- Email: [email protected]
Running experience with the vacuum system of the superconducting linac of the TESLA Test Facility
ARTICLE IN PRESS
Vacuum 73 (2004) 213–217
Running experience with the vacuum system of the superconducting linac of the TESLA Test Facility K. Zapfe* Deutsches Elektronen-Synchrotron DESY, Hamburg D-22603, Germany for the TESLA Collaboration
Abstract The superconducting linear accelerator of the TESLA Test Facility (TTF) at DESY/Hamburg is running successfully since several years. The main focus was so far on machine developments as well as on a proof of principle experiment for a self amplifying spontaneous emission free electron laser (SASE FEL) for the proposed 500 GeV e+e linear collider TESLA with integrated X-ray free electron laser (XFEL) laboratory. Presently, the machine is substantially modified to become a VUV-FEL user facility with tunable wavelengths in the nm range within 2004. The beam pipe of the accelerator contains sections operated at room temperature as well as at 2 K in the areas of the superconducting structures used for acceleration of the beam. Three cryogenic modules, each containing 8 solid niobium cavities have been tested. In addition to standard UHV requirements, the vacuum system for this machine needs to preserve the cleanliness of the superconducting cavity surfaces. Thus the preparation of all vacuum components includes cleaning steps to remove particle contaminations, installation of components into the machine under local clean rooms and special procedures for pump down and venting. r 2004 Elsevier Ltd. All rights reserved. PACS: 07.30Kf; 29.17.+w; 84.71. b Keywords: Accelerator vacuum; Dust contamination; Particle cleaning; Superconductiving cavities; TESLA
1. Introduction The TESLA collaboration has presented the design for a superconducting e+e linear collider with a center of mass energy of 500 GeV with integrated X-ray free electron laser (XFEL) laboratory [1] to several international committees including the German Science Council. The challenges of the superconducting technology are *Tel.: +49-40-8998-4642; fax: +49-40-8998-4448. E-mail address: [email protected] (K. Zapfe).
the production of multicell accelerating structures with an average gradient of 23.4 MV/m at reasonable costs. For the TESLA project 9-cell cavities operating at 1.3 GHz with an accelerating field of 25 MV/m at a quality factor of Q0>1010 have been developed. In order to demonstrate the technical feasibility of high gradients in superconducting cavities the TESLA Test Facility (TTF) has been set up at DESY (Hamburg). It comprises the complete infrastructure for treatment, assembly and test of superconducting cavities as well as a 250 m
0042-207X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2003.12.021
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
214
superconducting linear accelerator for developing and testing machine components. More than 52 institutes from 12 countries are contributing to TTF.
2. The TTF superconducting linear accelerator The construction of the 250 m long superconducting electron linac is divided into two stages. During phase I, which has recently been completed successfully, a 120 m long setup was mainly devoted to accelerator development [2] and a proof of principle experiment of an FEL operating in the self-amplified spontaneous emission (SASE) mode [3]. Starting phase II the linac will become a VUV-FEL user facility with tunable wavelengths in the nm range starting operation within 2004. Therefore the linac is presently extended to 250 m length and substantially modified to increase the energy to 1 GeV. Fig. 1 shows the schematic layout of phase II with a laser-driven RF-gun, several cryo modules—each containing 8 superconducting cavities—undulators, beam formation sections as well as electron and photon beam diagnostic areas. A bypass line will enable setting up the machine without steering the beam through the undulators.
thus limit the performance of the superconducting cavities. As the 2 K cold cavities are an integral part of the beam pipe they act as huge cryo pumps. Therefore the risk to contaminate the superconducting cavities with particles and to condensate gas from other vacuum components during assembly and operation needs to be absolutely avoided. In addition especially optical components for photon beam transport require a hydrocarbon free vacuum and are sensitive to particulates as well. As a consequence the preparation of all vacuum components includes, in addition to standard UHV procedures, cleaning in a clean room of at least class 100 to remove particles and the installation of components into the machine under local clean rooms. Although the pressure requirements for beam operation are moderate (10 8 mbar) a pressure o10 10 mbar is aimed for in areas close to the cold sections. Both beam-rest gas interactions as well as synchrotron radiation are negligible in case of the TTF linac. As RF-losses were expected to be low for phase I, standard components like bellows and valves without shielding were used. Due to the short bunches (o50 mm) aimed for in phase II proper shielding of components is required now as described below.
