STATUS OF SUPERCONDUCTING RF TEST FACILITY (STF)
Hitoshi Hayano, and STF group
High Energy Accelerator Research Organization (KEK), Tsukuba, JapanAbstract
The superconducting RF test facility (STF) in KEK is
the R&D facility for the International Linear Collider(ILC) cavities and cryomodule. The surface treatment
and field test of fabricated 9-cell superconducting
cavities are performed for the cryomodule installation.
As an international project, S1-Global cryomodule test
was successfully completed for the various studies ondifferent type of cavity system. The construction of theQuantum-Beam experiment accelerator, as part of STF
phase-2 development, has started in 2011, after theS1-Global cryomodule dis-installation from the tunnel.
The photocathode RF gun and the capture cryomodule
are constructed, installed and commissioned. All of theSTF development done in 2011-2012 is summarized inthis paper.

1 INTRODUCTION
During phase-2
component fabrication
andconstruction, we conduct several experiments, such as
S1-Global cryomodule experiment, and Quantum-beamexperiment for a compact high-flux X-ray generation [4].
In the S1-Global cryomodule experiment, wedemonstrated ILC-like cryomodule built and operated by
the international collaboration. In the compact high-flux
X-ray generation demonstration referred as ‘Quantum
Beam experiment’ which is founded by the MEXT
(Ministry of Education, Culture, Sports, Science andTechnology in Japan), the electron beam source andbeam capture cryomodule are demonstrated its
performance with high quality electron beam generation
and acceleration.
To do industrialization R&D study of cavity
fabrication, the new cavity fabrication facility including
electron beam welder was commissioned. KEK-#0 cavity
are fabricated and tested.
The TDR (Technical Design Report) design change
from RDR (Reference Design Report) [1] and SB2009( Straw-man Base line in 2009) for the linac acceleration
unit has been done [2][3]. The RDR-like accelerator
scheme becomes a new baseline design of TDR in
ILC-GDE (ILC Global Design Effort). Instead the single
tunnel design of the ILC main linac in SB2009, KEK
newly proposed a Kamaboko-tunnel as a cost-effective
excavation method in mountain region. The power
scheme was changed from the DRFS system back toRDR system which is using multi-beam-klystron andMarx modulator but supply the rf power to 39 cavities
instead of 26 cavities. The demonstration of this new RF
scheme is come to a milestone of the STF phase-2
construction and operation.

2 DISASSEMBLY OF S1-GLOBALCRYOMODULE
For the S1-Global cryomodule experiment, theconclusion of gradient performance of the contributedcavities was average 30.0MV/m before cryomodule
installation, 27.7MV/m for single cavity operation after
installation, and 26.0MV/m for 7 cavities simultaneousoperation.
Theothergoalistoperformplug-compatibility concept by building one set ofcryomodule from brought-in cavities and couplers ofeach laboratories. The half-size cryomodule-C was its
demonstration built from INFN cryostat, DESY cavities
and couplers, and FNAL cavities and couplers. The
connection of cryomodule-C and KEK cryomodule-A
was also another aspect of plug-compatibility (Fig. 1).
The 3D CAD base discussion in the design stage wasefficient to realize plug-compatibility.
During the experiment, the cavity gradient degradation
happened on TB9ACC011 and Z108 cavities. The
gradient was reduced 27% and 38% each. The coupler
break-down happened on MHI-05 and the available
gradient was limited to 16MV/m. The tuner mechanics
malfunction troubles happened on TB9ACC011 blade
tuner and MHI-09 lateral slide-jack tuner. Both cavities
were unable to control coarse frequency tuning, so thatthe simultaneous operation of 8 cavities, which required
to align the cavity frequency, was limited to 7. The oneof piezo element out of two in TB9ACC011 haddischarge problem and could not use it in the nominal
voltage.
The dis-assembly of the cryomodules was started fromApril 2011 through December 2011. In between, theassembly of Quantum beam cryomodule were inserted
for several month. The dis-assembly was also done bycollaboration effort with participation of collaborator
researchers as shown in Fig. 2. The cavities and input
couplers from FNAL and DESY were extracted and sent
back to the origin laboratories for further study. The fullreport of this collaborative effort was also completed,
and is waiting for final check.
The S1-Global program was the truly international
cryomodule experiment by the effort of GDE members
and GDE participation laboratories.	  The program has
demonstrated to realize the international cryomodule andtheir performance close to ILC specification. The issuesof the current cryomodule technologies and what weneed to solve in the next were identified.

