Superconducting radiofrequency accelerating structures
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Superconducting Radiofrequency Accelerating Structures. Lutz Lilje DESY -MPY- ‘Physics at the Terascale’ 406. WE-Heraeus-Seminar Bad Honnef 30.4.2008. Acknowledgement. Several people were supporting with viewgraphs etc. H. Hayano KEK H. Padamsee Cornell

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Superconducting radiofrequency accelerating structures

Superconducting Radiofrequency Accelerating Structures

Lutz Lilje

DESY -MPY-

‘Physics at the Terascale’

406. WE-Heraeus-Seminar

Bad Honnef

30.4.2008


Acknowledgement

Acknowledgement

  • Several people were supporting with viewgraphs etc.

    • H. Hayano KEK

    • H. Padamsee Cornell

    • J. Sekutowicz, D. Reschke, W. Singer DESY

Lutz Lilje DESY -MPY-


References

References

  • Superconducting RF

    • RF Superconductivity for Accelerators, H. Padamsee, J. Knobloch, and T. Hays, John Wiley & Sons, 1998.

    • The Superconducting TESLA Cavities, B. Aune et al., PRST-AB, 3, September 2000, 092001.

  • SRF Workshop Tutorials

    • http://www.lns.cornell.edu/public/SRF2005/program.html

    • http://www.pku.edu.cn/academic/srf2007/program.html#tutorial

  • Accelerators

    • XFEL: http://xfel.desy.de/tdr/tdr/index_eng.html

    • ILC: http://www.linearcollider.org/cms/

Lutz Lilje DESY -MPY-


Outline

Outline

  • Superconducting Radiofrequency Accelerating Sturctures (‘SRF Cavities‘)

    • History

    • Properties

    • Technology

  • Example for Accelerator Systems

    • XFEL and ILC

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

1. Introduction and History

Milestones that led to accelerators based on SRF

Superconductivity

RF Acceleration

1924: Gustaf Ising (Sweden)

The First Publication on the RF Acceleration, Arkiv för Matematik, Astronomi och Fysik,18 (1924) 1-4.

1908: Heike Kamerlingh Onnes (Holland)

Liquefied Helium.

1911: Heike Kamerlingh Onnes

Discovered Superconductivity.

1928: Rolf Wideröe (Norway, Germany)

Built the first RF Accelerator.

Arch. für Elektrotechnik 21 (1928),387-406.

1928-34: Walther Meissner (Germany)

Discovered Superconductivity of Ta, V, Ti and Nb.

1930: Russell and Sigurd Varian (USA)

Invented Klystron.

1947: Luis Alvarez (USA)

Built first DTL (32 MeV protons).

1947: W. Hansen (USA)

Built first 6 MeV e-accelerator, Mark I (TW-structure).

J. Sekutowicz, SRF2007 Beijing

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

1. Introduction and History

Superconductivity

RF Acceleration

1961: Bill Fairbank (Stanford Univ.) presented the first proposal for a superconducting accelerator.

1964: Bill Fairbank, Alan Schwettman and Perry Wilson (Stanford University)

First acceleration of electrons with sc lead cavity.

1967: John Turneaure (Stanford University)

Epeak =70 MV/m and Q~1010 in 8.5 GHz cavity !!

1968-1981: Mike McAshan, Alan Schwettman, Todd Smith, John Turneaure and Perry Wilson (Stanford University)

Development and Construction of the Superconducting Accelerator SCA.

J. Sekutowicz, SRF2007 Beijing

Lutz Lilje DESY -MPY-


Why superconducting cavities

Why Superconducting Cavities?

  • Superconducting cavities offer

    • a surface resistance which is six orders of magnitude lower than normal conductors (NC)

    • high efficiency

      • even when cooling is included

    • low frequency, large aperture

      • smaller wake-field effects

    • high accelerating gradients

      • Theoretical limit for the between 45-55 MV/m depending on the cavity geometry

Lutz Lilje DESY -MPY-


Sns spallation neutron source

SNS (Spallation Neutron Source)

