- Email: [email protected]
Cryogenic Distribution System for the ESS Superconducting Proton Linac
Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 67 (2015) 828 – 833
25th International Cryogenic Engineering Conference and the International Cryogenic Materials Conference in 2014, ICEC 25–ICMC 2014
Cryogenic distribution system for the ESS superconducting proton linac J. Fydrych *, P. Arnold, W. Hees, P. Tereszkowski, X.L. Wang, J.G. Weisend II 0F
European Spallation Source ESS, AB, P.O. Box 176, SE-22100 Lund, Sweden
Abstract The European Spallation Source is an accelerator-driven neutron scattering facility, currently under construction in Lund, Sweden. Its proton linac will include 43 superconducting cavity cryomodules. The nominal operating temperature for the cavities is 2 K, with 40-50 K thermal shielding. Required cooling powers will be provided by the accelerator cryoplant and delivered in 4.5 K and 40 K temperature levels. The 2 K temperature level will be produced at each cryomodule. The cryomodules will be connected with the cryoplant by a dedicated cryogenic distribution system. The system will be composed of a cryogenic transfer line with a splitting box and a cryogenic distribution line with 43 valve boxes and an end box. A number of high-level requirements for the ESS linac impose a highly branched structure for the cryogenic distribution system and strongly influence specific choices related to the detailed designs of valve boxes and cryogenic lines. The design of the valve boxes must allow for warming up and cooling down of one or more cryomodules without affecting the others. This feature will help to meet a high availability requirement for the ESS accelerator by shortening the duration of some potential and unavoidable cryomodule repairs. This paper describes main functional and technical requirements for the cryogenic distribution system and presents the ESS inhouse preliminary design. The paper also gives a few main points of the project execution plan, which points towards in- kind contribution from two different European institutions. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license ©2015 2014The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014. Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014 Keywords: ESS; liquid helium; distribution system; linac; cryomodule
* Corresponding author. Tel.: +0046-72-179-21-94 E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014 doi:10.1016/j.phpro.2015.06.139
829
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
1. Introduction The European Spallation Source (ESS) will be a neutron science facility dedicated for scientific investigations of the molecular building blocks of matter [1]. The facility is currently under construction in Lund, in the southwest of Sweden. ESS as an accelerator-driven neutron source will use a linear accelerator (linac) to create a high-energy proton beam, which will be delivered to a target. The target itself, which will be a helium-gas cooled rotating tungsten wheel, will not need cryogenics technologies, however the neutron moderators will use liquid hydrogen [2]. For these reasons ESS requires a sophisticated cryogenic system, which includes 3 separated cryogenic plants and distribution systems [3, 4]. The largest and most complicated part of the ESS cryogenics is the cryogenic system for the ESS linac. The superconducting portion of the linac will contain 146 superconducting radiofrequency cavities [5]. The first superconducting section will consist of 13 spoke cavity cryomodules, each with two double spoke cavities. This part will be followed by two sections of elliptical cavities, called medium-beta section and high-beta section, where beta is ratio of the proton speed to the speed of light. These two sections will contain 9 and 21 elliptical cavity cryomodules respectively, with 4 cavities per each cryomodule. The nominal operating temperature for both the spoke and elliptical cavities is 2 K and the total heat loads to the cavity cooling loops and their thermal shields are estimated as 3.0 kW and 10.8 kW [6]. The cooling scheme of the cavities will base on a saturated liquid helium bath at 2 K with active thermal shielding by cold gashouse helium at 40-50 K. The required cooling powers will be provided by the accelerator cryoplant (ACCP) and delivered in two temperature levels: 4.5 K and 