Effect of the nonuniformity of the magnetic field on the beam-plasma instability

The experimental investigation of the space charge wave instability of the spiral beam-plasma system in a nonuniform magnetic field is reported. The velocity distribution of the spiral electron beam is varied by the beam acceleration effect resulting from the parallel force due to the negative gradient of field intensity, which affects the trapping of beam electrons on the potential of the unstable wave. As a result, it is observed that the saturation length and the saturation level of the wave become extremely large. The brief theoretical analysis can explain the experimental results, consistently