Beta = 0.8

800 MHz

Beta = 0.6

Lutz Lilje DESY -MPY-


Rare isotope seperator

58 MHz

117 MHz

Rare Isotope Seperator

350 MHz

175 MHz

700 MHz

700 MHz

Lutz Lilje DESY -MPY-


Accelerator facilities with scrf cavities number of cavities total active length

Accelerator Facilities with SCRF CavitiesNumber of cavities/total active length

1. Introduction and History

Dismantled Facilities

Operating Facilities

  • SCA 428m

  • S-DALINAC 1010m

  • CESR 41.2 m

  • CEBAF 320160m

  • KEK B-Factory 82.4m

  • Taiwan LS 1+10.3m

  • Canadian LS 1+10.3m

  • DIAMOND 30.9m

  • SOLEIL 41.7m

  • FLASH / TTF 4850m

  • SNS 8165m

  • JLab-FEL 2414m

  • LHC 166m

  • ELBE 66m

  • TRISTAN 3249m

  • LEP 288490m

  • HERA 1619m

J. Sekutowicz, SRF2007 Beijing

Lutz Lilje DESY -MPY-


Livingston plot for srf cavities courtesy h padamsee

Livingston plot for SRF cavitiesCourtesy H. Padamsee

Total >1000 meters

> 5 GV

Nb/Cu Technology

Lutz Lilje DESY -MPY-


High luminosity rings cesr

High luminosity rings (CESR)

• Low Impedance Shape

• Beam Power > 270kW

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

LHC

400 MHz

16 Nb/Cu Cavities

Lutz Lilje DESY -MPY-


Niobium bulk cavities

Niobium bulk cavities

CERN 350 MHz

TESLA 1,3 GHz

Darmstadt 3GHz

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

Accelerator Facilities with SCRF Cavities IINumber of cavities/total active length

1. Introduction and History

Tomorrow Facilities

Day after Tomorrow Facilities

  • CEBAF-12GeV 400216m

  • SNS-upgrade 117 98m

  • XFEL 800832m

  • ERL-Cornell 310250m

  • BESSY 144152m

  • 4GLS ~40~42m

  • RHIC-cooling 44 m

  • Shanghai LS…….

  • BEPC II 20.6m

  • RIA option 180122m

  • X-Ray MIT option 176184m

  • LUX ~40~50m)

  • FERMI Proton Linac 384370m

  • ERHIC………

  • ELIC …..

  • ARC-EN-CIEL 4850m

  • ILC ~15764~16395m

J. Sekutowicz, SRF2007 Beijing

Lutz Lilje DESY -MPY-


Overall layout of the european xfel

Overall layout of the European XFEL

3.4km


Ilc layout

ILC Layout

e+ production

e- e+ damping rings

e- source+ pre-acceleration

e+ pre-acceleration

target

e- transport line

e+ transport line

undulator

2-stage bunch compression

e+ main linac

e- main linac

2-stage bunch compression

e- beam dump

e+ beam dump

IP and 2 moveable detectors

Total length: ~31 km

Global Design Effort


Outline1

Outline

  • Superconducting Radiofrequency Accelerating Sturctures (‘SCRF Cavities‘)

    • History

    • Properties

    • Technology

  • Example for Accelerator Systems

    • XFEL and ILC

Lutz Lilje DESY -MPY-


Properties of cavities

Properties of Cavities

Example: cylindrically symetric cavity - Pillbox

with

J0, J1 Besselfunctions

Frequency:

Stored Energy:

Dissipated power:

Quality factor:

Geometry factor:

Lutz Lilje DESY -MPY-


Field distributions in cavities

Electric Field (Pillbox):

Field Distributions in Cavities

TM010 : accelerating mode

L (side view)

Magnetic Field :

Other modes : e.g. deflecting modes

D (front view)

Lutz Lilje DESY -MPY-


Field distributions in cavities1

Field Distributions in Cavities

Elliptical cavity:

Numerical solution for surface fields:

Relations for the surface fields to acclerating gradient:

Epeak/Eacc = 1,98 minimize this to reduce field emission

Bpeak/Eacc = 4,17 [mT]/[MV/m] minimize because of maximum critical

field of the superconductor

Lutz Lilje DESY -MPY-


Why superconducting cavities1

Why Superconducting Cavities?