40 K [6]. Then, the 2 K temperature level will be produced at each cryomodule by isenthalpic expansion of the 4.5 K supercritical helium, previously sub-cooled to 2.2 K in a counter flow heat exchanger. Fig. 1 shows a schematic layout of the cryogenic system for the ESS linac. The cryomodules are connected to the ACCP by an extensive cryogenic distribution system (CDS). The CDS consists of a cryogenic transfer line (CTL), cryogenic distribution line (CDL) and a few auxiliary process lines. The CTL includes a splitting box that is equipped with a plugged cryoline terminal. The terminal is to allow for an easy and relatively quick connection of another cryogenic distribution line. This additional line will be dedicated for distributing cold helium to the contingency and upgrade cryomodules, in case of a future extension of the linac lattice [5]. The CDL comprises 43 valve boxes and an end box. The main function of the valve boxes is to allow for warming up and cooling down one or more cryomodules without affecting the others. The end box is for returning the remaining flows of helium in the main circuits back to the ACCP. These flows are to ensure a proper temperature of the cold helium in the inlet to the last cryomodules. 2. Functional and technical requirements A number of main functional and technical requirements for the CDS result from the top-level requirement of 95 % availability of the ESS linac itself [1]. It imposes that the linac equipment, and the CDS as well, must be extremely reliable throughout the expected lifetime of 40 years and must require a minimum of maintenance. Accelerator cryoplant Cryogenicc transfer line (75 m))
Cryogenic distribution line (310 m) comprising 43 valve boxes
Auxiliary process lines End E box b
Splitting box
21 high beta cryomodules (174 m)
9 medium beta cryomodules (75 m)
Fig. 1. Layout of the cryogenic system for the ESS linac.
13 spoke cryomodules (54 m)
830
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
The linac shall be operated remotely and continuously, 24 hours per day, for about 250 days per year, so the design of the equipment must facilitate easy repairs or even easy replacements of faulty components. Therefore the design and construction of the CDS must meet the following functional requirements: x suitable for smooth continuous operation with limited scheduled interruptions only, x ensure no deterioration of thermal and mechanical properties within the operation lifetime, x tolerate all possible pressurization and cool-down rates, x allow for warm-up and cool-down of a single cryomodule, while keeping the rest of the system at cryogenic temperatures. Apart of the ACCP and cryomodules, the CDS will be integrated with some other components of the ESS facility, such as vacuum system, control system and buildings. To allow smooth integration and co-functioning, the design of the CDS must meet also a number of technical requirements, which are described in details in [7]. Some of the main high level technical requirements for the CDS are as follows: x heat loads not higher than 420 W and 3.66 kW to the cold helium circuit and thermal shield, respectively, x supercritical helium temperature in the interfaces to the cryomodules below 5.2 K at nominal operation conditions, x vacuum insulation below 10-6 mbar at nominal working condition (below 5·10-3 mbar at ambient temperature with active vacuum pumping), x integral helium leak rate into the insulation vacuum below 510-7 mbarl/s, x tightness of the valve seats ≤ 110-4 mbarl/s, x all materials and components located in the linac tunnel resistant to the radiation dose of 5105 Gy. These high-level requirements not only imposed a highly branched structure for the CDS layout but also strongly influenced a number of choices related to the CDS flow scheme and detailed designs of the system components. 