FREIA Report 2015/03
18 May 2015
DEPARTMENT OF PHYSICS AND ASTRONOMY
UPPSALA UNIVERSITY
The Cryogenic System
at the
FREIA Laboratory
R. Ruber, R. Santiago Kern, K. Gajewski, L. Hermansson,
Å. Jönsson, V. Ziemann and T. Ekelöf
Uppsala University, Uppsala, Sweden
Department of
Physics and Astronomy
Uppsala University
P.O. Box 516
SE – 751 20 Uppsala
Sweden
Papers in the FREIA Report Series are published on internet in PDF format.
Download from http://uu.diva-portal.org
Uppsala University
FREIA Laboratory
FREIA Report 2015/03
26th May 2015
[email protected]
The Cryogenic System at the FREIA Laboratory
R. Ruber, R. Santiago Kern, K. Gajewski, L. Hermansson, Å. Jönsson,
V. Ziemann and T. Ekelöf
Abstract
This report describes the project status of the helium liquefier plant and horizontal cryostat system
which have been funded by a generous grant from the Knut and Alice Wallenberg Foundation
(KAWS).
1
Introduction
From the discovery of superconductivity in 1911 it took until the 1960’s before the first
superconducting magnets where developed and until the 1970’s for the first superconducting
accelerating cavities. Since then however these superconducting devices have become a
key element of many accelerators and experiments in fundamental physics research: Large
Hadron Collider (LHC) with the ATLAS and CMS experiments at European Organization
for Nuclear Research (CERN), European X-ray Free Electron Laser (XFEL) at Stiftung
Deutsches Elektronen-synchrotron (DESY), European Spallation Source (ESS) in Lund, the
proposed International Linear Collider (ILC) and the new Linac Coherent Light Source
(LCLS) II project in the US. Bio-medical research uses superconducting (SC) magnets in
their Magnetic Resonance Imaging (MRI) devices.
Uppsala University (UU) has a long tradition of excellent research with several Nobel
laureates among its professors. Throughout history special emphasis was put on building scientific instruments and accelerators that are used for fundamental, material and life sciences.
Superconductivity played an ever more important role as a fundamental research topic, but
importantly, as an enabling technology for new instruments and experiments. For example,
several modern particle accelerators employ superconductivity to accelerate particles in radio
frequency (RF) systems or guide them with magnets. With these developments in mind the
authors to proposed to establish the FREIA laboratory at Uppsala University in order to
support the development of instrumentation and accelerator technology [2, 3]. Key element
of FREIA is the capability to produce liquid helium in large quantities. The liquid helium
is used at both FREIA and other research groups in Uppsala to cool down research equip1
ment and test samples to 1.8 K. The FREIA Laboratory is equipped with a superconducting
radio frequency (SRF) cavity test facility centered around a 140 l/h helium liquefier and
the HNOSS, a horizontal cryostat that can be used to test two SRF cavities simultaneously
[4, 5, 6]. It can handle a peak heat load of up to 120 W at 4 K or 90 W at 2 K operation.
The layout of FREIA Laboratory is shown in Figure 1.
2
Project Overview
In 2010 the authors applied to the KAWS for funds to build up a cryogenic system, consisting of a helium cryogenic plant and test cryostat, of sufficient capacity to enable leading
development work at Uppsala University on superconducting particle accelerators. Funding
was granted by KAWS in 2011 after which the work started on technical specifications for
both the helium liquefier and the cryostat. Due to the complex design of these systems a
cooperation was started with CERN and Institut de physique nucléaire d’Orsay (IPNO).
Discussions where also started with the two companies that market liquefiers in Europe:
Air Liquide in France and Linde Kryotechnik in Switzerland. Accelerators and Cryogenic
Systems (ACS), an engineering company, was contracted for the detailed technical design of
the cryostat and subsequent follow-up of its manufacturing and commissioning. Personnel at
ACS and IPNO had previous experience from the design and commissioning of CHECHIA,
a horizontal cryostat at DESY [7], and CryHoLab, a horizontal cryostat at Commissariat à
bridge to
Ångström
Laboratory
cryogenics
control room
vertical cryostat
RF equipment
3 bunkers with
test stands and
horizontal cryostat
Figure 1: Layout of the FREIA Laboratory.
2
l’Énergie Atomique et aux Énergies Alternatives, centre de Saclay (CEA Saclay) [8].
The layout of the cryogenic system design is shown in figure 2. The blue boxes indicate
sub-systems while the yellow boxes indicate some of the main individual components. In the
top left parts is the helium liquefier including both the liquefier (4K) cold box and the helium
recycle compressor. The liquid helium (LHe) output of the cold box is connected to a storage
dewar with integrated valve box. The storage dewar has three transfer lines connected: to
transport dewar filling, to horizontal cryostat system and to vertical cryostat system. From
the cryostat systems the helium gas returns through a low pressure line back to the helium
liquefier. In parallel there is a low pressure return line to the sub-atmospheric pumping
system and gas helium recovery system to the internal purifier of the cold box and back into
the liquefier. The high pressure helium gas storage and liquid nitrogen (LN2) storage are
also indicated. A dashed line shows the liquid nitrogen distribution. The vertical cryostat
system is not part of this project but has been included for completeness of the design layout.
