R&D STATUS OF THE C-BAND RF-SYSTEM
H. Matsumoto, S. Takeda, KEK, Tsukuba
T. Shintake, RIKEN, Harima
M. Yoshida, Y. Takasu, University of Tokyo, Tokyo
J. S. Oh, PAL/POSTECH, Pohang, South Korea
Abstract
Hardware R&D on the C-band (5712-MHz) RF-system
for the e+e- linear collider started in 1996 at KEK. We
developed three conventional and a periodic permanent
magnet (PPM) type 50-MW class C-band klystrons(TOSHIBA E3746 series and E3748 series), a smart
modulator, a high power model of an rf-pulse compressor
cavity is now under fabricating and the first HOM-freeaccelerator structure (Choke-mode type, full-scale highpower model) [1], [2], [3].
As a upgrading program to 1 TeV c.m. energy scale,we developed a new PPM klystron in 1999. The first PPM
klystron was generated 37 MW with 2.5-µsec pulse widthand 50 pps repetition rate [4].
A very stable high voltage monitor using ceramic wassuccessfully tested up to 230 kV of voltage and 4.5 µsecof pulse width. It was obtained very good agreement withexpected a dividing ratio and the waveforms from the firsthigh power
The first high power model of an rf compressor cavity
was used a low thermal expansion material (super Invar)
to make stable operation with 200k of Q-value [5], and its
high power test will on a early 2002 in KEK.
The c-band linac rf-system will use for the SASE-FEL(SCSS) project in the SPring-8 [6], which is actually
make strings test of the main linac rf system for the linear
collider.

Fig.1: C-band main linac tunnels. It has diameter of 4.5-m for theklystron gallery and 3.0-m for the linac.

1 INTRODUCTIONAn e+e− linear collider is a large-scale machine. In themain linac for two beams, we use more than 7000 accelerating structures, 3500 klystrons and their pulse modulators. Therefore, we have to develop the hardware as tomeet the following demands:(1) High reliability,(2) Simplicity,(3) Lower construction cost,(4) Reasonable power efficiency andC-band LC
C-band LINAC RF-SYSTEM LINEAR COLLIDER(5) Operational ease.
AC POWER LINEThe above list provides a guideline and5712 MHz, S = 500 GeV FOR TWO LINACSSMART MODULATOR
RF-SYSTEM: 1789 UNITS
boundaryconditions to our design work.
MODULATORS: 3560KLYSTRONS: 3560Among the system parameters, the choice
ACC. STRUCTURES : 7120
of the drive rf frequency plays the most
ACTIVE LENGTH: 12.8 KM
WALL-PLUG POWER :130 MW
important role concerning the system
HV INVERTER POWER SUPPLY
performance as well as the hardware
50 MW KLYSTRON
PMdetails.
We proposed the C-band
frequency as being the best choice to meetAM
RF-PULSE
all of the demands listed above [2].
47kV, 37kJ/s

PFN
MODULEPFN
MODULEPFN
MODULE

23.5 kV
H.V. pulse

BEAM LOADING COMPENSATION USING PHASE -TO-AMPLITUDE MODULATION

50 MW
2.5 µsCOMPRESSORWAVEGUIDEø1ø2400 MW, 0.5 µs

x 4.0,η = 80%

Klystron
350 kV
317 A
100 ppsµ P = 1. 53
η = 45%

V295 MW, 0.5 µs
Q-MAGNET

Ea=36 (45) MV/m
ACCELERATOR
BPM

GIRDER
ACTIVE MOVER8m

3 π 4, a λ = 0.13~0.17, vg=0.012~0.035c, r=60 MOhm/m, Tf=286 ns,
τ = 0.53

ø2COMPRESS PULSE COMPRESSOR INPUTTO STRUCTURESOUTPUT RF-POWER

1.8 m-LONG

ø1V11:15

WR-187 Rectangular
LOSS ~5%

ACCELERATOR
Beam

100 MW
2.5 µsPHASE SHIFT

1:15

100 MW, 2.5 µs
0°

TIME

400 MW,0.5 µs

ACTIVE MOVER

ALIGNMENT TORELANCE : σ ~ 30 µm / STRUCTURE

TIME

Linear Collider
By T. Shintake (KEK)
March, 1998, H. MATSUMOTO & T. SHINTAKE, KEK