3. Flow scheme The flow scheme of the linac CDS was developed to ensure that each single cryomodule can be operated independently from the others. Fig. 2 shows the piping and instrumentation diagram (PID) for the CDL for the elliptical linac. The CDS system comprises four cold process lines that form the cold helium circuit (helium supply line and vapor low pressure line) and the thermal shield circuit (TS supply and return lines). These lines are used at nominal operation conditions and for the cool-downs and warm-ups of the entire ESS linac. The other four auxiliary process lines, which run alongside the CDL, are necessary for warming up and cooling down of a single cryomodule (HP and helium recovery lines), for collecting helium for the power coupler cooling circuits (helium recovery line), and for purging and flashing a single cryomodule (HP and purge lines). The valves that allow shutting off the cold circuits in the cryomodules are grouped in special valve boxes. Each valve box is equipped with six cryogenic control valves (CV03, CV04, CV06, CV60, CV61 and CV63) and some other process control elements, such as check valves (VN01 and VN02), warm control valves (CV05 and CV62), safety valves (SV02 and SV60) as well as pressure transmitters (PT01 and PT60) and temperature sensors (TT05, TT06, TT60 and TT65). The cryomodule is connected to the valve box via a branch cryoline, so-called jumper connection. As the cryomodule insulation vacuum has to be separated from that of the CDL, the jumper connection includes a vacuum barrier. During nominal operation conditions, as well as during the cool-down and warm-up of the whole linac cryogenic system, only CV03, CV04, CV60 and CV61 will be kept open in all the valve boxes. However for bringing a single cryomodule to the ambient temperature only CV05, CV06, CV62 and CV63 will be open. Then warm helium from the HP line will flow into the cryomodule circuits and back to the ACCP via the helium recovery line. The PID of the CDS for the spoke linac differs slightly from this for the elliptical linac. As the spoke cavities are larger in diameter there is less space for the other equipment in their cryomodules. Therefore, to enable cryomodule assembly it has been recently decided to move the heat exchanger (HX01), JT valve (CV01), filling valve (CV02) and some related temperature sensors, to the valve box.
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J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833 Auxiliary Process Lines Helium recovery line <1.1 bar, 4-300K HP line, 300K, 2-20 bar Purge return line, 300K, <1.1 bar SV relief line, < 1.1 bar, 4-300K
Cryogenic Distribution Line TS supply line, 40 K, 19.5 bara TS return line, 50 K, 19.0 bara He supply line, 4.5 K, 3.0 bar
HV60
CV61
VN02
CV63
CV05
SV60
SR2
CV62
CV04
to Cryogenic Transfer Line
CV03
Valve box
CV60
VLP line, 4 K, 27 mbar
Interface to the CDS for the spoke linac
CV06
VN01 PT 60
SV02
PT 01
Vacuum barrier Jumper connection
TT 60
TT 05
TT 06
TT 65
TT 94
PT 61
CV41
HV90
TT 93 TT 04
CV01
CV02
TT 92
RD91
SV91
RD90
TT 91
HX01
Cryomodule
SV70
PT 04
SV90
Interface to Cryomodule
Fig. 2. Piping and instrumentation diagram for the CDL for the elliptical linac.
4. Preliminary design In order to check the feasibility of the CDS construction and installation in the linac tunnel with respect to the functional and technical requirements ESS has developed a detailed preliminary design of the system [7]. Fig. 3 presents the preliminary design of the CDL section with the valve box for elliptical cavity cryomodules. The proposed design is based on a modular structure. Each module is 8.26 m in length and is connected to the adjacent modules with special interconnections. The module includes a valve box with two main cryoline sections and a jumper connection. The vacuum jacket of the jumper connection is equipped with two lateral compensators, whilst the branch process lines have flexible hoses. These components allow some adjustments when joining the cryomodules to the CDS. Due to limited space in the linac tunnel the valve box and cryoline sizes are limited to DN1000 and DN600, respectively. The design and location of the external supports is strongly affected by the routing of the cryomodule waveguides [8]. Below each CDL module in the elliptical linac section there are four waveguides, which run 735 mm above the floor and transversely to the CDL.
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J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
a)
b)
Branch pr oc
c) Cryogenic control valves
ess lines
Interface to the cryomodule
Vacuum barrier Fixed support of main process lines Sliding supports of main process lines
Main process lines (headers)
Valve box piping
Fig. 3. Preliminary design of the CDS and valve box for the elliptical cavity cryomodule, a) vacuum jacket, b) thermal shields, c) process pipes and supporting system.
