Linac RF Source
S. Fukuda

Proposal from Accelerator Group.
C-band High-power Klystron.
Modulator issues---Flat-top pulsewidth.
Possible layout plan for C-bandscheme.
Driving system study.
Conclusion

Kamitaniʼs Scheme• C-Band Scheme• ⇒Positron Energy Up to 8GeV with Using Cband RF Source, which Comprises 3 Sectors of＃３、＃４、＃５.
• C-band Accelerator Design and Parameters wereshown• ⇒２ｍ Waveguide x 4、42MV/ｍ• Attenuation Factor 0.676, Filling Time
0.365μs• Usage of SLED Type Energy Doubler• ⇒High Q SLED Cavity Using the TE038 Mode• ⇒Pulse Width ２μsec,
Multiplication Factor 1.84（at Q=180000）

C-band SLEDC-band SLED; Kamitani

Parameter

2.3

Multiplication Factor

2.2
2.1
2
1.9
1.8

Qo=180000

1.7

Qo=90000
Qo=75000

1.6
1.5
1.5

2.5

3.5
Pulse Width(us)

4.5

5.5

6.5

Study Points of C-band RF System• Klystron Galleryʼs Space is limited and All areinstalled there.
• Spacing, Modulator systems, Klystron Assemblies.
• ⇒Is it possible to construct C-band system with making
use of the existing infrastructures such as themodulator?
⇒Can we get enough pulse width in the realistic caseincluding the phase reversing interval time?
• ⇒2 C-band 50MW-Klystron in the existing 1 unit space• Other RF( C- band) Components⇒Driving System⇒How serious the phase stabilities comparing with Sband case?
• Relation between the construction schedule and KEKB, PFand AR experiments.

C-band KlystronC-band klystron developed:●Output Power
Maximum〜50 MW、●Applied Voltage 350kV, Pulsed Current 317A,
Microperveance １.５●Efficiency 45％, Gain 52-54dB, Required driving
power of about 300 W●2 klystrons from a modulator ⇒Microperveance 3（1.5 times larger than s-band case）
2 C-band 50 MW klystrons in the 1 unit modulator
spacing.

C‐Band50-MWKlystronPulse Flat-top Width• Study of Pulse flat-top width from power consideration.
• Power Conservation
IsVsT=PVs3/2T＝（1/2）CpfnVpfn2• where• Is：Secondary Pulse Current, Vs：Secondary Pulse Voltage、
T：Pulse Half Width,
P：Perveance of klystron• Cpfn：PFN Total Capacitance, Vpfn：PFN Charging Voltage、•T=Ttrj+Tflat=T0trjN+ Tflat
Vs=（1/2）VpfnN• Ttrj ：Rising and falling time, Tflat ：Pulse flat-top time,
T0trj：Ttrj / a turn,
N：Step-up ratio of pulse transformer

S-Band（KEKB/Pulse width vs PT Step-up Ratio)

Tpulse-Step-up Ratio

17

Step up ratio

16

S−band KEKB Cases for Ct=0.602μF(Good Agreement with Measurement)

15
1:13.61413123.92μｓ

11234

Pulse width56

KEKB S-Band(Pulse width vs Klystron Voltage）
Pulsed width-Klystron Voltage

Klystron Voltage

380
340300306kV, 1:13.6260

3.92 μｓ

22002

Pulse width46810Pulse Flat-top （Cband Klystron）
Pulse Flat top and Total Capacitor
14Ct=0.602μF, 3μP
Ct=0.602μF, 1.5μP
Ct=0.62μF, 3μP
Ct=0.70μF, 3μP
Ct=0.75μF, 3μP
Ct=0.80μF, 3μP

