The collective behavior of an intense, pulsed, space‐charge‐neutral proton beam (100 kV, 3 A/cm2, 0.8 msec) incident upon a transversely oriented magnetic field of 0–6 kG has been determined experimentally. At 6 kG, a floating potential probe shows longitudinal polarization creating a positive sheath (virtual anode) within the field boundary having a peak electrostatic potential equal to the ion accelerating potential. The sheath thickness is approximatelyv/wpi, wherevis the beam velocity and wpiis the ion plasma frequency. Oscillations in the sheath potential at wpiwere observed as predicted by previous computer simulations. Ions were observed to be accelerated out of the sheath in all directions. Transverse polarization of the beam as predicted by Schmidt’s polarization drift model was not observed although the plasma dielectric constant was approximately 102.