The main procurement was split in three steps:
• Helium cryogenic system (UH2011/64), launched on 12-Apr-2012. Two tenders were
received. The tender by Linde Kryotechnik AG was accepted as the most competitive.
The contract was signed on 07-Nov-2012. Delivery was partly in September 2013 and
partly in February 2014. Installation and commissioning was completed on 19-Mar2014 by liquefying helium.
• Horizontal cryostat system (UH2012/76), launched on 22-Apr-2013. Four tenders were
received. The tender by Cryo Diffusion was accepted as the economical most advantegeous. The contract was signed on 30-Sep-2013. Delivery was on 12-Aug-2014.
Installation and commissioning was completed on 09-Dec-2014 by reaching a temperature of 1.8 K in the cryostat.
• Sub-atmospheric pump system (UH2012/79), launched on 15-Nov-2013. Two tenders
were received. The tender by Low2High Vacuum AB (Swedish representative of Oerlikon Leybold Vacuum GmbH) was accepted as the economically most advantegeous.
The contract was signed on 04-Mar-2014. Delivery was on 22-Sep-2014. Installation
and commissioning was completed on 09-Dec-2014 by reaching a temperature of 1.8 K
in the cryostat.
The old Koch liquefier at the Ångström Kryocentrum was malfunctioning by the time the
new Linde liquefier was taken into operation. The Kryocentrum was moved to the FREIA
Laboratory in April 2014 after the inauguration of the new liquefier. The cold box of the old
Koch liquefier was given to the cryogenic laboratory at the Freie Universität Berlin which
will use it to recover spare parts for their liquefier. The old high pressure gas storage has
been incorporated in the high pressure storage at FREIA after cleaning and pressure test.
The remaining parts have been recycled after some three decades of usage.
3
The Cryogenic Plant
The cryogenic plant is built around a Linde Kryotechnik L140 liquefier cold box. An overview
of the main parameters is listed in table 1. It includes the following components:
3
Helium Liquefier
High Pressure Storage
Cooling Water
Oil Removal
Compressor
HP
Cryogenic System
Roger Ruber / 2015-05-18
LP
Dryer
Medium Pressure
Pure Gas Storage
Cold Trap (ext. purifier)
Gas Analyzer
Gas Helium Recovery
Gas
Analyzer
(option)
Oil Separater
Cooling
Water
Compressor
Adsorber
Turbine
Liquid
Nitrogen
Pre-cooling
Impurity
Monitor
Turbine
4K Cold Box
Gas Bag
Purifier
Adsorber
internal to
cold box with
LHe cooling
JT Valve
4K 2phase output and return
to GHe
Recovery
LN2
Transport
Dewar
LHe
Transport
Dewar
Inter
Connection
Box
Cooling
Water
Shielded Transfer Line
4K Dewar
to
Cryomodule
LN2
Storage
Sub-atmospheric
Pumping System
Spare
Shielded Transfer Line
Liquid Helium Storage Dewar
and Distribution Valve Box
Transfer Line
Cooling
Water
Cold
Gas
Heater
Cold
Gas
Heater
Thermal Radiation
Shield
- 80 K: LN2 cooled
80K Shield
Heater
Dewar Filling Station
4K Pot
Coupler
anchored
to 80K
Device Under Test
Support (4K)
Vertical Cryostat System
2K Pot
80K Shield
Horizontal Cryostat System
JT Valve
Spare
Figure 2: Layout of the cryogenic system.
4
from Dewar
Filling Station
4K Pot
JT Valve
LHe Bath
Device
Under Test
from
Ångström
Laboratory
via
Impurity
Monitor(s)
Table 1: Main parameters of the cryogenic plant.
Liquefier Cold box
- nominal capacity
- pre-cooling
- purifier min. inlet pressure
Linde L140
140 l/h at 1.15 bar
150 l/h at 1.23 bar
70 l/h liquid nitrogen
25 bar
Liquid helium dewar
- storage volume
- nominal working pressure
- working pressure with HNOSS
- max. test pressure
- filling speed mobile dewars
2000 l
1.15 bar
1.2–1.25 bar
2.86 bar
165 l/h (average)
Recycle compressor
- number of units
- mass flow capacity (per unit)
- nominal discharge pressure
- max. discharge pressure
Kaeser DSD238 SFC
1
43.5 g/s
11.5 bar
14 bar
Recovery gas balloon
- storage volume
100 m3
Recovery compressor
- number of units
- mass flow capacity (per unit)
- max. discharge pressure
Bauer G18.1-15-5-He
3
25 m3 /h
200 bar
Pure gas medium pressure storage
- storage volume
30 m3
- max. working pressure
14.5 bar
- max. pressure
23 bar
Impure gas high pressure storage
- storage volume
- max. pressure
10.85 m3
200 bar
Liquid nitrogen tank
- storage volume
- nominal pressure
- max. pressure
- filling speed mobile dewars
20 m3
3 bar
18 bar
300 l/h
5
• a compression system consisting of a Kaeser DSD238 SFC recycle compressor with a
gas flow of 43.5 g/s and 14 bar discharge pressure, an oil removal system with several
filters, a pressure regulation system and a 30 m3 pure helium medium pressure buffer
tank,
• a standard liquefier coldbox with 80 K and 20 K adsorbers for purification of the helium
gas plus an internal freeze-out purifier for the recovered helium gas,
• a custom built 2000 l liquid helium storage dewar with distribution valve box,
• a gas recovery system with a 100 m3 helium gas balloon and three 25 m3 /h high
pressure recovery compressors with max. 200 bar discharge pressure,
• a high pressure gas storage of 10.85 m3 at max. 200 bar,
• an external liquid nitrogen trap installed between the recycle compressor and cold box,
used as a bypass purifier when starting up the cold box after refilling with non-pure
gas or after a longer shutdown,
• an impurity monitor for the cold box feed gas that measures the ratios of nitrogen,
water, hydrocarbons and oil in the gas running from the recycle compressor to the cold
Figure 3: Photo of the liquefier installation with cold box, storage dewar and filling station.
