Vikas Jain RRCAT, Indore€¦ · Vikas Jain RRCAT, Indore Indo Japan Accelerator School cum Workshop IJAS - 2020, VECC, Kolkata. Outline • Introduction • Requirement of SCRF cavity

Vikas Jain

RRCAT, Indore

Indo Japan Accelerator School cum Workshop IJAS - 2020, VECC, Kolkata

Outline• Introduction

• Requirement of SCRF cavity

• Design methodology for Superconducting Cavity

• 650 MHz cavity design as an example

• Design loads

• Fabrication aspects

• Tuner for SCRF cavity

• Requirement of tuner in SCRF cavity

• Why SCRF Cavity resonance Challenging

• Two stage tuning system

• Dynamic LFD

• RRCAT’s works on Tuner

• Summary

SCRF Cavity and Tuner Related Technologies -Vikas Jain

Superconducting RF cavities are important for any modern accelerators essentially due to

their inherent advantage of higher voltage gradient and quality factor.

• Large particle accelerators are being built all over world with hundreds of cavities

• In some, like International linear collider (ILC) requirement is of 18,000 cavities and

lots R&D efforts are going for making the SCRF technology efficient.

• In DAE also a comprehensive plan has been adopted to address SCRF technology

issues for Indian projects.

Introduction

Typical Superconducting Cavity

Normal conducting vs Superconducting cavity

SCRF Cavity and Tuner Related Technologies -Vikas JainRef: https://cds.cern.ch/record/1533028/files/CERN-2013-001-p151.pdf

1. The cavity shall be fabricated from Niobium and Jacked using NbTi and Titanium to

house a 2 K helium bath ➔ Needs EBW welding for joining & Environment Controlled TIG

2. The cavity needs extra precaution after fabrication ➔ Processing and clean room

environment

3. It must meet the requirements of the ASME for pressure vessels and be rated at an

MAWP (Maximum Allowable Working Pressure) of no less than 2 bars at room

temperature and 4 bar at 2 K. ➔ Code compliances

4. Cavity has to equipped with effective magnetic field repulsion in the course of fast cavity

cooling. ➔ Proper Magnetic shielding

5. Cavity are very sensitive to dimension even small changes ➔ Tuner Mechanism

6. Cavity qualification ➔ Testing VTS & HTS …

Requirement of SCRF cavity


SCRF cavity development work at RRCAT

• RRCAT has taken up a R&D program to “Design and develop SCRF cavities and

associated infrastructure” for the SC LINAC for IFSR.

• RRCAT along other DAE laboratories (BARC & VECC) and IUAC is also a member of

Indian Institution Fermilab Collaboration (IIFC) and engaged in development of SCRF

cavities and associated technologies required for such accelerators.

• A variety of special infrastructure have been built for SCRF cavity manufacturing,

processing and testing.

• A number of 1.3 GHz and 650 MHz single cell and Multi-cell SCRF cavities have been

built and tested at 2K.

• Work on HB650 MHz Five-cell SCRF cavity is currently in progress. Four 650 MHz SCRF

cavities are fabricated and these are at different stages of processing or testing.SCRF Cavity and Tuner Related Technologies -Vikas Jain

Cavity Fabrication and Qualification Infrastructure

Internal optical inspection

Special CNC machining Centre120 T Press for forming 15 kW EBW machine

Mechanical inspection RF testing Vacuum leak testing

Fabrication Infrastructure

Qualification Infrastructure


Cavity processing, testing and dressing infrastructure

VTS Test Pit

Electro-polishingCentrifugal barrel Polishing High Pressure Rinsing

Heat Treatment FurnaceInsert cavity mounting VTS


Cavity dressing infrastructure

Material quality control infrastructure

RRR measurement facility

SIMS

Universal Testing machine( Mechanical properties)