3. The TTF vacuum system
3.1. Cold vacuum system
The accelerating structures of the TTF linac are operated at 2 K. All other sections are operated at room temperature. The requirements for the vacuum system are mainly determined by the ambitious goal to reach high accelerating gradients in the superconducting cavities. Dust particles can act as field emitters and
The superconducting cavities, fabricated from pure niobium, are surrounded by a titanium tank filled with superfluid helium. Eight cavities and a superconducting quadrupole with an integrated beam position monitor are grouped into 12 m long strings, which are assembled in a clean room class 10. The cavities are connected via copper-coated
experimental area
bypass
undulators
seeding
1000 MeV
400 MeV
150 MeV
bunch compressor
bunch compressor
collimator #7 #6 #5 #4
#3 #2
module #1
4 MeV
RF gun
Fig. 1. Schematic layout of the superconducting linac of the TESLA test facility for phase II with a laser-driven RF-gun, cryo modules—each containing 8 superconducting cavities—undulators, beam formation sections as well as electron and photon beam diagnostic areas. A bypass line will run parallel to the undulator sections.
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
bellows without RF-shields. The sealing system has been specially developed consisting of rigid niobium–titanium flanges (Nb/Ti55), electron beam welded to the niobium cavities and massive aluminum rings as gaskets [4]. After assembly the complete string is inserted into the module tank serving as isolation vacuum once the cavities are cooled down to 2 K. The main power RF input coupler attached to each cavity has two ceramic windows, one at a temperature of 70 K and one at room temperature. This design enables closure of the cavity completely in the clean room by mounting the coupler up to the first window, thus preventing any contamination during further assembly of the module. Additionally, gas and dust are prevented from entering the cavities in case a crack in one of the ceramic windows would occur during operation. Details of the cold vacuum system are given elsewhere [5]. 3.2. Warm vacuum system for phase I Most of the vacuum chambers of the warm system for phase I were made from stainless steel (316LN) which are vacuum fired at 950 C to reduce the outgassing of H2. Cu-Conflat gaskets are used for sealing. Additional cleaning to make the vacuum components particle free as well as the assembly work has been done in clean rooms using procedures similar to the treatment of the superconducting cavities. Local clean rooms were used for the installation into the linac. Special care is given to the pump down and venting procedures like using oil-free pump stations, small apertures for pump down and venting of sections to avoid strong turbulences of the gas flow, particle filters to clean the dry nitrogen for venting, etc. [6]. In situ bake out of the system has not yet been performed. The warm vacuum system is pumped by titanium sublimation pumps in combination with small ion getter pumps, which are also used for pressure readout. The system is segmented by all metal gate valves. In addition, fast shutters are installed downstream of the last module to protect the cold cavities in case of a vacuum break in the experimental area of the machine.
