Dielectric Multipactor with High Power mm-Waves

Sam Schaub

MIT

5:00pm  |  NW17-218

Implementation of Gas Puff Imaging (GPI) system on TCV and investigation of the GPI shadowing effect

Woonghee Han

MIT

Gas-Puff Imaging (GPI) measures the spatially-resolved fluctuations in the plasma edge and SOL by imaging emission from a local gas puff. In August 2018, a GPI system has been installed on TCV in Switzerland. First data were obtained in December 2018 and there is great signal-to-noise ratio for views around the spatial peak of the emission. GPI also captured the propagation of a blob in the SOL. It is typically assumed that the fluctuation in the emission in GPI is correlated with the plasma fluctuations without regarding the neutral density fluctuations. However, according to the GBS simulation result the neutral density fluctuation has significant impacts on the light emission. The neutral fluctuation results in the GPI “shadowing” effect which is expected to be prominent at the distance from the nozzle larger than the neutral mean-free-path. Experiments have been designed to explore the shadowing effect by comparing pairs of cases with different neutral mean-free-path in an identical background plasma.

5:00pm  |  NW17-218

Transport of alpha particles by 3D fields and MHD modes: perspectives from theory and modeling with implications for experiment

Elizabeth Tolman

MIT

Next-generation tokamak experiments operating with DT fuel will have a significant population of energetic alphas from fusion. Good confinement of these alpha particles is important to experiment performance. Two effects which can degrade alpha confinement are ripple and Alfvén Eigenmodes. In this tutorial-style talk, we provide a brief introduction to three theoretical and computational methods for studying transport of alphas by these effects: collisionless guiding center calculations, drift-kinetic theory, and Monte Carlo orbit-following codes.  In addition, we offer a preview of recent work to advance understanding in these areas.

5:00pm  |  NW17-218

Imaging Helium emission on TCV

Bryan Lee Lineman

MIT

The ratio of atomic line intensities from species of the same charge state are functions of Te and ne.  Experiments were performed last December with the aim of utilizing this relationship to measure Te and ne in over the divertor in 2D space on TCV.  Seven Helium lines were imaged simultaneously in the divertor with the new MANTIS diagnostic. This experiment and preliminary data analysis will be discussed at this talk.   
 

5:00pm  |  NW17-218

Observations of kinetic and multi-ion effects in DT and D3He implosions relevant to ICF shock phase

Neel Kabadi

MIT

During the shock-convergence phase of ICF implosions there are steep spatial gradients and the ion mean free path becomes long compared to the system size, indicating that multi-ion and kinetic effects may be important. Yet, almost all ICF simulations use an average-ion hydrodynamic approach. Previous work has indicated substantial burn averaged species separation and possibly other kinetic effects in D³He plasmas with conditions relevant to the NIF shock-phase. In this presentation I will show recent work conducted on the Omega laser facility recreating these conditions in DT plasmas. Both DT and D3He burn averaged observables are well modeled using an equilibrating two ion temperature model with little to no species separation. 

5:00pm  |  NW17-218

Results from fusion-based backlighter development at the OMEGA laser

Graeme Sutcliffe

MIT

Laser-driven implosions of D³He-filled capsules which generate mono-energetic 14.7-MeV and 3.0-MeV protons are used on the OMEGA and NIF lasers for both radiography and stopping-power studies. A new tri-particle mono-energetic backlighter based on a DT³He gas-filled capsule implosion that provides 14.7-MeV and 3.0-MeV protons plus 9.5-MeV deuterons from the T+³He reaction has now been demonstrated on OMEGA. Initial tests using 860 µm OD thin glass capsules filled with DT³He fuel were promising. Preliminary radiographs of laser-driven foils and measurements of stopping power in cold beryllium were made with the backlighted particles and the results are shown.

5:00pm  |  NW17-218

Physics precursors of disruptions and the challenge of predicting them on multiple tokamaks

Kevin Montes

MIT

5:00pm  |  NW17-218

Multipactor and dark current studies of a 17 GHz standing wave accelerator structure

Haoran Xu

MIT

We report our study on the internal dark current generation by multipactor inside a 17 GHz single cell standing wave disk-loaded waveguide accelerator structure. 

5:00pm  |  NW17-218

Design and characterization of a megawatt-class laser-driven semiconductor switch with application to high-gradient accelerator testing

Julian Picard

MIT

Laser-driven semiconductor switches (LDSS) are of great use in producing short RF pulses in the microwave to far-infrared range. Such short pulses have potential applications ranging from the investigation of material properties to testing of high-gradient accelerator concepts and DNP-NMR.

5:00pm  |  NW17-218

The 1-2 kHz fluctuation in W7-X and its impact on divertor heat loads

Sean Ballinger

PSFC

Fast-camera imaging in the visible range has been used to study the motion of high-density filaments in tokamak edge plasmas, shedding light on their role in boundary layer transport.

5:00pm  |  NW17-218

Diagnosing fuel areal density asymmetries in deuterium-tritium inertial

Raspberry Simpson

PSFC

In this work, we discuss the knock-on deuteron data obtained in the 1-D cryogenic DT Campaign at OMEGA. Preliminary data analysis reveals that there is a systematic asymmetry in the direction of one of the charged particle spectrometers of approximately 20%.

5:00pm  |  NW17-218

Demonstration of Prototype Mirror Langmuir Probe Control System Using a Red Pitaya Field Programmable Gate Array Board

William McCarthy

PSFC

High bandwidth, high spatial resolution measurements of electron temperature, density and plasma potential are valuable for resolving turbulence in the boundary plasma of tokamaks. While Langmuir probes can provide such measurements their temporal and spatial resolution is limited by the sweep rate for obtaining I-V characteristics or by the need to use multiple electrodes, each sampling a single plasma quantity at high bandwidth.

5:00pm  |  NW17-218

Can we truly isolate divertor operations from the core plasma?

Adam Kuang

PSFC

A set of experiments were performed in Alcator C-Mod during the 2016 campaign to attempt to better understand the impact of divertor conditions on scrape-off layer transport. Preliminary experimental and simulation results indicate that a combination of the closed divertor geometry in Alcator C-Mod, and magnetic shear enhanced polarization currents near the X-point effectively isolate divertor conditions from the main chamber and suggest a possible pathway forward.

5:00pm  |  NW17-218

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

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

On the inverse cascade of magnetic helicity in electron-temperature-gradient-driven turbulence

Lucio Milanese

We present preliminary results from numerical and analytical studies aimed at elucidating the potentially important role of the inverse cascade of magnetic helicity injected by ETG modes. The studies were performed in slab geometry, using a reduced gyrokinetic model (Zocco and Schekochihin, 2011).

5:00pm  |  NW17-218

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

A metamaterial wagon wheel structure for Wakefield acceleration by reversed Cherenkov radiation

Xueying Lu

PSFC

5:00pm  |  NW17-218

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

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

Effect of magnetic field strength on Alfvén eigenmode stability

Libby Tolman

PSFC

This talk introduces one area of particular significance to high-magnetic-field experiments which hope to demonstrate net energy: the stability behavior of Alfvén eigenmodes (AEs). 

5:00pm  |  NW17-218

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

Bayesian learning of impurity transport in tokamak high confinement regimes

Francesco Sciortino

PSFC

5:00pm  |  NW17-218

Predicting tokamak disruptions using machine learning

Kevin Montes

PSFC

5:00pm  |  NW71-218