Development Activities at KEK 2017/8/9 Topical workshop on high - - PowerPoint PPT Presentation

▶
development activities at kek
SMART_READER_LITE
LIVE PREVIEW

Development Activities at KEK 2017/8/9 Topical workshop on high - - PowerPoint PPT Presentation

Jul 06, 2023 595 likes •872 views

The CW and Pulsed SRF Linac Development Activities at KEK 2017/8/9 Topical workshop on high repetition-rate XFEL physics and technology @Shanghai, China Kensei Umemori (KEK) on behalf of KEK-SRF group Outline Introduction SRF

slide-1
SLIDE 1

The CW and Pulsed SRF Linac Development Activities at KEK

2017/8/9 Topical workshop on high repetition-rate XFEL physics and technology @Shanghai, China Kensei Umemori (KEK) on behalf of KEK-SRF group

slide-2
SLIDE 2

Outline

  • Introduction
  • SRF activities at KEK
  • Development of pulse SRF accelerator

➢ILC ➢STF

  • Development of CW SRF accelerator

➢Compact ERL (cERL) ➢ERL based EUV-FEL

  • SRF R&D

➢Nitrogen doping (for High-Q operation) ➢Nitrogen infusion (for High-Q and high-gradient operation) ➢CW SRF gun

  • Summary
slide-3
SLIDE 3

Merit of Superconducting cavity

  • High accelerating voltage can be obtained due to very small

surface loss.

➢For example, typical surface losses for 1.3GHz cavity are 10W for 10MV and 100W for 33MV (CW)

Demerit of superconducting cavity

  • He refrigerator is essential to cool SRF cavities and to keep

temperature.

➢Several hundreds times of electric power is needed for operation of He refrigerator to keep 2.0K. Lower heat load (high-Q operation) is important

  • High-Q (low heat load)

⇒ Reduce surface loss ⇒ Reduce cryogenic load ⇒ Reduce construction and operation cost

Surface resistance is 6 order smaller than normal conducting cavity (1.3GHz)

Introduction

𝑸 = 𝑾𝟑 𝑺

slide-4
SLIDE 4

Important parameters for SRF

Qo=2πf x U / P U: Stored energy in cavity [J] P: Loss at cavity surface [W] Qo∝1/Rs Rs: Surface resistance[Ω] Eacc: Accelerating gradient [MV/m]

One example of measurement for SRF cavity

Qo Eacc[MV/m] Rs[Ω] 1/T [1/K]

slide-5
SLIDE 5

SRF Activity at KEK

slide-6
SLIDE 6

6

Nano-beam R&D SRF R&D Cavity fabrication

6th IHEP-KEK SCRF Collaboration Meeting (July 15, IHEP)

cERL

CW SRF R&D

slide-7
SLIDE 7

ILC / STF

slide-8
SLIDE 8

ILC Acc. Design Overview (in TDR)

8

e- Source e+ Main Liinac e+ Source

e- Main Linac Item Parameters C.M. Energy 500 GeV Length 31 km Luminosity 1.8 x1034 cm-2s-1 Repetition 5 Hz Beam Pulse Period 0.73 ms Beam Current 5.8 mA (in pulse) Beam size (y) at FF 5.9 nm SRF Cavity G. Q0 31.5 MV/m Q0 = 1x10 10

main linac bunch compressor damping ring source pre-accelerator collimation final focus IP extraction & dump KeV few GeV few GeV few GeV 250-500 GeV

Nano-beam Technology SRF Accelerating Technology

Key Technologies

Physics Detectors Damping Ring

6th IHEP-KEK SCRF Collaboration Meeting (July 15, IHEP)

slide-9
SLIDE 9

ILC Site Candidate Location in Japan: Kitakami

Oshu Ichinoseki Ofunato Kesen-numa Sendai Express- Rail High-way IP Region

  • Preferred site selected by JHEP community,
  • Endorsed by LCC, in 2013

6th IHEP-KEK SCRF Collaboration Meeting (July 15, IHEP) 9

slide-10
SLIDE 10

15/Jul/2017 6th KEK-IHEP Collaboration Meeting

10

STF Cryomodules

STF Cavity Package

  • Proc. in IPAC16
  • Proc. in IPAC12
  • Proc. in SRF11
  • Proc. in SRF09

STF-1 (4 cavities) in 2008 Quantum Beam (2 cavities) in 2012 Capture CM in STF-2 accelerator S1-Global (4+4 cavities) in 2010 STF-2 (12 cavities) in 2014~

4 cavities per batch

slide-11
SLIDE 11

15/Jul/2017 6th KEK-IHEP Collaboration Meeting

11

Capture CM

(Two cavities)

CM1 + CM2a

(Twelve cavities)

STF-2 Accelerator Layout

To be constructed

Cold box Cold box RF Gun

Chicane

To be constructed

View from upstream View from downstream Waveguide system

slide-12
SLIDE 12

15/Jul/2017 6th KEK-IHEP Collaboration Meeting

12

Summary of Cavity Performance

Not measured in 3rd C.T.

