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

Starting point & Objectives 2 Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012 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 V cav and ϕ s for 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

3 Introduction   Beam tolerance to RF Faults - Methodology -Example : loss of a Spoke module - Status on different critical cases   Couplings (Q i ) choices - P RF & Q i are directly linked - Methodology - Results & consequences   RF specifications - Statistical study of errors - RF power required for each section Summary & Prospects Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012

4 Introduction   Beam tolerance to RF Faults - Methodology -Example : loss of a Spoke module - Status on different critical cases   Couplings (Qi) choices - P RF & Q i are directly linked - Methodology - Results & consequences   RF specifications - Statistical study of errors - RF power calculation for each section Summary & Prospects Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012

Method 5 Bouly F. MAX 4 th General meeting, Frankfurt  Beam tolerance to RF Faults ■ Simulations are based on the linac reference design (“strong focusing”option 1) (J-L. Biarrotte, “SC linac design & MEBT”)  I 0 = 4 mA ; Beam input parameters from injection line (C. ZHANG, “Injector layout & beam dynamics”) ■ Local compensation - E acc 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. ■ 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° ≲ ϕ s ≲ - 15°), in order to try to keep the longitudinal acceptance of the linac. 12 th November 2012

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

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

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

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

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

11 Bouly F. MAX 4 th General meeting, Frankfurt  Beam tolerance to RF Faults Example : Failure of a spoke cryomodule (6/6) Nominal TuningFault-recovery Longitudinal acceptance of the linac (SC linac + MEBT + HEBT) ε acc / ε RMS ≈ 5.25/0.075 = 70 ε acc / ε RMS ≈ 4.5/0.075 = th November 2012

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

13 Introduction   Beam tolerance to RF Faults - Methodology -Example : loss of a Spoke module - Status on different critical cases   Couplings (Q i ) choices - P RF & Q i are directly linked - Methodology - Results & consequences   RF specifications - Statistical study of errors - RF power required for each section Summary & Prospects Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012

Beam power & RF power amplifier 14 Bouly F. MAX 4 th General meeting, Frankfurt  Q i choice ■ Power delivered to the beam : ■ 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 Q i (in function of its (r/Q), ϕ s, V cav & I b0 ) ■ To find out the most adapted couplings : we look for the value of Q i which minimise P g /P b (i.e. which minimise the total RF power in nominal configuration)  To calculate the RF power requirements, one has to first choose the coupling values for each of the 3 linac sections. 12 th November 2012

Couplings choice & bandwidth 15 Bouly F. MAX 4 th General meeting, Frankfurt  Q i choice 5-cell Spoke ■ Frequency bandwidth  Spoke (β 0.35) : BW = Hz  5-cell (β 0.47) : BW = Hz  5-cell (β 0.65) : BW = Hz 12 th November 2012

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

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

18 Introduction   Beam tolerance to RF Faults - Methodology -Example : loss of a Spoke module - Status on different critical cases   Couplings (Q i ) choices - P RF & Q i are directly linked - Methodology - Results & consequences   RF specifications - Statistical study of errors - RF power calculation for each section Summary & Prospects Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012

RF Power - Errors & Attenuations 19 Bouly F. MAX 4 th General meeting, Frankfurt  RF specifications ■ RF generator power - general formula  V cav : ± 2%  ϕ s : ± 2°  I b0 : ± 2%  Δf : ± 20 Hz  Q i : ± 2 mm (± 20%)  (r/Q) : ± 10 % ■ Errors taken into account for statistical errors study Example : Cavity n° 76 (β 0.47) which is compensating a failure kW Maxi kW ■ + 10 % margins added from errors study to take into account attenuation and calibration errors draws 12 th November 2012

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

21 Introduction   Beam tolerance to RF Faults - Methodology -Example : loss of a Spoke module - Status on different critical cases   Couplings (Q i ) choices - P RF & Q i are directly linked - Methodology - Results & consequences   RF specifications - Statistical study of errors - RF power required for each section Summary & Prospects Bouly F. MAX 4 th General meeting, Frankfurt12 th November 2012

Conclusions 22 Bouly F. MAX 4 th General meeting, Frankfurt ■ 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 1 st 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... ) ■ The power coupler Q i requirements have been calculated :  Spoke section (β 0.35) : Q i =  BW = Hz  Elliptical 5-cell (β 0.47) : Q i =  BW = Hz  Elliptical 5-cell (β 0.65) : Q i =  BW = 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- recovery procedures & associated R&D”) 12 th November 2012

23 THANK YOU ! Frédéric Bouly MAX 3rd General meeting, Madrid12 th November 2012