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
Both the vacuum jacket and thermal shield of the valve box will have demountable bottom plates that provide access to the piping and cryogenic valve bodies when some reparations are needed. The cryogenic control valves will be fitted with significantly extended spindles with heat sinks thermally connected to the TS return pipes. The valves must be connected to the pipework and to the vacuum vessels of the valve boxes with permanent welded connections. Neutron radiation in the linac tunnel has a strong impact on the CDL design, especially on material choices and on the architecture of the control and instrumentation system. Materials sensitive to this radiation are not allowed. Therefore the control valves will have pneumatic actuators and electro-pneumatic positioners with remote electronic parts situated in a radiation free area. The electronic racks for the CDS valve boxes will be placed in the klystron gallery, in the distance of 50-100 m away from the valve boxes. 5. Project execution plan The linac CDS has been split into two subprojects, i.e. the CDS for the elliptical linac and the CDS for the spoke linac. In spite of this, their schedules are composed of the same following phases: 1) agreement and project initiation; 2) preliminary design; 3) detailed design; 4) fabrication and factory testing; 5) preparation for installation, 6) transportation, installation and site testing; 7) preliminary acceptance tests; 8) final acceptance tests. Factory and site testing comprise weld examinations and pressure and leak tightness tests, whilst phases 7 and 8 include the performance tests of the entire system and its components at cryogenic temperatures. The installation of both subsystems is scheduled in the second half of 2017, whilst the preliminary acceptance tests shall be completed in the beginning of 2019. The CDS will be deemed finally accepted when the preliminary acceptance tests show compliance with the specification and when 10 complete operating cycles in sequence are made without any degradation of thermal and mechanical properties. However the linac CDS will be ready to serve for the commissioning and later for the operation of the ESS linac just after its preliminary acceptance tests. The linac CDS will almost certainly be provided as two separate in-kind contributions. Negotiations with two European institutions are on-going and the partners most likely begin the design phases in the second half of 2014. 6. Summary The ESS linac requires an extensive cryogenic distribution system to link all its 43 separated cryomodules to the accelerator cryogenic plant. The layout of the linac CDS as well as a vast number of conceptual and detailed design choices are strongly affected by the linac top-level requirements, such as high availability and remote operation. A detailed preliminary design of the CDS has been recently developed at ESS to prove the feasibility of the system construction and installation in the linac tunnel. The design is based on a modular structure that simplifies production, factory testing and installation. The proposed design of the CDS valve boxes facilitates easy reparations of faulty components and allows smooth integration with the other linac components. References [1] Peggs S, 2013. ESS technical design report. http://europeanspallationsource.se/documentation.tdr.pdf, ISBN 978-91-980173-2-8, European Spallation Source ESS AB, Lund, Sweden, pp 650. [2] Jurns J.M., Arnold P., Weisend II J.G.,, Linander R., 2014. Cryogenic cooling ot the neutron source at the ESS. ICEC25, Enschede, the Netherlands, July 7-11 2014. [3] Weisend II J.G., Arnold P., Fydrych J., Hees W., Jurns J, Wang X.L., 2014. Cryogenics at the European Spallation Source. ICEC25, Enschede, the Netherlands, July 7-11 2014. [4] Arnold P., Fydrych J., Hees W., Wang X.L., Weisend II J.G., 2014. The ESS cryogenic system. IPAC2014, Dresden, June 16-20 2014. [5] Lindroos M., Eshraqi M., McGinnis D., 2013. The European Spallation Source. Proceedings of PAC2013, Pasadena, USA, pp 1448-1452. [6] Wang X.L., Arnold P., Fydrych J., Hees W., Jurns J, Piso D.,Weisend II J.G., 2014. Specification of ESS accelerator cryoplant. ICEC25, Enschede, the Netherlands, July 7-11 2014. [7] Fydrych J., 2014. Technical specification of the cryogenic distribution system for the elliptical linac. ESS technical document (controlled): ESS-0011735, pp 66. [8] Fydrych J., Tereszkowski, 2014. Placeholders of the RF waveguides under the cryogenic distribution line for the elliptical linac. ESS technical document (controlled): ESS-0012571, pp 6.
