The effects of both magnetic field and collisions on presheath properties are experimentally
 investigated in plasmas with electron temperatures much greater than ion temperatures.
 Measurements of plasma potential in collisionless plasmas show presheath thicknesses at
 boundaries oblique to magnetic field to be approximately (C,lw,;)sin I+$ where C, is the ion sound
 speed, wci is the ion gyrofrequency, and ‘4’ is the angle between the magnetic field and the normal
 to the wall boundary. Measurements of plasma potential in collisional plasmas find presheaths
 consisting of two distinctive regions. With ion-neutral collision mean-free path A,<( C,/w,i)sin ~4,
 the presheath region next to the sheath has collisional characteristics and a thickness of
 approximately (0.5 - 0.6)h, . The corresponding presheath region adjacent to the bulk plasma has
 magnetic characteristics and a thickness of approximately (0.5 - 0.9) (C,lW,i) sin $. Equipotential
 contours in the collisional region of this presheath are found to be parallel to the boundary, while
 those in the magnetic region are not.

http://dx.doi.org/10.1063/1.871153