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Sasha Novokhatski PEP-II MAC Review SLAC December 13, 2004

RECENT HOM CALCULATIONS HOM Dampers: Last Measurements and New Computer Designs. Sasha Novokhatski PEP-II MAC Review SLAC December 13, 2004. Last Measurements. HOM absorber in region 4. Bellows 2012. HOM Absorber. TSP 1162. Effect of absorber. Temperature.

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Sasha Novokhatski PEP-II MAC Review SLAC December 13, 2004

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  1. RECENT HOM CALCULATIONSHOM Dampers: Last Measurements and New Computer Designs Sasha Novokhatski PEP-II MAC Review SLAC December 13, 2004 SN PEP-II MAC REVIEW

  2. Last Measurements HOM absorber in region 4 Bellows 2012 HOM Absorber TSP 1162 1SN PEP-II MAC REVIEW

  3. Effect of absorber Temperature LER current SN PEP-II MAC REVIEW Nov. 2002-July 2004

  4. HOM Power in absorber SN PEP-II MAC REVIEW

  5. HOM Power Against RF Voltage HOM power vs. RF voltage for a positron current of 1400 mA. SN PEP-II MAC REVIEW

  6. Prediction for Future HOM Power In future: 10 kW Now we are here: 1kW SN PEP-II MAC REVIEW

  7. TSP in the next arc chamber 1153 We plan to install same type absorber in this chamber Nov. 2002-July 2004 SN PEP-II MAC REVIEW

  8. Absorber for chamber 1153 (J. Langton) SN PEP-II MAC REVIEW

  9. Searching for the source of HOM power • Beam was moved away from the collimators jaw Y2031 -13.5 mm in Y X2041+10 mm in X X2081+9.1 mm in X Y3011+12 mm in Y • Y2031 move reduced twice power in absorber placed in the first drift chamber in the arc 3. A. Kulikov A. Novokhatski F.-J. Decker S. Weathersby SN PEP-II MAC REVIEW

  10. HOM Power in Absorber and Beam position near Collimators HOM power in absorber (red line) and vertical beam position near 15m collimator (blue line) and 65m collimator (green line). SN PEP-II MAC REVIEW

  11. HOM Power and Beam Position Almost liner dependence for Y-collimators No dependence for X-collimators SN PEP-II MAC REVIEW

  12. Hottest Bellows 2012 Takes Power from Y and X Collimators Y and X collimators SN PEP-II MAC REVIEW

  13. Straight Section Bellows 2015 and 2022 Y-collimator 2032 is the main source of HOM power SN PEP-II MAC REVIEW

  14. Computer Simulations • We made an important step from theoretical general calculations of damping HOMs in different vacuum elements to simulation of real designs • To speed the calculation process we use geometrical files in STL or SAT format which are produced by the “Solid Edge” program, used for preparation of classical drawings. • Stephen Weathersby uses STL files as input files for MAFIA calculations. • Cho-Kuen Ng uses SAT files for his “OMEGA3P” calculations. SN PEP-II MAC REVIEW

  15. Computer Simulations • Currently we are running 7 projects: • Straight section bellows and HOM absorber (N.Kurita, M.Kosovsky) • Vertex bellows with an absorber inside (J. Brian Langton) • Q2-bellows HOM absorber (N.Kurita, Ho Dong) • Absorber for “Bong” collimator (N.Kurita,Nickolas Reeck) • Q4 LER NEG HOM absorber (Nadine Kurita) • Q4/Q5 bellows with an absorber inside (N.Kurita, Manuel Trigos) • Spoiler for abort kicker (Mohammad Dormiani) Wake fields physics study • HOMs from R4 collimators (Michael Kosovsky) • IP beam pipe trapped modes (J. Brian Langton) SN PEP-II MAC REVIEW

  16. IP wakes and Q2-bellows SN PEP-II MAC REVIEW

  17. IP wakes Computer model for IP region gives This bunch length dependence is very close to Stan Ecklund measurement Today Future SN PEP-II MAC REVIEW

  18. Bunch energy loss in open ceramic pipes. HEACC’92 page 537 Loss factor SN PEP-II MAC REVIEW

  19. Formula check with experimental measurements at Cornell PAC’95, page 3294 Parameters of absorber Ferrite TT2-111R (R.Chiang) Magnetic absorption m~1 14 Dielectric quality SN PEP-II MAC REVIEW

  20. Comparison with experimental measurements at Cornell Assuming m=1 in our frequency region Formula very well describes experimental results SN PEP-II MAC REVIEW

