LCLS-II Power Coupler
Nikolay Solyak, Ivan Gonin, Andrei Lunin
C.Adolphsen - SLAC
TTC meeting, March 23-27, 2014
AWLC2014, FNAL, May 12-16, 2014
1
Preliminary
Item
Design
Max Input Power
LCLS-II Coupler Technical Specs
Spec
Comment
EuXFEL Coupler
2009 Drawing Package with exceptions noted below
7 kW CW
Minimum Qext Foreseen
1e7
Maximum Qext Foreseen
5e7
Reduction in Antenna Length
Range of Antenna Travel
Predicted Qext Min Range
Qext Max Range
Warm Section Outer Cond Plating
8.5 mm
+/- 7.5 mm
3.6e6 – 4.7e6 – 7.5e6
1.0e8 – 1.1e8 – 1.5e8
10 um +/- 5 um, RRR = 30-80
Assume would run with full reflection
Allows 16 MV/m with no beam and 6.6 kW input,
and allows 6 MW beams with 33 kW input
Match for 0.3 mA beams at 16 MV/m, 26 Hz BW
Maintain 3 mm rounding
Range measured
Assuming +/- 5 mm transverse offsets
Nominal EuXFEL
Warm Section Inner Cond Plating
Cold Section Outer Cond Plating
Center Conductor HV Bias
100 um +/- 10 um, RRR = 30-80 Modified – Temp Rise < 150 degC for 14 kW
10 um +/- 5 um, RRR = 30-80 Nominal EuXFEL
Optional
Use flex copper rings that can be replaced with
existing capacitor rings if HV bias needed
Warm and Cold e-Probe ports req
No
Do not expect multipacting at low power
Warm Light Port Required
Motorized Antenna
RF Processing
No
Yes – max step = 50 um
Do not expect arcs at low power
Changes Qext by 1%
7 kW CW with full reflection – For initial couplers, use pulse power processing at
vary reflected phase by 180 deg SLAC
AWLC2014, FNAL, May 12-16, 2014
2
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
AWLC2014, FNAL, May 12-16, 2014
3
Inner conductor: Temperature distribution for different thickness of
copper coating and different RRR (15kW, TW-regime)
Tmax limit
Data is simulated for RRR=10
Copper plating at inner part is 100 microns
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.
AWLC2014, FNAL, May 12-16, 2014
4
LCLS-II Cavity Qext Computation
Qmin
LCLS-II specs
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
Nominal positions
Q ext– range for ±7.5mm antenna tuning
Antenna tip cut by 8.5 mm
Original XFEL antenna
Qext ~ 4.0·106
Qext ~ 2.4·107
R3
R3
AWLC2014, FNAL, May 12-16, 2014
A. Lunin, 12/13/13
5
Qext sensitivity to antenna displacements (ILC vs. LCLS-II)
Horizontal
LCLS-II
Horizontal
XFEL
Vertical
Vert. antenna tilt
(up and down)
XFEL
Horiz. antenna tilt
along 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
A.Lunin
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.
AWLC2014, FNAL, May 12-16, 2014
6
TTF-3 Coupler: Inner coating 30µm, outer coating 10µm.
Helium cooling of
the warm section
7kW TW
TTF3
original
I.Gonin
(FNAL)coupler
7kW TW
Helium,
P=1atm
Window force
160N
Power Losses
and max. Temp
Ivan Gonin,
FNAL
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
AWLC2014, FNAL, May 12-16, 2014
7
Full reflection: E-field distribution in LCLS-II coupler, Q=4e7, Pin=7kW
AWLC2014, FNAL, May 12-16, 2014
8
Coupler operation at 7kW CW at full reflection
PEC BC
L L=0 LCLS-II Coupler. Inner coating 100µm. Outer coating 10µm
Temperature distribution along surface of inner
conductor for TW and SW ( L=0mm & L=65mm )
Maximum Temperature vs. L
AWLC2014, FNAL, May 12-16, 2014 On resonance Tmax ~425K
9
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)
•
•
•
•
10
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
AWLC2014, FNAL, May 12-16, 2014
Active Magnetic shielding
500 mGs
- 500 mGs
Inside 1-layer magnetic shielding
Max magnitude < 45mGs
Inside 1-layer magnetic shielding
after active correction by coils
Max magnitude < 6mG
AWLC2014, FNAL, May 12-16, 2014
11
HTS test preliminary schedule
Test# and goals
1:HTS commissioning,
HOM feedthru, μ-phon
2: High Q0 cavity #1
3: FPC cold modif,
μ-phonics study
4: FPC modified;
μ-phonics study
5: High-Q cav. #2
FPC#1
6:High-Q#3 integrated
FPC#2
7: high-Q#2 integrated
Tuner reliability
Start
2014
Cav.
type
Helium
Vessel
HOM
antenna
Couple
Coupler
(cold)
now
RI26
ILC
XFEL
ILC
non
ILC
XFEL
ILC
JLAB
HQ#2
LCLS-II
XFEL
Sept.20 HQ#3
LCLS-II
JLAB
Oct.15
LCLS-II
XFEL
June 15 AES11
July 1
July 25
Aug 20
RI26 or
AES11
RI26 or
AES11
HQ#2
Assumptions about readiness:
• 2 modified “cold” parts of FPC: April (done)
• 2 modified “warm” parts of FPC: June
Tuner
RF
(warm)
Magn
shield
variable
None
1L+coil
Blade
50W
variable
None
1L+coil
None
50W
FPC
modif
FPC
modif
FPC
modif
FPC
modif
FPC
modif
FPC
He cooled
FPC#1
modif
FPC#1
modif
FPC#2
modif
FPC#1
modif
1L+coil
blade
IOT
1L+coil
blade
IOT
1L+coil
2-layer
2-layer
No
tuner
Lever
tuner
lever
tuner
IOT
IOT
IOT
• 4 LCLS-II type of Helium Vessels: end of July
• JLAB feedthru: end of June
• New lever tuner and 2-layer shielding: Sept.
AWLC2014, FNAL, May 12-16, 2014
12
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.
AWLC2014, FNAL, May 12-16, 2014
13