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PRODID:UW-Madison-Physics-Events
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SEQUENCE:1
UID:UW-Physics-Event-9603
DTSTART:20260223T180000Z
DTEND:20260223T190000Z
DTSTAMP:20260405T100909Z
LAST-MODIFIED:20260218T112542Z
LOCATION:Engineering Hall - 1227 
SUMMARY:Optical analogy for stellarators: Ridges as caustics and coils
  as singularities\, Plasma Physics (Physics/ECE/NE 922) Seminar\, Dr. 
 Wrick Sengupta \, Princeton Plasma Physics Laboratory
DESCRIPTION:Abstract: A common feature of most numerically optimized s
 tellarator geometries is the presence of sharp ridges on flux surfaces
 \, irrespective of the rotational transform. Despite their importance\
 , an analytical theory for their existence has been lacking. In this w
 ork\, we demonstrate that ridges are not artifacts but mathematical ne
 cessities. We develop such a theory for devices with quasi-axisymmetry
  (QA). We demonstrate that QA exhibits close connections with the theo
 ry of geometrical optics\, following Parker's ``optical analogy" (E.N.
  Parker 1989). By mapping vacuum QA to the eikonal equation of geometr
 ical optics\, we derive the conditions for ridge formation\, identifie
 d as caustics where magnetic field lines focus. Furthermore\, we prove
  a rigorous geometric theorem for stellarator coil design: filamentary
  coils must lie on the zero-determinant manifold of the magnetic gradi
 ent tensor. This topological constraint unifies the description of pla
 sma ridges and external coils\, providing a precise criterion for iden
 tifying valid coil locations and explaining the efficacy of the magnet
 ic gradient (LgradB) norm as a coil optimization parameter. We demonst
 rate that as the device becomes more compact\, sharp ridges naturally 
 form on the inboard side in QA. We support our analytical theory with 
 extensive numerical evidence.<br>
\n<br>
\nBio: I am interested in the
  theoretical aspects of plasma physics\, particularly kinetic theory a
 nd magnetic confinement. I develop analytically tractable reduced mode
 ls to provide insight into nonlinear interactions and geometry in conf
 ined plasmas. I focus on magnetic fields with hidden quasisymmetry\, w
 hich could benefit next-generation stellarators\, and I also explore p
 lasma turbulence using solvable models.<br>
\nPhD (2016) in plasma phy
 sics from the University of Maryland. Advisor: Adil Hassam\, co-adviso
 rs: Bill Dorland\, Tom Antonsen.<br>
\nPost doc (2016-2021): Courant I
 nstitute of Mathematical Sciences. PI: Harold Weitzner and Antoine Cer
 fon<br>
\nAssociate Research Scientist (2021 - present): Department of
  Astrophysical Sciences\, Princeton University\, PI: Amitava Bhattacha
 rjee<br>
\n<br>
\n
URL:https://www.physics.wisc.edu/events/?id=9603
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