First Experimental Measurements of the Plasma Potential throughout the Presheath and Sheath at a Boundary in a Weakly Collisional Plasma

Experimental data obtained with emissive probes and Langmuir probes show that the plasma potential profile in the presheath scales as -eφ/Tₑ=√(x₀-x)/λ, consistent with ion flux conservation, and that the sheath consists of a transition region and an electron-free collisionless sheath with thicknesses scaling as λ1/5λD4/5 and λD(eφ/Tₑ)3/4, respectively, where λ is the ion-neutral collision length. Results support Rieman's presheath and transitional region model [Phys. Plasmas 4, 4158 (1997)]. The potential drop over the presheath and transition sheath region were the order of Tₑ/e and 2Tₑ/3e, respectively, increasing with increasing pressure.