215
3.3. RF-gun The cesium telluride cathodes used at the laserdriven RF-gun are prepared under vacuum in a separate UHV system installed at INFN Milano. In order to reach a high quantum efficiency and long life time of the cathodes low oxygen and hydrocarbon partial pressures are required under all circumstances including storage and transport to DESY [7]. Connecting the chamber containing the cathodes to the RF-gun is done using a loadlock system. Although the compact design of the RF-gun body does not allow for optimal pumping the running experience using cesium telluride cathodes so far showed reasonable life times in the order of months [8] under beam conditions. 3.4. Vacuum control system The vacuum control system is an integral part of the general TTF linac control system DOOCS [9]. It is built in a way to guarantee a fail safe operation of all components like pumps, valves, etc. by using programmable logic controllers (PLC) and special micro-processors. All information is accessible by computer-controlled readout via network from terminals. All components are fully remote controlled. Automatic error diagnostic tools and long ranging archive systems are available as standard tools. 3.5. Running experience during phase I Phase I of the TTF linac was completed at the end of 2002 after more than 13,000 h of beam time. Four modules have been tested successfully achieving more than 20 MV/m accelerating gradient under stable beam conditions. No degradation of the cavity performance with time in the TTF linac has been observed so far. The vacuum system has been operated without major failures with pressures below 10 10 mbar in most parts of the linac. However, leaks did show up after warming up the modules several times, e.g. at several ceramic feedthroughs and electron pick-ups as well as at a ceramic window of the coupler. While these leaks so far did not prevent
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K. Zapfe / Vacuum 73 (2004) 213–217
operation of the machine, handling of the cavity strings during warm-up and venting as well as repair of the broken components are sometimes complicated and further improvements on reliability like cold test of all feedthroughs before installation are necessary. The experience at TTF is compatible with other superconducting linacs operating at lower gradients, e.g. [10]. 3.6. Preparation of phase II For phase II the machine is presently substantially modified and extended to 250 m length as shown schematically in Fig. 1. Beam operation will be started at the beginning of 2004 using five modules with the option for two further modules to be inserted at a later stage. The beam formation sections in the bunch compressor sections as well as the collimation section protecting the narrow undulator vacuum chambers from being hit with beam are densely packed with magnets and beam diagnostic elements. In order to conserve the highly demanding bunch properties needed to operate the SASE FEL, proper RF shielding of components is required for phase II. On the other hand, particle production must be avoided, and new solutions had to be developed for moving components. For bellows a demountable copper insert without touching fingers is used as an RF shield as shown in Fig. 2. In sections with smaller beam pipe diameter the gap of valves is shielded by introducing a tube with a small gap on both sides. Especially downstream of the third bunch compressor, most beam tubes are copper coated or fabricated from copper tubes to enlarge the conductivity of the beam pipe walls. Several components do not allow proper particle cleaning after fabrication due to its geometry. Here the cleaning process is an integral part of the construction process and the final step is welding of cleaned parts in a clean room class 100. In order to separate the particle cleaning of vacuum components from the facilities used for the preparation of superconducting cavities a new cleaning facility has been installed. Two ultrasonic baths, an ultra pure water rinsing bath and a dryer
Fig. 2. Drawing of a bellows with demountable copper insert without touching fingers used as an RF shield.
are available in a clean room class 100. Vacuum chambers as long as 4.8 m can be handled. More details of the facility and the improved procedures are given in [11].
4. Summary and outlook In order to prepare the TESLA 500 GeV e+e collider with integrated XFEL the TTF has been set up. During phase I the TTF linac was used to demonstrate the viability of a superconducting linear collider and a SASE FEL. For the successful operation of the superconducting cavities a high level of cleanliness of all vacuum components, especially with respect to particles, is required. Special cleaning and installation procedures under clean room conditions have been established to minimize the risk of particle and gas contamination of the superconducting cavities from other parts of the vacuum system. At present the TESLA Collaboration is extending the TTF linac to 1 GeV. The installation of the vacuum system is ongoing. The machine will turn into a VUV-FEL user facility with wavelengths down to 6 nm after commissioning in 2004.
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
Based on the successful operation of the TTF linac as well as on the evaluation of the German Science Council, the XFEL project has recently been approved by the German Federal Research Minister. In view of this support for the XFEL, the TESLA Collaboration has started a careful design review of basically all components tested so far. Most of this work has large overlap with the continuing international research towards the TESLA linear collider.
