"On Aluminum Impurity Transport and Ablation Cloud Shielding Effects of Tungsten Dust in Edge Plasmas," by Reema Hajjar (UCSD)

Date: 
Thursday, March 12, 2015 - 1:00pm to 2:00pm
Series: 
Plasma Seminars

Plasma Seminar

Physics and Astronomy Building (PAB) Room 4-330
Thursday, March 12, 2015
1-2 PM
Refreshments at 12:30 PM

Guest Speaker: Reema Hajjar (UC San Diego)

Talk Title: "On Aluminum Impurity Transport and Ablation Cloud Shielding Effects of Tungsten Dust in Edge Plasmas"

Abstract:

Understanding impurity transport and dust dynamics is of a major importance for the magnetic fusion community. Released from PFC material or intentionally injected into the divertor area, dust and impurities enter the SOL, contaminate the plasma and reduce its efficiency and may eventually cause a total loss of the plasma confinement. In order to study impurity transport and dust dynamics, previous attempts based on either a fluid approximation or a kinetic one were adopted. Hereafter a 1D kinetic model used to describe impurity transport in an edge-like plasma configuration is presented. The model that accounts for impurity/plasma collisions and generates additional details on the collision dynamics, is used to describe injection and propagation of Aluminum impurities in a steady state Helium plasma.  Atomic processes like multiple ionization and radial losses of Aluminum impurities are taken into account and included in the model. Comparing simulation results to experimental data obtained from PISCES machine, impurities are found to be almost immediately entrained by the background plasma flow and impurity dynamics are found to be highly affected by the plasma velocity shear in the radial direction.

On the other hand, keeping in mind the significant amount of dust expected to be released in next generation tokamkas, a fluid approximation used to investigate dust transport and dynamics in tokamaks is adopted. While previous numerical codes such as the coupled DUSTT-UEDGE code were initially developed using plasma-dust interaction models based on OML theory, it was shown that in high temperature plasmas, dust grains are always surrounded by dust material vapor cloud, which when dense enough can alter the dust-plasma interactions for grain radii larger than ∼ 1-10μm. This reduces the grain ablation rate and extends its lifetime and penetration towards the plasma core as compared to previous models neglecting this cloud effect. A new model describing dust shielding effects for high-Z materials was developed and implemented in a modified DUSTT code. The model considers the reduced heat flux to the dust grain as being due to electron heat conduction rather than electron free streaming. Here we investigate the vapor induced shielding effects on dust dynamics, as well as its impact on parameters of ITER-like plasma using the modified DUSTT code. Simulation results are compared to those obtained using an ad hoc dust shielding factor and a possible thermal bifurcation phenomenon is observed.

 

Location: 
PAB 4-330