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

Abstract

Experimental data obtained with emissive probes and Langmuir probes show that the plasma potential profile in the presheath scales as -ephi /T(e)= sqrt[(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 (4/5 )(D) 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.