BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-4806
DTSTART:20180416T170500Z
DURATION:PT1H0M0S
DTSTAMP:20260417T060219Z
LAST-MODIFIED:20180411T151034Z
LOCATION:2241 Chamberlin Hall
SUMMARY:Unique Solutions to the Challenges of Microwave Coupling in Ov
 erdense Plasmas\, Plasma Physics (Physics/ECE/NE 922) Seminar\, Dr. St
 ephanie J. Diem\, Oak Ridge National Laboratory
DESCRIPTION:Overdense plasmas\, where the electron plasma frequency ex
 ceeds the electron cyclotron frequency\, prohibit the use of electron 
 cyclotron (EC) heating and current drive methods often used to heat fu
 sion-grade plasmas. The electrostatic electron Bernstein wave (EBW) ca
 n propagate in overdense plasmas and is readily absorbed and emitted n
 ear EC harmonics. Additionally\, EBWs do not experience a density depe
 ndent cutoff. As such\, EBWs may enable local electron temperature mea
 surements and provide local heating and current drive. EBWs cannot pro
 pagate in vacuum but can couple to electromagnetic waves\, so for thes
 e applications efficient coupling between the EBWs and electromagnetic
  waves outside the plasma is needed. Results of the first experimental
  verification of EBW collisional damping and its mitigation by evapora
 ted lithium conditioning in overdense plasmas on the National Spherica
 l Torus Experiment (NSTX) will be presented. Initial measurements of E
 BW emission\, coupled from NSTX plasmas via double-mode conversion to 
 O-mode waves\, exhibited < 10% transmission efficiencies. Simulations 
 show 80% of the EBW energy is dissipated by collisions in the edge pla
 sma. Li conditioning reduced the edge collision frequency by a factor 
 of 3 and increased the fundamental EBW transmission to 60%. Expanding 
 upon this work\, recent results of EBW heating in the Proto-MPEX linea
 r device\, which takes advantage of resonance Doppler-broadening\, wil
 l be discussed. Calculations show that by utilizing the effects of Dop
 pler broadening resonance absorption\, power deposition near the cente
 rline of the Proto-MPEX device is possible. Significant collisional da
 mping with neutral particles\, leading to edge absorption\, is expecte
 d to occur due to high neutral pressure. Experiments were designed to 
 minimize these effects and resulted in electron temperature increase b
 y a factor of 4 during the injection of 28 GHz microwave power when th
 e neutral pressure is reduced below 0.13 Pa (~1 mTorr.). The results d
 iscussed are a product of active collaboration between the code develo
 pment groups\, experimentalists and theorists that allow our field to 
 bridge the gap between traditional theory/modeling and the experimenta
 l community.
URL:https://www.physics.wisc.edu/events/?id=4806
END:VEVENT
END:VCALENDAR