6
box,
• a liquid nitrogen system consisting of a 20’000 l storage dewar, a phase separator and
two filling stations for mobile dewars.
The cold box contains heat exchangers, cryogenic valves, two turbines and one JouleThomson valve for the liquefaction process. Liquid nitrogen pre-cooling of the first heat
exchanger is used to reach the nominal liquefaction rate of 140 l/h. Without this pre-cooling
the liquefaction rate is approximately a little less than half. Adsorbers at 80 K and 20 K
freeze out impurities from the helium gas during the cooling process. The 20 K adsorber
has been equipped with three extra cryogenic valves for inline regeneration preventing the
need to warm-up the whole cold box. This process has been included to prevent clogging
of the adsorber, observed in other installations during long term operation. Clogging of the
adsorber without the ability of an inline regeneration implies a forced warm-up of the cold
box, and thus stop of the liquefier.
The storage dewar has four connections for the distribution of liquid helium: one specific to fill mobile dewars and three with integrated cryogenic valves to connect to experiments. These three connections accept insulated transfer lines with bayonet type connection.
Figure 4: Photo of the helium gas and liquid nitrogen tanks.
7
The storage dewar acts as a buffer in case a different throughput than provided by the liquefier is required.
The main recycle compressor and the oil removal system are installed in a separate
“compressor” room together with the recovery system. This decreases the noise level in the
FREIA Laboratory main hall considerably. However, unfortunately, this also increased the
distance between the recycle compressor and the cold box to some 54 m due to a decision
by the university building agency on the location of the cold box. The compressor room is
at the end of the building, where the medium pressure buffer tank and liquid nitrogen tank
are located, while the cold box and storage dewar are at the other end (see figure 1).
The helium gas recovery system collects impure gas from experiments and compresses
it into the high pressure storage. It has been connected to the existing recovery lines from
the Ångström Laboratory and the Uppsala Biomedical Centre (BMC). Initially, the gas is
recovered in a balloon at atmospheric pressure after which it is compressed into the high
pressure storage by a set of so-called recovery compressors. The actual storage capacity of
the gas balloon is 10 to 20% lower than its nominal capacity due to rods placed along the
sides of the balloon to guide it when inflating and deflating. The recovered gas can have an
impurity level sometimes up to 10%. Gas analyzers are connected at the recovery lines from
different buildings to monitor the impurity levels and inform users if they are considered too
high. When being liquefied again, the impure helium gas stored in the high pressure storage
Figure 5: Photo of the helium gas recovery compressors with the (yellow) gas balloon in the
background.
8
is first sent through the purifier inside the cold box before being sent to the liquefier part of
the cold box. Note that the purifier has a minimum inlet pressure of 25 bar (table 1) and
that the high pressure gas storage therefore cannot be emptied below this pressure.
A liquid nitrogen storage dewar, outside the building, provides the liquid nitrogen for
the liquefier pre-cooling and also for the filling of mobile dewars. Two filling stations are
available: one inside and one outside the building. The latter is mainly used for larger dewars
(over 100 l)
Figures 3, 4 and 5 show photos of the installation. The system has been installed under
the procurement contract by Linde and one of its sub-contractors. The liquid nitrogen
installation was commissioned during Fall 2013 while the liquid helium installations were
commissioned in March 2014. A liquefaction rate of over 150 l/h was reached with liquid
nitrogen pre-cooling and about half without the pre-cooling enabled. On 1 April 2014 the
Uppsala Kryocentrum was relocated to the FREIA Laboratory. During the first year of
operation a total of 8’675 l of liquid helium and 54’150 l of liquid nitrogen have been provided
for experiments all over Uppsala University, Swedish University of Agricultural Science (SLU)
and Geological Survey of Sweden (SGU). Some of the liquid nitrogen has been delivered to
external users.
4
The Horizontal Cryostat System
With help of ACS and IPNO, FREIA has designed a versatile horizontal cryostat, called
HNOSS1 , for test of superconducting accelerator cavities, magnets or other devices [4, 5, 6].
The design studies included mechanical and thermal analysis [9, 10, 11]. Finite element
analysis (FEA) where performed with the ANSYS software [12] to define the mechanical
stress, buckling and displacement of the different vacuum vessels (HNOSS, valve box, interconnection box) in order to verify the choice of material and its thickness with respect to
the EN 13445 pressure vessel code. Mechanical FEA were also performed for the thermal
shield and supports of HNOSS to verify their strength with respect to gravity and their
ability to support the weight of a person, if so required, during installation or maintenance
work. Similar FEA of the 4 K and 2 K liquid helium reservoirs were performed. Thermal
and thermal-mechanical FEA were done on the cooling of the thermal shield and the cold
vapour heater.
