Design of the new 805 pillbox cavity Zenghai Li & Lixin Ge Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Outline • Cavity Design • Multipacting comparison • DC comparison Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
New Design With Low Surface Field Original New low field design slot 2 slot E E anose end bp B B • Large rounding and elliptical profile • Factor 0.55 reduction in surface E field • Factor 0.63 reduction in surface H field Q 0 =16060 Emax slot slot slot Emax Emax Emax Emax other slot Model# height rounding rounding 2 anose slot slot2 anose end bp surface Hmax angle Qext Original 15.2/6.4 3.175 0 11.4 69.81 44.95 32.88 46.22 0.304 53 12899 New (4c) 13.5/4.4 9.5 3.5 22 38.15 33.10 34.70 33.33 32.86 0.197 47.3 14645 Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting Simulation Using Track3P • Part of ACE3P (Omega3P, S3P, T3P, Track3P, etc) • 3D parallel particle tracking in high-order finite- element mesh • Analyze resonant trajectories • Use impact energy and SEY to estimate MP strength • Copper SEY peak around 800eV impact energy Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting Analysis • Field level scan: 0.1MV/m – 30MV/m, interval 0.1MV/m • Initial Particles distributed on all exterior surface • Each field level ran 50 RF cycles Original Design New Design Window Disk rounding Coupling iris Other Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting on Window Surface Original Design New Design Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting on Disk Rounding Original Design New Design Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting on Coupling Iris Original Design New Design Larger coupling iris rounding area in new design Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Multipacting other exterior surface Original Design New Design Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Field Emission Simulation To Study Relative Quantities • Gradient: 25 MV/m • Beta = 150 (normally use 50 for copper) • Emitted all the surface based on Folwer original Noheim field emission • No secondary • To compare, (as function of rf phase) – Impact Energy – Current – Distribution new Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
DC Analysis By Region Other surfaces Window Disk rounding Coupling iris Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Original Design New Design Energy v.s. Phase Window Disk rounding Coupling iris Other surfaces Current v.s. Phase (relative rf phase between original and new is arbitrary) Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
DC on Window • Similar impact energy Red: Original Design • Similar DC current on the window surface Green: New Design (same E field) (relative phase between two designs is arbitrary) Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
DC on Disk Rounding • Similar impact energy Red: Original Design • Higher current in the original design due to Green: New Design higher field enhancement on the disk (relative phase between rounding surface two designs is arbitrary) Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
DC on Coupling Slot • Similar impact energy Red: Original Design • Higher current in the original design due to Green: New Design higher field enhancement on the coupling (relative phase between slot surface two designs is arbitrary) Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
DC on Other Surfaces • Similar impact energy Red: Original Design • Higher current in the original design due to Green: New Design higher field enhancement (around the (relative phase between coupling slot and disk rounding regions) two designs is arbitrary) Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
Summery • New Design has incorporated large rounding around the coupling iris and elliptical profile around the disk area – Factor 0.55 reduction in surface E field – Factor 0.63 reduction in surface H field • Multipacting compared between original and new design, no improvement indicated. (MP can normally be processed through) • Relative DC reduced significantly at a given gradient • Would like to compare with measurement data to help understand HP processing Z. Li & L. Ge MAP Weekly Meeting, Jan 20, 2012
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