Acknowledgements The TTF linac vacuum system presented here is the result of the common effort of many members of the TESLA Collaboration. My grateful thanks are due to the members of the MVP vacuum group . at DESY, especially M. Bohnert, A. Brenger, O. Hensler, D. Hoppe, K. Rehlich, H. Remde, H.-P. Wedekind and J. Wojtkiewicz for their excellent work and technical support.
References [1] TESLA TDR, TESLA Report 2001-03, DESY 2001-011, 2001.
217
[2] Weise H. Operational experience with the test facilities for TESLA, In: Proceedings of the 21st International Linear Accelerator Conference, Gyeongji, Korea, 2002, http:// linac2002.postech.ac.kr/html/proceedings.html. [3] Andruszkow J, et al. Phys Ref Lett 2000;85:3825. [4] Zapfe K, et al. A new flange design for the superconducting cavities for TESLA. In: Palmieri V, Lombardi A, editors. Proceedings of the Eighth Workshop on RF Superconductivity, Abano Terme, 1997, (INFN, LNLINFN (Rep) 133/98) p. 457. [5] Zapfe K. Vacuum 2001;60:51. . [6] Bohnert M, et al. Oil-free pump stations for pumping of the superconducting cavities of the TESLA test facility, In: Proceedings of the Tenth Workshop on RF Superconductivity, Tsukuba, 2001, http://conference.kek.jp/ srf2001/. [7] di Bona A. J Appl Phys 1996;80:3024. [8] Schreiber S, et al. On the Photocathodes used at the TTF Photoinjector, In: Proceedings of the 20th Particle Accelerator Conference, Oregon, 2003. http://warrior.lbl. gov:7778/PAC PUBLIC/search.html. [9] Grygiel G, Hensler O, Rehlich K. Experience with an object oriented control system at DESY. In: Proceedings of the Second International Workshop on Personal Computers and Particle Accelerator Controls, Tsukuba, 1999 (KEK-Proceedings 98-14). [10] Reece C. Overview of SRF-related activities at Jefferson lab. In: Proceedings of the tenth Workshop on RF Superconductivity, Tsukuba, 2001, http://conference. kek.jp/srf2001/. [11] Hahn U, et al. A new cleaning facility for particle free UHV-components, Vacuum, these proceedings. doi:10.1016/j.vacuum.2003.12.020.
Vacuum 73 (2004) 213–217
Running experience with the vacuum system of the superconducting linac of the TESLA Test Facility K. Zapfe* Deutsches Elektronen-Synchrotron DESY, Hamburg D-22603, Germany for the TESLA Collaboration
Abstract The superconducting linear accelerator of the TESLA Test Facility (TTF) at DESY/Hamburg is running successfully since several years. The main focus was so far on machine developments as well as on a proof of principle experiment for a self amplifying spontaneous emission free electron laser (SASE FEL) for the proposed 500 GeV e+e linear collider TESLA with integrated X-ray free electron laser (XFEL) laboratory. Presently, the machine is substantially modified to become a VUV-FEL user facility with tunable wavelengths in the nm range within 2004. The beam pipe of the accelerator contains sections operated at room temperature as well as at 2 K in the areas of the superconducting structures used for acceleration of the beam. Three cryogenic modules, each containing 8 solid niobium cavities have been tested. In addition to standard UHV requirements, the vacuum system for this machine needs to preserve the cleanliness of the superconducting cavity surfaces. Thus the preparation of all vacuum components includes cleaning steps to remove particle contaminations, installation of components into the machine under local clean rooms and special procedures for pump down and venting. r 2004 Elsevier Ltd. All rights reserved. PACS: 07.30Kf; 29.17.+w; 84.71. b Keywords: Accelerator vacuum; Dust contamination; Particle cleaning; Superconductiving cavities; TESLA
1. Introduction The TESLA collaboration has presented the design for a superconducting e+e linear collider with a center of mass energy of 500 GeV with integrated X-ray free electron laser (XFEL) laboratory [1] to several international committees including the German Science Council. The challenges of the superconducting technology are *Tel.: +49-40-8998-4642; fax: +49-40-8998-4448. E-mail address: [email protected] (K. Zapfe).
