Reliability-oriented activities around the MAX 700 MHz...

Reliability-oriented activities around the MAX 700 MHz horizontal cryomodule

Frédéric Bouly (IPN Orsay – CNRS/IN2P3)

2nd Open Collaboration Meeting SLHiPP-2

INFN, Catania, SicilyFriday, May 4th 2012

Superconducting MYRRHA Linac

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Frédéric Bouly 2nd Open Collaboration meeting SLHIPP, Catania May 4th 2012

Introduction

3 sections : 48 Spoke Resonators : βg = 0.35 - 352.2 MHz - Eacc(@ βopt) = 6.2 MV/m 34 5-cell elliptical cavities : βg = 0.47 - 704.4 MHz - Eacc(@ βopt) = 8.2 MV/m 60 5-cell elliptical cavities : βg = 0.35 – 704.4 MHz - Eacc(@ βopt) = 11 MV/m

Reliability & Goals

3Introduction


Demonstrate the ADS Concept & Transmutation Coupling : Accelerator

+ spallation source + subcritical reactor

Avoid beam trips longer than 3 seconds to minimise thermal stresses and fatigue on target, reactor & fuel assemblies. Specifications : Less than 10 trips per 3 months operation cycle.

Consequences on Linac Design :

“Overdesign” of the component : Operation margin between operation and technological limitations (from beam optics to R&D)

Redundancy & Fault tolerance :Big phase and energy acceptance of superconducting cavities

Capabilities of fast retuning for “fast fault-recovery scenarios” and failures compensations.

Requires LLRF & control system for cavity tuning system operating in CW.

Myrrha_MYRRHA_DV-4.avi

Fault scenario

4Fault tolerance & reliability study


Typical case : One cavity loose its RF power supply. Region of interest of the MYRRHA superconducting Linac : βg = 0.47

Cavity voltage

Cavity synchronous phase

Losses along the linac

Without linac retuning the beam is lost.

Fault recovery scenario : compensation



Compensation Strategy : the failure of a cavity is compensated by the 4 neighbours cavities: 2 cavities placed upstream the failed one 2 cavities placed downstream the failed one

Cavity voltage

Cavity synchronous phase

Phases & accelerating fields have to be modified in less than 3 seconds.

No beam during the procedure.

Feasibility of retuning procedures



To study the retuning procedure of superconducting cavities a Matlab SimulinkTM model have been established. 2 feedback loops were modelled :

RF feedback loop Frequency tuning system of the cavity

feedback loop.

Model based on a βg = 0.47 5-cell elliptical cavity prototype (from TRASCO project).

Motor:«slow» action (~ 1 s)Large detuning (~ 250 kHz).

Piezoelectric actuators : «Fast» action (~ 1 ms) Fine detuning (~ 2 kHz).

Feedback loops modelled



RF feedback loop : Based on an existing digital LLRF system

Modelled as Delay + ZOH + BP filters + IOT transfer function. PI correctors tuned to minimise Beam loading

Fast tuning system feedback loop

Needed to minimise power consumption & compensate perturbations (Lorentz, microphonics)

Transfer function of piezo action have been measured and modelled.

Optimum frequency detuning :

Study of a retuning scenario (compensation example)



Cavity set points have to be changed in order to compensate another failed cavityin the linac

Beam switched off and on duringthe procedure

Synchronous phase has to bechanged

Accelerating field ramped up toenable the tuning system tocompensate Lorentz forces

Resonance frequency of cavityhas to be changed

Retuning scenario



RF power (kW)

Power delivered to the beam (kW)

Accelerating field (MV/m)

Synchronous phase (°)

Cavity detuning (Hz)

The cavity can be retuned in200 ms (i.e. one order ofmagnitude lower than 3 s)

When Eacc ramped-up anoverconsumption of RF poweris observed This iscompensated by the piezosfeedback loop in less than~100 ms.

A PI controller is used for thetuning system loop.

3 strong microphonicsperturbations are assumed :

@ 1Hz with ∆fperturbation = +/- 10 Hz@ 71 Hz with ∆fperturbation = +/- 10 Hz@ 120 Hz with ∆fperturbation = +/- 20 Hz

Control of the tuning system



Different control strategies studied

Simulations showed that an adaptive andpredictive system enable to minimise thepower consumption compare to a PIcorrection. It also adapt its correction effectwhen an unforeseen perturbation occurs.

Controller

Band-pass Filters

+∆fcav-errorPiezoscontrol action

Identified microphonics perturbations canbe compensated by applying a correction onthe perturbation frequency thanks to band-pass filters.

(Isaias Martin Hoyo, ADEX)

Tuning system requirements



The results shows that it is conceivable to retune the linac in less than 3 sec with a fast tuning system.

Another important results : To avoid beam “deceleration” in the unused cavity it is necessary to change its resonance frequency.

It has to be detuned by 13 kHz in less than 3 sec.Minimum detuning speed of 5 kHz per second.

An hardware scheme is currentlyunder development

Both “PID + Bandpass FiltersApproach” and “ADEX + BandpassFilters Approach” will be tested on theCold Tuning System of the 5 cellelliptical cavity prototype.

The horizontal cryomodule prototype

12Reliability test bench


A prototype of cryomodule has been installed in anexperimental pit at IPN Orsay . It holds a 5-cell ellipticalcavity equipped with its blade tuner.

Development achieved by LASA (INFN Milano) for thecavity + cryogenic vessel and by IPNO for the valve box.

Development achieved by LASA (INFN Milano) for thecavity + cryogenic vessel & by IPNO for the valve box.

GOAL :Dispose of a “real scale” experimental facility to Carryout Reliability-oriented experiments with a fully-equipped 700 MHz prototypical cryomodule controlledby feedback systems (RF and Fast Cold Tuning System).

Component robustness retuning procedures

Module description



First experimental results



Stepper motor capabilitiesMax detuning range (@ 4K): ~270 kHz Observed hysteresis 2 kHz

Several tries needed tomeasure the Q0 curves at 2Kbecause of cryogenic leaks.

Q0 obtained in critical couplingMultipacting easily processed Quench value a bit lower thanexpected (field unflatness) Still above MYRRHA requirements

Conclusions & Prospects

15Conclusion


A model of cavity + feedback system – based on measurement – has been developed tostudy fast fault recovery scenarios in the MYRRHA linac.

Results show it is possible to locally retune the linac to compensate a failure, but uponcondition that :

Dispose of a fast and efficient LLRF systemalready developed and tested The tuning system must be fast enough to correct Lorentz detuning and microphonics. It also has to detune the cavity on a large frequency range with a minimum speed of

5kHz/secMotor + Piezos & development of an hardware for adaptive and predictive control.

Robustness of many different components of the module has been tried and improved. Leaks on Helium Tank, modification of circuitry to improve cooldown speed, automation

of all the cryogenic procedures.

Promising results obtained with the test of the cavity in critical coupling (Q0

measurement in agreement with expectations)

Next step is the High Power tests. The conditioning of the power coupler is currently inprogress.

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THANK YOU !


Reliability-oriented activities around the MAX 700 MHz...

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