D project for a Geant4-based, Multi-scale Simulation Environment to Study the Radiation Effects on Electronic Devices • F4: Monte Carlo Applications III (Others) • Radioactive decay simulation with Geant4: experimental benchmarks and developments for X-ray astronomy applications