- 1188 -Fig. 1: S1-Global cryomodule experiment setup in STF
tunnel. Two cryomodules and the cold box wereconnected.

amplified and cut out to 1ms train, and then converted toUV. The UV pulse train is injected into the Cs2Te
photocathode on the molybdenum cathode base, and theelectron beam train is extracted. The commissioning ofthe RF gun followed by the RF process for reduction ofdark-current was started on February 2012. The 1msbeam train was successfully extracted from the RF gun inMarch 2012. The beam acceleration by the two
superconducting cavities was successfully performed inApril 2012. The beam focus tuning at the laser-electron
beam collision point is in progress.

Fig. 3: Installation STF accelerator for use ofQuantum Beam experiment.

Fig. 2: Dis-assembly of S1-Global cryomodule by
INFN and FNAL team.

3 CONSTRUCTION AND OPERATIONOF STF ACCELERATOR
The demonstration of the compact high-flux X-ray
generation named “Quantum-Beam Accelerator project”
is conducted as a part of the injector construction for theSTF phase-2 accelerator. The project is one of theassignments of the MEXT program to develop anddemonstrate the future compact X-ray source with highbrightness. The application target is for life science,medicalscience,andmicro-lithography.
TheQuantum-Beam accelerator is consist of the electron
beam source by the photo-cathode RF gun, two 9 cellsuperconducting cavities in the capture cryomodule, andthe compact X-ray generation beam line by theInverse-Compton scattering with 4-mirror laser storagecavity. The use of the superconducting cavities is comingfrom the requirement of the long beam pulse train
acceleration in order to generate high flux X-ray. The
accelerator illustration is shown in Fig. 3, the accelerator
layout is shown in Fig. 4, and the picture is shown in Fig.
5. Before cryomodule installation, two 9-cell cavities
were tested and successfully reached its gradient up to40MV/m and 32MV/m. The cavities were installed in thecapture cryomodule and connected to the 800kW DRFS
klystron power system. The capture cryomodule coolingpipes are connected to the newly fabricated 2K cold-box,
and then connected to the existent STF cryogenic system.
The cryomodule construction was started from 2010, theassembly and installation to the STF tunnel in 2011. Thebeam source and the beam line were installed in autumn
2011. The beam source consists of the photocathode RF
gun cavity and the ultra-violet (UV) laser system.
Synchronized 162.5MHz seed laser output of infrared is

The design parameters for the Quantum-Beamaccelerator and the STF phase-2 accelerator are listed inTable 1. The main difference of the electron beam is thebunch spacing and the charge in the bunch. The
Quantum-Beam accelerator uses 162.5MHz bunch
repetition frequency, that is, 6.15ns spacing with62pC/bunch. The peak current of the train is 10mA. On
the other hand, STF phase-2 accelerator uses 2.708MHz
bunch repetition frequency, that is, 369.27ns spacingwith 3.2nC/bunch. The peak current of the train is 8.7mA.
The different RF gun laser systems are used in theseaccelerators. The energy of the beam is 40MeV for theQuantum-Beam accelerator, 21.5MeV for STF phase-2.

Table 1: beam parameters of STF accelerator.
The beam line for the focusing and collision with laser isdesigned. Three 20 degree bending magnets are used forthis purpose. The electron beam has to come in and out
to the 4-mirror laser accumulation optical line (Fig. 6) byusing two 20 degree bending magnets. In the centre of
the two bending magnet, the electron beam is focusedaround 10µm beam size by the upstream optics. In order- 1189 -to tune the beam size easy, the optics between the firstbending magnet and the second bending magnet isdesigned as the symmetric transferred optics. The beam
size in the first focal point will be transferred to thesecond focal point automatically by the symmetrictransferred optics. The focal point tuning just before thefirst bending magnet will therefore give the tuning of thecollision point beam size. The beam focus tuning ismonitored by the 10µm tungsten wire scanners for theirbeam size. Since almost all the quadrupole magnet usedin the focus line are the one reserved in ATF, so theaperture of the chamber is limited to 24mm diameter.
There is few room for the loss-less beam transmission forthe large beta function region. The careful orbit tuning isrequired in order to reduce the background noise into theX-ray detectors.

second, without digital feedback for amplitude and phasein the pulse flattop.
In June 2012, the digital feedback of the amplitude andphase for the RF gun cavity and superconducting cavities
were successfully applied with reasonable small control
accuracy including beam loading. The 1ms long beamtrain was successfully accelerated up to 40MeV. The
intensity was 15pC/bunch, 1/4 of the target intensity as
shown in Fig. 7. The detailed beam study will beperformed in 2012.

Fig. 6: Illustration of Laser accumulation chamber.

Fig. 4: Schematic diagram of STF accelerator.

Fig. 7: Scope signal for accelerated1ms beam train.

