TRIUMF and A Facco INFN amp FRIB Nonelliptical cavities 17 Sept 2017 SRF Tutorial EuCAS 2017 E Jensen NonElliptical Cavities 1 17 Sept 2017 SRF Tutorial EuCAS 2017 E Jensen NonElliptical Cavities ID: 1042087
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1. Special thanks to R. Laxdal (TRIUMF) and A. Facco (INFN & FRIB)Non-elliptical cavities17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities1
2. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities2Why non-elliptical cavities?Applications and trendsCavity conceptsExamples of TEM cavitiesBasic principles of acceleration – figures of merit, beam dynamics for low betaCavity beta/frequency choiceOther cavity typesDesign issuesFabricationCryomoduleOn-going developmentsOutline
3. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities3 Heavy Ions (, ) Protons/H- (, ) Useful relations
4. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities4Particle velocity vs. kinetic energyelectron @ 50 MeVproton @ 91.8 GeV electron @ 511 keVproton @ 938 MeVelectron @ 5.4 keVproton @ 1 MeV
5. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities5Accelerating electrons vs. accelerating ions
6. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities6Various building blocks – different technologies, each optimized for a certain velocity rangeIonsCommon building blocks – all designed for . ElectronsAccelerating electrons vs. accelerating ions
7. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities7Elliptical cavities have been designed starting at for CW applications, for for pulsed (SNS, ESS). The -mode requires cell-to-cell distance of , but outer diameter , i.e. at low the cavity looks more like bellows, sensitive to LFD! Limitations of elliptical cavities
8. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities8Non-elliptical SRF Community around the world
9. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities9Quarter wave resonator (QWR) Half wave resonator (HWR) Single spoke resonator (SSR) Multi-spoke resonator (MSR) For comparison: Elliptical cavities Resonator types for low beta acceleration
10. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities10Consider a coaxial geometry with grounded end plates, an inner conductor with radius and an outer conductor with radius .A standing wave occurs with vanishing on the end walls at and .The remaining non-zero field components are,,where , Peak voltage: Coaxial resonator
11. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities11The most popular coaxial TEM mode cavity is the quarter wave resonator – capacitively loaded transmission lineThe inner conductor is open at one end with a resonant length of , For acceleration, is chosen.The maximum voltage builds up on the open tip – the maximum current at the root.A beam tube is arranged near the end of the tip. Quarter-wave resonator (QWR)
12. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities12In the HWR the beam port is at the centre of the inner conductor of a coaxial resonator, coincident with the maximum voltage for .Magnetic fields loop around the inner conductor with peak fields at the shorted ends.For acceleration, is chosen. Half-wave resonator (HWR)
13. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities13QWR is the cavity of choice for low beta applications where a low frequency is neededrequires ~50% less structure compared to HWR for the same frequency – rf power loss is ~50% of HWR for same frequency and . allows low frequency choice giving larger longitudinal acceptance. twice that of HWR.Asymmetric field pattern introduces vertical steering especially for light ions that increases with velocity – avoid use for .Less mechanically stable than HWR due to unsupported end (microphonics).HWR is chosen in mid velocity range () or where steering must be eliminated (i.e. high intensity light ion applications)produces twice rf losses for the same and .is 2x longer for the same frequency.Pluses are the symmetric field pattern and increased mechanical rigidity. QWR vs. HWR
14. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities14HWR vs. Single Spoke Resonator (SSR)A single spoke resonator (SSR) is another variant of the half-wave TEM mode cavity class.In HWR the outer conductor is coaxial with the inner conductor (with diameter ) while in the spoke cavities the outer cylinder is co-axial with the beam tube with diameter . It means that for the SSR has a larger overall physical envelop than the HWR for the same frequency.Thus for low beta applications () HWRs are chosen at , while SSRs are preferred at . The spoke geometry allows an extension along the beam path to provide multiple spokes in a single resonator giving higher effective voltage, but with a narrower transit time acceptance.
15. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities15Cavity types – QWRs Typical range:
16. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities16Cavity types – HWRs Typical range:
17. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities17Cavity types – SSRs Typical range:
18. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities18Cavity types – multi-cellCH: Crossbar H-mode
19. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities19Accelerating cavity velocity/frequency chart
20. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities20Transit Time factor vs. for multiple gaps
21. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities21High velocity spoke cavities with are being designed as alternative to elliptical cavitiesFeatures:relatively compactbetween 20% and 50% smaller (radially) for low- cavitiesfor high diameter close to TM counterpartsallows low frequency at reasonable sizemechanically stable – high shunt impedance High- spoke cavities
22. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities22Deflecting mode cavities
23. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities23Prototype HL-LHC Crab Cavity prototypes“DQW” (vertical deflection)“RFD” (vertical deflection)
24. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities24Geometry optimized to minimize peak field ratios (, ). Achieved: and for . Example: TRIUMF/RISP 325 MHz SSR for (balloon cavity)
25. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities25Driven by mechanical vibration in the environment.QWRs are particularly problematic due to the pendulum action of the inner conductor, which can have very low mechanical frequencies () need to reduce the RMS detuning to of the available BW to avoid nuisancethe other option is to increase the BW (lower , costs power)Mitigation: stiffening during design/manufacturecentering the inner conductor by plastic deformation so that .adding passibe dampersreduce environmental noise Microphonics
26. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities26For QWRs a tuning plate at the open end near the beam tube is generally used.For QWRs with removable tuning plate, a Nb puck can be welded to it – this reduces the cavity by increasing the equivalent .This puck can be trimmed after final fabrication Frequency compensation/tuningtuning plate
27. 17 Sept, 2017SRF Tutorial EuCAS 2017 E. Jensen: Non-Elliptical Cavities27Thank you very much!End of Non-elliptical cavities