The idea of HNOSS is based on HoBiCat at Helmholtz-Zentrum Berlin (HZB)2 [13].
HNOSS, like HoBiCat, can accept two superconducting accelerating cavities simultaneously.
Its dimensions, 3.2 m internal length by 1.3 m diameter, and access ports are designed to
accommodate both TESLA type 1.3 GHz and ESS type 704 MHz elliptical cavities as well
as ESS type 352 MHz double spoke resonators. HNOSS has an integrated internal magnetic
shield and a valve box located on top as shown in Figure 6. The temperature operation
range is down to 1.8 K with up to 90 W heat load.
The isolation of the superconducting device from the surroundings and the distribution,
storage and recollection of the cryogens needed to reach low temperatures is achieved through
1
In Norse mythology, Hnoss is one of Freia’s two daughters.
also known under its former name BESSY (Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung)
2
9
Figure 6: Photo of the HNOSS horizontal cryostat with on top the valve box (VB).
10
Table 2: Main parameters of HNOSS.
Helium bath
- temperature
- pressure
- pressure stability at 16 mbar
- cooling power at 1.8 K
1.8 – 4.45 K
16 – 1250 mbar
±0.1 mbar
90 W
Vacuum vessel
- material
- thickness
stainless steel 304L
8 mm
Magnetic screen
- material
- annealing
- thickness
- max. relative permeability µr
mu-metal
4 hours at 1170o C
1 mm
440’000
Thermal screen
- material
- cooling pipe
- thickness
- cooling
aluminium 5754 OH 111
aluminium 6061
2 mm
liquid nitrogen
Flanges
- for power coupler
- for tie-rods
7 × ISO F500
16 × ISO KF50
Internal dimensions
- length (excl. doors)
- overall length
- diameter thermal shield
- free space above table
3300 mm
3838 mm
1200 mm × 2 mm (t)
995 mm
External dimensions
- axis height from floor
- overall length
- overall height (including VB)
1.6 m
4.0 m
4.0 m
11
the horizontal cryostat. The main design parameters are listed in table 2. It includes the
following components:
• Interconnection Box (ICB): to distribute the liquid nitrogen and liquid helium towards
the horizontal cryostat and to a second cryostat inside the bunker.
• Valve Box (VB): contains the heat exchangers, cryogenic valves and liquid helium
reservoirs required for the cooling of the Device Under Test (DUT).
• Horizontal cryostat: houses the DUT isolating it from room temperature and the
Earth’s magnetic field.
• Heater: warms the vaporized helium to room temperature. Depending on the gas
pressure, the helium gas will be directed either towards sub-atmospheric pumps or the
gas recovery system of the helium liquefier.
• Sub-atmospheric pump system: warm pumps to regulate the pressure, and thereby
the temperature, of the liquid helium bath below 4 K. Consists of a combination of
dry roots and screw pumps with a flow capacity, at room temperature, from 10 g/s at
200 mbar down to 3.2 g/s at 10 mbar.
• Transfer lines: insulated lines to transport the cryogens.
• Vacuum pumps: for the insulation vacuum of the cryostat, ICB and the beam vacuum
of SRF cavities.
Figure 7: Block diagram of the horizontal cryostat system.
12
Figure 7 shows the block diagram of the connections between the subsystems and indicates
the expected temperatures and pressures. The detailed engineering design was prepared
by ACS. The system was manufactured by a French consortium led by Cryo Diffusion and
including Meca Magnetic for the magnetic shield, Sominex for the main vacuum vessel and
ISII-Tech for the controls. The installation was performed by FREIA personnel with help of
local companies for the electric and piping work. The system is installed in the largest of the
bunkers located in the centre of the FREIA Laboratory building (see figure 1). The bunker
has an internal dimensions of 10.4 m × 4.0 m × 5.2 m (height), a 2.4 m wide access door for
equipment, an entrance chicane for personnel and 80 cm thick walls made of a double layer
of concrete blocks with magnetite ballast.
Figure 8 shows the inner layout of HNOSS equipped with two spoke cavities and some
dimensions. HNOSS can house up to two SRF cavities of different design like the ESS
double-spoke or elliptical or the TESLA/ILC type elliptical cavities. It can also be used for
other devices like superconducting magnets. A collection of vacuum flanges is available to
provide feedthroughs for ancillary equipment like the cavity power couplers and tuners or
magnet current leads. These flanges are arranged such that power couplers can be connected
horizontal (left or right) or vertical (bottom). HNOSS is indeed unique due to the fact that
it can house up to two devices, having independent paths for the cryogens. Separate sets of
vacuum pumps are required for the insulation vacuum of the cryostat and the internal beam
Figure 8: Basic dimensions and inner layout of HNOSS with two spoke cavities installed.
