AWLC2014, FNAL, May 12-16, 2014 1

LCLS-II Power Coupler

Nikolay Solyak, Ivan Gonin, Andrei LuninC.Adolphsen - SLAC

TTC meeting, March 23-27, 2014

AWLC2014, FNAL, May 12-16, 2014 2

Item Spec CommentDesign EuXFEL Coupler 2009 Drawing Package with exceptions noted below

Max Input Power 7 kW CW Assume would run with full reflection

Minimum Qext Foreseen 1e7 Allows 16 MV/m with no beam and 6.6 kW input, and allows 6 MW beams with 33 kW input

Maximum Qext Foreseen 5e7 Match for 0.3 mA beams at 16 MV/m, 26 Hz BW

Reduction in Antenna Length 8.5 mm Maintain 3 mm rounding

Range of Antenna Travel +/- 7.5 mm Range measuredPredicted Qext Min Range Qext Max Range

3.6e6 – 4.7e6 – 7.5e61.0e8 – 1.1e8 – 1.5e8 Assuming +/- 5 mm transverse offsets

Warm Section Outer Cond Plating 10 um +/- 5 um, RRR = 30-80 Nominal EuXFEL

Warm Section Inner Cond Plating 100 um +/- 10 um, RRR = 30-80 Modified – Temp Rise < 150 degC for 14 kWCold Section Outer Cond Plating 10 um +/- 5 um, RRR = 30-80 Nominal EuXFELCenter Conductor HV Bias Optional Use flex copper rings that can be replaced with

existing capacitor rings if HV bias neededWarm and Cold e-Probe ports req No Do not expect multipacting at low power

Warm Light Port Required No Do not expect arcs at low powerMotorized Antenna Yes – max step = 50 um Changes Qext by 1%

RF Processing 7 kW CW with full reflection – vary reflected phase by 180 deg

For initial couplers, use pulse power processing at SLAC

LCLS-II Coupler Technical SpecsPreliminary

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Fundamental Power Coupler (FPC)

• XFEL (modified TTF3) coupler is not meet LCLS-II requirements– Tuning range (1.e6-1.e7) not cover required Qext=4.e7– Overheating of the internal bellow in warm section at 7kW CW power at

full reflection (effective power ~14kW)

• Two modifications were proposed to address these problems (R&D program: Four coupler modification test)

– Cut antenna 8.5mm to increase Qext

– Increase copper plating of internal inner conductor of warm section from 30 μm to 100-150 μm to eliminate overheating

TTF-3 design

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Inner conductor: Temperature distribution for different thickness of copper coating and different RRR (15kW, TW-regime)

Copper plating at inner part is 100 micronsData is simulated for RRR=10

Conclusion: TTF3 Coupler need to be modified for LCLS-II. 100-150 μm Cu plating inner conductor in warm section of coupler is possible solution.

Tmax limit

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Qext ~ 2.4·107

Antenna tip cut by 8.5 mm

Qmin Qnom Qmax

Original coupler 1.106 3.5·106 1.8·107

Tip cut by 7 mm 3.8·106 1.6·107 8.5·107

Tip cut by 8.5mm 5.0·106 2.4·107 12·107

R3

A. Lunin, 12/13/13

Nominal positions

R3

Original XFEL antenna

Qext ~ 4.0·106

LCLS-II Cavity Qext Computation

LCLS-II specs

Q ext– range for ±7.5mm antenna tuning

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Conclusion• For LCLS-II coupler the most sensitive parameter is a horizontal antenna shift/tilt. • ± 5 mm shift change Qext by -5%/+50%. Vertical tolerances are relaxed.

Vert. antenna tilt(up and down)

Horiz. antenna tiltalong cavity axis

Qmin Qnom Qmax

Original coupler 0.7·105 (3.0 .. 6.5) ·106 3.0·107

Tip cut by 8.5 mm 5.5·106 (2.3 .. 3.8)*·107 1.2·108

XFEL

LCLS-II

XFEL

Qext sensitivity to antenna displacements (ILC vs. LCLS-II)

A.Lunin

Horizontal

Vertical

Horizontal

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TW TW power

2K, W 4K, W 80K, W Tmax K

TTF-III as is 7kW 0.13 1.24 14.2 404

Helium, 1atm 7kW 0.13 1.27 17.3 316

LCLS2 (100µm) 7kW 0.13 1.25 15.5 326

LCLS2; 100/200µm 15kW 0.26 2.28 29.2/30 425/356

Power Losses and max. Temp

I.Gonin (FNAL)

TTF-3 Coupler: Inner coating 30µm, outer coating 10µm.

