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 -ephi/T-e=root(x(0)-x)/lambda, consistent with ion flux conservation, and that the sheath consists of a transition region and an electron-free collisionless sheath with thicknesses scaling as lambda(1/5)lambda(D)(4/5) and lambda(D)(ephi/T-e)(3/4), respectively, where lambda 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 T-e/e and 2T(e)/3e, respectively, increasing with increasing pressure.