Design Methodology for Superconducting Cavity


RF Dimension

HB650 b=0.92 ➔ 500 MeV to 800 MeV E-Mag Data➔

650 MHz Cavity Design as an example

RF Dimension added with cavity thickness

End Group MC endEnd Group Tuner end or FP end

Dumbbell 1 Dumbbell 2 Dumbbell 3 Dumbbell 4


Dressed Cavity Cross-section

Cavity Jacketed using NbTi & Ti vesselSCRF Cavity and Tuner Related Technologies -Vikas Jain

Dressed Cavity Components

It consists of following components:-1. Long Cylinder2. Transition ring MC end3. Transition ring FP end4. Bellow assembly5. Support lugs6. Lifting lugs7. Helium inlet8. 2-phase pipe assembly9. Tuner mounting lugs10. Safety bracket or tuner

11. Main Coupler port12. Pick up port13. Magnetic shielding

(External)14. HOM port (optional)15. Invar post (optional)

Long Cylinder

Transition ring MC end

Transition ring FP end

Bellow assembly

Support lugs

Helium inlet

2-phase pipe assembly

Tuner mounting lugs

Bellow restrains

Lifting lugs


Simplified Model For Mechanical Analysis

2D Axisymmetric

3DSCRF Cavity and Tuner Related Technologies -Vikas Jain

Different Loads on SCRF cavityLoad Case Condition Simulated Cavity temperature and Loads

LC1 Warm Pressurization

1. T= 300K

2. P2 = 0.2 MPa

3. P1 = P3 = 0

LC2Cold operation, full LHe, maximum

pressure – no thermal contraction

1. T= 2K

2. P2 = 0.4 MPa

3. P1 = P3 = 0

LC3Cool down and tuner extension, no

primary loads

1. T= 2K

2. Tuner extension of 2 mm

(Cavity compressed by 2

mm)

LC4

Cold operation, full LHe inventory,

maximum pressure – primary and

secondary loads

1. T= 2K2. Tuner extension of 2 mm3. P2 = 0.4 MPa 4. P1 = P3 = 0

LC5Insulating and beam vacuum upset,

helium volume evacuated

1. T= 300K

2. P2 = 0

3. P1 = P3 = 0.1 MPaSCRF Cavity and Tuner Related Technologies -Vikas Jain

Coupled Analysis for df/dp & LFD ➔ Emag & Structural analysis


E Field

H Field

Cavity boundary (mm)

(Pa)

Radiation pressure

Coupled Analysis for LFD(650 MHz cavity Data)

Tuner stiffness and df/dp, LFD and Mech. modes

Effect of Tuner stiffness on df/dp, LFD, Mechanical Modes

Tuner plays important in SCRF cavity

SCRF cavity tuner

End tuner

Co-axial TunerSCRF Cavity and Tuner Related Technologies -Vikas Jain

Equivalent spring model

.

▪ Tuners are the devices mounted on SCRF cavities to keep them in correct

resonating frequency after cool down to SC state and during operation.

▪ Role of SCRF cavity tuner is precise as its quality factor Q0 > 109, hence

narrow resonance bandwidth for tuning ~ few Hz

Tuner facilitates axial deformation of SCRF cavity within elastic limit.

A. It tunes the resonating frequency of cavity to matched with the sourcefrequency.

B. During operation the cavity experiences detuning forces, which need

fast (online) correction of frequency.

SCRF Cavity Tuner

Tuner

SCRF cavity

▪ Tuning range should have at least 0.03% of the RF cavityfrequency (e.g. for 1300 MHz RF cavity need to tune ~400 kHzfrequency).

▪ Should be cryo-compatible and cryogenic losses should be low.

▪ Operates inside a cryomodule and remotely controlled fromoutside

▪ High Repeatability

▪ High resolution

▪ High MTBF (mean time between failure)

▪ Two stage tuning (Firstly tuning to overcome the initial shift offrequency during cool down to 2K,secondly tuning during RFpulse operation.

