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Dark Current Tracking & Collimation from Cathode Edge, Charge Assignment Findings

Exploring dark current tracks from cathode edge with possible collimation; charge assignment based on FN parameters; normalized sum of charges to 1 Coulomb. Detailed findings on particle distribution, charged particles behavior, and collimator efficacy. Analysis available at http://www-physics.lbl.gov/seminars/old/Sannibale.pdf.

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Dark Current Tracking & Collimation from Cathode Edge, Charge Assignment Findings

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  1. LCLS-II dark current tracks from cathode edge and possible collimation

  2. Charge assignment from FN parameters • Used the parameters from measurement to assign charges to the dark current particles based on their initial longitudinal E-field. • Particles are uniformly distributed in time and at radius 5mm (the edge of the cathode puck) • The sum of all charges is normalized to 1(Coulomb) http://www-physics.lbl.gov/seminars/old/Sannibale.pdf

  3. Particles from r = 5 mm on cathode colored by charge (red is higher charge)

  4. Particles lost colored by charge (red is higher)

  5. Particles escaping colored by charge (red is higher)

  6. Particles lost backwards 0.25% of the current turns around and hits the cathode

  7. Current lost per meter

  8. Forward moving particles in frontend

  9. Collimator at z = 2 m These are the particles passing z=2m in the forward direction. The fraction captured current for a given collimator radius. Note that some current was already lost prior to this location

  10. Collimator placement after buncher summary This extends the previous plot to all possible z locations for collimation. For example: A collimator with radius 5 mm placed at z=1.5 m would capture 80% of the dark current A collimator with radius 10 mm placed at z = 2.0 m would capture 70% of the dark current

  11. Tracks including HTR, Col0 sections

  12. Tracks including HTR, Col0 sections .02% survive

  13. Tracks including HTR, Col0 sections

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