  • SC cavities offer

    • a surface resistance which is six orders of magnitude lower than normal conductors (NC)

    • high efficiency

      • even when cooling is included

    • low frequency, large aperture

      • smaller wake-field effects

    • high accelerating gradients

      • Theoretical limit for the between 45-55 MV/m depending on the cavity geometry

Lutz Lilje DESY -MPY-


Enter superconductivity pure elements

Superconductor (Blue) / Superconductor under pressure (Light Blue)

From: SUPERCONDUCTING MATERIALS – A TOPICAL OVERVIEW, R. Hott et al. FZK

Enter Superconductivity: Pure Elements

Lutz Lilje DESY -MPY-


Enter superconductivity pure elements1

Superconductor (Blue) / Superconductor under pressure (Light Blue)

From: SUPERCONDUCTING MATERIALS – A TOPICAL OVERVIEW, R. Hott et al. FZK

Enter Superconductivity: Pure Elements

Lutz Lilje DESY -MPY-


Critical magnetic field for the rf case

Critical magnetic field for the RF case

  • RF field at 1,3 GHz is ‘ON’ for less than 10-9 s

  • If there are no nucleation centers (surface defects...) the penetration of the magnetic field can be delayed. Superheating!

Superheating fields:

Niobium properties:

 Theoretical accelerating field limits

What is really the fundamental limit for RF cavities?

}

Lutz Lilje DESY -MPY-


Rf superconductivity

RF superconductivity

  • The superconducting Cooper pairs have inertia.

  • Therefore the unpaired normalconducting ‘feel’ also a part of the electromagnetic RF fields.

     Superconductors have for temperatures T>0 K a surface resistance!

Lutz Lilje DESY -MPY-


Electric conductivity and surface resistance

Electric conductivity and Surface resistance

Surface resistance in two-fluid model (analogous to skin depth):

  • Resistance depends

    • strongly on the temperature, we need 2 K

    • quadratically on frequency: Limit for 3 GHz would be 30 MV/m.

    • on the mean free path, what purity do we need?

Surface resistance for superconductors in BCS theory:

Effective penetration depth:

Lutz Lilje DESY -MPY-


Surface resistance r s

Geometry factor:

G = 270 Ohm

Surface resistance:

Surface resistance Rs

RBCS(T)

700 nOhm @ 4,2K

RRES

~10 nOhm @ 2K

Lutz Lilje DESY -MPY-


Flux penetration into a superconductor

Flux penetration into a superconductor

Electron holography is used to make magnetic fluxons visible (Tonomura et al.)

Fluxons stick to defects !

This is good for magnets, but bad for cavities.

Lutz Lilje DESY -MPY-


Surface resistance and accelerating gradient

Surface resistance and accelerating gradient

  • One usually measures the Q(Eacc) curve:

    • Q0~(1/ Rsurf)

    • Quality factor will tell you how much you have to pay for the cooling power

    • Depends on the accelerating gradient e.g. field emission

    • Helps to understand the loss mechanisms especially is supported by temperature mapping

Lutz Lilje DESY -MPY-


Surface resistance and accelerating gradient1

Surface resistance and accelerating gradient

Test temperature: 1,6 K

Test temperature: 2K

XFEL

ILC

One-cell cavities

Lutz Lilje DESY -MPY-


Outline2

Outline

  • Superconducting Radiofrequency Accelerating Sturctures (‘SCRF Cavities‘)

    • History

    • Properties

    • Technology

      • Limitations and Remedies

  • Example for Accelerator Systems

    • XFEL and ILC

Lutz Lilje DESY -MPY-


Temperature mapping system

Temperature Mapping System

  • Example of a Temperature mapping:

  • the picture shows a Mercator projection of a single-cell cavity

  • strong localised heating spot on the equator

  • another band of heating around the equator in the high magnetic field (high current) region

Lutz Lilje DESY -MPY-


Example of a material defect

Example Of A Material Defect

Defect found with X-ray technique: Tantalum

Heating on the outside surface measured with carbon resistors

Lutz Lilje DESY -MPY-


Quality control of nb for cavities

Quality Control Of Nb For Cavities

  • Eddy current scanning of all sheets

    • measures change of electric resistance

    • 0.5mm depth, 40 μm defect dia. sensitivity

    • rejection rate of sheets about 5 %

  • SQUID scanning under development

  • Some special investigations are possible on demand

    • x-ray radiography (defect visualization)

    • x-ray fluorescence (defect element determination)

    • neutron activation (Ta distribution)

Lutz Lilje DESY -MPY-


Eddy current scanning

Eddy Current Scanning

  • Large tantalum inclusions (~200 mm) and places with irregular patterns from surface preparation (grinding)

Grinding mark

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

Result of eddy current scanning a Nb disc, dia. 265 mm

Real and imaginary part

of conductivity at defect,

typical Fe signal

Global view, rolling marks

and defect areas can be seen

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

Principal arrangement of SQUID scanning

Measured response from the back side of the sheet

Nb test sheet with .1mm Ta inclusions

Lutz Lilje DESY -MPY-


High resolution optical inspection

High-Resolution Optical Inspection

  • New development by japanese colleagues to reduce reflections

    • Improved lighting technique using flat electro-luminescense strips

    • Damping of vibrations

  • Resolution down to a few micrometer!

