3.9 GHz Deflecting Mode Cavity

1. 3.9 GHz Deflecting Mode Cavity History of 3.9 GHz DMC Cell Shape Cavity Simulations The “Other Modes” concern and modeling R/Qs Wake Field Simulations Design: OM couplers Infrastructure Timothy W. Koeth October 3 & 4, 2005

2. OFF 13 CELL CAVITY head is deflected up B-Field ON 13 CELL CAVITY tail is deflected down Deflecting Mode Cavity History The Deflecting Mode Cavity (DMC) was initially planned for use in the CKM fixed target experiment’s beam line, but now it finds it’s primary use as a diagnostic tool. The operating frequency, 3.9 GHz, was chosen to be a multiple of the A0 facility’s 1.3 GHz system. This will permit the use of the cavity as a beam-slicing device that can measure the longitudinal profile of a short bunch.

3. Cell shape CONSIDERATION (R/Q)’, G1, and Bmax-surf were studied for 9 shapes G1 does not strongly depend on iris radius: A-series: 250Ω B-series 230Ω C-series 228Ω

4. Cell shape CONSIDERATION Frequency separation between the π-mode and the 12π/13-mode needed to have a relative separation greater than 3E-4 C15 Profile was chosen. End cells have a slighly different shape to match the beam tube to the structure.

5. Beam Line Simulations Full 3-D E-M field made for 13 cell polarized model was generated in HFSS Iris Uniformity map of the the integrated transverse kick along the the 13 cell cavity The peak magnetic field along the cavity. (illustrating field flatness) The electric field along axis is zero

6. Viewing screen Vertical Projection CAV. OFF [Meters] [Meters] [Meters] Intesity [arb] CAV. ON [Meters] [Meters][Time] [Meters] Intesity [arb] The 3-D field map was used with the ASTRA code to understand the cavity’s time resolution Beam Line Simulations The simulation consisted of a bunch composed of two Gaussian peaks of different intensity and generation time. This enabled us to compare the time to spacial correlation preservance. BLUE: Vertical Position GREEN: Time domain 2.0mm  730fsec Resolution: 10 to 20 fsec

7. Lower, Same, and Higher Order Modes Requirement: to be maintain the DMC in “standby” in the beam line at 4.5 K. Does the cavity have any “problematic” modes sitting near the light cone ? Using MAFIA, dispersion curves for modes up to cut-off were checked m = 0 modes m = 1 modes m = 2 modes not shown, but modeled.

8. Determination of R/Q We show the R(m)/Q values for all the modes found in the 13 cell MAFIA simulation, in units of Ω for m = 0, Ω/m2 for m = 1, and Ω/m4 for m = 2. Possible Modes of Concern: TM010: -9π/13 R/Q:187 -10 π/13 R/Q:354 -11 π/13 R/Q:129 TM110: - π (2nd Polr.) R/Q:2.3x106 !

9. LOM, SOM, HOM Couplers INPUT COUPLER Qext: 107 SAME ORDER MODE COUPLER: 90o rotated Qext:105 Qext-op:108/9

10. Input Coupler • Qext: 107 • Power Requirement ~400 Watts • Coaxial feed through

11. HOM Coupler HOM coupler a modification of DESY design HOM COUPLER Qext at 3.9GHz 109/10 Qext else: 104/5

12. Trapped HOMs ? A study of possible trapped HOM above cut-off, and were compared to R/Q determined by MAFIA. An example of a potential trapped mode Freq: 5322 R/Q 243Ω/m2 Possible solution is to increase energy in the end cells by compressing end cell more than the body cell. Knowledge comes from measurement !

13. SOM COUPLER LOM COUPLER LOM Coupler LOM at opposite end of input coupler to reduce direct capacitive losses from the input coupler Qext: 109/10 @ 3.9GHz Qext: 104/5 @ 3.9GHz Current design has pertruding tip only 11mm from cavity axis

14. F=2702.3 Q=697 LOM Coupler Modeling in HFSS HFSS model was build from I-DEAS surface mesh file. Both resonances close to design frequency of 2830 MHz. Notch frequency is 4100 MHz. All resonances in final tuning range. F=2945 Frequency [MHz]

15. SOM COUPLER LOM COUPLER SOM Coupler SOM coupler will be mechanically adjusted to find the node of the TM110 mode SOM COUPLERS Qext: 104/5 @ 3.9GHz

16. Polarization Splitting Δf ~ 50kHz

17. Polarization Splitting Polarization separation with a copper model Typical compression is 3mm, which is about 10MHz separation

18. Wake Field Simulations Typical Input Parameters: Position & angle of offset beam: i.e. The 17th bunch, entering 0.5 mm away from the center looses ~200keV and is kicked 32 μrad A WORK IN PROGRESS !

19. Vertical Dewar Test Results Cavity design parameters 13 cells BMAX = 80 mT EMAX = 18.6 MV/m L EFF = 0.5 m P = 5 M V/m

20. Vertical Dewar Test Results Brief Testing History: Cavity: “Short” Cavity: “Soft” Cavity: “Thick” • Possible cause for poor surface resistance: • Contaminated water system(s) • Hydrogen poisoning from long acid etch • Cavity orientation wrt to environmental flux lines ? • Hydrogen in welded region at about 1ppm ? • Losses on tip of Input Coupler

21. Horizontal Cryovessel FNAL already has a prototype horiztonal cryovessel that will host two 3.9 GHz cavities. With minor modification, we will retrofit for use in the PhotoInjector Beam line. Cryogenics Feed Thermometry, LOM, SOM, HOM ports Capable of hosting two 3.9 GHz cavities. RF input Coupler(s)

22. DMC HLRF We have a 3kW CW 3.9 GHz Klystron for CKM operation Power requirement is only 400W for 13 cell

23. DMC LLRF Using DESY’s SimCon Series for LLRF control. Developement and testing with Superconducting cavities underway at DESY and Fermilab. Successful demonstration of Piezoelectric suppression of microphonics.

24. HiGHLY RECOMMENDED READING: Deflecting Mode Cavity Status: FERMILAB-TM-2144 May 2001 RF Design of a Transverse Mode Cavity for Kaon Separation Fall 2005: Fine tuning L/S/HOM design December 2005: Cavity assemblies in construction Summer 2006: Finish cavity production Fall 2006 : Assembled cavity in cryovessel Winter/Spring 2007: Commission with beam Acknowledgements Helen Edwards, Leo Bellantoni, Timergali Khabiboulline, Don Mitchell, Mike Foley, Allan Rowe, Bill Soyars, Peggy Crayton