Significantly degraded in 3rd C.T. Kt for CAV#1 and #8 was never changed!

slide-13
SLIDE 13

15/Jul/2017 6th KEK-IHEP Collaboration Meeting

13

Vector-sum Operation with 8 Cavities

30 min

35.9 MV/m 35.7 MV/m 31.8 MV/m 28.3 MV/m 30.6 MV/m 27.3 MV/m 30.1 MV/m 27.8 MV/m

30.9 MV/m ± 0.02 MV/m 46Hz ± 1.8Hz

Each pulse for 8 cavities Trend graph of Ave. Eacc and Δf during vector-sum operation

They satisfy the ILC specification!

slide-14
SLIDE 14

Compact ERL

slide-15
SLIDE 15

Injector-linac Dump

Recirculation (return) loop

Merger

Compact ERL

Photocathode DC gun (Not SRF Gun)

Main linac module Main-linac

Input couplers Cryostat Tuner HOM absorber Two 9-cell SC cavities

e- HOM damped (for 100mA circulation to suppress HOM-BBU in design) 9-cell cavity (ERL-model2)× 2 Requirement was satisfied at V.T. Heavy F.E was met @9-10MV/m after string assembly.

3MeV 20MeV

Input Coupler

HOM Coupler & RF Feedthrough 2-cell Cavity

Tuner

Cryostat

e-

Injector module

2-cell cavity × 3 Double coupler

RF frequency: 1.3 GHz Input power : 10kW/coupler (10mA, 5MeV) 180kW/coupler (100mA, 10MeV) Eacc: 7.6MV/m（5MeV） 15MV/m (10MeV) Unloaded-Q: Q0 > 11010

Target Energy : 35MeV  Change 20MeV due to field emission

RF frequency: 1.3 GHz Input power : 20kW CW (SW) Eacc: 15 MV/m（design） Unloaded-Q: Q0 > 11010

Requirement was satisfied at V.T and for initial 10mA requirement . 15

Nominal beam energy 35 MeV  20MeV Nominal Injector energy 5 MeV 2.9MeV Beam current 10 mA (initial goal) 100mA (final) Normalized emittance 0.1 ‒ 1 mmmrad Bunch length (bunch compressed) 1-3ps (usual) 100fs (short bunch) Design parameters of the cERL

Prototype for 3-GeV class ERL light source

  • r high-current CW linac
slide-16
SLIDE 16

Beam current upgrade

2016 Japan Accelerator Society Meeting, Shogo Sakanaka

Apr/2015 An X-ray image of a hornet which was taken using LCS-produced X-ray (2015.Apr)

SDD

HyPix-3000 from RIGAKU

Experiment① Laser Compton scattering

Bright X-ray LCS beam can be generated by using 0.9 mA with low emittance beam. Imaging was successfully taken.

Experiment② THz generation

Electron bunch was compressed to ~250fs using sextupole magnet. THz component generated by a coherent transition radiation (CTR) monitor is analyzed by a Michelson interferometer.

  • Beam current increased step by step.
  • Now 1mA(CW) electron beam is operated with energy recovery mode.

From a rough estimation by CTF spectrum, 250 fs bunch length was achieved by bunch compression THz radiation was successfully generated

slide-17
SLIDE 17

E=2.9 MeV E=19.9 MeV E=2.9MeV ML1 ML2

Energy recovery at main linac

Cavity voltage： 8.56 MV (ML1), 8.57 MV (ML2) Current: 0 ～ 900uA

Pin – Pref ～ Ploss + Pbeam Δ(Pin – Pref) ～ Pbeam ← Beam loading

ML1+ML2 ML1 ML2

Energy recovery ML1:Acc ML2: Decc Energy loss measured from the graph = 4 W. (+-4W) Required power without recovery is : 17.14 MV x 900 uA = 15.4 kW

Energy Recovery is almost 100.0% (error +-0.03%) ※ different slop of ML1/ML2 come from energy difference of (acceleration – deceleration) beam ML

slide-18
SLIDE 18

Typical one day operation of cERL SRF

8 hours Vc (ML1&2) 8.57MV

Vac.(ML1) (~10^-7Pa)

  • Vac. (ML2) (~10^-8Pa)

Piezo voltages Df = 1kHz

Piezo feedback works well

8 hours

Vacuum pressure in cavities (~ 10-7 Pa)

