KCS Operational Issues

1. KCS Operational Issues Chris Adolphsen, Chris Nantista and Faya Wang GDE PAC Review at KEK 12/12/12

2. Klystron Cluster Scheme  KCS + cryo shaft  KCS shaft 25 • 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. 26 26 26 26 26 26 I.P. Shaft Layout and ML Units Powered e- beam 26 26 26 26 I.P. 26 26 26 26 undulator main linac totals: 12 shafts 22 KCS systems 567 rf units (285+282) 1,701 cryomodules 14,742 cavities e+ beam 26 26 25 25 25 25 26

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

4. 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

5. 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 with 7.4 us (propagation delay) RF Amplitude Nominal Minimum Phase (deg)

6. 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.

7. 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). Lossat this diameter = 8.44 %/km Bends: 90 bends are needed to bring the KCS main waveguide to the linac tunnel. Electric field pattern TE01 TE01 TE20 TE20 Mode converting sections allow the actual bending to be done in the rectangular TE20 mode. WC1375 ports connect to WC1890 through step-tapers.

8. KCS Tolerances 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: 240.03 mm mean: 239.7 mm max-min: 1.08 mm std.: 0.234 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. = 187,230 Q0, meas. = 181,310

9. KCS Losses 49.97 MW (83.2%) 16.8%

10. Ten Meter Test Setup CTO cold tests input assembly transmission tests 12.894 m 9.990 m resonant line tests Location: Roof of NLCTA bunker Power source: SNS modulator and Thales “5 MW” klystron

11. Forty Meter Test Setup CTO coupling RF power from P1 Marx-driven Toshiba MBK into TE01 mode in resonant line using KEK circulator. Shorted bend with input mode converter at end of run. 40 m of pressurized (30 psig) , 0.48m diameter circular waveguide. 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 1.3005025 GHz fr = 1.300502 GHz (cold, unpress.) QL = 78,839 b = 1.2997 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, Pin = 1.18 MW.

16. In FY12: Installed 40 m of pipe system and bend prototype (have an additional unused 40 m of pipe) Resonant Line 1.0 MW 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-in tap-off 80 m of WC1890 300 MW

17. 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 is at minimum equal to 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

18. Other Questions • Modulator • What is the plan to prove reliability of the Marx modulator design? • We have not tested the P2 MARX enough to know where improvements need to be made. For the P1 Marx, the concern is still with the capacitor lifetime, but since we are focusing on the P2 and have little funds anyway, there is no further plans to develop the P1 or continue long-term testing it. • How to find weak components in the design? • We plan to do long term testing of the P2 starting next Feb. • A large number of modulators operated at 5Hz would have an impact on the electrical grid. How is constant power consumption from the mains achieved ? • The charging supply will present a constant load to the grid, so this should not be a problem • What is the strategy for industrialization? • We have been trying to find companies that will license the P2 design - Thompson showed some interest but have not followed up. Also, KEK has a DTI Marx modulator that they will evaluate - if it works well, maybe Toshiba or other companies will buy them

19. Other Questions (cont) • Klystron: • How is klystron lifetime defined? • The expected klystron lifetime is based on the cathode loading - we have ran our MBK at 10 MW with 0.8-1.6 ms pulses for 5000 hours at 5 Hz without major incident (except for the cavity detuning from a one-phase loss of AC power to the solenoid when the klystron beam was off), so at least we know the MBK lifetime is not very low - for either the KCS or DKS layout, there is no need to have a long lifetime other than cost since the klystrons are readily accessible if they fail. • What is the plan to handle non-conforming klystrons during conditioning and testing, which takes place not at the manufacturers site? • I would hope that the klystron contract would be such that the manufacturer would replace any non-conforming tubes as I believe the failure rate will be low

20. Other Questions (cont) • Waveguide: • What is the plan to prove reliability of the waveguide distribution system? • We have already tested the rf distribution systems sent to FNAL at full power, but only for an hour or so. Hopefully, FNAL will be able to run them longer. • There are some components which have sliding contacts, which seem to have poor reliability at high power. • I believe only the U-bead phase shifters have the sliding contacts - they seem to work fine in the full power for the testing done so far (no breakdowns and no arcing damage observed) - note also that these shifters should not have to be adjusted often. • Operation at overpressure might need approval by the national authorities ( TÜV or similar). This might lead to higher prices during the production process. Has that been considered? • The waveguide has been designed for high pressure operation (and certified in most cases by the vendor) and costed accordingly. Unlike He systems, designing and qualifying for 3 atm absolute operation is not that difficult (e.g. to qualify our 40 m big pipe + bend + CTO, we pressurized system at 25% above design for a few hours).