PSFC Student Seminars

All Seminars are on Wednesday at 5:15pm, unless otherwise noted.
NW17-218, 175 Albany Street, Cambridge
For further information: info@psfc.mit.edu

Oct 23, 2018

Criteria for the Importance of Multi-Scale Turbulence in Tokamak Plasma Transport Simulations

Alex Creely

PSFC

Recent work at MIT has shown that for some plasmas, one requires incredibly computationally expensive multi-scale gyrokinetic simulations in order to accurately model the plasma, while in other cases significantly faster ion-scale simulations are sufficient.  Knowing which type of simulation is required to predict future device performance is vital before one trusts these predictions.  This question is answered using a gyro-fluid code, TGLF, to model more than fifteen plasma conditions on both the Alcator C-Mod and ASDEX Upgrade tokamaks.  These runs led to the discovery of two physical criteria that distinguish plasmas for which multi-scale simulations are necessary from those for which ion-scale simulations are sufficient.

5:00pm  |  NW17-218

Oct 16, 2018

Physics of Rotation Reversal Hysteresis in Alcator C-Mod L-mode Plasmas

Norman Cao

PSFC

Analysis and modeling of a new set of rotation reversal hysteresis experiments unambiguously show that changes in turbulence are responsible for the intrinsic rotation reversal and the Linear to Saturated Ohmic Confinement (LOC/SOC) transition on Alcator C-Mod.

5:00pm  |  NW172-218

May 15, 2018

High power millimeter wave initiated vacuum discharges

Sam Schaub

PSFC

The Waves and Beams group at MIT has a tradition of pointing the output of our 1.5 MW, 110 GHz gyrotron at things to watch them burn. Putting this pastime to use, we have been most recently studying multipactor discharges on dielectric in high vacuum.

5:00pm  |  NW17-218

May 1, 2018

More on runaway electrons

Alex Tinguely

PSFC

Highly energetic runaway electrons (REs) pose a major risk to future tokamak reactors. The spatiotemporal dynamics of REs has been explored in Alcator C-Mod. This talk will focus on the analysis of visible camera images which capture RE synchrotron radiation. The new synthetic diagnostic SOFT [M. Hoppe, et al., NF 58 (2018)] is used to reproduce experimental images, giving insight into the radial profile of REs. Apparent increased radial transport and subsequent loss of confinement is consistent with observation of MHD activity.

5:00pm  |  NW17-218

Apr 24, 2018

Atomic physics and multi-spectral imaging in the divertor

Bryan Linehan

PSFC

The Multi-Spectral Imaging (MSI) diagnostic is a new instrument that captures simultaneous spectrally filtered images of atomic line radiation from a common sight view while maintaining a large etendue and high spatial resolution.  In short, the diagnostic can be thought of as a 2D spectrometer.  By observing atomic emission in 2D, we may infer the temperate, density, and transport along the divertor.   The MSI was installed at CMOD in Fall 2016 and was installed at TCV in Summer 2017.  This talk will review the relevance of atomic physics to MFE and the work currently being done with the MSI at TCV.

5:00pm  |  NW17-218

Apr 3, 2018

New dual/tri-particle monoenergetic backlighting/stopping power platform for NIF and OMEGA

Graeme Stucliffe

PSFC

The D3He backlighter platform, based on laser-driven implosions of D3He-filled capsules, generates mono-energetic 14.7-MeV and 3.0-MeV protons and has been used with success on OMEGA and the NIF for both radiography and stopping-power studies. We now propose a three-particle mono-energetic backlighter based on a DT3He gas-filled capsule implosion that will provide 14.7-MeV and 3.0-MeV protons plus 9.5-MeV deuterons from the T3He reaction.

5:00pm  |  NW17-218

Dec 5, 2017

Towards a quantitative comparison between electron scale turbulence experiment and simulation

Juan Ruiz Ruiz

PSFC

In this talk Ruiz will explain how electron scale turbulence can be studied experimentally and numerically in spherical tokamaks, emphasizing the importance of designing synthetic numerical experiments that mimic tokamak experimental measurements, called synthetic diagnostics, in order to validate plasma turbulence models against experiments. He will present his current efforts to design a synthetic diagnostic to study electron scale turbulence and the transport of electron heat in the National Spherical Tokamak eXperiment (NSTX).

5:00pm

Nov 28, 2017

Core turbulence and intrinsic rotation reversal hysteresis in tokamak plasmas

Norman Cao

PSFC

This work provides strong evidence against the long-standing conjecture that the LOC/SOC transition is indicative of a change in the dominant ion-scale drift-wave instability, and suggests the importance of subdominant modes in determining the qualitative behavior of plasmas.

5:00pm  |  NW17-218

Nov 21, 2017

Using secondary nuclear reaction products to infer the fuel areal density, convergence, and electron temperatures on OMEGA and the NIF

Brandon Lahmann

PSFC

In deuterium-filled inertial confinement fusion (ICF) implosions, DD-tritons can undergo secondary fusion reactions with the thermal deuterium plasma to create secondary DT neutrons. On the National Ignition Facility (NIF), both the primary reactions (via DD-neutrons) and the secondary DT neutrons are routinely measured from several lines of sights using neutron time of flight (nTOF) spectrometers. The ratio of these secondary and primary reactions are used to infer the areal density (ρR) and the convergence of the fuel region. Additionally, the shape of the secondary DT neutron spectra can be used to infer the final asymmetry of the imploded capsule. Convergences inferred using x-ray imaging techniques are consistently larger than those inferred by this secondary DT neutron technique. These apparent discrepancies are not currently understood, but potential explanations are discussed. This work is supported in part by the U.S. Department of Energy and Lawrence Livermore National Laboratory.

5:00pm  |  NW17-218

Nov 7, 2017

Turbulence in tokamaks and the validation of gyrokinetic codes

Alex Creely

PSFC

This talk will describe the methodology behind validation in general, and will then focus specifically on the validation of gyrokinetic simulations of fusion plasmas.  The emphasis will primarily be on the high level comparisons of different measurements, rather than the details of the simulations or of the experimental measurements themselves.

5:00pm  |  NW17-218

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