- Post Doctoral
MIT Unit Affiliation:
- Nuclear Science and Engineering
Post Doc Sponsor / Advisor:
Date PhD Completed:
Top 3 Areas of Expertise:
I am an engineer, a scientist, an adventurer, an artist, and a maker of many things. I am interested in energy technology, particle accelerators, robotics, aerospace, and variety of other things. In recent years, I have been working on nuclear fusion energy research as a student and as a researcher at MIT. I completed my doctorate at the MIT Plasma Science and Fusion Center in February 2014 and am currently a postdoc working on projects and design studies related to my doctoral research. I'm always interested in exciting new projects and am looking forward to the places that my life and my career take me next.
Expected End Date of Post Doctoral Position:
- Development of accelerator based diagnostic techniques for in-situ analysis of plasma facing components in magnetic fusion devices.
- Development of simulation tools for charged particle beams in complex fields.
- Materials studies using ion beam analysis techniques.
- Hardware development for linear accelerators and beam optics.
- Design studies for fusion reactors/experiments
- Design study for ion beam facility for radiation-materials science.
Plasma-material interactions (PMI) in magnetic fusion devices pose significant scientific and engineering challenges for the development of steady-state fusion power reactors. Understanding PMI is crucial for the develpment of magnetic fusion devices because fusion plasmas can significantly modify plasma facing components (PFC) which can be severely detrimental to material longevity and plasma impurity control. In addition, the retention of tritium (T) fuel in PFCs or plasma co-deposited material can disrupt the fuel cycle of the reactor while contributing to radiological and regulatory issues.
The current state of the art for PMI research involves using accelerator based ion beam analysis (IBA) techniques in order to provide quantitative measurement of the modification to plasma-facing surfaces. Accelerated ~MeV ion beams are used to induce nuclear reactions or scattering, and by spectroscopic analysis of the resulting high energy particles (gamma, p, n, alpha, etc.), the material composition can be determined. PFCs can be analyzed to observe erosion and deposition patterns along their surfaces which can be measured with spatial resolution down to the ~1 mm scale on depth scales of 10-100 um. These techniques however are inherently ex-situ and can only be performed on PFCs that have been removed from tokamaks, thus limiting analysis to the cumulative PMI effects of months or years of plasma experiments. While ex-situ analysis is a powerful tool for studying the net effects of PMI, ex-situ analysis cannot address the fundamental challenge of correlating the plasma conditions of each experiment to the material surface evolution. This therefore motivates the development of the in-situ diagnostics to study surfaces with comparable diagnostic quality to IBA in order resolve the time evolution of these surface conditions.
To address this fundamental diagnostic need, the Accelerator-Based In-Situ Materials Surveillance (AIMS) diagnostic was developed to, for the first time, provide in-situ, spatially resolved IBA measurements inside of the Alcator C-Mod tokamak. The work presented in this thesis provided major technical and scientific contributions to the development and first demonstration AIMS. This included accelerator development, advanced simulation methods, and in-situ measurement of PFC surface properties and their evolution.
The AIMS diagnostic was successfully implemented on Alcator C-Mod yielding the first spatially resolved and quantitative in-situ measurements of surface properties in a tokamak, with thin boron films on molybdenum PFCs being the analyzed surface in C-Mod. By combining AIMS neutron and gamma measurements, time resolved and spatially resolved measurements of boron were made, spanning the entire AIMS run campaign which included lower single null plasma discharges, inboard limited plasma discharges, a disruption, and C-Mod wall conditioning procedures. These measurements demonstrated the capability to perform inter shot measurements at a single location, and spatially resolved measurements over longer timescales. This demonstration showed the first in-situ measurements of surfaces in a magnetic fusion device with spatial and temporal resolution which constitutes a major step forward in fusion PMI science.
In addition, an external ion beam system was implemented to perform ex-situ ion beam analysis (IBA) for components from Alcator C-Mod Tokamak. This project involved the refurbishment of a 1.7 MV tandem linear accelerator and the creation of a linear accelerator facility to provide IBA capabilities for MIT Plasma Science and Fusion Center. The external beam system was used to perform particle induced gamma emission (PIGE) analysis on tile modules removed after the AIMS measurement campaign in order to validate the AIMS using the well established PIGE technique. From these external PIGE measurements, a spatially resolved map of boron areal density was constructed for a section of C-Mod inner wall tiles that overlapped with the AIMS measurement locations. These measurements showed the complexity of the poloidal and toroidal variation of boron areal density between PFC tiles on the inner wall ranging from 0 to 3 um of boron. Using these well characterized ex-situ measurements to corroborate the in-situ measurements, AIMS showed reasonable agreement with PIGE, thus validating the quantitative surface analysis capability of the AIMS technique.
5 Recent Papers:
Sorbom, B.N., J.R. Ball, T.R. Palmer, F.J. Mangiarotti, J.M. Sierchio, P. Bonoli; C. Kasten, D.A. Sutherland, H. S. Barnard, C.B. Haakonsen; J. Goh, C. Sung; D.G. Whyte. "ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets" Submitted to Fusion Engineering and Design (2014)
Hartwig, Z.S., H. S. Barnard, R.C. Lanza, B.N. Sorbom, P.W. Stahle, D.G. Whyte. "An in situ accelerator-based diagnostic for plasma-material interactions science on magnetic fusion devices." Review of Scientific Instruments 84, no. 12 (2013): 123503
Olynyk, G. M., Z. S. Hartwig, D. G. Whyte, H. S. Barnard, P. T. Bonoli, L. Bromberg, M. L. Garrett, C. B. Haakonsen, R. T. Mumgaard, and Y. A. Podpaly. "Vulcan: A steady-state tokamak for reactor-relevant plasma-material interaction science." Fusion Engineering and Design (2012).
Barnard, H. S., Z. S. Hartwig, G. M. Olynyk, and J. E. Payne. "Assessing the feasibility of a high-temperature, helium-cooled vacuum vessel and first wall for the Vulcan tokamak conceptual design." Fusion Engineering and Design (2012).
Barnard, H. S., B. Lipschultz, and D. G. Whyte. "A study of tungsten migration in the Alcator C-Mod divertor." Journal of Nuclear Materials 415, no. 1 (2011): S301-S304.