Princeton Plasma Physics Laboratory

About: Princeton Plasma Physics Laboratory is a facility organization based out in Plainsboro Center, New Jersey, United States. It is known for research contribution in the topics: Tokamak & Plasma. The organization has 2427 authors who have published 4475 publications receiving 106926 citations. The organization is also known as: PPPL.

Taming the plasma–material interface with the 'snowflake' divertor in NSTX

Abstract: Steady-state handling of divertor heat flux is a critical issue for ITER and future conventional and spherical tokamaks with compact high-power density divertors. A novel 'snowflake' divertor (SFD) configuration was theoretically predicted to have significant magnetic geometry benefits for divertor heat flux mitigation, such as an increased plasma-wetted area and a higher divertor volume available for volumetric power and momentum loss processes, as compared with the standard divertor. Both a significant divertor peak heat flux reduction and impurity screening have been achieved simultaneously with core H-mode confinement in discharges with the SFD using only a minimal set of poloidal field coils.

Negative plasma potential relative to electron-emitting surfaces.

Abstract: Most works on plasma-wall interaction predict that with strong electron emission, a nonmonotonic ``space-charge-limited'' (SCL) sheath forms where the plasma potential is positive relative to the wall. We show that a fundamentally different sheath structure is possible where the potential monotonically increases toward a positively charged wall that is shielded by a single layer of negative charge. No ion-accelerating presheath exists in the plasma and the ion wall flux is zero. An analytical solution of the ``inverse sheath'' regime is demonstrated for a general plasma-wall system where the plasma electrons and emitted electrons are Maxwellian with different temperatures. Implications of the inverse sheath effect are that (a) the plasma potential is negative, (b) ion sputtering vanishes, (c) no charge is lost at the wall, and (d) the electron energy flux is thermal. To test empirically what type of sheath structure forms under strong emission, a full plasma bounded by strongly emitting walls is simulated. It is found that inverse sheaths form at the walls and ions are confined in the plasma. This result differs from past particle-in-cell simulation studies of emission which contain an artificial ``source sheath'' that accelerates ions to the wall, leading to a SCL sheath at high emission intensity.

The Plasma Sheath

Abstract: Outline: Section 2 simply describes, without attempt at explanation, what happens electrically when a plasma is in contact with a solid surface. The practical implications of the interaction are briefly described. Section 3 provides a physical explanation of why these effects occur and deduces initial estimates of the plasma-solid voltage difference and the spatial extent of this voltage drop. Section 4 deduces the Bohm Criterion (ion drift velocity out of the plasma must equal the ion acoustic speed) using ion fluid models. The Criterion is obtained from both the plasma and the sheath equations separately. Section 5 deduces simple formulae for the particle and energy flux which is transmitted by a sheath, both for electrically floating and biased objects. Section 6 gives a brief indication of how the sheath particle and energy transmission characteristics influence the modeling of the edge plasma in magnetically confined plasma devices, while Section 7 gives a similar brief introduction to their use in the interpretation of plasma probe data.