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An electron beam is injected into a low density neutral gas in the presence of electric and magnetic fields. The beam produces a low density plasma which provides neutralization and current closure in steady state. The beam electrons are visible through excitation of light by collisions with atoms and ions. The electron motion in magnetic fields can exhibit helical trajectories, mirror reflection, gradient and curvature drifts in nonuniform fields, drifts and acceleration/deceleration in the presence of electric felds. Observe the following effects:

1. Electric Fields (B=0).

Bias a grid so as to reflect the electron beam. Observe the formation of a sheath. Infer the electric field distribution from the beam deflection.

2. Uniform Magnetic Field (E=0).

Inject a beam of known energy at an angle with respect to the field B. Find the direction and strength of B and check the pitch of the helix .

3. Mirror Reflection.

Inject the electron beam obliquely to an increasing magnetic field and observe the mirror reflection. Check the variation of the mirror point with injection angle , theoretically given by .

4. Drifts in Electric Fields .

Bias a grid so as to create an electric field perpendicular to a uniform magnetic field. Observe the drift. Estimate the electric and magnetic field directions and magnitudes from the particle energy and motion.

5. Drifts in Nonuniform Magnetic Fields (E=0).

(i) Inject the beam off-axis into a converging magnetic field and observe gradient and curvarture drifts. Estimate the drift velocity. (ii) Inject the beam into a magnetic cusp field and observe the particle motion near a magnetic null point. Explain the motion qualitatively.

A set of typical questions that may be asked for these experiments on single particle motions is available. Also, a set of images depicting many of the observable effects can be viewed.

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