1. ILC High Power Distribution
Chris Adolphsen, Chris Nantista and Faya Wang
SLAC

2. ILC: Distributed Klystron Scheme (DKS)
Similar to two tunnel RDR design but in one ‘Kamaboko’ shaped tunnel with a cement partition (shielding)

3. Klystron Cluster Scheme
RF power sources clustered in surface buildings.
Power combined, transported through overmoded waveguide, and tapped off locally at each ML Unit.
Two KCS systems per building/shaft feed upstream and downstream, ~1 km each.
Shaft Layout and ML Units Powered
 KCS + cryo shaft
 KCS shaft 26
e- beam 26 25 26 26 26 26 26
I.P.
undulator
main linac totals:
12 shafts
22 KCS systems
567 rf units ( )
1,701 cryomodules
14,742 cavities 26 26
e+ beam 26 26 25 25 25 25 26
I.P.

4. Combining and Tapping Off Power
Combine power from 19 klystrons – effectively a 190 MW klystron 1 2 3 l …
-3 dB
-4.8 dB
-7 dB
-6 dB …
Tap-Off 10 MW every 38 m (three cryomodules) 1 2 3 l
-3 dB
-4.8 dB …
WC1890
CTO

5. Klystron to CTO
Considered remote-controlled mechanical rf switches to isolate region upstream of CTO if circulators fail – removed to save cost
KLY
5 MW
Circulator
CTO
Switch
and Load

6. RF Control Overview
Have rf feedback loop to control net combined power from 19 klystrons
Only need precise power summation when running at full beam energy
Run klystrons in saturation and use alternating +phi/-phi phasing to control amplitude: phi nominally 22 deg to give 5% useable rf overhead
Can shutoff rf at breakdown site within 7.4 us (propagation delay)
RF Amplitude
Minimum
Nominal
Phase (deg)

7. Coupling into the Circular Waveguide
To couple power to the pipe, developed a “coaxial (wrap-around) tap-off”, or CTO
Couplings range from -3 dB to ~-14 dB are needed, controlled by gap width
CTO (Coaxial Tap-Off) 2
|E| on cut planes
|H| on surfaces
determines coupling
3 dB design
Coupling due to beating with TE02 3
customized to coupling gap 1
Prototype CTO’s built for R&D program.

8. KCS Power Transmission
Main Waveguide:
For low-loss and high power handling, the TE01 mode is used in pressurized (3 bar N2), copper-plated, overmoded, 0.48m-diameter circular waveguide (WC1890).
Loss at this diameter = 8.44 %/km
Bends: 90 bends are needed to bring the KCS main waveguide to the linac tunnel.
TE01
TE20
Electric field pattern
Mode converting sections allow the actual bending to be done in the rectangular TE20 mode. WC1375 ports connect to WC1890 through step-tapers.

9. KCS Tolerances Q0, theor. = 187,230 Q0, meas. = 181,310
The 0.48m-diameter KCS Main Waveguide supports 20 parasitic modes.
To avoid significant mode conversion losses, we set the radius tolerance at ~±0.5 mm. This was achieved within a factor of ~2.
Because TM11 is degenerate with TE01, tilt (local and cumulative), should be kept within ~ 1 (17 mrad).
target: mm
mean: mm
max-min: mm
std.: mm
For the CTO and bend, fabrication tolerances were set at ~±127mm for critical dimensions and ~±178mm for concentricities. Our transmission tests with 2 CTO’s shorted for launching (not fine tuned) demonstrated ~9899% transmission and a CTO match of ~-2128 dB.
For ILC, may tune CTO coupling after fabrication
The Q0 for the 40 m resonant waveguide with CTO at one end and a bend at the other measured within 3.2% of the theoretical value! This is a good indication that mode conversion wasn’t a problem.
Q0, theor. = 187, Q0, meas. = 181,310

10. Ten Meter Test Setup CTO cold tests input assembly transmission tests
resonant line tests
Location:
Roof of NLCTA bunker
Power source:
SNS modulator and
Thales “5 MW” klystron

11. Forty Meter Test Setup
Operated 100+ hours breakdown free at field levels that would be seen in the ILC KCS with the beam current upgrade
CTO coupling RF power from P1 Marx-driven Toshiba MBK into TE01 mode in resonant line using KEK circulator.
40 m of pressurized (30 psig) , 0.48m diameter circular waveguide.
Shorted bend with input
mode converter at end of run.
Recording run data.

12. Surface Electric Field in 90 Degree Bend
|Es|pk = 3.34 MV/m for 37.5 MW input
(= 75 MW full geometry  300 MW TW equiv. at SW anti-nodes)
Equivalent to 72 MW TW in WR650 !