Helium, P=1atm

Window force 160N

Ivan Gonin, FNAL

Helium cooling of the warm section

7kW TW

TTF3 original coupler 7kW TW

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Full reflection: E-field distribution in LCLS-II coupler, Q=4e7, Pin=7kW

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L=0 LCLS-II Coupler. Inner coating 100µm. Outer coating 10µm

Maximum Temperature vs. LOn resonance Tmax ~425K

Temperature distribution along surface of inner conductor for TW and SW ( L=0mm & L=65mm )

PEC BC

L

On resonance

Off resonance

Coupler operation at 7kW CW at full reflection

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Coupler test in HTS -1

Operational for ~5 yrs (~2 cavity/month throughput)– 1.3 GHz and 3.9 GHz cavities, ~1.5 ms and 9ms RF pulses– Now HTS upgraded for CW operation (commissioning)– Priorities in FY14 (CW regime)

• HOM feedthu’s (XFEL and JLAB designs)• 3 tests of high-Q0 dressed cavity (1 dressed to ILC helium vessel and 2 dressed to LCLS-II vessel)• 2 modified at SLAC Power Couplers• Integrated test of dressed cavity with Slow/Fast tuners, Frequency control and μ-phonics

Active Magnetic shielding

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500 mGs

- 500 mGs

Inside 1-layer magnetic shielding Max magnitude < 45mGs

Inside 1-layer magnetic shieldingafter active correction by coilsMax magnitude < 6mG

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HTS test preliminary scheduleTest# and goals Start

2014 Cav. type

Helium Vessel

HOM antenna

Couple(cold)

Coupler(warm)

Magn shield

Tuner RF

1:HTS commissioning, HOM feedthru, μ-phon now RI26 ILC XFEL variable None 1L+coil Blade 50W

2: High Q0 cavity #1 June 15 AES11 ILC non variable None 1L+coil None 50W

3: FPC cold modif, μ-phonics study July 1 RI26 or

AES11 ILC XFEL FPCmodif

FPCHe cooled 1L+coil blade IOT

4: FPC modified; μ-phonics study July 25 RI26 or

AES11 ILC JLAB FPCmodif

FPC#1modif 1L+coil blade IOT

5: High-Q cav. #2 FPC#1 Aug 20 HQ#2 LCLS-II XFEL FPC

modifFPC#1modif 1L+coil No

tuner IOT

6:High-Q#3 integrated FPC#2 Sept.20 HQ#3 LCLS-II JLAB FPC

modifFPC#2modif 2-layer Lever

tuner IOT

7: high-Q#2 integrated Tuner reliability Oct.15 HQ#2 LCLS-II XFEL FPC

modifFPC#1modif 2-layer lever

tuner IOT

Assumptions about readiness:• 2 modified “cold” parts of FPC: April (done)• 2 modified “warm” parts of FPC: June

• 4 LCLS-II type of Helium Vessels: end of July• JLAB feedthru: end of June• New lever tuner and 2-layer shielding: Sept.

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Conclusion

• XFEL coupler not meet LCLS-II specifications. Problems: Qext range and overheating

• 2 major modification was proposed: shorter antenna (by 8.5mm) and thicker (>100μm) Cu plating of inner conductor in warm section to address these problems:

• Modifications are in progress at SLAC (cold part modification was done, warm sections of couplers will be ready by the end of June 2014, plated at CPI and processed at SLAC).

• HTS tests is essential part of design verification program for LCLS-II.– 3 high Q0 (N2 doped) integrated tests , (HOM feedtru’s, FPC, Helium vessel, Tuner,

magnetic shielding)– two modified FPC assembled on high-Qo cavity.

• Next step: start FPC procurement after HTS tests.– Documentations and review.