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Beam tolerance to RF faults & consequences on RF specifications

Beam tolerance to RF faults & consequences on RF specifications. Frédéric Bouly. MAX 1 st Design Review WP1 - Task 1.2. Bruxelles , Belgium Monday, 12 th November 2012. INTRODUCTION. Evaluate the minimum RF power required to enable fault-recovery procedures.

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Beam tolerance to RF faults & consequences on RF specifications

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  1. Beam tolerance to RF faults & consequences on RF specifications Frédéric Bouly MAX 1st Design Review WP1 - Task 1.2 Bruxelles, Belgium Monday, 12th November 2012

  2. INTRODUCTION • Evaluate the minimum RF power required to enable fault-recovery procedures. • Take Margins as regard to control errors : cavity theoretical parameters (ex: (r/Q)), accuracy of control systems, measurement errors. • It depends on coupling (from the power couplers) - A choice has to be made for each section of the linac. • Re-tuning beam dynamic studies will give the new Vcavand ϕsfor each compensation cavity. • Carry out beam study based on the reference linac design to : •  Give an exhaustive list of critical retuning cases •  Evaluate the retuning feasibility • From these typical scenarios evaluate the power consumption of recovery cavities in every linac sections Starting point & Objectives MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  3. Introduction •  Beam tolerance to RF Faults • - Methodology • -Example : loss of a Spoke module • - Status on different critical cases • Couplings (Qi) choices • - PRF & Qi are directly linked • - Methodology • - Results & consequences • RF specifications • - Statistical study of errors • - RF power required for each section • Summary & Prospects MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  4. Introduction •  Beam tolerance to RF Faults • - Methodology • -Example : loss of a Spoke module • - Status on different critical cases •  Couplings (Qi) choices • - PRF & Qi are directly linked • - Methodology • - Results & consequences •  RF specifications • - Statistical study of errors • - RF power calculation for each section • Summary & Prospects MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  5.  Beam tolerance to RF Faults • Simulations are based on the linac reference design (“strong focusing”option 1) • (J-L. Biarrotte, “SC linac design & MEBT”) • I0 = 4 mA ; Beam input parameters from injection line • (C. ZHANG, “Injector layout & beam dynamics”) • Local compensation - Eacc nominal chosen to enable a ~30 % increase (based on the SNS): •  1 failed cavity (or 1 Cryomodule) is compensated by 2 cavities (or 2 Cryomodules) placed upstream & 2 cavities (or 2 Cryomodules) placed downstream. Method • Procedure developed during previous project : • PDS-XADS () : Procedure setup - Identification of the difficulty to apply local compensation below 15 MeV.(J-L. Biarrotte, D.Uriot ,M. Novati, P. Pierini , H Safa “Beam dynamics studies for the fault tolerance assessment of the PDS-XADS linac design” , EPAC 2004). • EUROTRANS : Transient effect study - Definition of dynamic retuning scenario (J-L. Biarrotte, D.Uriot,“Dynamic compensation of an rf cavity failure in a superconducting linac” , Phy. Review, May 1998). • The synchronous phases are kept in a range similar to nominal conditions (i.e. -40° ≲ϕs ≲ -15°), in order to try to keep the longitudinal acceptance of the linac. MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  6.  Beam tolerance to RF Faults 5-CELL ELLIPTICAL (β 0.47) SECTION TraceWin Calculations SPOKE SECTION Example : Failure of a spoke cryomodule (1/6) Failed module (2 cavities) Longitudinal size diagnostic 4 re-tuned modules (8 re-tuned cavities) Energy diagnostic Energy & Phase diagnostics MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  7.  Beam tolerance to RF Faults Cavities voltage Beam Energy Example : Failure of a spoke cryomodule (2/6) Synchronous phase Cavities RF power (Beam loading) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  8.  Beam tolerance to RF Faults Nominal Tuning Fault-recovery Example : Failure of a spoke cryomodule (3/6) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  9.  Beam tolerance to RF Faults Example : Failure of a spoke cryomodule (4/6) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  10.  Beam tolerance to RF Faults Nominal Tuning Fault-recovery Example : Failure of a spoke cryomodule (5/6) Emittances (rms) Emittances (rms) Lattices phase advance Lattices phase advance MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  11.  Beam tolerance to RF Faults Longitudinal acceptance of the linac(SC linac + MEBT + HEBT) Example : Failure of a spoke cryomodule (6/6) Nominal Tuning Fault-recovery εacc/ εRMS ≈ 5.25/0.075 = 70 εacc/ εRMS ≈ 4.5/0.075 = 60 MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  12.  Beam tolerance to RF Faults Summary :studied scenarios - Failure of the last cavity - Failure of the last Cryomodule - Failure of 1 cavity - Failure of a Cryomodule - Failure of 1 cavity - Failure of a Cryomodule - Failure of 1 Cryomodule - Failure of 1cavity 11 identified scenarios - Failure of the 1st cavity - Failure of the 1st Cryomodule (in progress) - Failure of the last cavity Spoke β 0.35 5-cell β 0.47 5-cell β 0.65 MAX 4th General meeting, Frankfurt October 1st 2012 Bouly F.