  21. Using this formula for Q2 Beam energy loss in Q2-bellows Today In future SN PEP-II MAC REVIEW

  22. Method for absorber calculations “MAFIA” can not match well wake fields at the boundaries! We use special approach for these calculations. • For a given absorber configuration, simulated electromagnetic waves of a particular mode ( TM monopole, TE dipole or TE quadrupole) for a range of frequencies propagates through the structure. • The wave is matched at the entry and exit ports of the structure. • The phase and amplitude of transmitted and reflected waves are monitored at the entry and exit ports of the structure from which the Reflection, Transmitted and Absorbing Coefficients are computed. SN PEP-II MAC REVIEW

  23. Input waves: TM monopole TE dipole Two polarizations TE quadrupole The TM monopole mode has the bunch field structure, so it has the potential to affect the beam. The goal is to minimize absorption for the monopole mode while maximizing the absorption for the TE dipole and TE quad modes. SN PEP-II MAC REVIEW

  24. Absorption - Red lines Q2-bellows Produce new TM monopole M D1 Absorb TE dipoles D2 Absorb TE quadrupoles Q A.Novokhatski S. Weathersby N. Kurita Ho Dong SN PEP-II MAC REVIEW

  25. We studied about 40 models. Some examples Q2_28 Smaller thickness of tiles moves absorption to higher frequencies SN PEP-II MAC REVIEW

  26. Q2_27 Metal conductors between tiles J.Seeman SN PEP-II MAC REVIEW

  27. Q2_25 Metal conductors between thicker tiles J.Seeman SN PEP-II MAC REVIEW

  28. Q2_29 model Monopole is damped completely, but dipole absorption is very small SN PEP-II MAC REVIEW

  29. Some physics study. Only two metal stripes add. High frequency Two polarizations. Electric fields. Low frequency SN PEP-II MAC REVIEW

  30. Comparison with no stripes Change absorption for another dipole polarization 2 metal stripes change a little absorption for monopole No stripes No great change for one polarization of dipole mode (high frequency) SN PEP-II MAC REVIEW

  31. Summery for Q2-bellows. We tried 38 versions but did not find better solution. Trade off between HOM damping and HOM production. May be not to change current design for Q2 before damping HOMs in the vertex bellows SN PEP-II MAC REVIEW

  32. Different proposals for placing water-cooled absorber inside vertex bellows A.Novokhatski S. Weathersby J. Brian Langton Bellows cavity Ceramic tiles Last Version SN PEP-II MAC REVIEW

  33. Absorber inside bellows cavity reduced strongly the problem of HOM heating. Q-values for radial and side brazing Q-value of HOMs inside bellows cavity with absorber SN PEP-II MAC REVIEW

  34. Some modes F=5.96 GHz f=8.999 GHz SN PEP-II MAC REVIEW

  35. Vertex bellows and Beam pipe. Geometry for calculation SN PEP-II MAC REVIEW

  36. Cho-Kuen Ng Mesh Only half of the model simulated Spring finger Surface mesh Contact finger SN PEP-II MAC REVIEW

  37. Cho-Kuen Ng First results: Eigenmode Calculation: TE21 • 5.947 GHz • quadrupole (TE21) mode Magnetic field SN PEP-II MAC REVIEW

  38. Cho-Kuen Ng First result: Eigenmode Calculation: Bellows • 6.368 GHz • monopole (TM01) Magnetic field SN PEP-II MAC REVIEW

  39. Q4/Q5 bellows with absorber Good damping! SN PEP-II MAC REVIEW

  40. Examples of field distributions in Q4/Q5 f=1.44 GHz f=2.593 GHz f=2.725 GHz SN PEP-II MAC REVIEW

  41. Q4 LER NEG HOM absorber ( water-cooled absorbing antenna) Ceramic tiles Good absorption for so long chamber SN PEP-II MAC REVIEW

  42. Absorber for “bong” collimatorProblem of absorption for vertical dipole mode. SN PEP-II MAC REVIEW

  43. Two TE dipole polarizations One polarizing is damped! Dipole mode. Other polarizing is not damped! SN PEP-II MAC REVIEW

  44. Straight section bellows and HOM absorber Bellows convolutions not used in simulation 1/4 Ceramic tiles SOLD EDGE Bellows shielded slots not used in simulations No polarization problem for a round chamber. MAFIA SN PEP-II MAC REVIEW

  45. Result of optimization for the best dipole and quadrupole absorption Absorption coefficient Frequency [Hz] SN PEP-II MAC REVIEW

  46. Possible Place in region 4 to Test this HOM Absorber SN PEP-II MAC REVIEW

  47. Spoiler for abort beam (A.Kulikov) Stored beam Abort beam Ceramic tiles SN PEP-II MAC REVIEW

  48. HOM Power and Absorption SN PEP-II MAC REVIEW

  49. Summary • The source for High Order Modes in LER ARC 3 is found: collimators. • New HOM absorber is ready to be installed in the second arc chamber. • Computer absorber designs for vertex bellows and straight bellows are almost finished. • More work is needed for Q2-bellows and other projects. SN PEP-II MAC REVIEW

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