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

Courtesy Kyoto University / KEK

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

AC80: cat’s eye

@cell#5_equator

100μm

Courtesy Kyoto University / KEK

1mm

Lutz Lilje DESY -MPY-


Electron effects field emission

Electron Effects:Field Emission

  • Emission of e- from cavity surface in presence of high surface E-fields

  • Emitted e- impacts elsewhere on cavity surface, heating the surface and increase Rs

  • Limits the achievable Eacc in cavity

  • Primary limitation over past 5-10 years

    • Strongly related to the cavity handling

    • Very clean surface preparation and handling are needed

      • This is by no means trivial!

        • Especially for multi-cell cavities

      • On-going effort needed in quality control

Lutz Lilje DESY -MPY-


Field emission

Field Emission

Pictures taken from: H. Padamsee, Supercond. Sci. Technol., 14 (2001), R28 –R51

Particle causing field emission

Temperature map of a field emitter

Simulation of electron trajectories in a cavity

Lutz Lilje DESY -MPY-


Superconducting radiofrequency accelerating structures

Cleanroom Technology for SC Cavities

  • the small surface resistance of the superconducting necessitates avoidance of NC contaminations larger than a few mm

    • detailed material specification and quality control need to be done

    • tight specification for fabrication e.g. welds have to be implemented

    • clean room technology is a must (e.g. QC with particle counts, monitoring of water quality, documentation of processes)

The inter-cavity connection is done in class 10 cleanrooms

Lutz Lilje DESY -MPY-


State of the art multi cell accelerating structures for xfel and ilc

State-of-the-Art:Multi-cell Accelerating structures for XFEL and ILC

XFEL

ILC

Lutz Lilje DESY -MPY-


Outline3

Outline

  • Superconducting Radiofrequency Accelerating Sturctures (‘SCRF Cavities‘)

    • History

    • Properties

    • Technology

      • Limitations and Remedies

  • Example for Accelerator Systems

    • XFEL and ILC

Lutz Lilje DESY -MPY-


Properties of xfel radiation

Properties of XFEL radiation

  • X-ray FEL radiation (0.2 - 14.4 keV)

    • ultrashort pulse duration<100 fs (rms)

    • extreme pulse intensities1012-1014 ph

    • coherent radiationx109

    • average brilliancex104

  • Spontaneous radiation (20-100 keV)

    • ultrashort pulse duration<100 fs (rms)

    • high brilliance

spontaneous

radiation


Overall layout of the european xfel1

Overall layout of the European XFEL

3.4km


Xfel site in hamburg schenefeld

XFEL site in Hamburg/Schenefeld


After construction computer simulation

… after construction (computer simulation)

Building Phase 1


Xfel international project organization

  • XFEL Steering Committee ISC(Chair: J. Wood, UK)

  • Representatives of all countries intending to contribute to the XFEL facility

  • 13 countries have signed MoU (project preparation phase) in 2004

  • Nomination of European Project Team (Leader: Massimo Altarelli)

WG on Scientific and Technical issues STI(chair: F. Sette, ESRF)

WG on Administrative and Funding issuesAFI(chair: H.F. Wagner, Germany)

XFEL International Project Organization

Bi-lateral negotiations between Germany and signature countries on funding contributions are ongoing


Xfel principle schedule

XFEL Principle Schedule

2012/13

2014/15

2004

2006

preparation

construction

beam operation

2009: LCLS start operation (SLAC)

SASE1

SASE2+3,

project

start

spont. rad

industrialization of all Linac sub-systems

production

commissioning

acceptance test and installation

FLASH FLASH FLASH operation experience XFEL XFEL XFEL


Xfel tunnel

XFEL Tunnel

The XFEL tunnel layout was developed in several iterations.

A mockup is currently under construction.

Installation procedures

are under

study.


