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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-9335
DTSTART:20250808T150000Z
DTEND:20250808T170000Z
DTSTAMP:20260413T084150Z
LAST-MODIFIED:20250714T185024Z
LOCATION:B343 Sterling or https://uwmadison.zoom.us/j/94014298365?pwd=
 6dvdDdkZDykib5djQPCEDDhwEMftfA.1
SUMMARY:Characterization of Tearing Mode Dynamics with the Radial Inte
 rferometer-Polarimeter on DIII-D\, Thesis Defense\, Rachel Myers\, Phy
 sics PhD Graduate Student
DESCRIPTION:The Faraday-effect Radial Interferometer-Polarimeter (RIP)
  diagnostic on DIII-D measures line-integrated magnetohydrodynamic flu
 ctuations\, such as tearing modes\, at all radii\, including modes not
  detected with external sensing coils. RIP results are compared to a s
 ynthetic line-integrated eigenfunction\, corresponding to the mode amp
 litude on coils\, using the linear code TJ. Even modes are finite on R
 IP\, where the cylindrical approximation shows them vanishing. It is c
 onfirmed that RIP measures odd sidebands generated by linear coupling 
 to toroidicity\, which scales with inverse aspect ratio\, and shaping.
  Experimentally measured shaping effects on RIP and tearing stability 
 in inner-wall limited plasmas\, which have more shape flexibility\, ar
 e presented. Stability is calculated with DCON\, which relies on equil
 ibrium reconstructions with kineticEFIT. Modes grow as they approach t
 he ideal-wall stability limit\, which is near the classical tearing li
 mit. These low-safety factor plasmas were dominated by sawteeth\, whic
 h did not trigger tearing modes as expected. Tearing modes were driven
  as the plasma approached the ideal-wall limit\, as opposed to the tri
 ggered\, pressure-driven neoclassical tearing modes found in higher-pe
 rformance plasmas. Even modes were less attenuated than previously mea
 sured because low safety factor induces a strong\, detectable odd side
 band to the even mode. RIP amplitudes varied over time due to nonlinea
 r effects. RIP also experimentally confirms nonlinear coupling between
  edge harmonic oscillation (EHO) components in quiescent H-mode (QH-mo
 de)\, previously predicted by nonlinear MHD simulations. We observe wi
 th RIP\, but not sensing coils\, nonlinear coupling of the EHO to core
 -resonant tearing modes\, which interrupts the EHO and prevents access
  to long-lived QH-mode. This is concerning because QH-mode has an H-mo
 de pedestal without edge localized modes (ELMs)\, which is attractive 
 for ITER or a fusion reactor. Bicoherence values above 99% significanc
 e reveal that the first three EHO components are coupled throughout th
 e QH phase\, reflecting the cascade that sustains the EHO. In a case w
 here QH-mode ceases and ELMy H-mode arises\, we detect with RIP\, but 
 not with the coils\, an intermittently returning EHO nonlinearly coupl
 ed to two core-resonant tearing modes. Coupling to tearing modes has c
 aused the coupling between EHO components to vanish. The EHO becomes i
 ntermittent\, while ELMs persist.
URL:https://www.physics.wisc.edu/events/?id=9335
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