Events on Monday, April 27th, 2026
- Plasma Physics (Physics/ECE/NE 922) Seminar
- How low recycling lithium walls change the tokamak
- Time: 12:00 pm - 1:00 pm
- Place: Engineering Hall - 1227
- Speaker: Dick Majeski , Princeton Plasma Physics Laboratory
- Abstract: Almost all tokamaks operate in a regime where the recycling coefficient approaches 1. The recycling coefficient is defined, in the absence of other fueling, simply as (the # of particles entering the plasma)/(the # of particles exiting the plasma). WIth a high recycling wall, plasma which diffuses across the last closed flux surface in a tokamak, and is lost from the scrape off layer, is reflected or desorbed as ions, electrons, and neutral atoms from the limiters, divertor plates, and other plasma facing surfaces. The LIthium Tokamak eXperiment (LTX) is - or was - the only magnetic confinement device to have demonstrated operation with a measured recycling coefficient < 0.5, through the use of clean, solid or liquid, lithium walls and plasma limiting surfaces. Here we discuss the modifications to the plasma core and edge which result from the imposition of a low recycling lithium boundary on a tokamak plasma, as documented in LTX.
- Host: Steffi Diem
- Theory Seminar (High Energy/Cosmology)
- No Shift, Sherlock: No Shift Symmetries in AdS/CFT
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: José Calderón-Infante, Caltech
- Abstract: The absence of global symmetries is a long-standing conjecture about quantum gravity. In this talk, I will focus on continuous global shift symmetries in AdS/CFT, with the goal of developing a CFT-based argument against them. First, I will discuss how a shift symmetry in the bulk is reflected on the boundary CFT. This raises the question of whether local, unitary CFT can exhibit such property. I will present an argument that, under a certain assumption, rules out this possibility. Then, I will introduce some CFTs that do not satisfy this assumption and argue that this leads to an exotic type of shift symmetry gauging in the bulk. A key role will be played by the CFT stress tensor, which is dual to the graviton in the bulk. To see how theories without gravity avoid our argument, I will describe how it fails in the boundary theory of a massless free scalar in AdS, namely the generalized free field theory of a marginal operator. Finally, if time permits, I will address whether this type of argument could lead to a bound on how much the shift symmetry must be broken. Event recording:
- Host: Gary Shiu