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ScienceDirect Physics Procedia 67 (2015) 828 – 833
25th International Cryogenic Engineering Conference and the International Cryogenic Materials Conference in 2014, ICEC 25–ICMC 2014
Cryogenic distribution system for the ESS superconducting proton linac J. Fydrych *, P. Arnold, W. Hees, P. Tereszkowski, X.L. Wang, J.G. Weisend II 0F
European Spallation Source ESS, AB, P.O. Box 176, SE-22100 Lund, Sweden
Abstract The European Spallation Source is an accelerator-driven neutron scattering facility, currently under construction in Lund, Sweden. Its proton linac will include 43 superconducting cavity cryomodules. The nominal operating temperature for the cavities is 2 K, with 40-50 K thermal shielding. Required cooling powers will be provided by the accelerator cryoplant and delivered in 4.5 K and 40 K temperature levels. The 2 K temperature level will be produced at each cryomodule. The cryomodules will be connected with the cryoplant by a dedicated cryogenic distribution system. The system will be composed of a cryogenic transfer line with a splitting box and a cryogenic distribution line with 43 valve boxes and an end box. A number of high-level requirements for the ESS linac impose a highly branched structure for the cryogenic distribution system and strongly influence specific choices related to the detailed designs of valve boxes and cryogenic lines. The design of the valve boxes must allow for warming up and cooling down of one or more cryomodules without affecting the others. This feature will help to meet a high availability requirement for the ESS accelerator by shortening the duration of some potential and unavoidable cryomodule repairs. This paper describes main functional and technical requirements for the cryogenic distribution system and presents the ESS inhouse preliminary design. The paper also gives a few main points of the project execution plan, which points towards in- kind contribution from two different European institutions. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license ©2015 2014The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014. Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014 Keywords: ESS; liquid helium; distribution system; linac; cryomodule
* Corresponding author. Tel.: +0046-72-179-21-94 E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICEC 25-ICMC 2014 doi:10.1016/j.phpro.2015.06.139
829
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
1. Introduction The European Spallation Source (ESS) will be a neutron science facility dedicated for scientific investigations of the molecular building blocks of matter [1]. The facility is currently under construction in Lund, in the southwest of Sweden. ESS as an accelerator-driven neutron source will use a linear accelerator (linac) to create a high-energy proton beam, which will be delivered to a target. The target itself, which will be a helium-gas cooled rotating tungsten wheel, will not need cryogenics technologies, however the neutron moderators will use liquid hydrogen [2]. For these reasons ESS requires a sophisticated cryogenic system, which includes 3 separated cryogenic plants and distribution systems [3, 4]. The largest and most complicated part of the ESS cryogenics is the cryogenic system for the ESS linac. The superconducting portion of the linac will contain 146 superconducting radiofrequency cavities [5]. The first superconducting section will consist of 13 spoke cavity cryomodules, each with two double spoke cavities. This part will be followed by two sections of elliptical cavities, called medium-beta section and high-beta section, where beta is ratio of the proton speed to the speed of light. These two sections will contain 9 and 21 elliptical cavity cryomodules respectively, with 4 cavities per each cryomodule. The nominal operating temperature for both the spoke and elliptical cavities is 2 K and the total heat loads to the cavity cooling loops and their thermal shields are estimated as 3.0 kW and 10.8 kW [6]. The cooling scheme of the cavities will base on a saturated liquid helium bath at 2 K with active thermal shielding by cold gashouse helium at 40-50 K. The required cooling powers will be provided by the accelerator cryoplant (ACCP) and delivered in two temperature levels: 4.5 K and 40 K [6]. Then, the 2 K temperature level will be produced at each cryomodule by isenthalpic expansion of the 4.5 K supercritical helium, previously sub-cooled to 2.2 K in a counter flow heat exchanger. Fig. 1 shows a schematic layout of the cryogenic system for the ESS linac. The cryomodules are connected to the ACCP by an extensive cryogenic distribution system (CDS). The CDS consists of a cryogenic transfer line (CTL), cryogenic distribution line (CDL) and a few auxiliary process lines. The CTL includes a splitting box that is equipped with a plugged cryoline terminal. The terminal is to allow for an easy and relatively quick connection of another cryogenic distribution line. This additional line will be dedicated for distributing cold helium to the contingency and upgrade cryomodules, in case of a future extension of the linac lattice [5]. The CDL comprises 43 valve boxes and an end box. The main function of the valve boxes is to allow for warming up and cooling down one or more cryomodules without affecting the others. The end box is for returning the remaining flows of helium in the main circuits back to the ACCP. These flows are to ensure a proper temperature of the cold helium in the inlet to the last cryomodules. 2. Functional and technical requirements A number of main functional and technical requirements for the CDS result from the top-level requirement of 95 % availability of the ESS linac itself [1]. It imposes that the linac equipment, and the CDS as well, must be extremely reliable throughout the expected lifetime of 40 years and must require a minimum of maintenance. Accelerator cryoplant Cryogenicc transfer line (75 m))
