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HOM Status Summary

This report summarizes key achievements and ongoing research and development efforts in Higher Order Mode (HOM) design conducted by the BNL team, in collaboration with CERN. Significant accomplishments include innovative filter designs achieving an impressive wide stop band performance and optimal Qext measurements for multiple HOMs. Current challenges involve impedance mismatches affecting Qext values, along with new strategies for power estimation and filtering optimizations aimed at mitigating multipacting issues. Future work focuses on refining designs to enhance performance and meet cavity requirements.

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HOM Status Summary

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  1. HOM Status Summary Binping Xiao On behalf of DQWCC team, BNL In collaboration with CERN

  2. Quick Reminder: achievements • Filter design • wide stop band (<80dB, several tens of MHz) at 400MHz, high pass at frequency 570MHz~2GHz • Hook coupler design • 471 Qext at 579.8MHz (1st HOM), • 507 Qext at 682.6MHz (2nd HOM), • 233 Qext at 697.3MHz (3rd HOM). • HOM mapping • frequency, Qext, R/Q, mode configuration etc., up to 2GHz are calculated by Silvia (without filter) and Zenghai (with filter). 10mm x 20mm

  3. Quick Reminder: problems • Qext problem (Silvia) • with filters, the calculated Qextfrom CST MWS for the 1st HOM is ~7000 (Silvia), while from Ace3P is ~2000 (Zenghai). • Some high Qext modes (Binping) • caused by impedance mismatch between the hook and the filter. • High Qext -> high shunt impedance • High magnetic field area (Binping) • For the fundamental mode, a high magnetic field area (14% higher than the max on the cavity inner surface) appears in the corner between the first rod inductor and the hook. 81mT/ 3.4MV

  4. Recent R&D • Filter optimization • Qext optimization • Power estimation • Prototyping

  5. Recent R&D: filter optimization Slope for multipactingsuppression Bleding for field suppression Next: Put the output port aside, Mod to avoid conflict on flange. 20mm in diameter 580 MHz -2.6 dB 742 MHz -1.9 dB 683 MHz -10.7 dB 400±30 MHz

  6. Recent R&D: Qext(1) Idea: change the LC of filter and hook to get better impedance match. 45°, possible 60°? Plate 3mm Hook shape Hook position

  7. Recent R&D: Qext(2) Longitudinal shunt impedance (Ohm/cavity) Meet the requirement

  8. Recent R&D: Qext(2) Vertical shunt impedance (Ohm/m/cavity) 1.172GHz Qext Original design: w/o filter 900 w/ filter 10^4 Modified design: w/ filter 10^7 Mismatch? 45/60degree solution: what happened at 1.172GHz?

  9. Recent R&D: Qext(2) Horizontal shunt impedance (Ohm/m/cavity) 45/60degree solution: needs a little bit more optimization

  10. Recent R&D: power estimation • Use the beam spectrum provided by Rama • Use the shunt impedance provided by Zenghai • Direct calculation gives 115 Watt/Cavity • Manually adjust each HOM frequency in ±1 MHz range to match the “worst case” of beam spectrum, the HOM power changes to 1003 Watt/Cavity • Calculation needs to be re-done before finalizing the HOM design.

  11. Recent R&D: Prototyping Will figure out the ports connection based on new design.

  12. miscellaneous • Difference on R/Q (Silvia and Rama) • Shunt impedance budget (Sergey) • Bead pulling is on-going based on PoP cavity • Find a solution for 45 degree ports (Binping)

  13. End

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