Fig. 5: Picture of STF accelerator in tunnel.
The commissioning of the STF accelerator followed by
the capture cryomodule cool-down and tuning of thesuperconducting cavities, was started on April 2012. The
optics of the beam line was set to the ‘commissioning
optics’ which has relatively small beta function for thetransportation part, and has large beta function in thecollision point, in order to make beam transportationeasy. The beam energy was set to 40MeV. The
accelerating field of the superconducting cavities wereadjusted for beam to go through the bending magnet with
40MeV setting. In order to match the beta function at thedownstream of the cryomodule, the solenoid field of theRF gun was adjusted. As a result, the accelerated beam
was 40MeV energy, 41pC/bunch of intensity, total 28
bunches in a train with 5Hz repetition. The input powerof the gun cavity was 2.2MW. It corresponds to
34.6MV/m of extracted field at the cathode. The energy
at the gun exit was measured to 3.3MeV. The setting
values of the superconducting cavities field were
20.15MV/m for the first cavity and 21.5MV/m for the4 TDR POWER SCHEME
Since KEK newly proposed Kamaboko-tunnel (Fig. 8)
for Japanese mountain site, the RDR-type RF power
scheme became a cost effective baseline for TDR rather
than DRFS (Distributed RF System) small klystronsystem. Kamaboko tunnel has thick concrete wall in thecentre makes the room divided to the accelerator tunneland klystron tunnel. The RF power source consist of a10MW multi-beam klystron and a Marx modulator,
supply 1.3GHz 1.6ms pulse RF power into 39 cavities
with circulator in each input (Fig. 9). The power can besplit with flexibility by a variable hybrid. Also, a phaseof RF input can be controlled by a phase shifter in eachof cavity input line. A coupling of cavity can becontrolled by an input coupler insertion length. In order
to control each cavity power input and loaded-Q of eachcavity (Pk-QL control) among vector-sum controlled
cavities, the above variable adjustment are controlledremotely.

- 1190 -In STF phase 2 accelerator, this type of new RF power
scheme will be installed and demonstrated. The 10MW
multi-beam klystron (MBK) is used for the power source(Fig.10), and DTI Marx modulator (coming fromcollaborator SLAC) (Fig.11) drives the MBK. Thesystem will be tested in this autumn. STF will purchase
one more MBK and one more Marx modulator, as areplacement of #1 power station.

Fig. 8: Kamaboko-tunnel design for Japanesemountain site.

5 CAVITY INDUSTRIALIZATION R&D
The cavity fabrication facility (CFF) was constructedin the utility building of the former proton synchrotron
accelerator. The clean room was built inside of the utilitybuilding. It includes an electron beam welder (EBW), apress machine, a trimming machine, a chemical room,and several instrumentations. The delivery of EBW wason April 12, 2011, however, the development study wasalready started for EBW parameter optimization using
the same type of EBW at job-shop company in Tokyo.
The press machine optimization study was also done
together with press-die optimization. The fabrication
cavity without HOM named KEK-#0 (Fig. 12) wasstarted a year ago through these optimization, and thecenter cell part of 8-dumbbells were completed theirwelding in July 2011 using job-shop company. The end
group part was fabricated and connected to the center
cell part by using CFF EBW. The performance of thisfirst produced cavity was 29MV/m, close to ILC
qualification gradient. KEK-#1 cavity under fabrication
has HOM couplers in both end beam pipes. It is ILC
cavity with full-use of CFF machines. The completion ofthis cavity will be in October 2012.
Mass-production study for EBW process, HOM couplerand end-group pipes are in progress. It will be explainedin other paper.

Fig. 9: RF power distribution scheme of TDR.
Fig. 12: KEK-#0 cavity fabricated at Cavity
Fabrication Facility and job-shop.

6 ACKNOWLEDGEMENT

Fig. 10: 10MW Multi-Beam-Klystron.

The author would like to thank all the members ofSTF group for their effort to develop ILC
superconducting accelerator technology. The support of
the LC supervisor, S. Yamaguchi, and the support ofAccelerator Laboratory director, K. Oide, trustee of theexecutive board, Y. Kamiya, F. Takasaki, and director
general of KEK, A. Suzuki, are gratefully appreciated.

7 REFERENCE

Fig. 11: SLAC-DTI Marx modulator[1] ILC Reference Design Report, ILC-Report-2007-001(2007);
http://www.linearcollider.org/cms/?pid=1000437[2] R&D plan in TDP-2, release 4 (July, 2010);
http://ilc-edmsdirect.desy.de/ilc-edmsdirect/file.jsp?edmsid=*813385[3] ILC A Technical Progress Report, 2010;
http://www.linearcollider.org/about/Publications/interim-report[4] Hitoshi Hayano, “KEK-STF status,” Proc. of the 8thJapanese Accelerator Society meeting, 2011.

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