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Title:F-TRIDYN: A Monte-Carlo, BCA code for modeling ion-surface interactions with rough materials and coupling plasma and material codes
Author(s):Drobny, Jon Thomas
Advisor(s):Ruzic, David N.
Contributor(s):Curreli, Davide
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Plasma Material Interactions
Binary Collision Approximation
Surface Roughness
Fractal Geometry
Abstract:Fractal-TRIDYN (F-TRIDYN) is a modified version of the widely used Monte Carlo, Binary Collision Approximation code TRIDYN that has been upgraded to include an explicit model of surface roughness and additional output modes for coupling to plasma edge and material codes. Surface roughness plays an important role in ion irradiation processes such as sputtering; roughness can significantly increase the angle of maximum sputtering and strongly affect the sputtering yield. The complete effect of surface roughness on sputtering and other ion irradiation phenomena is not completely understood. Many rough surfaces can be consistently and realistically modeled with fractals, using the fractal dimension and fractal length scale as the sole input parameters to control surface morphology and roughness. F-TRIDYN includes a robust fractal surface algorithm that is more computationally efficient than those in previous fractal codes and which reproduces available experimental sputtering data from rough surfaces. Fractals provide a compelling path toward a complete and concise understanding of the effect that surface geometry plays on the behavior of plasma-facing materials. Fractals also have simple relationships to other models of surface roughness, including RMS roughness. This link has been studied and used to approximate fractal surfaces with normally-distributed statistical surfaces, which may prove more computationally efficient than explicit fractal surfaces. F-TRIDYN is a flexible code for simulating ion-solid interactions and coupling to plasma and material codes for multiscale modeling. Results from F-TRIDYN show that at high angles of incidence, sputtering yields for fusion-relevant materials increase significantly; for the case of Argon on Tungsten this is an increase of a factor of 3.5. This may effect fusion reactor performance by releasing more impurity atoms into the plasma and increasing Bremsstrahlung radiation losses. Additionally, the effect of surface morphology is significant only for ions whose mean free path in the target is on the same order as or less than the characteristic scale of the surface. Higher energy ions will experience fewer collisions at depths where the surface morphology is relevant. Code coupling has been a major focus of F-TRIDYN development, and recent results of code-coupling to a variety of codes, including material and plasma codes, have been achieved. These preliminary results indicate that the existence of Helium impurities in a Tungsten target will increase the retention of further implanted Helium ions.
Issue Date:2017-12-13
Rights Information:Copyright 2017 Jon Drobny
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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