12Pulse Flat top

1086１Mod.-1 Klystron

42１Mod.-２Klystrons

Tflat=1μｓ

011121314
Step-up Ratio

151617Problem for 1 modulator 2klystrons
It is necessary to increase the total PFN capacitance of 30% to get the2μs Flat.
●30% increase to the vertical direction⇒Adding PFN capacitors●30% increase in length ⇒Exchanging whole PFN capacitors○Increase the packing factor of the Capacitor element⇒ Exchanging whole PFNcapacitors◎Change the capacitor element⇒Exchanging whole PFN capacitors◎Adopting the commercial compact capacitors ⇒Exchanging whole PFN capacitors
Larger Thyratron
Step-up ratio １：１５, Secondary Voltage 350kV,634A⇒Primary23.3kV、9510A。
It is necessary to use larger thyratron
Is it possible to use other components for PFN capacitance increase of 30%?
Charging Choke?―――――ＯＫ？(For the recently revised version)
ＩＶＲ――――――――――It is necessary to change
Facility electricity?
How about the compact inverter HV P/S? ――――― exceed 30kW average power, needmore than two module.

The case of 1 modulator 1klystron•

It is possible to decrease 30% of total capacitance to get 2μs flat in
the case of 1 modulator 1klystron.
Klystron galleryʼs spacing is important.
⇒Usage of Compact inverter DC HV power supply eliminates the use ofIVR, charging choke and deʼQing circuit.
Possibility to use the discharging cabinet of existing modulator.
(see the plan of configuration)
Existing PFN Capacitors are possible to be used again.
⇒ example, 14 steps, parallel PFN circuits
Ci=0.0155μF, Li=1.5μH↓Flat pulse width of 2μs, half width of 4.8μs(see simulation )Present Configuration of Modulator and Klystron
4800
600

Modulator

Klystron

Proposed C-band Configuration
600
RF and Coil P/S560

InverterModulator
Control

1200
600

800

Klystron

R1L

1K

1 V
0

1.3u

L0

1.55u

X0 V0L9

1.55u

IVm

1L
. 138u1L. 149
75 Ru

L11.55u
0 C.
0155L10 u
1.55uL2

1.55u
0 C
. 0
0
155L11 u
1.55u

0 C
. 80
155u0 C. 90
155u

L31.55u
0 C. 10
155L12 u
1.55u

L41.55u
0 C. 2
01
55L13 u
1.55u

0 C
. 1
0 0
1
55u

0 C
. 1
0 1
155u

L5

1.55u
0 C
. 30
1
55
L14 u
1.55u
0 C
. 1
0 2
1
55u

L6

1.55u
0 C
. 40
1
55
L15 u
1.55u
0 C
. 10 3
155u

L7

1.55u
0 C
. 50
1
55
L16 u
1.55u

L8

1.55u
0 C
. 6
0
155L17 u
1.55u

0 C. 10 4
155u0 C. 10 5
155u

L21

1.55u
0 C
. 7
0
155L22 u
1.55u
0 C. 10 6
1
55u

L23

1.55u
0 C
. 1
0 8
1
55
L24 u
1.55u
0 C
. 10 9
1
55u

L25

1.55u
0 C
. 20 0
155
L26 u
1.55u
0 C
. 20 1
155u

L27

1.55u
0 C
. 20 2
155
L28 u
1.55u

L29

1.55u
0 C
. 20 4
155L30 u
1.55u0 C. 20 6155u

0 C. 20 5155u0 C. 20 7155u0 C. 20 3155u

PFN 14 steps 2-parallel, with Rp=5Ω0PFN̲C.ckt-Transient-2(V)+3.0000.0+2.000u+4.000u+6.000u+8.000u+10.000u

Time (s)+12.000u+2.000+1.0000.0-1.0004.8µs-2.000-3.000-4.000-5.000Flat top 2µs-6.000TIME+5.032u

V(IVM)-4.971

D(TIME)+1.700u

D(V(IVM)) -349.045u+14.000u+16.000u+18.000u+20.000u

Klystron Assembly•Step-up ratio of １:１５ Pulse transformer⇒Is it possible to use the existing pulse transformer?
⇒Is it possible to use the existing pulse transformer tank?
( the focusing magnet is fatter than the old one.)••

Assemblies configuration has been already shown.
Cost of the C-band klystrons per present one unit is twice as muchhigh as the one of S-band case.
totally 48 sockets!
It is necessary to compete the klystron quality among the severalvendors.