13
LHe
Inter
Connection
FT200
CV550 FV550
FV556
FT550
L005
FV555
FV552
SV202
CV552
TS550
PRV201
TT550
SV201
System
FT202
EV201
PRV200
SV200
H000
L006
FV100
L003
PT200
L004
H550
FV551
CV551
PT552
SV550
PT300
System
PT551
to vertical
cryostat
TT309
FV581
PT102
PT100
PT002
EH550AC
FV554
Helium
Pumping
FT552
FV553
Purging
Manual
FT551
Manual
SV203
CV201
CV200
to Kaeser circuit
PT550
W550
LS550
Cryogenic lines
to gas bag
Re-heater
HV550
LN2
Box
FT201
Valve box and Cryostat
L001
PT101
SV100
FT301
SV300
PT301
FT302
EV200
TT310
TT308
TS203
TT205
TT206
F300
TT212
TS200
EH203
EH200
To LHe 2K
EH201 EH202
TT200
TT213
EH205
TS201
TT123
TT204
A
TS202
TT100
Supercritical
EH106AB
TT124
TT129
LHe 4K
TT127
Magnetic
CV104
TT312
CV101
2
CV105
TT106
To
TT145AB
EH105AB
TT109
1
LHe 2K
S101
PT003
EH102AB
TT113
LT101
TT207
TT114
FV001
Table
EH208
A
TT125
TT303
TT126
TT117
CAVITY 1
EH107
TT217
TT143AC
TT144AC
EH103AC
EH104AC
J001
SV001
TT306
TT118
TT115
Vacuum
Pumping
System
TT215
TT305
PT004
TT142AB
TT107
FV200
EH207
TT112
TT108
TT209
Couplers
SV101
PT101
TT208
TESLA
H000
TT119
TT103
TT210
TT203
System
TT141
TT111
CV103
Purging
EH101
HX100
TT102
V001
TT302
CV102
TT201
FV300
EH300
HX300
TT120
TT110
LT100
SH300
S100
TT140AD
Shield
TT214AC
Production
TT301
TT121
EH100AD
TT101
SV301
Helium
CV100 FV101
TT146AB
FV301
FV302
TT300
TT128
TT130
EH204AC
TT311
CV302
TT307
TS301
TT122
TT211
TS302
CV301
EH302
EH301
EH303
PT302
TT304
CAVITY 2
EH108
TT116
TT147
TT148
TT104
TT105
V002
TT202
TT216AF
EH206AF
22/04/2015
Figure 9: Detailed layout of the HNOSS and Valve Box (VB) cryogenic scheme.
14
vacuum of SRF cavities.
The cryostat housing the DUTs shall insulate them from room temperature heat load
and from the Earth’s magnetic field. The design is thus a vacuum vessel with both a
magnetic shield and a thermal radiation shield. The vacuum vessel is made of stainless steel
and evacuated to a pressure in the order of 10−4 mbar. The magnetic shield is at room
temperature, directly connected to the vacuum vessel, and made of mu-metal. It reduces
the Earths magnetic field within the vessel by a factor of 5. The thermal radiation shield
is made of aluminium and cooled by liquid nitrogen to ca. 80–90 K. It intercepts heat
radiating from the vacuum vessel (at room temperature) and serves as a thermalization
point for cabling and other components that go from room to liquid helium temperature
regions. To further reduce heat in-leaks, 30 layers of multi layer insulation (MLI) are placed
between the magnetic and the thermal shield. The DUTs can be either supported by a
liquid helium cooled table on the bottom of the cryostat or they can be suspended from the
vacuum vessel wall by several tie-rods. The table eases installation of the DUT but can be
removed to create more space for larger DUTs.
The most complex component is the VB, situated on top of HNOSS. It contains the
necessary piping, cryogenic valves, heat exchangers and liquid helium pots to store incoming
helium from the cryogenic plant at 4 K, distribute it to the DUTs and cool them down
further to 1.8 K. The detailed cryogenic scheme is shown in figure 9. Liquid helium (LHe)
and liquid nitrogen (LN2) enter from the top left into the VB. Cold helium gas returns at
the top right hand via the re-heater and sub-atmospheric helium pumping system to the
gas bag or the helium liquefier (marked as Kaeser circuit). The liquid helium arrives at
the so-called 4K pot, a small storage dewar, from which it can be distributed to cool the
Purging
System
To Cryomodule
L002
To Cryostat
L001
H000
FV502
PRV400
SV400
SV401
SV502
PT500 SV500
SV501
EV400
PT001
PT000
EH400
TT400
TT404
TT405
FV401
TT402
TT502
TT501
FV501
FV400
SV000
FV500
FV000
TT500
TT403
J000
TT401
EH401
LHe
From Cold Box
Vacuum
Pumping
System
V000
InterConnection Box (ICB)
L000
10/10/2013
LN2
Figure 10: Detailed layout of the interconnection box (ICB) cryogenic scheme.
15
cryostat table, the DUT marked as cavity 1 and 2, and the so-called 2K pot marked as LHe
2K. The initial cool down of a cavity DUT is done from the bottom of the DUT until the
liquid helium level is filled up to a level inside the 2 K pot. Then the liquid helium flow is
modified to fill from the top into the 2 K pot. A heat exchanger and Joule-Thomson (JT)
valve are installed between the 4 K and 2 K pots. The temperature in the 2 K pot and the
DUT can then be lowered below 4 K by lowering the pressure of the helium bath with help
of the sub-atmospheric pumps while re-filling of the 2 K pot is done through the JT valve.
The heat exchanger is cooled by the outlet of the 2 K pot to the sub-atmospheric pumps
and cools down the inlet before the JT valve.