Requirement of tuner in SCRF cavity


Why SCRF Cavity resonance Challenging

1.3 GHz

Typical SCRF cavities (Tesla 1.3 GHz)

Q0 factor ~1010 and Loaded

QL~5x106 Bandwidth ~250Hz

Shape of cavity (length) determines its resonance frequency

High precise tuning system

is required to save RF power

3.17μm 1kHzCavity length over 1.3 meter

Cavity sensitivity 315 Hz/mm


Why SCRF Cavity resonance Challenging

Ref: Shuichi Noguchi, SRF 2007, https://accelconf.web.cern.ch/accelconf/srf2007/TALKS/WE303_TALK.pdf

Loads seen by a tuner while assembly to cool down

Ref: Care report 2008-018-SRF1300 MHz cavity as an exampleSCRF Cavity and Tuner Related Technologies -Vikas Jain

Slow Tuner:- Mechanism of these tuners are driven by cryo-compatible steppermotors or DC motors.

Slow tuner provides linear movements up to few mm in the coarse tuning rangewhich changes RF frequency up to few hundreds of kHz (max.)

Fast tuner:- is required to overcome/ reduce the effect of microphonic detuning,active vibration detuning and Lorentz dynamic detuning.

This tuner can operate at a fine frequency range of the order of few Hz and themovement provided is a few mm to few tens of mm.

The motion in fast tuner is obtained using PZT (lead zirconate titanate),Magnetostrictive material etc.

Two stage tuning system


Typical Tuning system requirements for 650 MHz cavity

Slow tuning control

• A cryo-compatable geared stepper motor is used in tuning

• Slow tuning is done by controlling the motion of stepper motorin cryogenic ambient

To stepper motor

GUIRS232

Current controlled Stepper motor driver

FPGA IO card

Phase sequencerDriver

Geared (256:1) Cryo-compatable stepper motor(-270°C to 40 °C)Torque = 30Nm

The current in stepper motorwinding is controlled bychopping the voltagewaveform.


Fast tuning control• A multilayer Piezo-actuator is used in fast tuning mechanism

• Piezo-driver has been developed to excite piezos with half-sinusoidal pulses with pulse width ≥ 1 ms at repetition rate of 50 Hz

Piezo-actuator

GUIRS232

FPGA IO card

12-bit DACLow pass

filter

Clock

Piezo-amplifier

To Piezo-actuatorsFree stroke = 56 μmBlocking force= 4 kN


Dynamic LFD

The dynamic behavior of the LFD

during the 0.8 ms flattop of RF pulse at

10Hz is shown:

• Several hundreds of Hz of

detuning are expected during the

flat-top phase when gradients of 20

MV/m or more are achieved

•At 34MV/m detuning is -800 Hz

1300 MHz Tesla Cavity as an example


Mitigating effect of dynamic LFD by Driving Piezo in PulseLongitudinal tuning sensitivity =315 Hz/μm

Actual LFD =-800 Hz

Cavity longitudinal displacement due to LFD =

Piezo Signal:

• Piezo pulse shape = Single half sinusoidal pulse

• Piezo Pulse Width = 2.5 ms

• Piezo Pulse repetition rate = RF pulse repetition rate

• Piezo pulse amplitude = 0 - 200V (depending upon the detuning value an hysteresis curve)

https://jra-srf.desy.de/e86/e575/e605/infoboxContent614/care-thesis-08-001.pdf

Tuner assembly with single cell cavity

• Tuner end rings is attached with cavity with special linkage .

• Two Piezo-electric actuators are assembled in series withblade tuner.

