Plasma Physics Seminar
 
   
  Fall 2018 Schedule  
 
January 16, Wednesday 3:30PM
ERF 1207, Large Conference Room
Novimir Pablant, Princeton Plasma Physics Laboratory
Role of neoclassical transport and the radial electric field in Wendelstein 7-X

The role of the radial electric field in high performance ion-root plasmas on Wendelstein 7-X (W7-X) is examined and compared with neoclassical predictions. In stellarator plasmas the neoclassical radial electric field (Er) is not intrinsically ambipolar, and is instead strongly tied to the plasma profiles. The properties of the Er profile strongly influence neoclassical transport of heat, particle and impurities.

Measurements of the core radial electric field (Er) have confirmed that ion-root conditions (negative Er in the plasma core) have been achieved in W7-X with high density plasmas, central ERCH heating and temperature equilibration (Te close to Ti). This is an important achievement as these are precisely the plasma conditions for which W7-X has been optimized. These measured Er profiles agree well with the neoclassical ambipolar Er predicted by the code SFINCS. This good agreement provides confidence in the validity of neoclassical calculations in high-density ion root conditions, and enables initial studies on the role of neoclassical transport in the optimized high-density regime of W7-X.

Experimental radial electric field profiles are inferred from the perpendicular velocity, as measured by the XICS diagnostic, and available with a high time resolution of up to 10ms. These diagnostic measurements provide the detailed profile evolution of the radial electric field in response to changes to the plasma density and heating power. Profile measurements of electron temperature (Te), ion temperature (Ti) and electron density (ne) along with approximations for the average value of Zeff have been used as inputs to the SFINCS code to calculate the ambipolar Er profile along with neoclassical ion and electron heat flux profiles (Qi, Qe). Finally the total experimental energy input to the electrons and ions, from ECRH heating and collisional heat transfer, has been compared to the neoclassical heat fluxes to provide a first estimate for the fraction of transport that can be attributed to neoclassical processes in reactor relevant high-density ion-root conditions.
January 23, Wednesday 3:30PM
ERF 1207, Large Conference Room
Fulvia Pucci, Princeton Plasma Physics Laboratory
Energy transfer and electron energization in collisionless magnetic reconnection for different guide-field intensities

Electron dynamics and energization are a key component of magnetic field dissipation in collisionless reconnection. In 2D reconnection, the main mechanism that limits the current density and provides an effective dissipation is most probably the electron pressure tensor term, that has been shown to break the frozen-in condition at the x-point. In addition the electron- meandering-orbit scale controls the width of the electron dissipation region, where the electron temperature is observed to increase both in recent MMS observations as well as in laboratory experiments (MRX). By means of two-dimensional, full-particle simulations in an open system (Pei et al. 2001; Ohtani and R. Horiuchi 2009), we investigate how the energy conversion and particle energization depends on the guide field intensity. We study the energy transfer from the electromagnetic field to the plasma, and the threshold guide field separating when parallel and perpendicular energy transfers dominate, confirming recent MRX results, in agreement with MMS observations. We calculate the energy partition between fields and kinetic and thermal energy of different species, from the electron scales to ion scales, showing there is no significant variation for different guide field configurations. We study electron distribution functions and self consistently evolved particles orbits for high guide field configuration, investigating possible mechanisms for electron perpendicular heating. Finally I will give an idea of our 2D simulations with plasmoids for which the setup can be easily extended to study 3D reconnection, thanks to GPU technology.
January 30, Wednesday 3:30PM
ERF 1207, Large Conference Room
Adrian Fraser, University of Wisconsin


February 6, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


February 13, Wednesday 3:30PM
ERF 1207, Large Conference Room
Denis St-Onge, Princeton Plasma Physics Laboratory
Fluctuation Dynamo in a Collisionless, Weakly Magnetized Plasma

February 20, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


February 27, Wednesday 3:30PM
ERF 1207, Large Conference Room



March 6, Wednesday 3:30PM
ERF 1207, Large Conference Room
Chris Smiet, Princeton Plasma Physics Laboratory
The topological structure of the field line mapping during a sawtooth cycle in tokamaks

March 13, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


March 20, Wednesday 3:30PM
ERF 1207, Large Conference Room
No seminar. Spring break.


March 27, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


April 3, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


April 10, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


April 17, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


April 24, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


May 1, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open


May 8, Wednesday 3:30PM
ERF 1207, Large Conference Room
Open