Cryogenic distribution line (310 m) comprising 43 valve boxes
Auxiliary process lines End E box b
Splitting box
21 high beta cryomodules (174 m)
9 medium beta cryomodules (75 m)
Fig. 1. Layout of the cryogenic system for the ESS linac.
13 spoke cryomodules (54 m)
830
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
The linac shall be operated remotely and continuously, 24 hours per day, for about 250 days per year, so the design of the equipment must facilitate easy repairs or even easy replacements of faulty components. Therefore the design and construction of the CDS must meet the following functional requirements: x suitable for smooth continuous operation with limited scheduled interruptions only, x ensure no deterioration of thermal and mechanical properties within the operation lifetime, x tolerate all possible pressurization and cool-down rates, x allow for warm-up and cool-down of a single cryomodule, while keeping the rest of the system at cryogenic temperatures. Apart of the ACCP and cryomodules, the CDS will be integrated with some other components of the ESS facility, such as vacuum system, control system and buildings. To allow smooth integration and co-functioning, the design of the CDS must meet also a number of technical requirements, which are described in details in [7]. Some of the main high level technical requirements for the CDS are as follows: x heat loads not higher than 420 W and 3.66 kW to the cold helium circuit and thermal shield, respectively, x supercritical helium temperature in the interfaces to the cryomodules below 5.2 K at nominal operation conditions, x vacuum insulation below 10-6 mbar at nominal working condition (below 5·10-3 mbar at ambient temperature with active vacuum pumping), x integral helium leak rate into the insulation vacuum below 510-7 mbarl/s, x tightness of the valve seats ≤ 110-4 mbarl/s, x all materials and components located in the linac tunnel resistant to the radiation dose of 5105 Gy. These high-level requirements not only imposed a highly branched structure for the CDS layout but also strongly influenced a number of choices related to the CDS flow scheme and detailed designs of the system components. 3. Flow scheme The flow scheme of the linac CDS was developed to ensure that each single cryomodule can be operated independently from the others. Fig. 2 shows the piping and instrumentation diagram (PID) for the CDL for the elliptical linac. The CDS system comprises four cold process lines that form the cold helium circuit (helium supply line and vapor low pressure line) and the thermal shield circuit (TS supply and return lines). These lines are used at nominal operation conditions and for the cool-downs and warm-ups of the entire ESS linac. The other four auxiliary process lines, which run alongside the CDL, are necessary for warming up and cooling down of a single cryomodule (HP and helium recovery lines), for collecting helium for the power coupler cooling circuits (helium recovery line), and for purging and flashing a single cryomodule (HP and purge lines). The valves that allow shutting off the cold circuits in the cryomodules are grouped in special valve boxes. Each valve box is equipped with six cryogenic control valves (CV03, CV04, CV06, CV60, CV61 and CV63) and some other process control elements, such as check valves (VN01 and VN02), warm control valves (CV05 and CV62), safety valves (SV02 and SV60) as well as pressure transmitters (PT01 and PT60) and temperature sensors (TT05, TT06, TT60 and TT65). The cryomodule is connected to the valve box via a branch cryoline, so-called jumper connection. As the cryomodule insulation vacuum has to be separated from that of the CDL, the jumper connection includes a vacuum barrier. During nominal operation conditions, as well as during the cool-down and warm-up of the whole linac cryogenic system, only CV03, CV04, CV60 and CV61 will be kept open in all the valve boxes. However for bringing a single cryomodule to the ambient temperature only CV05, CV06, CV62 and CV63 will be open. Then warm helium from the HP line will flow into the cryomodule circuits and back to the ACCP via the helium recovery line. The PID of the CDS for the spoke linac differs slightly from this for the elliptical linac. As the spoke cavities are larger in diameter there is less space for the other equipment in their cryomodules. Therefore, to enable cryomodule assembly it has been recently decided to move the heat exchanger (HX01), JT valve (CV01), filling valve (CV02) and some related temperature sensors, to the valve box.
