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Summary from the slides of M.Holz presented on 3/7/2012 at LIU-SPS- ecloud

Multipactor test stand. Summary from the slides of M.Holz presented on 3/7/2012 at LIU-SPS- ecloud. M.Taborelli. Reminder: Goals and Experimental Set-up. Quality control for different carbon coatings in the vacuum chamber, independent from the beam and accelerator’s schedule

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Summary from the slides of M.Holz presented on 3/7/2012 at LIU-SPS- ecloud

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  1. Multipactor test stand Summary from the slides of M.Holz presented on 3/7/2012 at LIU-SPS-ecloud M.Taborelli

  2. Reminder: Goals and Experimental Set-up • Quality control for different carbon coatings in the vacuum chamber, independent from the beam and accelerator’s schedule • A tungsten wire drawn along a SPS magnet vacuum chamber (6.4 m): geometry of a coaxial transmission line (transversal electromagnetic waves). The chamber becomes a resonator and we use standing wave pattern to achieve the necessary E-Field strength Michael Holz BE-RF-BR

  3. Summary of 2011 • Only a single test was performed on carbon coated chambers • For all measurements with magnetic field below 3 kA, no reflected power nor outgassing could be observed, corresponding to complete suppression of multipacting • When using 3 kA through the magnet, a single rise in reflected power occurred, but was not reproducible. However, pressure activity remained for all consecutive measurements.

  4. 2012 uncoated MBB013 Reflected power Pressure rise • chamber as-received from chemical cleaning • Reflection at very low power threshold as expected • Cyclotron resonance at the expected value • pressure rise is not well correlated with the reflected power influence of the history of conditioning (sequence of measurements)? E F D C B A

  5. 2012 carbon coated MBB013 (hollow cathode) • Reflection observed at higher power threshold compared to uncoated • Almost independent from the dipole magnetic field strength:  possibly multipacting occurs outside the dipole chamber • Pressure rise is one order of magnitude lower than for uncoated • NB: the chamber of coated in hollow cathode (only top and bottom faces are coated)…and the lowest threshold of power is for B=0

  6. High magnetic field @130.1 MHz, coated • No change with respect to lower magnetic fields (in 2011 we had a non reproducibility issue in these conditions)

  7. Conclusions • only slight reflected power and pressure rises in a hollow cathode coated chamber • possibility of multipacting outside the dipole: put solenoids to verify this • redo pressure rise measurements with a well defined conditioning state • Calculate the field pattern to verify the possibility of multipacting at the uncoated regions (sides) of the chamber

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