  13. Introduction •  Beam tolerance to RF Faults • - Methodology • -Example : loss of a Spoke module • - Status on different critical cases • Couplings (Qi) choices • - PRF & Qi are directly linked • - Methodology • - Results & consequences •  RF specifications • - Statistical study of errors • - RF power required for each section • Summary & Prospects MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  14.  Qi choice • Power delivered to the beam : Beam power & RF power amplifier • RF power required from the generator when cavities gets their optimal frequency tuning : with • Optimum for coupling :  Ideally, each cavity would have its own power coupler with an optimised Qi(in function of its (r/Q), ϕs, Vcav & Ib0) • To calculate the RF power requirements, one has to first choose the coupling values for each of the 3 linac sections. • To find out the most adapted couplings : we look for the value of Qiwhich minimise Pg /Pb(i.e. which minimise the total RF power in nominal configuration) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  15.  Qi choice Couplings choice & bandwidth 5-cell Spoke • Frequency bandwidth 5-cell • Spoke (β 0.35) : BW = 160.2 Hz •  5-cell (β 0.47) : BW = 86.05 Hz •  5-cell (β 0.65) : BW = 102.2 Hz MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  16.  Qi choice Impact on RF consumption Total RF power increase is negligible : 0.74% (from 2.335 MW to 2.352 MW) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  17.  Qi choice • Once the Qi has been chosen it is therefore possible to calculate the RF power increase for the recoverycavitiesin the ideal case : the cavities frequency are perfectly tuned, errors & attenuations are not taken into account. Return on Spoke failure example MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  18. Introduction •  Beam tolerance to RF Faults • - Methodology • -Example : loss of a Spoke module • - Status on different critical cases •  Couplings (Qi) choices • - PRF & Qi are directly linked • - Methodology • - Results & consequences • RF specifications • - Statistical study of errors • - RF power calculation for each section • Summary & Prospects MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  19.  RF specifications • RF generator power - general formula RF Power - Errors & Attenuations Example : Cavity n° 76 (β0.47) which is compensating a failure • Errors taken into account for statistical errors study 22.35 kW •  Vcav : ± 2% • ϕs : ± 2° • Ib0 : ± 2% • Δf : ± 20 Hz •  Qi : ± 2 mm (± 20%) •  (r/Q) : ± 10 % • 2.106 draws • + 10 % marginsaddedfrom errors study to take into account attenuation and calibration errors. Maxi. 24.9 kW MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  20.  RF specifications Summary on RF needs MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  21. Introduction •  Beam tolerance to RF Faults • - Methodology • -Example : loss of a Spoke module • - Status on different critical cases •  Couplings (Qi) choices • - PRF & Qi are directly linked • - Methodology • - Results & consequences •  RF specifications • - Statistical study of errors • - RF power required for each section • Summary & Prospects MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  22. Beam fault-tolerance to a module failure has been demonstrated in each section • Same simulation method applied in each scenario •  A special tool should be developed to enable the calculation of the retuning set-points during the linac operation • One scenario to improve : failure of the 1st Spoke cryomodule - More tricky because bunchers before the failed module have to be retuned  In progress • Carry out simulation with several fault-recoveries in the linac & include errors (misalignments ... ) Conclusions • The power coupler Qi requirements have been calculated : • Spoke section (β 0.35) : Qi = 2.2 106 BW = 160.2 Hz • Elliptical 5-cell (β 0.47) : Qi = 8.2 106 BW = 86.05 Hz •  Elliptical 5-cell (β 0.65) : Qi = 6.9 106 BW = 102.2 Hz • Evaluation of the power requirements to anticipate on control errors + attenuations + fault-recovery scenarios : • Study with faults showed that a reasonable choice for the RF amplifier power would correspond to take a minimum margin of ~70 % (75% foreseen) compare to the nominal required Power (errors + attenuations + fault recovery). • Spoke section (β 0.35) : 15 kW • Elliptical 5-cell (β 0.47) : 30 kW • Elliptical 5-cell (β 0.65) : 55 kW • R&D activities for fault-recovery procedures study on a real scale experiment will be presented tomorrow. (R. PAPARELLA, “SC elliptical cavities design & associated R&D” - F. BOULY, I. MARTÍN, “Fault-recoveryprocedures & associated R&D”) MAX 4th General meeting, Frankfurt 12thNovember 2012 Bouly F.

  23. THANK YOU ! MAX 3rd General meeting, Madrid 12thNovember 2012 Frédéric Bouly

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