Winston Comprehensive

7/31/2019 Winston Comprehensive

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Electron Transport in

Hall Thrusters

Winston FriasGraduate Student

University of Saskatchewan

May 9 2012

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Outline of the talk

I. Hall ThrustersII. Electron Transport in Hall ThrustersIII. Future Work

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I. HallThrusters

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Introduction

- Hall thrusters are electrostatic coaxial plasma accelerators.- Developed and successfully operated in USSR from 1960s

(>240 missions), SPT100 last decade used in USA andEurope.

- Main features:

- High specific impulse,- High efficiency,- Low thrust.

- Well suited for station keeping and orbit transfer.- Two main types:

- Stationary plasma thruster (SPT),- Thruster with anode layer (TAL).

- SPT most common and best studied configuration.

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Hall Thrusters

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Hall Thruster

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Propellant Xe


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Current Issues in Hall Thruster Research

- Hall thruster applications are expanding. New requirementson

reliability , performance, lifespan, efficiency, etc.

- New and more sophisticated computer codes to simulateHall thrusters.

Fluid, fully kinetic, hybrid or PIC codes.

- Major physics problem has not been resolved: How toexplain and predictanomalously large electron current

- Plasma fluctuations. Fundamental problem - plasmaturbulence induced electron transport- Near wall conductivity (enhanced collisions with the

walls)

- Problems common to other devices e.g. magnetron

discharges, PIII. 77


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II. ElectronTransport

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Classical Electron Transport inAbsence of Magnetic Fields

- Steady-state and large collision frequency assumed.

- Fluid Equation

- Solve for v assuming isothermal plasma to obtain

- The mobility and diffusion coefficients are then given by:

- Related via Einstein relation

Mobility Diffusion

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Classical Electron Transport inPresence of Magnetic Fields

- Particle is magnetized if undergoes many gyrations beforecolliding. Its Hall parameter is high

- Solve for electron velocity:

LargeHallParameter

Mobilityproportional to 1/B2

1010

electron

collision

E B drift(azimuthal)

E

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Fluctuation Induced Transport- Instabilities give rise to transport.- Using continuity equation, perturbed density and velocity for

ions and electrons can be obtained. The time average isgiven by

- Current has two contributions:

Fluctuating current. Time averagenot zero due to relative phasedifference, even when timeaverage of the individualperturbations is zero. Notpredicted by classical theory.

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Characterized by effectiveHallParameter


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Near Wall ConductivityElectron collisions with the wall lead to decorrelation of

particle motion and enhanced transport

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- Proposed byMorozov

- Channel width

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