Two Mechanisms Limiting the Emitted Electron Current from a Cathode to an Anode.

Area of Science:

• Plasma physics
• Electron transport phenomena
• Applied physics

Background:

• Electron emission current in plasmas typically saturates due to the space charge effect, forming a potential well near the cathode.
• Previous models often simplified the cathode sheath, neglecting interactions with the interior plasma and anode sheath.

Purpose of the Study:

• To identify and demonstrate a novel electron current saturation mechanism in plasma diodes.
• To investigate the interplay between cathode sheath dynamics and interior plasma conditions in limiting global current.

Main Methods:

• Full plasma diode modeling was employed to simulate electron transport and potential structures.
• Analysis focused on the conditions leading to the weakening of the cathode sheath and subsequent electron backflow.

Main Results:

• A new saturation mechanism, termed "backflow saturation," was identified, often imposing a more severe current limitation than the space charge effect.
• The study revealed four distinct current limitation regimes: backflow alone, space charge alone, stable cooperative saturation, and competing oscillatory saturation.

Conclusions:

• Backflow saturation is a critical, previously underappreciated factor limiting global current in plasma diodes.
• Accurate modeling of the entire plasma diode is essential to capture complex saturation phenomena.