CAVITY DIAGNOSTIC SYSTEM FOR THE PERFORMANCE TEST OF
THE 1.3GHZ SUPERCONDUCTING 9-CELL CAVITY
Y. Yamamoto#, H. Hayano, E. Kako, S. Noguchi, M. Sato, T. Shishido, K. Umemori, K. Watanabe,
KEK, Tsukuba, 305-0801, Japan,
H. Sakai, ISSP, Univ. of Tokyo, Kashiwa, 277-8581, Japan,
T.X. Zhao, IHEP, Beijing, 100049, China
INTRODUCTION
The new test facility for the superconducting cavity
(STF) is completed at KEK. It is included the electropolishing (EP) device for the surface treatment of the
cavity, the chemical polishing (CP) system around the
flanges of the beam pipes, the high pressure rinsing
(HPR) with ultra-pure water, the clean-room for the
assembly working of the cavity, the pre-tuning system for
the frequency tuning of the cavity, and the test facility for
the cavity performance test (vertical test). During the
vertical test, the temperature mapping (T-mapping)
system using the carbon resistor is normally used to
identify the heating spot, which is considered as the
defect or the contamination. On the other hand, the x-ray
monitoring using the PIN diode is effective for the
observation of the field emission [1].
New vertical test facility for the superconducting 9-cell
cavity (Figure 1) was completed in STF at the beginning
of 2008 [2]. One superconducting 9-cell cavity
(AES#001) was sent from FNAL for the system check of
the facility. This cavity was totally measured seven times
in U.S. The achievable accelerating field was 15.2MV/m.
The heating was detected at #3 cell by FNAL’s Tmapping system in the vertical test at FNAL. The three
suspicious points were found at #3 cell from the result of
the observation with Kyoto Camera [3], and one
suspicious point was found at #7 cell. As the pilot test of
the new vertical test facility, the vertical tests are done
totally a few times using this cavity within 2008.
introduced to detect the heating during the high power rf
measurement. After finding the heating spot, it is also
important to inspect the cavity inside using the optical
inspection system. The T-mapping system and the optical
inspection system are complementary each other and vital
to improve the performance of the superconducting cavity,
which is used for ILC (International Linear Collier) and
ERL (Energy Recovery Linac).
NEW VERTICAL TEST FACILITY & NEW
T-MAPPING SYSTEM (FISH-BONE)
In the new vertical test facility (Figure 2), there are two
holes for the two cryostats in the pit, the iron shield for
the radiation which is automatically moved, the pumping
system composed of 2 rotary pumps and 1 mechanical
booster pump with the high exhaust velocity, the clean
booth for the assembly of the T-mapping system, the
control room and the four cavity stands. The 400W highpower amplifier is used for the RF measurement.
Figure 2: The new vertical test facility in STF.
Figure 1: The Superconducting 9-cell Cavity.
After first CP and HPR at STF, the first vertical test
was done on Oct/2008. The new T-mapping system was
The new T-mapping and x-ray monitor system is
shown in Figure 3. It is called “Fish-Bone” structure.
Although the number of the carbon resistors is about 150
now, it will be attained several hundred channels in the
future. The resistors will be attached every 30 degrees at
each cell and the number per cell is 36. The PIN diodes
are attached to the top and bottom flanges for the
observation of the field emission, and near the stiffening
ring.
SUMMARY & FUTURE PLAN
Figure 3: The new T-mapping and x-ray monitor system.
VERTICAL TEST & RESULT
The first vertical test using AES#001 cavity was done
in 8-9/Oct./2008. The achievable field was 15.9MV/m
and consistent with FNAL’s result. The different points
between FNAL and KEK are the coupler type (variable or
fixed) and the use of the magnetic shield (with or without).
The heating was observed at #3 cell using Fish-Bone.
In π, 8π/9, 6π/9 and 5π/9 mode, #3 cell was heating and
limited to the achievable field. The heating at the
suspicious point was highest and other points were lower
than that (Figure 4), when the cavity was quenched. On
the other hand, although #6 cell was temporarily heating
by the multi-pacting in 7π/9 mode, it eventually
disappeared in the end of the measurement [4].
The new vertical test facility was completed in STF and
the new T-mapping system was also introduced. The first
vertical test in STF was done using it. It was successful to
detect the heating at #3 cell, which result is same as that
in FNAL. It found that the achievable field was limited by
#3 cell in four pass-band modes. On the other hand, it was
possible to observe the temporary phenomenon by multipacting.
The number of the carbon resistors will be increased
more and more in the future, and it will be about 350 by
the end of 2008. Similarly, the number of the PIN diodes
will be increased. To avoid the use of many cables, it is
necessary to introduce the switching circuit and it is under
consideration.
The T-mapping system and the optical inspection
system is complementary each other. Inspecting the cavity
before and after each vertical test, and detecting the
heating by T-mapping, it will find out whether any
suspicious spot is problematic or not. It is crucial for the
fabrication of the cavity and helpful for the understanding
of the cavity performance [4]. In STF, many cavities will
be tested in the future and the systematic understanding
for the cavity performance will be advanced.
ACKNOWLEDGMENTS
The authors wish to express our special thanks to S.
Mishra, B. Kephart, M. Champion and C. Ginsburg in
FNAL for the rental of AES#001 cavity, H. Padamsee in
Cornell, W. Moeller in DESY and Y. Morita in KEK for
providing the carbon resistors, T. Okada and M. Iitake for
the assembly working of the T-mapping.
REFERENCES
[1] Y. Yamamoto et al., SRF 2007, Beijing, China,
(2007) WEP13.
[2] Y. Yamamoto et al., EPAC’08, MOPP044.
[3] Y. Iwashita et al., EPAC’08, WEOBM03.
[4] https://indico.desy.de/conferenceOtherViews.py?
view=standard&confId=946
Figure 4: The heating at #3 cell during the rf measurement.
It found that the other cells can achieve around
30MV/m, although #3 cell was limited around 15MV/m,
from the result of the measurement using seven pass-band
modes.
For monitoring the x-ray emission, the x-ray level was
below several hundred μSv/h in π mode measurement.
From the result of Q-E curves, the trend of the field
emission was observed in 8π/9, 7π/9 and 4π/9 mode.