Dr. Seth Dorfman
Reseach ScientistWelcome!
I'm an associate researcher at UCLA (and research scientist at the Space Science Institute) working with plasma, the
fourth state of matter. To find out more about why plasma
matters, see the video of me on the "Outreach" tab. Click any of
the other tabs to learn more about my work.RESEARCH
I look at key processes using basic laboratory experiments, satellite data, and analytic theory to see how plasma behaves. Click the circles below for more!- I'm interested in non-linear
interactions between Alfvén waves, the
fundamental magnetic mode of plasmas. Alfvén waves are
thought to play a key role in the heating of the solar
corona, the nature of the turbulent solar wind, and
energetic particle loss in tokamaks. In all three
contexts, the decay of a large amplitude Alfvén wave may
be an important mechanism. Experiments we conducted
on the Large
Plasma Device (LAPD) represent the first fundamental
laboratory study of the non-linear interactions
responsible for Alfvén wave decay instabilities,
including:
--- First measurement of Parametric Decay Instability growth rate. (Read our PRL)
--- Laboratory observation of the Alfvén-acoustic mode coupling at the heart of the Parametric Decay Instability. (Read our PRL)
--- The first observation of a sheer Alfvén wave parametric instability in the laboratory. (Read our PRL) - A key future goal of my research is to create magnetized plasma turbulence in the laboratory for detailed study. Such turbulence can be generated by interactions between counter-propagating Alfvén waves in the solar wind, but given limited available spacecraft data, key questions about the fundamental nature of the process remain. Read
our JPP paper on how this may be accomplished with the next generation of laboratory experiments.
My work with former postdoctoral researcher Dr. Mel Abler (hired 2021, now staff at SSI) concerns residual energy in solar wind turbulence -- excess energy in the magnetic fluctuations compared to the velocity fluctuations. Dr. Abler obtained the first experimental measurement residual energy in a non-linear Alfvén wave interaction. I also have a recent theory paper that argues residual energy comes from a symmetry breaking associated with the initial condition used. - The ion foreshock region upstream of the Earth's bow shock is a prime natural laboratory for the study of non-linear Alfvén wave interactions. An ion beam accelerated from the shock front back into the solar wind may interact with the solar wind core to generate large-amplitude, Ultra Low Frequency (ULF) waves at a small fraction of the ion cyclotron frequency.
In this GRL paper, we show the first satellite measurement of the ULF wave growth rate. The measured growth rate is consistent with dispersion solver results for observed ion distributions, validating resonant beam instability theory. Results will inform future missions near shocks and future non-linear studies related to turbulence and dissipation in the heliosphere.
Former postdoctoral researcher Dr. Kun Zhang (hired 2020, now staff at UCLA) has conducted a similar analysis in numerical simulations, where it is easier to distinguish between the space and time behavior of the waves. - Plasma waves in space physics are routinely measured using spacecraft which are expensive to launch and maintain. As a result, scientists rely on assumptions about the structure of the wave to measure wave properties using data at a limited number of locations. In this 2023 paper, we show that large spatial variations in electromagnetic wave amplitude can break these assumptions, causing the most commonly used single-spacecraft analysis method to return nonsense results. In this situation, the divergence free condition of the magnetic field requires a modification to the plane of polarization that some common techniques incorrectly interpret as a change in the physical wave vector direction. In the Earth's ion foreshock region where the geometry of the waves is well known, we clearly identify incorrect single-spacecraft results and use them as a novel way to detect edges in the wave amplitude profile.
- I’m currently working to put together the hardware necessary to deploy a relativistic electron beam on the Large Plasma Device (LAPD) to study the waves generated and how the beam propagates through the plasma. The physics we learn will aid future missions to put electron beams on spacecraft where they can trace magnetic field lines, allowing us to see how space weather disturbs the field. Results will also improve our understanding of radio bursts thought to be generated by energetic electron beams on the sun. Preliminary experiments with a lower energy (20keV) beam show robust wave generation via a Landau resonance process.
- I completed my PhD work with Drs. Hantao Ji and Masaaki
Yamada on the Magnetic
Reconnection Experiment (MRX) at Princeton. We
studied impulsive reconnection events
observed in the experiment in which a build-up of magnetic
energy is followed by a quick release and concluded that
3-D physics is necessary to explain the observations. This
has implications for similar events that occur in space
and laboratory plasmas, including the Earth's magnetotail.
Read
our GRL paper here.
Earlier in my PhD work, I modified and ran 2.5-D, fully kinetic PIC simulations with MRX geometry and boundary conditions under the guidance of Drs. Bill Daughton and Vadim Roytershteyn. We found a that the ion-scale features of these simulations well match MRX data, but discrepancies persist in the electron-scale physics. Read our PoP paper here.
PUBLICATIONS
Scroll down for more.AWARDS
UCLA Chancellor's Award for Postdoctoral Research, Honorable Mention (2015)
NASA Jack Eddy Postdoctoral Fellowship (2014)
AGU Basu United States Early Career Award (2013)
AGU Scarf Award for Outstanding PhD Thesis (2013)
DOE Fusion Energy Sciences Postdoctoral Fellowship (2011)
National Defense Science and Engineering Graduate Fellowship (2007)
DOE Fusion Energy Sciences Fellowship (2006)
Thomas H. Stix Prize in Plasma Physics (2006)
Joel Matthew Orloff Award for Highest Scholarship in Physics at MIT (2005)
Carl Oberman Fellowship in Plasma Physics (2005)
Princeton First Year Science and Engineering Fellowship (2005)
Inducted into Phi Beta Kappa and Sigma Pi Sigma (2005)
National Merit $2500 Scholarship (2001)
Derivation of Shot Noise theory added to Junior Lab Course Reader (2004)
OUTREACH
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Play the video on the left to watch me explain plasma in three minutes. |