KCS Operational Issues

Chris Adolphsen, Chris Nantista and Faya WangGDE PAC Review at KEK

12/12/12

KCS + cryo shaft KCS shaft e- beam

e+ beam

undulatorI.P.

I.P.

26 26 26 26 26 26

26 26 26 26

25

26 26 25 25 262525

26 26 26 26main linac totals:12 shafts22 KCS systems567 rf units (285+282)1,701 cryomodules14,742 cavities

• 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.

Klystron Cluster Scheme

Shaft Layout and ML Units Powered

…

Combine power from 19 klystrons – effectively a 190 MW klystron

12

3

l

12

31

2

31

2

3…

-3 dB -3 dB -4.8 dB -7 dB

2

3-6 dB

1

Combining and Tapping Off Power

1

23

l1

231

23

-3 dB-3 dB-4.8 dB

… …WC1890 WC1890CTO

Tap-Off 10 MW every 38 m (three cryomodules)

Klystron to CTOConsidered remote-controlled mechanical rf switches to isolate

region upstream of CTO if circulators fail – removed to save cost

CTO

KLY

Switchand Load

5 MWCirculator

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)

0 5 10 15 20 250.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

RF

Am

plitu

de

Phase (deg)

Min

imum

Nom

inal

Prototype CTO’s built for R&D program.

|E| on cut planes

|H| on surfaces

CTO (Coaxial Tap-Off)

Coupling into the Circular Waveguide

determines coupling

To couple power to the pipe, developed a “coaxial (wrap-around) tap-off”, or CTOCouplings range from -3 dB to ~-14 dB are needed, controlled by gap width

3 dB design

1

2

3

customized to coupling gap

Coupling due to beating with TE02

TE01

TE20TE20

Electric field pattern

TE01

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

KCS Power Transmission

Bends: 90 bends are needed to bring the KCS main waveguide to the linac tunnel.

Mode converting sections allow the actual bending to be done in the rectangular TE20 mode. WC1375 ports connect to WC1890 through step-tapers.

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).

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.

1 2 3 4 5 6 7 8 9 10239

239.5

240

240.5

241

Azimuthal Location

Mea

sure

d R

adiu

s (m

m)

target: 240.03 mmmean: 239.7 mmmax-min: 1.08 mmstd.: 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 ~9899% transmission and a CTO match of ~-2128 dB.

KCS Tolerances

Q0, theor. = 187,230 Q0, meas. = 181,310

For ILC, may tune CTO coupling after fabrication

into beam16.8%not into beam83.2%

inefficiencies & losses52.6%

ACRF43.2%transmission losses9.4%

kly to ML unit: 6.8%LPDS: 2.6%

into loads30.6%

operational28.7%

fill time: 21.4%beam phase: 0.31%LLRF overhead: 3.9%

due to gradient spread1.9%

statistics: 0.61%unoptimized match: 1.3%

KCS system (19 kly) Full Machine (413 kly)

AC power 2.764 MW 60.08 MW

lost above ground 1.404 MW 30.52 MW

lost below ground 0.895 MW 19.45 MW

into beam 0.465 MW 10.11 MW

49.97 MW (83.2%)

16.8%

KCS Losses

CTO cold tests

Ten Meter Test Setup

12.894 m9.990 m

input assembly

transmission tests

resonant line tests

Location:Roof of NLCTA bunker

Power source:SNS modulator andThales “5 MW” klystron

Forty Meter Test Setup

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.

|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 !

Surface Electric Field in 90 Degree Bend

1.3003 1.3004 1.3005 1.3006 1.3007-20

-15

-10

-5

0

Frequency (GHz)

|S11

| (dB

)

0.45 0.46 0.47 0.48 0.49 0.5 0.51 0.52 0.53 0.54 0.55-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Frequency - fo (MHz)

|S11

| (dB

)

1.3005025 GHz

-0.2 0 0.2 0.4 0.6 0.8 1

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

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0.5

0.6

Real

Imag

inar

y

fr = 1.300502 GHz (cold, unpress.)QL = 78,839b = 1.2997Q0 = 181,310

1.3002 1.3003 1.3003 1.3004 1.3004 1.3005 1.3005 1.3006 1.3006 1.3007 1.30070

0.1

0.2

0.3

0.4

0.5

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0.7

0.8

0.9

1

frequency (GHz)

|S11

|

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

delta f

tan(

Psi

)

Cold Test of 40 m Setup

0 20 40 60 80 100 120 140 160 180 2000

200

400

600

800

1000

1200

1400

Time with rf on (Hours)

RF

pow

er t

o th

e B

igP

ipe

(kW

)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

1. Coupling coefficient β = 1.172. Power needed for equivalent field of 300 MW, Pin = 1.18 MW.

0 20 40 60 80 100 120 140 1600

500

1000

1500

Time with rf on (Hours)

RF

pow

er t

o th

e B

igPi

pe (k

W)

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

Resonant Line1.0 MW

Equivalent Field for 300 MW Transmission

40 m of WC1890back-shorted tap-in

Resonant Ring

300 MW

80 m of WC1890directional coupler

In FY12: Installed 40 m of pipe system and bend prototype

(have an additional unused 40 m of pipe)

tap-off tap-in

phase shifter

In FYxx: Use resonant ring to test ‘final design’ bends and tap-in/off

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

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

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

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).