GV open GV close

34 m3/h; ML cavities OFF Eacc in cavities (~3.2 MV/m) 3.5 hours

12:00 18:00

QL~1*10^7

55 m3/h; ML cavities ON

12:00 24:00

Control voltages for piezo tuners (for 3 cavities)

Df = 2 kHz

Piezo FB: ON

12:00 18:00

Piezo tuner Piezo tuner Field & Vac Field & Vac & loss

24:00 12:00

Injector Main linac

Drift due to temperature change of tuner system (Stop 2K operation during night time)

No data

Synchronized with 80K line temperature

INJ ML

slide-19
SLIDE 19

Proposal of 10kW class ERL based EUV-FEL

Injector Linac

Beam Dump

1st Arc

2nd Arc Gun

Merger

Parameter Specification Wavelength 13.5 nm Output power 10 kW Bunch chare 60 pC Beam energy 800 MeV Accelerating gradient 12.5 MV/m (main linac) Number of SRF cavity 9-cell cavity×64 Beam repetition 162.5 MHz Beam current 9.75 mA

10MeV, 10mA 10MeV, 10mA 10kW FEL

  • utput

Presented by Norio NAKAMURA ERL2015（https://www.bnl.gov/erl2015/ ）

Bunch compressed decompressed

Energy recovery Is needed.

Design strategy (main linac) Epeak/Eacc is 1.5 times reduced from cERL cavity to

  • vercome field emission.

8.6 MV/m  12.5MV/m

Example of high current ERL-FEL

slide-20
SLIDE 20

SRF R&D

slide-21
SLIDE 21

N-infusion N-dope

  • A. Grassellino 「High grad/high Q via N

infusion」(LCWS2016) TTC meeting（2014/Dec） A. Melnychuk 「Update on N doping at Fermilab」

25mTorr N2 @800 deg C, 2min 25mTorr N2 @120 deg C, 48hours

  • S. Aderhold / A. Grassellino (TTC@Saclay)

High-Q High-Q & High-G

  • A. Romanenco (Linac14)

N goes to several tens um N goes to around ten nm

High-Q for CW linac (ex. CW XFEL) High-Q & high-G for pulse linac (ex. ILC)

slide-22
SLIDE 22

Without N-dope ↓ ↑ Without N-dope

Results of N-doping at KEK large furnace (2.7 .7Pa N-dope, , 20min in )

All cases, Q-value became worse after N-doping.

  • We tried N-doping at KEK furnaces, but

results were not successful.

  • KEK furnace pumped by a diffusion

pump.

slide-23
SLIDE 23

N-dope/N-infusion trial using J-PARC furnace

  • J-PARC has oil-free furnace with

cryo-pump(10,000 litter/sec) and three TMPs(3,000 litter/sec x 3).

  • Vacuum level reached to ~1e-6 Pa.
  • Normally used for degassing of

beam-duct and components.

slide-24
SLIDE 24

VT results of N-doping

VT4(reference) Rs=3.3nΩ VT5(N-dope) Rs=1.8nΩ VT6(add EP) Rs=1.2nΩ VT4(reference measurement) N-doping 15um EP  VT5 Additional 10um EP →VT6

  • Magnetic field canceled. (< 1mG)
  • Cooled down with thermal gradient

Very high Q up to high field Q = 2.4e11@11MV/m, 1.4K Q = 3.3e10@14MV/m, 2.0K Quench at 19MV/m No field emission First success in Japan

Quench

slide-25
SLIDE 25

VT results for N-infusion

Q-slope above Eacc > 5 MV/m

VT11: 2.9 nΩ VT12: 2.9 nΩ

  • Magnetic field canceled. (< 1mG)
  • Cooled down with thermal gradient
  • Transfer to KEK
  • HPR (No EP applied)
  • Assembly

 Degradation was

  • bserved for > 5 MV/m

 Eacc was limited at 33MV/m by quench at 225 degree equator  No field emission

slide-26
SLIDE 26

SRF gun development

107 108 109 1010 1011 0.01 0.1 1 10 100 10 20 30 40 50 60 70 80 8th VT pi-mode pi-1st pi-2nd pi-1st pi-2nd Qo X-ray High sensitivity [uSv] Esp[MV/m] Qo X-ray

No X-ray

pi

Quench

  • SRF gun cavity, for high-current

CW, was designed, fabricated and tested.

  • With choke structure and

cathode rod, it could reach Esp=75MV/m.

  • Test with cathode is now ongoing.

Target

slide-27
SLIDE 27

Summary

  • KEK developed technology for L-band superconducting

cavities.

  • Following activities are introduced.

➢ILC / STF (pulse) ➢cERL (CW)

  • R&D is on-going to realize high performance of SRF

cavities.

➢High-Q operation (Nitrogen doping) ➢High-Q and high-gradient operation (Nitrogen infusion)