13. Cold Test of 40 m Setup
GHz
fr = GHz (cold, unpress.)
QL = 78,839
b =
Q0 = 181,310

14. First Run: 1 MW input (255 MW field equivalent – ILC needs only 190 MW initially), no breakdown in 120 hours with 1.6 ms pulses at 3 Hz

15. Second Run: 1.25 MW input (313 MW field equivalent – ILC needs only 190 MW initially), one breakdown in 140 hours with 1.6 ms pulses at 3 Hz
Coupling coefficient β = 1.17
Power needed for equivalent field of 300 MW is 1.18 MW.

16. Breakdown Rate at Various N2 Pressures
ILC Max with
9 mA upgrade
Peak Surface Field (MV/m) in the Bend

17. Resonant Line Resonant Ring
In FY12: Installed 40 m of pipe system and bend prototype
(have an additional unused 40 m of pipe)
1.0 MW
Resonant Line
back-shorted tap-in
40 m of WC1890
Equivalent Field for 300 MW Transmission
In FYxx: Use resonant ring to test ‘final design’ bends and tap-in/off
Resonant Ring
phase shifter
directional coupler
tap-off
tap-in
80 m of WC1890
300 MW

18. Quantifying the CTO-to-CTO Reliability
Want to verify that each 1.0 km CTO-to-CTO region either breaks down rarely (< 0.1/year) if the repair time is long (24 hours), or break downs modestly (< 1/day) if the recovery is quick (1 minute).
For ILC
Power in tunnel (P) = Po*(L – z)/L, where z is distance from first feed and L = distance from first to last feed
RF shut off time (t) = (zo + z)*2.25/c where zo is the distance from the cluster to first feed
Max of P*t/Po = 3.2 us for zo = 100 m, L = 1.0 km
Max t = 7.4 us for zo = 100 m, L = 1.0 km
For an 80 m resonant ring, t equals the rf roundtrip time = 0.33 us, so P*t would be at least ~ 1/10 of the max at ILC.
Would need ~ 1 km of pipe and thee 10 MW klystrons to ensure the maximum energy absorption (P*t) of ILC
But it would be delivered at ~ twice the power in ~ half the time

19. Local RF Distribution at DESY
TESLA/TTF/FLASH and ILC RDR – use fixed power dividers along a main waveguide feed
EXFEL: Streamlined, no back termination, customizable dividers
Cost Driver: 400 kW isolator

20. Achieving a Flat Gradient Profile with a 20% Gradient Spread
With 39 to 676 cavities having a common source timing, achieving a constant cavity gradient during the pulse is possible by adjusting Pk and Qe for each cavity depending its relative gradient (V/Vo), although some power is reflected into the isolator loads.
For a flat distribution over 0.8  V/V0  1.2,
5.4 % extra power is needed on average
QL/QL0
P/P0

21. ILC Local Power Distribution System
Unused power can be dumped to the loads
Power to ½ CM’s fully adjustable without affecting phases.
pressurizable, 0-100%, phase stable
non-press., limited range
pressure window
5 MW load
from CTO
9 cavities
4 cavities quad 4 cavities
Each cavity feed line has a phase shifter, isolator, bi-directional coupler, and flex guide

22. SLAC Variable Power Divider
Tested to 2 MW
No significant field enhancement or mismatch
Rate of phase change with mechanical position independent of position
Mean loss: ~0.51% ( dB)
Max reflection: ~0.025% (-36 dB)

23. KEK Variable Power Divider
Uses an H-shaped hybrid (2 mode) power splitter design with pontoon-shaped conductors to control split – has limited range of power division and changes phase as well.

24. Phase Shifters
DESY/SPA Ferrite
KEK/Toshiba

25. SLAC Air-to-Air Window
High power tested up to 3 MW, 1 ms.
Ceramic Plug Pressure Window

26. Local RF Distribution for FNAL CM’s
Same components used in distribution systems built for FNAL: all commercially made except U-bend phase shifters and pressure window
One of eight, 2-cavity feed systems assembled by SLAC for FNAL – all parts tested successfully at full power

27. 26 ML Unit KCS Average Power Flow Diagram
“Wall plug”
Heat Loads
Flow (MW)
2.764
2.543
2.416
1.5703
1.492
1.477
1.373
1.349
1.285
1.208
1.133
0.465
Power supplies (.92)
221 kW
127 kW
846 kW
78.5 kW
14.9 kW
103 kW
24.7 kW
63.4 kW
77.1 kW
74.9 kW
668.5 kW
Modulator (.95)
19 klystrons (.65)
Klystron waveguide + circ. (.95)
50.8%
Combining circuit (.99)
Kly circulator loads (for 7% O.H.)
Surface
Shaft & bends (.982)
Tunnel
KCS tunnel waveguide (Cu) (.953)
Local PDS waveguide + circ. (.94)
32.4%
Distribution end loads (.938)
Cavity circulator loads ( )
16.8% Efficient
57% AC  RF
30% RF  Beam
Beam