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J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833 Auxiliary Process Lines Helium recovery line <1.1 bar, 4-300K HP line, 300K, 2-20 bar Purge return line, 300K, <1.1 bar SV relief line, < 1.1 bar, 4-300K
Cryogenic Distribution Line TS supply line, 40 K, 19.5 bara TS return line, 50 K, 19.0 bara He supply line, 4.5 K, 3.0 bar
HV60
CV61
VN02
CV63
CV05
SV60
SR2
CV62
CV04
to Cryogenic Transfer Line
CV03
Valve box
CV60
VLP line, 4 K, 27 mbar
Interface to the CDS for the spoke linac
CV06
VN01 PT 60
SV02
PT 01
Vacuum barrier Jumper connection
TT 60
TT 05
TT 06
TT 65
TT 94
PT 61
CV41
HV90
TT 93 TT 04
CV01
CV02
TT 92
RD91
SV91
RD90
TT 91
HX01
Cryomodule
SV70
PT 04
SV90
Interface to Cryomodule
Fig. 2. Piping and instrumentation diagram for the CDL for the elliptical linac.
4. Preliminary design In order to check the feasibility of the CDS construction and installation in the linac tunnel with respect to the functional and technical requirements ESS has developed a detailed preliminary design of the system [7]. Fig. 3 presents the preliminary design of the CDL section with the valve box for elliptical cavity cryomodules. The proposed design is based on a modular structure. Each module is 8.26 m in length and is connected to the adjacent modules with special interconnections. The module includes a valve box with two main cryoline sections and a jumper connection. The vacuum jacket of the jumper connection is equipped with two lateral compensators, whilst the branch process lines have flexible hoses. These components allow some adjustments when joining the cryomodules to the CDS. Due to limited space in the linac tunnel the valve box and cryoline sizes are limited to DN1000 and DN600, respectively. The design and location of the external supports is strongly affected by the routing of the cryomodule waveguides [8]. Below each CDL module in the elliptical linac section there are four waveguides, which run 735 mm above the floor and transversely to the CDL.
832
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
a)
b)
Branch pr oc
c) Cryogenic control valves
ess lines
Interface to the cryomodule
Vacuum barrier Fixed support of main process lines Sliding supports of main process lines
Main process lines (headers)
Valve box piping
Fig. 3. Preliminary design of the CDS and valve box for the elliptical cavity cryomodule, a) vacuum jacket, b) thermal shields, c) process pipes and supporting system.
