Electron physics and ambipolarity in the tokamak scrape-off layer

Technical Report · Fri Apr 01 04:00:00 EST 1994

DOI:https://doi.org/10.2172/10156317· OSTI ID:10156317

Hazeltine, R D ^[1]; Catto, P J ^[2]

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1. Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
2. Massachusetts Inst. of Tech., Cambridge, MA (United States)

Models of the electron behavior in the scrape-off layer (SOL) of diverted and limited boundary conditions that occurs tokamak plasmas must retain the abrupt change in boundary conditions that occurs across the separatrix or last closed flux surface as well as the electron reflecting Debye sheath established at the limiter or divertor plates. The balance between ion radial diffusion and streaming to the plates sets the SOL width and the electrons must adjust the Debye sheath at the plates to main tain quasineutrality and ambipolarity in the SOL beyond the last closed flux surface. We consider the long mean-free-path limit where a bounce-averaged kinetic electron model results in a steady-state balance in the SOL between radial diffusive feed from the core and velocity space diffusive loss to the plates due to collisional detrapping. In this double diffusion model a velocity space boundary layer occurs about the trapped-passing boundary where strong velocity space gradients must balance the streaming of the newly de-trapped electrons to the plates. The behavior of the electron distribution function in the velocity provides the information needed to evaluate the Debye-sheath-dependent electron loss rate.

• Research Organization: Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: FG05-80ET53088
• OSTI ID: 10156317
• Report Number(s): DOE/ET/53088--656; IFSR--656; ON: DE94012764; BR: 39KG01000/AT0520240
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700330
700420
AMBIPOLAR DIFFUSION
DIVERTORS
ELECTRONS
KINETIC EQUATIONS
LIMITERS
PLASMA KINETICS, TRANSPORT, AND IMPURITIES
PLASMA SCRAPE-OFF LAYER
PLASMA-FACING COMPONENTS
TOKAMAK DEVICES