Available at the VB is also liquid nitrogen and 5 K supercritical helium used for, respectively, the cooling of the thermal shield and ancillary equipment of the DUT. Of special
importance here is the cooling of the fundamental power couplers of SRF cavities. The
supercritical helium is produced in a secondary helium circuit that is cooled by a heat exchanger on the exhaust of the 2 K pot. The helium gas in this secondary circuit is fully
separated from the helium gas circuit in the cryogenic plant.
The ICB is a small cryostat that contains cryogenic valves to direct the flow of the
liquid helium and liquid nitrogen cryogens to either the VB or another cryostat as shown in
figure 10. The ICB is installed on the incoming transfer lines from the liquid helium storage
(a)
(b)
Figure 11: Photos of the sub-atmospheric pumps (a) and the cryogenic interconnection box
(ICB) (b).
16
Table 3: Main parameters of the sub-atmospheric pump system.
Root pump
- quantity
Leybold RUVAC WH2500FU
3
Roughing pump
- quantity
Leybold DRYVAC DV650Helium2.1
2
Ultimate pressure
0.19 mbar
Mass flow rate
(measured)
- at 10 mbar, 300 K 7250 m3 /h (≈3.2 g/s)
- at 15 mbar, 300 K 6747 m3 /h (≈4.3 g/s)
- at 70 mbar, 300 K 2995 m3 /h (≈9.3 g/s)
dewar towards the VB, as can be seen in figure 11. The liquid helium (LHe) and liquid
nitrogen (LN2) arrive at the bottom and can be distributed to two cryostats on the top left
and right, marked as cryomodule and (horizontal) cryostat respectively. In the near future
it is planned to test complete accelerator cryomodules with superconducting cavities in the
same bunker. The cryomodule can then be installed adjacent to HNOSS and, with help of
the ICB, the cryogen flow can be adjusted between the two installations without having to
physically modify the transfer line connection.
The installation was commissioned during the Fall of 2014 and on 9 December a dummy
cavity volume was successfully cooled down to 1.8 K. A first experimental campaign with
a single-spoke cavity, kindly lent by IPNO, started in March 2015. It is being used to
benchmark and refine the cooling and measurement techniques [3].
5
The Sub-atmospheric Pump System
The sub-atmospheric pump system is used to lower the pressure of the liquid helium bath
in the 2 K pot and thereby the temperature of the 2 K pot and the DUT below the pressure
and temperature of the liquid helium bath in the 4 K pot. The dominant constraint for the
minimum temperature is the pressure that can be reached by the pumps, which in turn is
dependent upon the return helium gas mass flow at the lowest pressure.
The sub-atmospheric pump system is essentially a three stage set of vacuum pumps as
shown in figure 11. The first stage consists of two roots pumps in parallel, the second stage
consists of a single roots pumps and the third stage consists of two dry roughing pump sets
connected in parallel. Each of these roughing pump sets consists of two pumps in parallel.
The (helium) gas going through the pumps is compressed and thereby heated at each stage.
Water cooled heat exchangers refrigerate the gas between the stages. Pressure regulation is
achieved either by speed regulation of the pumps or a butter-fly valve between the pumps
and the VB. The design requirements for the pump set mass flows were 3.2 g/s at 10 mbar,
300 K (7182 m3 /h); 4 g/s at 15 mbar, 300 K (5989 m3 /h); 10 g/s at ≥200 mbar, 300 K
(1123 m3 /h). The measured mass flow rates surpassed the design values (see table 3) but it
17
was not possible to confirm the mass flow rate at 200 mbar due to constraints of the mass
flow rate into the helium gas recovery system.
The installation was commissioned in combination with the commissioning of the horizontal cryostat system.
6
The Vertical Cryostat System
Based on the experience with the HNOSS horizontal cryostat, the FREIA Laboratory is
working on the design of a vertical cryostat, “Gersemi”3 , with help of ACS. The vertical
cryostat is intended for the test of a DUT either in a liquid helium bath or in vacuum. Test
of a DUT in a liquid helium bath is preferred in the early stages of development before a
proper helium cooling pipe or vessel has been attached to the DUT. Only after attaching
the cooling pipe and/or vessel the DUT can be tested in vacuum condition like in HNOSS.
A 5 m deep and 2 m diameter hole in the floor of the FREIA Laboratory is available
to receive the vertical cryostat. The VB, heater and transfer lines will be copied, with
slight improvements, from the horizontal cryostat. The same sub-atmospheric pump set will
3
In Norse mythology, Gersemi is one of Freia’s two daughters.
Figure 12: Layout of the vertical cryostat “Gersemi”. The main dimensions are given in (a)
with the VB and gas heater cryostats visible on top and the 2000 l storage dewar on the top
left hand.
18
Table 4: Main parameters of “Gersemi”.
Helium bath
- temperature
1.8 – 4.45 K
- pressure
16 – 1250 mbar
- pressure stability at 16 mbar ±0.1 mbar
- cooling power at 1.8 K
90 W
(a)
Internal dimensions
- diameter
- height
Open bath condition
1000 – 1500 mm
2600 mm
Internal dimensions
- diameter
- height
Vacuum condition
870 – 1370 mm
3350 mm
Internal dimensions
- diameter
- height
Without inner vessel
1700 mm
3700 mm
External dimensions
- diameter
- height
1.8 m
4.5 m
(b)
(c)
Figure 13: The vertical cryostat inserts for open liquid helium bath (a), for vacuum operation
(b) and “large” vacuum operation without inner vessel and additional thermal shield.
