J. A. Halbleib

ITS: the integrated TIGER series of electron/photon transport codes-Version 3.0

The ITS system is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Version 3.0 is a major upgrade of the system with important improvements in the physical model, variance reduction, I/O, and user friendliness. Improvements to the cross-section generator include the replacement of Born-approximation bremsstrahlung cross section with the results of numerical phase-shift calculations, the addition of coherent scattering and binding effects in incoherent scattering, an upgrade of collisional and radiative stopping powers, and a complete rewrite to Fortran 77 standards emphasizing Block-IF structure. Improvements in the Monte Carlo codes are also described.<<ETX>>

The Integrated TIGER Series (ITS) of Coupled Electron/Photon Monte Carlo Transport Codes

ITS is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-integrated coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Our goal has been to simultaneously maximize operational simplicity and physical accuracy. Through a machine portable utility that emulates the basic features of the CDC UPDATE processor, the user selects one of eight codes for running on a machine of one of four (at least) major vendors. The ease with which this utility is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems. Physical rigor is maximized by employing the best available cross sections and sampling distributions, and the most complete physical model for describing the production and transport of the electron/photon cascade from 1.0 GeV down to 1.0 keV. Flexibility of construction permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications through simple update procedures.

Measurement of electron energy deposition necessary to form an anode plasma in Ta, Ti, and C for coaxial bremsstrahlung diodes

Measurements are made of surface doses necessary to initiate an anode plasma by electron bombardment of Ta, Ti, and C anodes for coaxial geometries characteristic of high‐power electron‐beam diodes. Measured lower and upper bounds of doses necessary to form an anode plasma are 54±7–139±16 J/g in Ta, 214±23–294±71 J/g in Ti, and 316±33–494±52 J/g in C. Within these bounds, probable values for the threshold are given under specific assumptions. The measurements are consistent with a thermal desorption model for plasma formation.

Pencil-like mm-size electron beams produced with linear inductive voltage adders

This paper presents design, analysis, and first results of the high brightness electron beam experiments currently under investigation at Sandia. Anticipated beam parameters are: energy 12 MeV, current 35-40 kA, rms radius 0.5 mm, pulse duration 40 ns FWHM. The accelerator is SABRE, a pulsed LIVA modified to higher impedance, and the electron source is a magnetically immersed foilless electron diode. 20 to 30 Tesla solenoidal magnets are required to insulate the diode and contain the beam to its extremely small sized (1 mm) envelope. These experiments are designed to push the technology to produce the highest possible electron current in a submillimeter radius beam. Design, numercial simulations, and first experimental results are presented.

Dynamics of electron flow in extended planar-anode diode operating at 19 MV and 700 kA

The electron flow in a planar‐anode diode having an extended anode‐cathode gap operating on the HERMES III accelerator is characterized and compared with predictions of a computational model. The model combines a particle‐in‐cell code with Monte Carlo radiation transport. The comparisons confirm the model and show that the diode provides both a matched load and a versatile large‐area source of γ rays for the study of nuclear radiation effects. Electrical and spatial parameters of the beam at the diode and the downstream radiation fields from a graphite target are presented as a function of the anode‐cathode gap.

Coupled electron photon collisional transport in externally applied electromagnetic fields

The model presented describes the time‐independent production and transport of the electron/photon cascade in two‐dimensional cylindrical material/void configurations in the presence of static electromagnetic fields of arbitrary spatial dependence. The range of phenomena that can be studied with the model is carefully delineated. The underlying assumptions required for coupling condensed‐history collisional Monte Carlo with macroscopic field transport are set forth in detail. The method is applied to specific problems in electron‐beam‐excited high‐pressure gas laser research, high‐intensity flash x‐ray source development, and electron‐beam‐fusion research. Results are compared with the predictions of earlier theoretical models and with experimental data. Comparisons between the theoretical models clearly demonstrate the importance of the additional capabilities achieved in the model described here. Because of the complexity of the experiments, comparisons between the theoretical predictions and the experimental data are not especially definitive; where comparisons are possible, however, there appears to be at least qualitative agreement.

A hybrid multigroup/continuous-energy Monte Carlo method for solving the Boltzmann-Fokker-Planck equation

A hybrid multigroup/continuous-energy Monte Carlo algorithm is developed for solving the Boltzmann-Fokker-Planck equation. This algorithm differs significantly from previous charged-particle Monte Carlo algorithms. Most importantly, it can be used to perform both forward and adjoint transport calculations, using the same basic multigroup cross-section data. The new algorithm is fully described, computationally tested, and compared with a standard condensed history algorithm for coupled electron-photon transport calculations.

Radiation Output and Dose Predictions for Flash X-Ray Sources

Calculations are made of target parameters required to maximize the photon fluence from flash x-ray sources for electron energies from 0.5 to 15.0 MeV. Doses and effective absorption coefficients for critical materials located downstream of the target are also obtained.

Accuracy of Coupled Monte-Carlo/Next-Event-Estimator for Bremsstrahlung Dose Predictions

The accuracy of an efficient hybrid Monte Carlo/ analytic method for predicting the spatial dependence of x-ray energy deposition in common dosimetry is determined by comparing its predictions with those of full Monte Carlo Transport. For x-ray simulators, the hybrid model underpredicts energy deposition in thermoluminescent dosimetry by failing to account for Compton buildup and overpredicts deposition in gold calorimetry by failing to account for the lack of electron equilibration and fluorescence escape. For gamma simulators, the method accurately predicts the deposition in thermoluminescent dosimetry. We also find that the 2.16-mm Al electron equilibrators used with our standard thermoluminescent dosimeters are excessive for x-ray simulators and insufficient for gamma simulators.

Gradient B drift transport of high current electron beams

A 1‐MeV, 200‐kA electron beam was transported 89 cm in a low pressure background gas via gradient B drift in the 1/r azimuthal magnetic field of a current carrying wire. The electron drift velocity was measured and found to be in good agreement with theory. Measurements of x‐ray production in the target indicated high transport efficiency.