CER SEMINAR

Developing experimental platforms for atomic physics studies at extreme conditions

Dr. Michael MacDonald, University of California, Berkeley
January 29, 2018, 11:00am - 12:00pm, SERF Room 232

ABSTRACT:

X-rays provide a unique tool capable of probing extreme states of matter relevant to astrophysical systems and nuclear fusion. A variety of x-ray diagnostics have been developed to study fusion-relevant plasmas, exploiting various aspects of x-ray-matter interactions to directly probe plasma conditions and material properties. In this talk, I will discuss experimental platforms I have developed using x-ray fluorescence (XRF) imaging and spectroscopy, streaked x-ray radiography, and x-ray Thomson scattering (XRTS) to study atomic physics at extreme conditions. First, I will present a platform using XRF imaging and spectroscopy to diagnose shock-compressed matter at the Trident and OMEGA laser facilities. Initial experiments at Trident demonstrated the ability to measure density and ionization state profiles in shocked foams using XRF imaging and spectroscopy. By constraining the density at the shock front using XRF imaging and modeling the XRF spectral lineshape using the atomic kinetics and radiation code CRETIN, were able to infer the plasma temperature at the shock front. Follow up XRF experiments are scheduled at the OMEGA laser facility, adding XRTS to the platform to constrain the plasma temperature and improve atomic models used to interpret XRF spectra. Applying similar analysis to Cu XRF spectra obtained from Be capsule implosions at the NIF, we show that the atomic models used in post-shot hydrodynamic simulations may be under-predicting the ionization state in the ablator layers. To conclude, I will discuss future experiments awarded two shot days through the NIF Discovery Science program to make high precision equation of state (EOS) measurements of warm dense matter. In these experiments, colliding planar shocks will generate large volumes of homogenous CH plasmas at pressures of 50–200 Mbar and temperatures of 20–50 eV. In these experiments, streaked x-ray radiography and XRTS will be used to make high precision density, temperature, and ionization state measurements to benchmark and improve EOS models.

   

BIO:

Michael MacDonald is currently a Postdoctoral Scholar in the Department of Physics at the University of California, Berkeley. He received his Ph.D. in Applied Physics from the University of Michigan in 2016. His primary research interests include x-ray spectroscopy, material properties at extreme conditions, and x-ray instrumentation. As part of his current research on atomic properties at extreme conditions, Michael is a co-PI on a Discovery Science campaign at the National Ignition Facility to measure the equation of state of materials at pressures of 50–200 Mbar compressed to 4–6 times ambient density. He is also leading the effort to develop x-ray fluorescence spectroscopy as a diagnostic technique to measure conditions in warm dense matter. Before joining Berkeley, Michael was a visiting scientist at SLAC National Accelerator Laboratory, where he conducted much of his thesis work on x-ray diffraction studies of shock-compressed materials. Michael was the recipient of the National Science Foundation Graduate Research Fellowship while at the University of Michigan and is a coauthor on 23 peer reviewed publications.