-
TESTS OF THE ACCELERATING CRYOMODULES FOR THEEUROPEAN X-RAY FREE
ELECTRON LASER
M. Wiencek, B. Dzieza, W. Gaj, D. Karolczyk, K. Kasprzak, L.
Kolwicz-Chodak, A. Kotarba,A. Krawczyk, K. Krzysik, W. Maciocha, A.
Marendziak, K. Myalski, Sz. Myalski, T. Ostrowicz,
B. Prochal, M. Sienkiewicz, M. Skiba, J. Swierblewski, J.
Zbroja, A. Zwozniak,
The H. Niewodniczanski Institute of Nuclear Physics Polish
Academy of Sciences, Krakow, Poland
AbstractThe European X-ray Free Electron Laser (XFEL) is
cur-
rently under construction in Germany in Hamburg area.A 2.1 km
long superconducting linear accelerator, part ofthe XFEL, consists
of 101 accelerating cryomodules. TheXFEL cryomodule is assembled
with eight superconduct-ing RF cavities, one cold magnet and Beam
Position Mon-itor (BPM). The cryomodules are tested in dedicated
testfacility before installation in the XFEL tunnel. The
testingprocedures for the cryomodules were prepared with use ofDESY
expertise from TTF (Tesla Test Facility) Collabo-ration and FLASH
(Freie-Elektronen-Laser in Hamburg).This paper describes the full
set of testing procedure andincoming and outgoing inspections as
well.
INTRODUCTIONThe cryomodules for accelerating part of the XFEL
are
assembled in CEA Saclay (France) and delivered to DESY(Hamburg).
After delivery the cryomodules are beingchecked during so called
incoming inspection and followedby their preparation for the tests.
Next step is cooling downof the cryomodule to the temperature of
2K. Then, RF andcryogenics measurements are performed. The
cryomoduleis being warmed up while the measurements are nished.The
nal step is performance of the outgoing inspection.According to the
current estimation 14 working days orga-nized in two shifts are
needed to complete the test of onecryomodule. All of the steps
mentioned above are done byThe H. Niewodniczanski Institute of
Nuclear Physics Pol-ish Academy of Sciences (IFJ PAN) team [1].
Currentlyover 30 enginners and technicians from IFJ PAN are
in-volved in testing the cryomodules and RF cavities in newAMTF
(Accelerator Modules Test Facility) Hall at DESYin Hamburg.
Performance of all cryomodules tests is a partof Polish in-kind
contribution for European XFEL.
INCOMING INSPECTIONDuring transportation the cryomodules are
equipped
with vacuum monitoring system and shock loggers. Datafrom these
devices are read as the rst step of the incominginspection. If
results of the read are acceptable the restora-tion of high vacuum
in the coupler line is performed. Next,mechanical and electrical
checks are performed. The me-chanical inspection consists of
removal of transport caps
and visual checks of all anges and process pipes. Theelectrical
inspection consists of checks of all connectorand feedthroughs and
functionality test of cavities and cou-plers tuners. The
measurements of the fundamental modespectra of each cavity follow
the mechanical and electri-cal checks. Finally, resistance test of
the magnet coils isperformed.
PREPARATION FOR TESTSAfter the incoming inspection the
cryomodule is in-
stalled on the test stand. At the beginning the cryomoduleis
mounted on a special trolley, transported to test stand andaligned.
Next step is to connect the beam line to the vac-uum system in a
clean room conditions. The mass spec-trometry is performed to
ensure that there is no contamina-tion in the beam line. Example of
the mass spectrometryresults are shown in Figure 1.
Figure 1: Mass spectrum of the beam line.
Then the following mechanical operations are per-formed:
• connection of process pipes,• closing sliding muffs,• leak
check of the process pipes and the cryomodule,• wrapping the
process pipes with MLI (Multi LayerIsolation),
• installation of the thermal shields,• wrapping the thermal
shields with MLI,• pump down of the isolation vacuum
When the preparation is done the electrical and waveg-uides
connections are made. Finally, a warm coupler con-ditioning is
performed to clean impurities from couplers.
MOP054 Proceedings of SRF2013, Paris, France
ISBN 978-3-95450-143-4
244Cop
yrig
htc ○
2013
byth
ere
spec
tive
auth
ors
09 Cavity preparation and production
K. Technical R&D - Large scale fabrication
-
COOL DOWN
Test of the XFEL module is performed at 2K, thus allcomponents
of the cryomodule are step by step cooleddown to operation
temperature. One can highlight fewphases in the cool down process.
During the rst phase thetemperature of the module is lowered to 80K
with manytemperature and pressure constraints. This prevents
themodule from thermal stresses caused by large
temperaturegradients. Around 80K most of dislocations in the
mate-rial are blocked, thus, the cool down process of the mod-ule
is proceed to 4.5K. When all vessels are lled up byliquid helium
the last phase of the cool down can be per-formed. The pressure
above liquid helium bath is loveredto 31 mbar. This provides
temperature of 2K and the cooldown process is considered as nished.
The cool down pro-cess is shown in Figure 2. Conditioning of the
couplers isalso performed during the cooling down.
Figure 2: Automatic cool down procedure plot.
RFMEASUREMENTS AT 2K
The RF measurements in cryogenic conditions are di-vided in two
phases. The rst phase is measurements atlow RF power while the
second one is - at high RF power.The former measurements are
performed by means of Vec-tor Network Analyser (VNA) an RF ampli
ers if needed.The latter measurements are performed with
klystron.