• Tuning analysis for single cell cavity has been carried-outusing a combined electromagnetic-structural model inANSYS

• Tuning sensitivity of ~2.5 kHz/microns was computed

• Stiffness of the cavity was found to 290 kg/mm

RRCAT’s works on Tuner

650 MHz SCRF cavitity Tuner Development

HB650 cavity with IIFC’s Lever Tuner

Fabricated Tuner Assembly


Tuner Assembly with Test Stand

Spring stiffness Kc = 5.68 kN/mm

Tuner Mechanism mechanical advantage N0 = 18.98 @ No Load

Tuner Mechanism mechanical advantage NL = 21.65 @ 5.6kN Load

Tuner Stiffness KT = KC*(NL – N0 )/ N0 ~ 40.3 kN/mm (Using approx. formula)

Estimation of Tuner Stiffness

Testing of Tuner at load and no load

Stiffness of 4 Belleville Spring : ➔ Stiffness of cavity


Test Setup of HB650 single-cell cavity with X-link tuner at 77K

❖ Stepper motor actuation at 77K in 2.5 rotation of power screw changes RF frequency by 80kHz.

➔ shows slow tuning resolution = 0.64 Hz/step which is better than expected value of 10Hz/step

❖ Piezo-actuator is operated at 77K at in pulse mode and changes in the maximum RF frequency of 1.12 kHz is

observed at 88V.




Patent on X-link SCRF cavity tunerA patent on “A method and device for tuning SCRF Cavity”– (Japanese, European and American) has been granted.

Experimental Results of Amplitude, Phase, Slow tuning by motor and Fast Tuning by Piezo


Summary

➢SCRF cavities are future of any modern accelerator

➢SCRF cavity design needs multi-domain knowledge

➢Cavity needs dedicated facilities for fabrication, processing, VTS testing,

Dressing and HTS testing.

➢Most of SCRF infrastructure available at RRCAT.

➢Frequency tuner designs have advanced significantly to meet the needs

of the high gradient and/or pulsed superconducting accelerators

➢Testing of cavity tuner with single-cell cavity is a unique idea to qualify

tuner and its associated systems


1. H.Padamsee, J. Knobloch, T. Hays “ RF Superconductivity for Accelerators”, John Wiley&Sons, Inc; ISBN 0-471-15432-6

2. Proceedings of the Workshops on RF Superconductivity 1981 –2014 –Available online from www.jacow.orgup to 2013

3. A.W.Chao, M. Tigner “Handbook of Accelerator Physics and Engineering”, World Scientific PublishingCo, P.O.Box128, Farrer Road, Singapore, ISBN 981023500

4. Mechanical Characterizations of the piezo blade tuners (CARE note2006-003-HIPPI)

5. The fast piezo blade tuners for SCRF resonators C. Pagani, A. Bosotti, P. Michelato INFN Milano LASA

6. ILC Coaxial blade tuner :C. Pagani, A. Bosotti, P. Michelato INFN Milano LASA etc.

7. Active Compensation of Lorentz Force detuning of A TTF 9 cell cavity in cryholab. G. Devanz, P. Bodland,M. Jaques etc. CEA –Saclay, 91191Gifsur- Yvette Cedex France.

8. Compansation of Lorentz Force detuning of a TTF-9-cell cavity with a new integrated piezo tuner. By G. Devanz ,P. Bodland,M. Jaques etc. CEA –Saclay, 91191Gifsur- Yvette Cedex France

9. Mechanical Study of SACLY Piezo tuner (PTS, piezo tuning system), P Bosland,Bo Wu, DAPNIA-CEA Saclay. CARE note 2005-004-SRF

10. A new tuner for tesla by D. Barni, A Boscotti, C. Pagani INFN Milano, LASA Italy, R lenge H.B. Peters DESY.

11. New Approach to tuning of Tesla resonator. By H. Kaiser, DESY, Hamburg. Geramny.

12. Magnetostrictive tuners for SRF cavities. A. Mavanur C-Y tai, C. H joshi etc.Energen encarporation, Lowell, MA01854 USA. PAC2003.

References:



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Vikas Jain RRCAT, Indore€¦ · Vikas Jain RRCAT, Indore Indo Japan Accelerator School cum Workshop IJAS - 2020, VECC, Kolkata. Outline • Introduction • Requirement of SCRF cavity