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The Self-Modulation I nstability

Affects long drive beams. Long beam enters plasma. Free e- pulled towards proton beam. E- overshoot the proton beam. Ion region left behind head of proton beam. E- pulled back on axis by ions Impinge on proton beam. The Self-Modulation I nstability. +. +. -. -.

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The Self-Modulation I nstability

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  1. Affects long drive beams. Long beam enters plasma Free e- pulled towards proton beam E- overshoot the proton beam Ion region left behind head of proton beam E- pulled back on axis by ions Impinge on proton beam The Self-Modulation Instability + + - - Weak wakefield co-propagates with beam + - + + + + + - - + Ion regions force beam protons away - + + + E- regions focus beam and keep on axis Long proton beam After some time, half the proton beam is discarded, leaving micro-bunches Neutral plasma Microbunches are spaced λp apart. Charge density increased. Micro bunch lengths are much closer to the ideal driver length of: σideal = λp / π√2 These properties then allow the modulated beam to drive a wakefield much more effectively. Neutral plasma Self-modulated driver beam

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