Fig. 2: One unit of the C-band main linac.

hiroshi.matsumoto@kek.jp
http://c-band.kek.jp

2 SYSTEM DESCRIPTION

180°

Each unit in the main linac rf-system iscomposed of two 50-MW klystrons, theirpulsedmodulators,onerf-pulse
compressor, four 1.8-m-long Choke-mode
accelerating structures and associatedwave-guide-system as shown in Figure 2.

The accelerating gradient is 36-MV/m under the beamloading. The total number of the RF-system to achieve
500-GeV c.m. energy is 2000 units.

3 RESULTS OF HARDWARE R&D
In April 1996, we started hardware R&D, and up tonow (June 2002) we have developed all of the hardware
components and tested those performances, except the rf
pulse compressor high-power model.

3σ) for 4 hour run at 50 pps [8], [9].
The second step of the smart modulator will install into
the insulation oil filled one box metal cabinet with very
compact size 150 (Width) x 100 (Height) x 100 (Deep)cm as shown in Figure 4 [9]. A prototype is now underconstruction by NICHIKON Co. in Japan, and it will begin testing by the end of this year (2002).

3.1 Klystron R&D
We have successfully developed the 50-MW class klystron, which meets specifications of the 500-GeV linear
collider. In Phase-II R&D, we have to refine the design
details to reduce cost before starting the mass-production.
As a part of the R&D program toward 1 TeV c.m. energy
scale linear collider, we developed the first PPM klystronin 1999 as shown in Figure 3 [4]. We chose the NdFeB
magnet (Model N40A,Shin-Etsu Co. in Japan.
Hot isostatic pressing(HIP) technique has been
firstly applied to fabricate
a magnetic circuit in a
PPM klystron. An output
power of 37 MW wasgenerated with 2.5-µsec
pulse width and 50 pps
repetition rate.

3.2 Modulator Power
SupplyAccordingly we focussed our R&D work onFig. 3: Cut away view of the first C- reducing the fabrication
band (5712-MHz) 50 MW-class cost and improving thePPM type klystrons (TOSHIBAreliability. In 1993, theE3747).
concept of the “SmartModulator” was proposed by Prof. M. H. Cho and theauthor [7], [8]. As a first step, we developed a prototypemodulator, whose features are:(1) Direct HV charging from an inverter power supply,(2) No de’Q-ing circuit,(3) Much smaller size than the usual modulator,(4) Use existing reliable circuit components.
To reduce the modulator size and allow removing thede’Q-ing circuit from PFN, we employed an inverter type
DC-HV power supply: Model EMI-303L (Electric Measurement Inc. The smart modulator was installed in a metalcabinet of compact size 160 (w) x 200 (H) x 120 (D) cm.
It is now in daily use for driving the 50-MW klystron.
The total run time has exceeded 10,000 hours. The fluctuation of the measured output voltage was lower than
±0.17% (at 3σ), which meets the energy stability requirement for the linear collider. The timing variation(jitter and drift) of the pulse output is around 2-nsec (atFig 4: Closed type compact modulator.

3.3 Pulsed High-Voltage Monitor
We have been developing a very stable and accurate
high-voltage monitor use for a monitoring the klystronpulsed beam voltage. Since it uses a ceramic material as
the capacitive type divider, the monitoring capacitancebecomes quite stable against temperature change, orchange in set-up configuration, or mechanical stress applied to the monitor port through the input read. We madetwo different types of high-voltage dividers using ceramic
as shown in Figure 5 [10].

5-a : Cup type5-b: Disk typeFig 5: Pulsed high-voltage monitor using ceramic material. Up: Cup
type. Bottom: Disk type.

