High-resolution x-ray microcalorimeter on MST

The effort to develop fusion for energy generation has been described as “bringing a star to earth.” Recently, a type of instrument similar to those being used to study the emission from hot, extraterrestrial plasma, such as from stars, black holes, and supernova remnants, has been installed on the MST experiment at UW-Madison to study hot terrestrial plasma.
This instrument, called an x-ray microcalorimeter spectrometer was commissioned on MST by a team from Lawrence Livermore National Laboratory, Wisconsin Plasma Physics Laboratory, and NASA/Goddard Space Flight Center. The first run campaign with this instrument on MST, which took place during the last two weeks of August 2019, produced highly encouraging results, despite the challenge of observing a pulsed plasma in an electrically noisy environment. Expected lines from He-like aluminum ions (Al11+) were observed with acceptable resolution, and data was recorded for a variety of MST plasma conditions. The next steps are to further hone data analysis techniques, improve in-situ spectral calibration, and increase instrument flexibility to adapt to plasma conditions. The combination of high spectral resolution and broad spectral coverage provided by the spectrometer will provide plasma diagnostic capability important to the development of fusion.


This work was performed, in part, under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences.

Scilight: Spectroscopic technique sheds insights on how confined plasmas flow

Flow measurements in reversed field pinch
A recent Physics of Plasmas article by Darren Craig (Wheaton College) is highlighted in the AIP’s Scilight: Spectroscopic technique sheds insights on how confined plasmas flow” DOI: 10.1063/1.5119247.
The Scilight reports:

Craig et al. have reported the first direct measurements of plasma flows in a reversed field pinch, a device used to generate and confine plasmas. Their findings which validate many common assumptions about plasma flow behavior and identify eddy currents as the dominant momentum loss mechanism during improved confinement are published in Physics of Plasmas.

Co-author Darren Craig said the team used a technique called charge exchange recombination spectroscopy. The method works by first exciting impurity ion emission with a neutral atom beam and then measuring the Doppler shift to determine the velocity of the ions.To make the measurements, the team had to overcome several technical challenges.
“First, we built a custom high-throughput spectrometer to enable measurements with high time resolution” Craig said.”Second, we had to develop techniques to deal with a high background signal in the MST plasmas we studied.”?
Developing a reliable absolute wavelength calibration was the final step that enabled the authors to measure how the plasma flows varied in space and time.
The article is available here:
Intrinsic flow and tearing mode rotation in the RFP during improved confinement? by D. Craig, E. H. Tan, B. Schott, J. K. Anderson, J. Boguski, D. J. Den Hartog, T. Nishizawa, M. D. Nornberg and Z. A. Xing, Physics of Plasmas (2019). The article can be accessed at https://doi.org/10.1063/1.5095620.

Steph Kubala wins Blewett Fellowship

Steph Kubala, awarded M.Hildred Blewett Fellowship
Steph Kubala received M.Hildred Blewett Fellowship
WiPPL graduate student Steph Kubala has received a Blewett Fellowship from the American Physical Society (APS). After pausing her research to care for an ailing parent, Ms. Kubala has resumed her research, where she specializes on MST’s Thomson scattering diagnostic. Her thesis work focuses on characterizing how magnetic field fluctuations scale with Lundquist number, a parameter that characterizes magnetic fluctuations and the quality of confinement in the RFP plasma. The Blewett Fellowship will enable Ms. Kubala to continue her work toward completing her Ph.D.

Read the full article at: https://www.aps.org/programs/women/scholarships/blewett/2018-recipients.cfm

Pursuing high thermal pressure plasmas with tangled magnetic fields

In February 2019, the Big Red Ball (BRB) was operated for an initial investigation of compact toroid (CT) collisions as proposed by a Los Alamos National Laboratory (LANL) group. LANL researchers Scott Hsu and Tom Byvank visited WiPPL to work with UW-Madison physics graduate student Doug Endrizzi on these experiments. A chief motivation for the work was a hypothetical plasma state described by Dmitri Ryutov [Fusion Science and Technology 56, 1489 (2009)] wherein the normalized thermal pressure is high (beta>1) yet the plasma is magnetized (wt>1) by a tangled field. Such a state might be of interest as a compression target for magnetized target fusion or as a laboratory setting with connections to astrophysical molecular clouds.

Byvank and Endrizzi operated BRB in order to inject and collide two CT plasmas, diagnosing their speed, magnetic structure, and kinetic properties with moveable arrays of internal probes. Each CT plasma was formed and injected with one of two CT injectors at WiPPL, one on loan from TAE Technologies, Inc., the other designed by Endrizzi based on the TAE design and built by WiPPL. The video below shows an example of the collision process, with the two CT plasmas colliding together in the core region of BRB where the diagnostic probe arrays are visible. The results of these initial experiments are promising, and further collaborations are being planned.