Beam tolerance to RF faults & consequences on RF specifications

Beam tolerance to RF faults & consequences on RF specifications

Frédéric Bouly

MAX 1st Design ReviewWP1 - Task 1.2

Bruxelles, Belgium Monday, 12th November 2012

Starting point & Objectives

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Bouly F. MAX 4th General meeting, Frankfurt 12th 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 Vcav and ϕs 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

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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


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Introduction






- RF power calculation for each section

Summary & Prospects


Method5

Bouly F. MAX 4th 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”)

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.

■ 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.

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Example : Failure of a spoke cryomodule (1/6)

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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

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Cavities voltage

Synchronous phase

Beam Energy

Cavities RF power (Beam loading)

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Example : Failure of a spoke cryomodule (3/6) Fault-recoveryNominal Tuning

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Nominal Tuning Fault-recovery

Emittances (rms) Emittances (rms)

Lattices phase advance Lattices phase advance

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Nominal Tuning Fault-recovery

Longitudinal acceptance of the linac (SC linac + MEBT + HEBT)

εacc/ εRMS ≈ 5.25/0.075 =

70 εacc/ εRMS ≈ 4.5/0.075 = 6012th November 2012

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Bouly F. MAX 4th General meeting, Frankfurt October 1st 2012


Summary : studied scenarios

Spoke β 0.35 5-cell β 0.47 5-cell β 0.65

- 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 1st cavity - Failure of the 1st Cryomodule (in progress)

11 identified scenarios

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Introduction







Summary & Prospects


Beam power & RF power amplifier14


Qi 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 Qi (in function of its (r/Q), ϕs, Vcav & Ib0)

■ To find out the most adapted couplings : we look for the value of Qi which minimise Pg /Pb (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.

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Couplings choice & bandwidth15


Qi choice

5-cell

5-cell

Spoke

■ Frequency bandwidth

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

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0 20 40 60 80 100 120 1400

5

10

15

20

25

30

35

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

Pg with Qiopt

Pg with Qi choosed

Power consumption increase between Qiopt & Qi chosen

Cavity number

RF P

ower

(kW

)

Incr

ease

on

RF P

ower

Impact on RF consumption16


Qi choice

Total RF power increase is negligible : 0.74%

(from 2.335 MW to 2.352 MW)

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Return on Spoke failure example17


Qi choice

■ Once the Qi 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.

31 32 33 34 35 36 37 38 39 400

1

2

3

4

5

6

7

8

9

10

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

45.00%

50.00%

Nominal power

Fault-recovery power

RF power increase (%)

Cavity number

Pow

er (k

W)

RF P

ower

incr

ease

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Introduction






- RF power calculation for each section

Summary & Prospects


RF Power - Errors & Attenuations19


RF specifications

■ RF generator power - general formula

Vcav : ± 2% ϕs : ± 2° Ib0 : ± 2% Δf : ± 20 Hz Qi : ± 2 mm (± 20%) (r/Q) : ± 10 %

■ Errors taken into account for statistical errors studyExample : Cavity n° 76 (β 0.47) which is

compensating a failure

22.35 kW

Maxi.24.9 kW

■ + 10 % margins added from errors study to take into account attenuation and calibration errors.

2.106 draws

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Summary on RF needs20


RF specifications

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Introduction







Summary & Prospects


Conclusions22


■ Beam fault-tolerance to a module failure has been demonstrated in each sectionSame 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 ... )

■ 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-recovery procedures & associated R&D”)

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THANK YOU !

Frédéric Bouly MAX 3rd General meeting, Madrid 12th November 2012

Documents

Beam tolerance to RF faults & consequences on RF specifications