Ghost Beam Studies

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Current Explanation

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The following is the currently accepted theory on the formation of the observed "Ghost Beam". To organize the explanation by what has been proven/shown to be true, the explanation text is color coded based on theoretical predictions, simulations, and experimental data/observations:

  1. Theoretically predicted, but not yet shown in simulations or in experiment
  2. Observed in simulation, but not yet explained in theory or shown in experiment
  3. Observed in experiments, but not yet explained in theory or in simulation
  4. Theoretically predicted and shown in simulations, but has not yet been observed experimentally
  5. Observed in simulation and experiment, but has not yet been explained theoretically
  6. Theoretically predicted and observed in experiment, but has not yet been shown in simulations
  7. Theoretically predicted, shown in simulations, and observed in experiment

Explanation

At GTS, electrons in a real electron beam can ionize residual gas, resulting in ions and secondary electrons. After the real electron beam is turned off, ions and secondary electrons can be trapped in various places in the accelerator due to the magnetic mirror effect. The three main places the ions and secondary electrons can be trapped are between the anode and magnetizing solenoid and within the first two solenoid lenses. Eventually, the ions and secondary electrons recombine and emit light, some of which is incident on the photocathode, producing a "ghost beam" that we see on the viewers. Although the ghost beam has been observed to last for many hours , it cannot be self-sustaining in this manner (i.e. through photoemission from recombination light); there must be either a direct or an indirect source of ions or electrons to sustain the ghost beam

Observations

The ghost beam is made of electrons that originate from the photocathode. We know this due to how the ghost beam steers with corrector magnets upstream of the viewers. The higher the vacuum levels during the prior electron beam run, the more intense the ghost beam is on the viewers .