Items from 4th meeting of Geant4 Technical Forum

Hosted at Vanderbilt University, May 12th 2004 as part of the Geant4 Space Users Forum.

 

Meeting notes

DRAFT

Created:  21st July 2004

Version:  0.2 of 7th September 2004

Editor: J. Apostolakis

Initial Issues:

1.)     G4 distillers & engineering tools

2.)     www tools, interfaces

3.)     Heavy Ion hadronic physics

4.)     EM physics down to 10s of eV

5.)     Geometry input and CAD/STEP (Main tools: Autocad, likely also Catia)

6.)     Parallelization

7.)     Tech forum, HyperNews, direct communication

8.)     Other: Usability, Biological effectiveness

 

Use cases:

 U401.) "Radiation studies": radiation environment in spacecraft, studies of radiation on human Mars expedition, ...

 U402.) "Microelectronics in space: detailed simulation"

 U403.) Identifying key elements of radiation environment affecting a component and/or small element (likely using reverse Monte Carlo) and simulate in detail only this small element and its local environment (source: R. Reed, NASA Goddard Space Center) 

 U404.) The LISA spacecraft’s simulation and other sensitive detector techologies, such as those used for JWST. The simulation must cope with a large set of length scales, starting from the inter-spacecraft scales, and reaching down to the level of onboard semiconductor devices. The best possible treatment of physics processes that effects the charging of the test-masses, and in particular EM physics down to the lowest possible energy scale (10 eV if possible) is seen as priorities.

 U405.) Simulating Single Event Upsets: need accurate spatial and temporal distribution of space charges. (Note: need for temporal information is new.)

 

Considerations/Constraints

 1.) Potential for use of Geant4-based applications as engineering tools for several specific cases: with simple setups, short running-time.

 2.) Strong interest to obtain 'conservative' estimates of radiation effects, even at the expense of some accuracy.

 

New Requirements and Requests: Toolkit

0401) Enable the direct use of CAD-created files for geometry input

 

Need for input from CAD systems to enable fast turnaround in using Geant4 with a new or revised spacecraft geometry.  The current need to create ‘by hand’ a geometry for simulation in Geant4, can take a few weeks.  The goal is to reduce this to a few hours (or less) by utilizing a new module and/or tool.

Constraints:

-          Utilizing an approximate geometry (e.g. obtained via triangulation) was seen as acceptable.

-          Agreed that a potential slowdown of a factor of 3x-10x is likely acceptable (preferred: 3x).

Additional issues, to be considered:

-          material properties

-          surface properties

-          potential optimizations to improve the run-time performance of a triangulated solid (e.g. using voxelisation to decrease the surfaces intersected);

-          advance properties of a material (e.g. honeycomb structure)

Note: A new STEP application protocol for space applications is currently being developed under a contract by ESA (TEC-EES), and is taking into account G4-related requirements

 

0402) Enable the use of geometry setups of almost any scale

Enable Geant4 to cope with geometry setups whose diameter can be either:

-          larger than the diameter of a planet (or the solar system, or a fraction of our galaxy), and

as small as a current semiconductor device (i.e. tens of nanometers across).

 

0403) Extend Ion Physics

Potential improvements mentioned included to

-          extend to higher energies. In particular introduce total cross sections for high energies;

-          further enhance the verification and validation, ...

-          extend to heavier nuclei (?)

-          assess the efficacy of current models for use in simulating single event upsets;

 

0404) Identify extensions to EM physics towards a 10eV production threshold

The relevant use cases are driven by the need to simulate at very small scales:

-          the use for semiconductor device simulation

-          to provide input for device level atomic simulations

Identify conservative estimates of the accuracy of available modeling and cross sections.

 

New Requirements and Requests: Documentation, processes, ...

 

0410) Effort to validate physics configurations and modeling for microscopic use  cases

Need to exchange experiences regarding the validation of these physics lists & models.

A community effort is required.

Establish a process to exchange information on physics comparisons relevant to space use cases.

 

0411) Learning curve and its steepness

Use case: Users coming to Geant4 for the first time report difficulties in getting started.

Quote: "Do not make it any harder to pick Geant4 and use it". 

Adding more capability that will add complexity is seen as a double-edged sword by several users.

Issue: A new user today must understand a significant part of the Geant4 system in order to be confident that there are no ‘hidden’ features or options that would spoil the results of their application.

Need: Avoid changes that will increase this load. Consider as a desirable quality, used to evaluate potential future changes, how much it flattens the user’s learning curve.

Consequences: Identify what functionality or modules are optional – so that people need to understand it only if they need it or choose to try it.

 

0412) Maintain linkage between Geant4 source and formulae of physics processes

 

Use case: Someone wishes to understand the implementation of a physics process, and to check the relation between the theoretical description and the code. Today he/she has little information to assist him/her to distinguish which part of the source code implements which equation.

Suggestions raised:

 Extra comments in source code:

 - referring to the original paper (and the Physics Reference Manual [PRM] ),

 - providing a short summary of the model / approach / …

 - creating a traceability map between code and physics model references (low-EM)

 

0413) Provide additional explanations for physics lists, especially for their choice of models

 

Add information:

-          about the choice of physics models in a particular physics list and its relation to the requirements of the use case;

-          identify where one model can (or always does) invoke another at a (lower) energy: eg a cascade that hands over a resulting excited nucleus to the pre-compound and evaporation models.

 

0414) Identify a set of Space Use Cases and create a set of corresponding Physics Lists

 

A first set of potential use cases included:

 - microelectronics

 - shielding

For further information, for the moment refer to P. Truscott’s talk at the G4 Space Workshop 2004.

 

0415) Documenting changes and improvements

 

Include information in Release Notes on bug fixes of problem reports. 

 

0416) Could classes with names starting with “G4” come only from Geant4 itself ?

 

Users are confused whether classes whose names start with “G4” come from Geant4 or not. Address the widespread confusion about the origin of classes named "G4Something".  Many such classes currently originate from other parties, and are not 'blessed' by G4.

A user suggestion was to consider (at least) encouraging a new practice: to limit the use of class names starting with "G4" to those in the Geant4 toolkit. For other uses, we can propose that all authors use other prefixes to name the classes in their prototypes, candidate contributions, etc.

 

Source: Hindi Munther (Lockheed Martin)

 

 

Smaller Items:

 

0451) Examine the Shielded Coulomb Scattering

Ensure that the same interactions are not counted twice