19
LHe
LN2
Liquid Helium open bath
System
L011
Re-heater
Vertical Cryostat
To Purging
L010
to He gas
PT580
recovery system
W580
LS580
CV580
FV583
FV600
SV601
FT581
CV581
SV700
PT700
FV580
FT580
L018
PT600
PRV700
FV582
L017
SV600
L016
SV602
EV700
EH700
TT700
PT581
TT580
SV744
EH580AC
PRV744
V050
TS700
TS580
System
FV581
PT660
PT661
EV744
TT701AB
Pumping
PT582
HV580
SV580
To Helium
CV582
PT050
0
EH701AB
TT706
TT705
PRV740
0
TT602
To Purging
SV740
PT051
System
EV740
TS744
CV600 FV601
FV050
LHe 4K
Vacuum
System
S600
TT603
TT600AD
CV602
HX600
TT745
TT741AC
TT643
PT052
PT053
TT605
TT743AF
TT606
EH743AF
CV603
TT608
TT642
TT747
0
TT703AC
CV601
TT746
TT641
EH601
EH741AC
EH744
TT601
LT600
SV661
FV660
V051
TT607
TT604
EH703AC
SV741
TT680AC
EH740
SV051
SV050
SV641
TT740
J050
EH600AD
SV640
TT744
TS740
Pumping
TT610
V053
TT665
L012
FV605
EH661AC
TT664
CAVITY
TT609
TT661AC
FV604
FV603
TT663
FV602
TT704
FV700
Vacuum
TT702AB
LHe
LN2
PRV700
FV051
System
12/02/2015
EH640AF
TT644
TT640AF
EH742AC
TT742AC
J051
In Vacuum Condition
System
L011
Re-heater
Vertical Cryostat
To Purging
L010
to He gas
PT580
recovery system
W580
LS580
CV580
FV583
FV600
SV601
FT581
CV581
SV700
PT700
FV580
FT580
L018
PT600
FV582
L017
SV600
L016
SV602
EV700
EH700
TT700
TS580
PT581
TT580
SV744
EH580AC
PRV744
V050
TS700
SV580
EV744
TT701AB
Pumping
PT582
System
FV581
HV580
L015
PT660
Vacuum Pumping
PT661
System
PRV740
0
FV050
LHe 4K
System
S600
EH740
HX600
EH601
CV601
TT669
TT746
TT642
S660 LHe
TT747
TT660AC
TT666
TT665
L012
EH661AC
TT664
TT661AC
FV604
FV603
TT663
FV602
TT764
FV700
TT662
EH762AC
Vacuum
EH702AB
TT763AF
CAVITY
TT609
TT702AB
EH763AF
EH743AF
FV605
TT704
TT741AC
EH660AC
TT667
TT743AF
TT606
EH741AC
TT765
TT668
0
CV603
TT608
TS760
EH760
EH761AC
TT643
TT641
PT052
PT053
TT605
TT760
EH744
TT601
CV602
EV760
FV052
SV052
FV660
V051
TT703AC
SV741
SV660
TT761AC
TT745
TT607
TT604
EH703AC
SV051
SV050
TT600AD
TT744
TS740
V052
SV640 SV641
TT740
J050
EH600AD
TT603
LT600
Vacuum
Pumping
TT610
System
L013
EV740
TS744
CV600 FV601
PRV760
To Purging
L014
SV740
PT051
TT602
J052
SV760
0
EH701AB
TT706
TT705
To Helium
CV582
PT050
12/02/2015
LT640
TT748
Pumping
EH702AB
TT644
Pumping
System
LT660
TT762AC
EH640AF
TT640AF
LT640
TT748
FV051
EH742AC
TT742AC
J051
Figure 14: Cryogenic operation scheme of Gersemi with open liquid helium bath (top) and
vacuum condition (bottom).
20
be used. Temperature range and cooling power is therefor similar to HNOSS. An ICB is
not necessary as the vertical cryostat will be located next to the 2000 l storage dewar and
connected to one of the two remaining cryogenic valves. A removable magnetic shield is
foreseen outside the vacuum vessel as this shield is required when testing SRF cavities but
should not be used when testing SC magnets. Gersemi’s layout and main dimensions are
shown in figure 12 and listed in table 4. The final dimensions have not yet been decided. The
outer vacuum vessel will be choosen to have the largest dimension suitable (1.8 m diameter
and 4 m height). The inner vessel diameter will be choosen within the range of 1.0 to 1.5 m
to be reasonable for the projects under study in order to limit the volume of liquid helium
required for open bath operation. It can be replaced in the future if a larger diameter is
required for a specific test, without having to replace the outer vacuum vessel and thermal
shield.
Different types of insert will be used depending on operation with open liquid helium bath
or vacuum condition, as shown in figure 13. In vacuum condition an extra thermal shield is
used which decreases the volume available for the DUT slightly. For testing of a large DUT in
vacuum condition, the inner vessel can be removed and “Gersemi” can be operated with the
outer vacuum vessel and thermal shield only. The main cryogenic connections are attached
on the side of the cryostat to make the inserts and their connection simpler. In addition
only a single cold gas return line from the insert to the VB has to be connected. For vacuum
operation, a short transfer line needs to be installed to connect the insert to the cryogenics
supply in the cryostat. Figure 14 shows the schematics of the cryogenic connections and
operation. The idea is similar as presented in figure 9 for HNOSS. Liquid nitrogen (LN2) is
used to cool the thermal shield. The liquid helium (LHe) enters into a so-called 4 K pot and
can then either be used for direct filling of the helium bath or DUT or, via heat exchanger
and JT valve, for the filling of the 2 K pot. In case of open helium bath operation, the
bath is the 2 K pot while for vacuum operation a separate 2 K pot is mounted in the insert
together with the DUT.
