V-Shaped Double Layers Formed by Ion Beam Reflection

A potential double layer is observed when an ion beam is injected into a collisionless magnetoplasma along converging magnetic field lines and reflected at a positive electron-absorbing boundary. The double layer is $V$ shaped, highly stationary, strong ($\frac{e\varphi }{k{T}_e}\lesssim 25$) with amplitude determined by the beam energy ($\varphi \lesssim V_b$), and occurs with magnetized (${\mathrm{H}}_2^{+}$) and unmagnetized (${\mathrm{Ar}}^{+}$) ions. Distribution function measurements show self-consistently formed trapped electrons on the high-potential side.