J. Fydrych et al. / Physics Procedia 67 (2015) 828 – 833
Both the vacuum jacket and thermal shield of the valve box will have demountable bottom plates that provide access to the piping and cryogenic valve bodies when some reparations are needed. The cryogenic control valves will be fitted with significantly extended spindles with heat sinks thermally connected to the TS return pipes. The valves must be connected to the pipework and to the vacuum vessels of the valve boxes with permanent welded connections. Neutron radiation in the linac tunnel has a strong impact on the CDL design, especially on material choices and on the architecture of the control and instrumentation system. Materials sensitive to this radiation are not allowed. Therefore the control valves will have pneumatic actuators and electro-pneumatic positioners with remote electronic parts situated in a radiation free area. The electronic racks for the CDS valve boxes will be placed in the klystron gallery, in the distance of 50-100 m away from the valve boxes. 5. Project execution plan The linac CDS has been split into two subprojects, i.e. the CDS for the elliptical linac and the CDS for the spoke linac. In spite of this, their schedules are composed of the same following phases: 1) agreement and project initiation; 2) preliminary design; 3) detailed design; 4) fabrication and factory testing; 5) preparation for installation, 6) transportation, installation and site testing; 7) preliminary acceptance tests; 8) final acceptance tests. Factory and site testing comprise weld examinations and pressure and leak tightness tests, whilst phases 7 and 8 include the performance tests of the entire system and its components at cryogenic temperatures. The installation of both subsystems is scheduled in the second half of 2017, whilst the preliminary acceptance tests shall be completed in the beginning of 2019. The CDS will be deemed finally accepted when the preliminary acceptance tests show compliance with the specification and when 10 complete operating cycles in sequence are made without any degradation of thermal and mechanical properties. However the linac CDS will be ready to serve for the commissioning and later for the operation of the ESS linac just after its preliminary acceptance tests. The linac CDS will almost certainly be provided as two separate in-kind contributions. Negotiations with two European institutions are on-going and the partners most likely begin the design phases in the second half of 2014. 6. Summary The ESS linac requires an extensive cryogenic distribution system to link all its 43 separated cryomodules to the accelerator cryogenic plant. The layout of the linac CDS as well as a vast number of conceptual and detailed design choices are strongly affected by the linac top-level requirements, such as high availability and remote operation. A detailed preliminary design of the CDS has been recently developed at ESS to prove the feasibility of the system construction and installation in the linac tunnel. The design is based on a modular structure that simplifies production, factory testing and installation. The proposed design of the CDS valve boxes facilitates easy reparations of faulty components and allows smooth integration with the other linac components. References [1] Peggs S, 2013. ESS technical design report. http://europeanspallationsource.se/documentation.tdr.pdf, ISBN 978-91-980173-2-8, European Spallation Source ESS AB, Lund, Sweden, pp 650. [2] Jurns J.M., Arnold P., Weisend II J.G.,, Linander R., 2014. Cryogenic cooling ot the neutron source at the ESS. ICEC25, Enschede, the Netherlands, July 7-11 2014. [3] Weisend II J.G., Arnold P., Fydrych J., Hees W., Jurns J, Wang X.L., 2014. Cryogenics at the European Spallation Source. ICEC25, Enschede, the Netherlands, July 7-11 2014. [4] Arnold P., Fydrych J., Hees W., Wang X.L., Weisend II J.G., 2014. The ESS cryogenic system. IPAC2014, Dresden, June 16-20 2014. [5] Lindroos M., Eshraqi M., McGinnis D., 2013. The European Spallation Source. Proceedings of PAC2013, Pasadena, USA, pp 1448-1452. [6] Wang X.L., Arnold P., Fydrych J., Hees W., Jurns J, Piso D.,Weisend II J.G., 2014. Specification of ESS accelerator cryoplant. ICEC25, Enschede, the Netherlands, July 7-11 2014. [7] Fydrych J., 2014. Technical specification of the cryogenic distribution system for the elliptical linac. ESS technical document (controlled): ESS-0011735, pp 66. [8] Fydrych J., Tereszkowski, 2014. Placeholders of the RF waveguides under the cryogenic distribution line for the elliptical linac. ESS technical document (controlled): ESS-0012571, pp 6.
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