7
Summary
The FREIA Laboratory at Uppsala University has been equipped with a cryogenic installation consisting of helium liquefier, liquid helium and nitrogen distribution facilities, helium
gas recovery system and a unique horizontal test cryostat HNOSS. The equipment was installed and commissioned in 2014. First measurements of a superconducting cavity started
during Spring 2015. The installation gives the FREIA Laboratory and Uppsala University
an outstanding opportunity to continue research and development of advanced accelerators
and instrumentation.
8
Acknowledgements
The authors like to thank their colleagues at the FREIA Laboratory and Uppsala University
for their support during this project. The authors are very grateful for the support and
advice received from their colleagues at IPNO, CERN and ACS. This work was supported
by the Knut and Alice Wallenberg Foundation.
21
References
[1] R. Ruber, V. Ziemann and T. Ekelf, FREIA: Facility for Research Instrumentation and
Accelerator Development, Uppsala University, Memo RR/2010/01 (2010).
[2] R. Ruber et al., The New FREIA Laboratory for Accelerator Development, Proceedings
IPAC’14, Dresden, Germany (2014) THPRO077.
http://cern.ch/AccelConf/IPAC2014/papers/thpro077.pdf
[3] M. Olvegård et al., Progress at the FREIA Laboratory, Submitted to IPAC’15, Richmond,
USA (2015) WEPMN065.
[4] T. Junquera et al., Design of a New Horizontal Test Cryostat for SCRF Cavities at the
Uppsala University, Proceedings SRF’13, Paris, France (2013) MOP080.
http://cern.ch/AccelConf/SRF2013/papers/mop080.pdf
[5] N.R. Chevalier et al., Design of a horizontal test cryostat for superconducting RF cavities
for the FREIA facility at Uppsala University, AIP Conf. Proc. 1573 (2014) 1277.
http://dx.doi.org/10.1063/1.4860853
[6] R. Santiago Kern et al., The HNOSS Horizontal Cryostat and the Helium Liquefaction
Plant at FREIA, Proceedings IPAC’14, Dresden, Germany (2014) WEPRI110.
http://cern.ch/AccelConf/IPAC2014/papers/wepri110.pdf
[7] P. Clay et al., Cryogenic and Electrical Test Cryostat for Instrumented Superconducting
RF Cavities (CHECHIA), DESY TESLA 95-21 (1995).
http://flash.desy.de/sites2009/site_vuvfel/content/e403/e1644/e1259/
e1260/infoboxContent1998/tesla1995-21.pdf
[8] H. Saugnac et al., Cryogenic Installation Status of the ”CRYHOLAB” Test Facility Proceedings SRF’01, Tsukuba, Japan (2001) PZ007.
http://cern.ch/AccelConf/srf01/papers/pz007.pdf
[9] N. Chevalier, J-P. Thermeau, P. Bujard, T. Junquera, Design of the Test Cryostat for
the FREIA Facility, ACS Deliverable 2 (2013).
[10] N. Chevalier, J-P. Thermeau, P. Bujard, T. Junquera, Calculation Notes, ACS Deliverable 3 (2013).
[11] P. Duchesne, P. Duthil and N. Chevalier, Horizontal Test Cryostat for Uppsala University: Mechanical and Thermal Studies, ACS Deliverable 4 (2013).
[12] www.ansys.com
[13] J. Knobloch et al., HoBiCaT - A Test Facility for Superconducting RF Systems, Proceedings SRF’03, Lübeck/Travemünder, Germany (2003) MOP48.
http://cern.ch/AccelConf/SRF2003/papers/mop48.pdf
22
Glossary
ACS . . . Accelerators and Cryogenic Systems
BMC . . Uppsala Biomedical Centre
CEA SaclayCommissariat à l’Énergie Atomique et aux Énergies Alternatives, centre de
Saclay
CERN
. European Organization for Nuclear Research
DESY . . Stiftung Deutsches Elektronen-synchrotron
DUT . . Device Under Test
ESS . . . European Spallation Source
FEA . . . finite element analysis
FREIA . Facility for Research Instrumentation and Accelerator Development
HNOSS . Horizontal Nugget for Operation of Superconducting Systems
HZB . . . Helmholtz-Zentrum Berlin
ICB . . . Interconnection Box
ILC . . . International Linear Collider
IPNO . . Institut de physique nucléaire d’Orsay
JT . . . . Joule-Thomson
KAWS . Knut and Alice Wallenberg Foundation
LCLS . . Linac Coherent Light Source
LHC . . . Large Hadron Collider
MRI . . . Magnetic Resonance Imaging
RF . . . . radio frequency
SC . . . . superconducting
SGU . . . Geological Survey of Sweden
SLU . . . Swedish University of Agricultural Science
SRF . . . superconducting radio frequency
UU
. . . Uppsala University
VB
. . . Valve Box
XFEL . . European X-ray Free Electron Laser
23