3.4 RF Pulse Compressor
A new scheme was proposed as a flat-pulse rf-pulse
compressor by T. Shintake in 1996, and the demonstrated
generation of a flat-pulse, which have obtained the 3.25 ofpower gain with 65% of efficiency. The first high powermodel is using an invar metal as the rf cavity with copper
plating, the temperature control system to the rf compressor will be simplified and contributes to reduce cost of thetotal system. The high power model is now under fabricating, and it will be tested end of this year (2002) inKEK. A set up is shown in Figure 6.

power efficiency of higher than 50%.
For the next step, in order to examine the system performance in a realistic situation, one unit of the C-band
system has to be installed and tested with beam in an existing machine.
The c-band linac rf system now under fabricating for 1GeV electron injector linac for the SCSS project (SASEFEL) in SPring-8 [13]. Its comprises of 1-GeV injector
include the buncher system and 20-m long vacuum typeundulator can be applied the water-window with range of1- and 10-nm of the light wavelength. The first operationof the c-band linac at beam energy of 500-MeV will starton a early 2004, second step will accelerates the beamenergy of 1-GeV in a early 2007.

5 REFERENCES
Fig 6: High power test stand for RF pulse compressor cavity.

3.3 The C-band accelerating structure
The C-band Choke-Mode type damped structure wasdeveloped in 1998, its performance was tested withASSET at SLAC as shown in Figure 7. The powerful
HOM damping performance was proven. We found parasitic resonance at very high frequency around 23 GHz,
which is caused by EM field trapping inside the cavity. It
can be solved by changing the cavity dimensions by small
amount. For the beam alignment, the cavity type RF-BPM
was developed and its performance was tested withASSET beam [12]. The position accuracy of 10-µm andthe resolution of 1-µm were confirmed. High power testof the structure will start in middle of 2002 in SPring-8.

Fig 7: C-band HOM free accelerating structure (high power model).

4 FUTURE R&D
The first stage of the C-band R&D between 1996 and1998 was successfully completed. For 1999, the first priority is to develop a 50-MW class PPM type klystron with

[1] T. Shintake et al., “C-band Main Linac RF System for
Linear Collider ”, KEK preprint 96-122, September.
1996.
[2] H. Matsumoto et al, “Fabrication of the C-band (5712MHz) Choke-Mode Type Damped Accelerator Structure”, KEK preprint 98-143, September 1998.
[3] T. Shintake et al., “The first Wakefield Test on the Cband Choke-Mode Accelerating Structure”, KEK preprint 99-11, May 1999.
[4] H. Matsumoto et al., "DEVELOPMENT OF THE CBAND (5712 MHz) 50 MW CLASS PPM Klystron(II)", 26th Linear Accelerator Meeting in Japan,
Aug.01~03,2001, Tsukuba, Japan[5] M. Yoshida et al., "RF Pulse Compressor using Low
Thermal Expansion Invar Material", 26th Linear Accelerator Meeting in Japan, Aug.1~3, 2001,[6] T. Shintake et al., "The SPring-8 Compact SASE
Source (SCSS)", SPIE2001, 29 July – 3 August 2001,
San Diego, California, USA[7] J-S. Oh et al, “Efficiency Analysis of the First 111MW C-band Klystron–Modulator System for LinearCollider”, KEK Preprint 98-32, March 1998.
[8] H. Baba et al., “Pulsed Modulator for C-band Klystron”, 1st APAC98, March 23-27, 1998, KEK[9] H. Baba et al., “Closed type Compact Modulator for 50
MW C-band Klystron”, Power Modulator Conference& High Voltage Workshop, June 30 – July 3, 2002,
Hollywood, CA.
[10] Y. Takasu et al., “Pulsed High Voltage Monitor Using
Ceramic”, 27th Linac meeting August 7-9, 2002,
Kyoto.
[11] M. Yoshida et al., “RF Pulse Compressor System”,
27th Linac meeting August 7-9, 2002, Kyoto.
[12] T. Shintake, "Development of Nanometer Resolution
RF-BPMs", HEAC99.
[13] T. Shintake et al., “Status of SCSS Project at SPring8”, 27th Linac meeting August 7-9, 2002, Kyoto.