# Presentation: 179862

## The MARS15 Code

- 2nd High-Power Targetry Workshop
-  Oak Ridge, TN
- October 10-14, 2005

***Fermilab***

_**High-Power Targetry**_

- Nikolai Mokhov, Fermilab

## OUTLINE

- Introduction
- Transported Particles
- Nuclear Cross-Sections
- Biasing
- Inclusive and Exclusive Event Generators
- Correlated Energy Loss and Coulomb Scattering
- Geometry Options, Histograming and Tagging
- MAD-MARS Beam Line Builder
- Graphical-User Interface
- Multiprocessing
- Modeling Radiation Damage, Ablation and Hydrodynamics

## MARS15 CODE INTRODUCTION

-  The MARS code system is a set of Monte Carlo programs for detailed simulation of hadronic and electromagnetic cascades in an arbitrary 3-D geometry of shielding, accelerator, detector and spacecraft components with energy ranging from a fraction of an electronvolt up to 100 TeV. It has been developed since 1974 at IHEP, SSCL and Fermilab. The current MARS15 version combines the well established theoretical models for strong, weak and electromagnetic interactions of hadrons, heavy ions and leptons with a system which can contain up to 105 objects, ranging in dimensions from microns to hundreds kilometers. A setup can be made of up to 100 composite materials, with arbitrary 3-D magnetic and electric fields. Powerful 2-D and 3-D user-friendly GUIis used for visualization of the geometry, materials, fields, particle trajectories and results of calculations. MARS15 has 5 geometry options and flexible histograming options, can use as an input MAD optics files through a powerful MAD-MARS Beam Line Builder, and provides an MPI-based multiprocessing option, with various biasing and other variance reduction techniques.

## PARTICLES TRANSPORTED IN MARS15

## PION AND ANTIPROTON X-SECTIONS

## NEUTRON- AND CARBON-NUCLEUS X-SECTIONS

## BIASING

- Many processes in MARS15, such as electromagnetic showers, most of hadron-nucleus interactions, decays of unstable particles, emission of synchrotron photons, photohadron production and muon pair production, can be treated either analogously or inclusively with corresponding statistical weights.The choice of method is left for the user to decide, via the input settings.
- Other variance reduction techniques used in MARS: weight-window, splitting and Russian roulette, exponential transformation, probability scoring, step/energy cutoffs.
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## MARS INCLUSIVE APPROACH

- The basic model for the original MARS program, introduced in 1974, came from Feynman's ideas concerning an inclusive approach to multiparticle reactions and weighting techniques.  At each interaction vertex, a particle cascade tree can be constructed using only a fixed number of representative particles (the precise number and type depending on the specifics of the interaction), and each particle carries a statistical weight w = f(x)/S(x), which is equal, in the simplest case, to the partial mean multiplicity of the particular event. Energy and momentum are conserved on average over a number of collisions. It was proved rigorously that such an estimate of the first moment of the distribution function f(x) is unbiased. A disadvantage of this approach is the impossibility of directly studying fluctuations from cascade to cascade, or of studying particle production correlations.

## INCLUSIVE PROTON PRODUCTION IN MARS15

- Proton inclusive spectra in pp-interactions are described in resonance region xF > 1-2.2/p0 as a sum of five Breit-Wigner
- resonances; in diffractive dissociation region 1-2.2/p0 < xF < 0.9 via triple-Reggeon formalism; in fragmentation region
- 0.4 < xF < 0.9 via phenomenological model with a flat behavior on longitudinal and exponential on transverse momenta;
- in central region 0 < xF < 0.4 via fit to experimental data. For pA, it is factorized then with R(A,p,p0) function adjusted
- with additive quark model, with quasielastic scattering and Fermi-motion modeled in addition, supplied with a phenomenological model for cascade and evaporation nucleon production.

## INCLUSIVE NEUTRON AND KAON PRODUCTION

- MARS15 vs data

## MARS15 EXCLUSIVE EVENT GENERATORS

- The improved Cascade-Exciton Model code, _**CEM03.01**_, combined with the Fermi break-up model, the coalescence model, and an improved version of the Generalized Evaporation-fission Model (GEM2) is used as a default for hadron-nucleus interactions below 5 GeV.
- The Los Alamos Quark-Gluon String Model code, _**LAQGSM03**_, was implemented into MARS15 for particle and heavy-ion projectiles at 10 MeV/A to 800 GeV/A. This provides a power of full theoretically consistent modeling of exclusive and inclusive distributions of secondary particles, spallation, fission, and fragmentation products. Further development of this package is underway.
- For quite some time, MARS has used the Dual-Parton Model code, _**DPMJET3**_,for the very first vertex in a cascade tree. This is used in our numerous studies for the LHC 7x7 TeV collider and its detectors, and at very high energies up to 100 TeV.

## NUCLEON YIELDS in 0.56 and 8 GeV/A REACTIONS

## NUCLIDE PRODUCTION AND PION SPECTRA FOR AA

## dE/dx and CORRELATED COULOMB SCATTERING

- 50-GeV protons on 10 g/cm2 H2

## GEOMETRY DESCRIPTIONS IN MARS15

## GEOMETRIES AND MATERIALS IN MARS15

## EXAMPLE OF FLUKA-MARS15 LINK

- CMS detector as seen in MARS-GUI

## HISTOGRAMING AND TAGGING IN MARS15

- In addition to previous volume and surface tally and histograming options in the code, a new user-friendly flexible XYZ-histograming module in MARS15 allows scoring numerous distributions – total an partial particle fluxes, star density, energy deposition, DPA, temperature rise, prompt and residual dose rates, particle spectra etc – in boxes arbitrary positioned in a 3D system, independent of geometry description.
- A refined tagging module in MARS15 allows one to tag the origin of a given signal/tally – geometry, process and phase-space - invaluable in studying a source term and for sensitivity analysis.

## GRAPHICAL-USER INTERFACE

## MARS MODELING OF CDF DETECTOR

- CDF detector, experimental hall, Tevatron beamline elements
- and neutron fluence isocontours as seen in MARS15 GUI

## MAD-MARS BEAM LINE BUILDER

## BEAMLINE MODELING AND VISUALIZATION 

## MULTIPROCESSING IN MARS15

- Since 2004, parallel processing is default in all CPU-hungry applications of MARS15. It is based on the Message Passing Interface(MPI) libraries. Parallelization is job-based, i.e. the processes, replicating the same geometry of the setup studied, run independently with different initial seeds. A unique master process -- also running event histories -- collects intermediate results from an arbitrary number of slaves and calculates the final results when a required total number of events has been processed. Intermediate results are sent to the master on its request generated in accordance with a scheduling mechanism. The performance scales almost linearly with the number of nodes used (up to tens of nodes at Fermilab clusters).

## NEUTRINO FACTORY AND MERIT EXPT TARGETS

- MARS14

- MARS15

## ENERGY DEPOSITION AND DPA MODELING

- DPA is calculated in MARS15 within a damage energy concept, taking into account
- recoil nuclei in elastic and inelastic hadron-nucleus interactions.

## MODELING BEAM ACCIDENT AT TEVATRON