SRF Technology
Low-level RF control/microphonics
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WEPWB109 PI Loop Resonance Control for the Dark Photon Experiment at 2 K using a 2.6 GHz SRF cavity 847
 
  • C. Contreras-Martinez, B. Giaccone, O.S. Melnychuk, A.V. Netepenko, Y.M. Pischalnikov, S. Posen, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Two 2.6 GHz cav­i­ties are being used for dark pho­ton search at VTS in FNAL. Dur­ing test­ing at 2 K the cav­i­ties ex­pe­ri­ence fre­quency de­tun­ing caused by mi­cro­phon­ics and slow fre­quency drifts. The ex­per­i­ment re­quires that the two cav­i­ties have the same fre­quency within 5 Hz. These two cav­i­ties are equipped with fre­quency tuners con­sist­ing of three piezo ac­tu­a­tors. The piezo ac­tu­a­tors are used for fine-fast fre­quency tun­ing. A PI loop uti­liz­ing the piezos was used to main­tain both cav­i­ties at the same fre­quency, and the re­sults are pre­sented.  
poster icon Poster WEPWB109 [1.151 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB109  
About • Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 18 July 2023
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WEPWB110 Prevention of Dual-Mode Excitation in 9-Cell Cavities for LCLSII-HE 852
 
  • P.D. Owen
    JLab, Newport News, Virginia, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
Dual-Mode Ex­ci­ta­tion, also re­ferred to as mode-mix­ing, is a su­per­po­si­tion of two pi modes in an SRF cav­ity. In 9-cell TESLA cav­i­ties used for the LCLSII-HE pro­ject, the two modes that are com­monly ex­cited are the pi mode (1300.2 MHz), and the 7/9 pi mode (1297.8 MHz). Dur­ing ver­ti­cal cav­ity qual­i­fi­ca­tion test­ing, it is reg­u­larly ob­served that emit­ted power at the fre­quency of the 7/9 pi mode grows, de­spite the RF sys­tem only dri­ving the pi mode. When this hap­pens, the RF power mea­sure­ment sys­tem is un­able to dif­fer­en­ti­ate be­tween the su­per­im­posed modes which in­val­i­dates any data taken. A new RF con­trol so­lu­tion pre­vents the 7/9 pi mode from being ex­cited. A sec­ond RF con­trol sys­tem is con­nected to drive the 7/9 pi mode. The loop phase for dri­ving this mode is de­ter­mined, then shifted by 180 de­grees, thus pro­vid­ing a neg­a­tive feed­back to the un­de­sired mode. Be­cause this off-res­o­nance power can be very small, it does not in­ter­fere with the high-power mea­sure­ments of the fun­da­men­tal pi mode. At Jef­fer­son Lab, we are now able to test a cav­ity for the LCLSII-HE pro­ject with no com­pli­ca­tions from mode-mix­ing, which al­lows for CW pro­cess­ing of high-gra­di­ent mul­ti­pact­ing. 		 
poster icon Poster WEPWB110 [1.818 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB110  
About • Received ※ 19 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 13 July 2023
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WEPWB128 Experimental Study of Mechanical Dampers for the FRIB β=0.041 Quarter-Wave Resonators 898
SUSPB036   use link to see paper's listing under its alternate paper code  
 
  • J. Brown, W. Chang, W. Hartung, S.H. Kim, T. Xu
    FRIB, East Lansing, Michigan, USA
  
  Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award numbers DE-SC0018362 and DE-SC0000661 and Michigan State University.
The ’pen­du­lum’ me­chan­i­cal mode of quar­ter-wave res­onators (QWR) often causes an issue with mi­cro­phon­ics and/or pon­dero­mo­tive in­sta­bil­ity un­less oth­er­wise the inner con­duc­tors are prop­erly stiff­ened and/or damped. FRIB QWRs are equipped with a Leg­naro-style fric­tional damper in­stalled in­side of the inner con­duc­tor such that it coun­ter­acts the os­cil­la­tions of the inner con­duc­tor. In cry­omod­ule tests and linac op­er­a­tion, we ob­served that the damp­ing ef­fi­ciency is dif­fer­ent for a few β=0.041 QWRs. This study aimed to ex­per­i­men­tally char­ac­ter­ize the damp­ing ef­fi­cacy as a func­tion of damper mass and sur­face rough­ness. We pre­sent damp­ing mea­sure­ments at room tem­per­a­ture and at two dif­fer­ent masses and sur­face rough­ness as well as dis­cuss fu­ture stud­ies for damper re-op­ti­miza­tion based on this fol­low-on study. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB128  
About • Received ※ 20 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 August 2023
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