Measurements at Low RF PowerThere is a necessity to measure
attenuation of the cables
inside the module at 2K. This measurement is performed asa S11
measurement and has to be done inside the test stand.All the other
mentioned measurements can be done outsideof the test stand using
cables for high RF power measure-ments. After that a fundamental
mode spectra of each cav-ity is measured. Then the cavities are
roughly tuned to thedesign resonance frequency (1.3 GHz). In
parallel, an ex-ternal quality factor of the couplers is set by
coupler mo-tors. Finally, the High Order Mode (HOM) Spectra
mea-surement is performed. The results panel is shown in Fig-ure
3.After these operations test stand is closed and secured by
the Personal Interlock.
Figure 3: HOM Spectra measurements application.
Measurements with igh RF owerThere is no possibility to tune the
cavities to the exact
resonance frequency with the VNA. Therefore the ne tun-ing with
use of the LowLevel RF (LLRF) system is needed.This is the rst
operation performed with the klystron. Af-ter ne tuning, the
cavities are calibrated at low gradient (5MV/m) to determine the
following parameters:
• Kt - calibration coef cient used to calculate the
gra-dient,
• Qext - External quality factor adjusted during tuningwith VNA;
measurement of Qext is much more accu-rate at high RF power
• Qprobe - Quality factor of the Probe antenna• QHOM1 and QHOM2
- Quality factor of the HOMsantennas
A new software for cavities calibration has been writtenby IFJ
PAN Team (Figure 4)
Figure 4: Calibration application.
After calibration the cavities are tested one by one. Be-cause
of the power distribution system there is a necessityto detune all
cavities except one. Most important results ofthis measurement are
listed below:
• Quench limit [MV/m],• Operating gradient - Value of Gradient
when radiationdo not exceed 10−2 mGy/min [MV/m],
• Xrays start - Value of Gradient when radiation
starts[MV/m],
• Xrays quench - Value of radiation just before cavityquench
[mGy/min],
H P
Proceedings of SRF2013, Paris, France MOP054
09 Cavity preparation and production
K. Technical R&D - Large scale fabrication
ISBN 978-3-95450-143-4
245 Cop
yrig
htc ○
2013
byth
ere
spec
tive
auth
ors
-
• Pfor - power used to drive a cavity to the quench limit
The measurements results of a pre-series XFEL cry-omodules
(XM-3) are shown in Figure 5. After completingthe performance test,
all cavities are again tuned to the res-onance frequency in order
to perform the cryogenic mea-surements.
Figure 5: Results of the performance test.
CRYOGENICMEASUREMENTSThe cryogenic measurements are divided into
two
phases. The rst phase is a static measurements, whenthere is no
powering inside either cavities or the magnet.The second one, so
called Heat LoadsMeasurements is per-formed with the powered
cavities.
Static MeasurementsThe thermal performances of the accelerator
modules is
a vital issue to estimate the load budget of the
refrigeratorsystem. Variety of measurement considers the losses
oncryogenic lines such as 2K, 4.K and 40/80K are performed.
Heat Loads MeasurementsThis measurements are performed by two
operators: one
from cryogenic site and another from RF site (RF
operatorapplication is shown in Figure 6). First, the zero
measure-ment is performed in order to obtain the cryogenic
loadwithout power. Then all cavities in cryomodule are pow-ered to
certain level of the gradient. Next the series ofmeasurements at
different gradients are proceeded. Duringthose measurements a few
points are obtained: at gradientjust below the Xrays start, when
radiation exceeds 10−2mGy/min (if available). Next at 23.6 MV/m
(XFEL goalgradient) and just below the lowest cavity quench limit.
Ifthere is only one cavity with low limit in cryomodule thecavity
is detuned. The cryomodule is operated without theweakest. The
cryogenic calculation of heat loads are shownon Figure 7. From
cryogenic load total Quality factor of allcavities inside the
cryomodule is calculated. Thus, Qualityfactor from this
measurements is averaged for each cav-ity. Software for this
measurements has been written byIFJ PAN Team.
Figure 6: Heat Loads measurement - RF operator applica-tion.
Figure 7: Heat Loads measurement - Cryogenic calcula-tions.
WARM UP, DISASSEMBLY, OUTGOINGINSPECTION
After measurements at 2K the cryomodule is warmed upand
disassembled from the test stand. Next, the outgoinginspection is
performed in order to con rm that there wasno damages during the
tests procedure. Results of outgoinginspection is put into Outgoing
Inspection Report. Finally,the cryomodule is handed over to the
next work packagesfor further installation.
ACKNOWLEDGMENTThis work is being funded by the Ministry of
Science
and Higher Education in Poland (MNiSzW) as a part of thePolish
contribution to construction of the European XFEL.We would like to
thank the DESY management and expertsfor their support during our
work.
REFERENCES[1] A. Kotarba, P. Borowiec, W. Daniluk, M. Duda, B.
Dzieza,
W. Gaj, E. Gornicki, D. Karolczyk, K. Kasprzak, L.
Kolwicz-Chodak, J. Kotula, A. Krawczyk, K. Krzysik, W. Maciocha,A.
Marendziak, K. Myalski, Sz. Myalski, T. Ostrowicz,B. Prochal, M.
Skiba, M. Stodulski, J. Swierblewski, M.Wiencek, J. Zbroja, A.
Zwozniak, ”Proc. SPIE”, vol 9803,8903-97 (2013)
MOP054 Proceedings of SRF2013, Paris, France
ISBN 978-3-95450-143-4
246Cop
yrig
htc ○
2013
byth
ere
spec
tive
auth
ors
09 Cavity preparation and production
K. Technical R&D - Large scale fabrication