Scheme of Driver System
Possible scheme for the Driving RF to the high power klystrons（１）Similar as the present sub-booster system- Driving 8 units from a SB
klystron･deliver S-band to each sector⇒amplification⇒2-times multiplier SB
klystron ⇒driving 16 C-band klystrons.
･deliver S-band to each sector⇒amplification⇒2-times multiplier⇒amplification ⇒ C-band SB klystrons ⇒driving 16 C-band klystrons.
･deliver C-band to each sector⇒amplification⇒ C-band SB klystrons⇒driving 16 C-band klystrons.
Constructing a sector (8 modulators, 16 tubes) in every fiscal year.
（２）Similar as the present sub-booster system- Driving 4 units from a SB
klystron･deliver S-band to each sector⇒amplification⇒2-times multiplier SBklystron ⇒driving 8 C-band klystrons.
･deliver S-band to each sector⇒amplification⇒2-times multiplier⇒amplification ⇒ C-band SB klystrons ⇒driving 8 C-band klystrons.
･deliver C-band to each sector⇒amplification⇒ C-band SB klystrons⇒driving 8 C-band klystrons.
Constructing half sector (4 modulators, 8 tubes) x n in every fiscal
year.
It is easy to co-use S-band and C-band in the Tangent period.

Scheme of Driver System(Cont)（３）One large klystron feeds all of 48 C-band klystrons.
⇒ How to construct? It is not easy to adjust the beam acceleration
timing with the RF timing from SLED which delays gradually.
（４）Semiconductor C-band amplifier for each 50 MW C-band klystron.
･Merit ――― Easy feedback system, easy phase adjustment, no middlepower class phase shifter.
･Demerit―――Amplifier output power of about 500Ｗ 48
or amplifier output power of about 1 kW x 24
Price is roughly equal or more than a SB klystron.
(５) Driving Line consideration
Phase stabilized co-axial line presently used is not available.
Attenuation, Higher mode, Stop manufacturing⇒Rectangular waveguide with well temperature controlled.

Present Layout of Unit Sector

SB-3

3-1

3-2

3-3

3-4

3-5

3-6

3-7

3-8

3-6

3-7

3-8

Proposed Layout of C-band Unit Sector

SB-3

3-1

3-2

3-3

3-4

3-5

Attenuation of 39D Coaxial Line
Attenuation of Coaxial 39D
0.12
0.11

Attenuation ofCoaxial 39D

0.1

Att(dB/m)

0.09
0.08

TE11モード

0.07
0.06

5712MHz

0.05
0.04

2856MHz

0.03
0.02
0.01
0012

34

frequency(GHz)567Attenuation comparison between
the various waveguide
WG Attenuation
98Attenuation(dB)

76S-band WRJ3C-band WRJ5
S-39DC-39D
C-CircularTE01

5432
100204060Length(m)80100

Existing C-band 200kW klystron (MELCO) ⇒Retune to 5712MHｚ
Similar operating scheme performed by the present subbooster（100kW at the 30kV) is expected.
It is possible to feed C-band klystrons if the rectangular waveguide(WRJ-5 or 6) is used.
⇒Good cost performance
Constant-temperature water is necessary to keep the drive line constant.
(±0.1 degree fine controlled water)
Phase stability, Minimum phase jitter is required for the C-band case.
⇒It is necessary to study the phase stability intensively.

Conclusion• 2 klystrons and 2 modulators are installed in the present
one unit space.
• Each modulator comprises a pulse discharging circuit anda compact inverter P/S.
• Existing modulator components are possible to be reused.
• C-band 50-MW klystron is used as main RF source..
• C-band 200kW klystron is used as the SB amplifier.
• Drive-line WG is kept constant temperature using highly
controlled water.
• Consideration for the phase stability is very important.