Distribution of workload

Distribution of Workload

  • Accelerator technology was and is a collaborative effort

    • Build on TESLA Collaboration

    • Some R&D support for from EU FP6 programs

      • E.g. CARE, EUROFEL, EUROTeV

  • Common In-Kind Proposal for XFEL cold linac by several labs


Accelerator technology collaborative effort

Accelerator Technology:Collaborative Effort

Length quantized n/2 (possibility of ERL)

Industrial study module assembly (M6 done, M8 autumn 2007)

Superferric magnet (CIEMAT)

BPM (Saclay)

2 more cryostats (TTF3/INFN) delivered

Integrated HOM absorber

TTF3-type coupler

Industrialization launched (Orsay)

Tuner w/piezo (Saclay)

LLRF development (collab. Warsaw/Lodz)


Xfel accelerator module cryomodule

XFEL Accelerator Module (Cryomodule)

2 K return

70 K shield

2.2 K forward

magnet current feedthrough

5 K forward

80 K return

40 K forward

8 K return

4 K shield

RF main coupler

2 K 2-phase

cavity


Performance of accelerator modules

Performance of Accelerator Modules


Outline4

Outline

  • Superconducting Radiofrequency Accelerating Sturctures (‘SCRF Cavities‘)

    • History

    • Properties

    • Technology

      • Limitations and Remedies

  • Example for Accelerator Systems

    • XFEL and ILC

Lutz Lilje DESY -MPY-


Ilc layout1

ILC Layout

e+ production

e- e+ damping rings

e- source+ pre-acceleration

e+ pre-acceleration

target

e- transport line

e+ transport line

undulator

2-stage bunch compression

e+ main linac

e- main linac

2-stage bunch compression

e- beam dump

e+ beam dump

IP and 2 moveable detectors

Total length: ~31 km

Global Design Effort


Main linac layout

Main Linac Layout

  • Length ~11 km x 2

  • Average gradient 31.5 MV/m

  • 2 tunnels diameter 4.5 m

Penetrations:

Cable & Plumbing

Waveguide

LLRF, Controls,

Protection Racks

Charger

Main Modulator

HV Pulse Transformer

Horizontal Klystron

LCW Chiller

AC Switchgear

Waveguide Distribution

System

Dwg: J. Liebfritz

Global Design Effort


State of the art multi cell accelerating structures for xfel and ilc1

State-of-the-Art:Multi-cell Accelerating structures for XFEL and ILC

XFEL

ILC

Lutz Lilje DESY -MPY-


Alternative developments for ilc

Alternative Developments for ILC

  • Cost reduction is a strong driving force for ILC

    • ~16000 cavities

  • New Material

    • Large-grain niobium Material

    • Less fabrication steps than standard material

  • New Shapes

    • ‘Low-loss‘ and ‘Re-entrant‘

    • Could reduce power dissipation at cryogenic temperatures

Global Design Effort


Large grain material jlab

Large Grain Material (JLab)

Global Design Effort


Xfel large grain multi cell with ep

XFEL: Large Grain Multi-cell with EP

Large-grain niobium material with etch (BCP) and electropolishing (EP)

Behaviour similar to DESY observations on single-cells

Global Design Effort


Alternative cavity shapes

Alternative Cavity Shapes

Global Design Effort


Superconducting radiofrequency accelerating structures

K. Saito et al.

Global Design Effort


60mm aperture re entrant cavity best eacc 59 mv m cornell kek collaboration

60mm-Aperture Re-Entrant CavityBest Eacc = 59 MV/mCornell-KEK Collaboration

H. Padamsee et al. WEPMS009

Global Design Effort


Summary and outlook

Summary and Outlook

  • Superconducting accelerating structures have become a standard tool in particle accelerators

    • High efficiency and high accelerating gradients are available

  • Technology for superconducting cavities is challenging

    • High gradients necessitate very small level of contamination

    • Quality control is key to good performance

  • XFEL will be an important stepping stone for ILC

    • Technology is fully transferable

    • Industrialization experience is very valuable

  • ILC Gradients have been achieved in several multi-cell cavities already

Lutz Lilje DESY -MPY-


Backup

Backup

Lutz Lilje DESY -MPY-


Xfel accelerator module cryomodule1

XFEL Accelerator Module (Cryomodule)

module to module connection

cold mass with cavities, magnet / BPM, HOM abs. beam pipe, valve

module end group

manual valve

beam position monitor

magnet package


Main linac rf unit overview

Main Linac RF Unit Overview

  • Bouncer type modulator

  • Multibeam klystron (10 MW, 1.6 ms)

  • 3 Cryostats (9+8+9 = 26 cavities)

  • 1 Quadrupole at the center

Global Design Effort


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