Thermodynamic Study on Plasma Expansion along a Divergent Magnetic Field

Area of Science:

• Plasma Physics
• Nonlocal Thermodynamics
• Space Plasma Physics

Background:

• Traditional thermodynamic concepts are often applied to plasmas, assuming local thermodynamic equilibrium.
• Low-collisionality plasmas, common in space and laboratory settings, may significantly deviate from this equilibrium.
• Previous studies indicate complex electron behavior in such environments, necessitating revised thermodynamic models.

Purpose of the Study:

• To re-evaluate thermodynamic properties of electrons in low-collisionality plasmas using nonlocal electron energy probability functions.
• To investigate the apparent contradiction between observed polytropic behavior and expected adiabatic electron evolution in a helicon double layer experiment.
• To understand the role of nonlocal electron thermodynamics in ion acceleration mechanisms.

Main Methods:

• Analysis of experimental data from a laboratory helicon double layer experiment.
• Application of nonlocal electron energy probability functions to describe electron behavior.
• Derivation of conservation relations for effective electron enthalpy and potential energy.

Main Results:

• Observed polytropic correlation (γe=1.17±0.02) suggests nearly isothermal behavior, contradicting adiabatic expectations (γe=5/3) due to nonlocal effects.
• Effective electron enthalpy conservation confirms no net heat transfer during electron evolution in this nonlocal regime.
• Nonlocal momentum equilibrium is established, with effective electron pressure and enthalpy driving ion acceleration.

Conclusions:

• Electron behavior in nearly collisionless plasmas is nonlocal and far from local thermodynamic equilibrium.
• Effective electron enthalpy, governed by nonlocal thermodynamics, is the primary driver for ion acceleration.
• Traditional thermodynamic concepts can yield erroneous conclusions about thermal conductivity in these plasma systems.