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High beta cavity simulations and RF measurements

High beta cavity simulations and RF measurements. Alessandro D’Elia- Cockroft Institute and University of Manchester. HIE-ISOLDE upgrading stages. 1.2MeV/u*. 3MeV/u*. 5.5MeV/u*. 10MeV/u*. * A/q= 4.5.

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High beta cavity simulations and RF measurements

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  1. High beta cavity simulations and RF measurements Alessandro D’Elia- Cockroft Institute and University of Manchester

  2. HIE-ISOLDE upgrading stages 1.2MeV/u* 3MeV/u* 5.5MeV/u* 10MeV/u* * A/q= 4.5 Stage 1 is shown at the top, while stage 2 can be split into two sub-stages depending on the physics priorities: the low energy cryomodules will allow the delivery of a beam with better emittance; the high energy cryomodule will enable the maximum energy to be reached M. Pasini, D. Voulot, M. A. Fraser, R. M. Jones, ”BEAM DYNAMICS STUDIES FOR THE SCREX-ISOLDE LINAC AT CERN”, Linac 2008, Victoria, Canada

  3. High beta cavity Resonator (/4) 784.5mm Beam Coupler and Pick up seats 300mm

  4. Tools “calibration” In order to get reliable cavity parameters values from simulations, a comparison between the results coming from HFSS and CST Microwave has been performed using Superfish as a benchmark

  5. Superfish vs CST Microwave and HFSS

  6. Frequency CST Meshing HFSS Meshing (5m) HFSS Meshing (20m)

  7. E field* * All field values are normalized to give 1J stored energy in the cavity (CST Normalization)

  8. H field* * All field values are normalized to give 1J stored energy in the cavity (CST Normalization)

  9. Comparison tables

  10. “Real” structure

  11. Remarks • Never being confident to post-processing results!! • Even if HFSS and CST results are consistent and very close to Superfish, when we start to complicate our structure (tuner plate, coupler and pick-up), the possibility of having a finer refinement on surface meshing gets HFSS results more reliable • The above statement are not general!!

  12. Cavity Parameters * V. Zvyagintsev et al., “Development, Production And Tests Of Prototype Superconducting Cavities For The High Beta Section Of The Isac-ii Heavy Ion Accelerator At Triumf”, RuPAC 2008, Zvenigorod, Russia ** G. Devanz, “SPIRAL2 resonators” talk held at SRF05

  13. Q0 values TRIUMF*: Q0=7∙108 with Pcav=7W and Eacc=8.5MV/m SPIRAL2**: Q0=109 with Pcav=10W and Eacc=6.5MV/m * V. Zvyagintsev et al., “Development, Production And Tests Of Prototype Superconducting Cavities For The High Beta Section Of The Isac-ii Heavy Ion Accelerator At Triumf”, RuPAC 2008, Zvenigorod, Russia ** G. Olry et al., “Tests Results Of The Beta 0.12 Quarter Wave Resonators For The Spiral2 Superconducting Linac”, LINAC 2006, Knoxville, Tennessee USA

  14. Some word about the hot frequency The cold frequency has to be 101.28MHz In air:  -32kHz 101.248MHz In superconducting mode of operation (shortening of the length of the antenna,…):  -332kHz 100.916MHz skin depth variation:  -11kHz 100.905MHz Other contributions (chemistry,…): ???? ~ 100.900MHz

  15. Study of RF tuning plate

  16. Frequency with tuner plate Pick up length=-1mm, coupler length=5mm Triumf tuner coarse range 32kHz

  17. Measurements vs Simulations25/03/2009 * Resonator longer of 0.4mm with respect to the nominal length (135kHz/mm) ** These new measurements have been done in a much noisy environment that explain the  13kHz of difference with respect to the previous ones

  18. Expected final hot frequency

  19. External Q Let us assume Q0=5x108 and a condition of perfect coupling (c=1) Qload=2.5x108 • Therefore we want • Qext of RF coupler of 2.5x106 in order to be undercoupled (c=200 ∆f  40Hz) (larger bandwidth) • Qext Pick-up of 1010 in order to be overcoupled (negligible power flowing from the pick-up)

  20. Q measurements • Hot measurements are important to test and calibrate the coupler and pick-up before going to cryostate • Very difficult to get reliable measurements allowing for such a high Qext values • Cold measurements are needed for the final characterization • It is not possible going through standard frequency domain measurements as • Two different strategies for hot and cold measurements

  21. RF Coupler Pick-up Network Analyzer β measurements Pc Pin = Pf-Pr = Pc+Pe Pf Pr Pe Pin Dividing everything by Pe and rearraging, by considering that Note: the system is symmetric so that I can feed from the pick-up and meauring c

  22. Qexthot measurements • Measuring SWR from S11 • Measuring S21 pu • Measuring Qload • Evaluating Qext Legend W/o pick-up Lpu_in=22mm Lpu_in=-1mm Max Error= 3.6%

  23. Q cold measurements as Q0109 ∆f0.1Hz By feeding the cavity by a rectangular pulse By switching off I can measure Knowing c, we get Q0 We can use for c value the one we got from the hot measurementsor we can feed the cavity by a rectangular pulse, in the steady-state c

  24. Coupler Macor • Dust free sliding mechanism 7500 < Qext < 5∙109 • -10mm Linsertion 60mm

  25. Coupler

  26. Internal Reflections

  27. Conclusions • E-m design of the high beta cavity is finished • The machining of the copper part is finished • Measurements show a very good agreement with simulations • First prototype of the tuner already available, sputtering on the end of June • Mechanical design and fabrication of the coupler is started, deliviring date, end of July • Starting the design of the low beta cavities

  28. Reviewer comments • The cavity parameter list represents a challenging but attainable specification and would represent the state of the art in sputtered heavy ion linac performance • CERN has applied for EuCARD to develop quarter wave sputtering using a magnetron or other techniques and this R+D would benefit HIE-Isolde but also the world community as new material searches are ongoing to improve cavity performance while reducing production costs. • A study of the power dissipation in the RF coupler at different coupling factors is needed in order to define the heat deposited to the Helium space • The tuning sensitivity of the bottom tuning plate at 13kHz/mm should be adequate to meet the coarse tuning range required in the cavity. However it may be preferable to reduce this sensitivity somewhat to allow a reduced specification on the tuner resolution since in this case a tuner position change of only 1 micron corresponds to more than the expected full cavity bandwidth. A factor of two reduction would help. This would also reduce the rf currents on the tuning plate where thermal conduction may be limited due to a marginal pressed contact

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