the production of multicell accelerating structures with an average gradient of 23.4 MV/m at reasonable costs. For the TESLA project 9-cell cavities operating at 1.3 GHz with an accelerating field of 25 MV/m at a quality factor of Q0>1010 have been developed. In order to demonstrate the technical feasibility of high gradients in superconducting cavities the TESLA Test Facility (TTF) has been set up at DESY (Hamburg). It comprises the complete infrastructure for treatment, assembly and test of superconducting cavities as well as a 250 m
0042-207X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2003.12.021
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
214
superconducting linear accelerator for developing and testing machine components. More than 52 institutes from 12 countries are contributing to TTF.
2. The TTF superconducting linear accelerator The construction of the 250 m long superconducting electron linac is divided into two stages. During phase I, which has recently been completed successfully, a 120 m long setup was mainly devoted to accelerator development [2] and a proof of principle experiment of an FEL operating in the self-amplified spontaneous emission (SASE) mode [3]. Starting phase II the linac will become a VUV-FEL user facility with tunable wavelengths in the nm range starting operation within 2004. Therefore the linac is presently extended to 250 m length and substantially modified to increase the energy to 1 GeV. Fig. 1 shows the schematic layout of phase II with a laser-driven RF-gun, several cryo modules—each containing 8 superconducting cavities—undulators, beam formation sections as well as electron and photon beam diagnostic areas. A bypass line will enable setting up the machine without steering the beam through the undulators.
thus limit the performance of the superconducting cavities. As the 2 K cold cavities are an integral part of the beam pipe they act as huge cryo pumps. Therefore the risk to contaminate the superconducting cavities with particles and to condensate gas from other vacuum components during assembly and operation needs to be absolutely avoided. In addition especially optical components for photon beam transport require a hydrocarbon free vacuum and are sensitive to particulates as well. As a consequence the preparation of all vacuum components includes, in addition to standard UHV procedures, cleaning in a clean room of at least class 100 to remove particles and the installation of components into the machine under local clean rooms. Although the pressure requirements for beam operation are moderate (10 8 mbar) a pressure o10 10 mbar is aimed for in areas close to the cold sections. Both beam-rest gas interactions as well as synchrotron radiation are negligible in case of the TTF linac. As RF-losses were expected to be low for phase I, standard components like bellows and valves without shielding were used. Due to the short bunches (o50 mm) aimed for in phase II proper shielding of components is required now as described below.
3. The TTF vacuum system
3.1. Cold vacuum system
The accelerating structures of the TTF linac are operated at 2 K. All other sections are operated at room temperature. The requirements for the vacuum system are mainly determined by the ambitious goal to reach high accelerating gradients in the superconducting cavities. Dust particles can act as field emitters and
The superconducting cavities, fabricated from pure niobium, are surrounded by a titanium tank filled with superfluid helium. Eight cavities and a superconducting quadrupole with an integrated beam position monitor are grouped into 12 m long strings, which are assembled in a clean room class 10. The cavities are connected via copper-coated
experimental area
bypass
undulators
seeding
1000 MeV
400 MeV
150 MeV
bunch compressor
bunch compressor
collimator #7 #6 #5 #4
#3 #2
module #1
4 MeV
RF gun
Fig. 1. Schematic layout of the superconducting linac of the TESLA test facility for phase II with a laser-driven RF-gun, cryo modules—each containing 8 superconducting cavities—undulators, beam formation sections as well as electron and photon beam diagnostic areas. A bypass line will run parallel to the undulator sections.
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
bellows without RF-shields. The sealing system has been specially developed consisting of rigid niobium–titanium flanges (Nb/Ti55), electron beam welded to the niobium cavities and massive aluminum rings as gaskets [4]. After assembly the complete string is inserted into the module tank serving as isolation vacuum once the cavities are cooled down to 2 K. The main power RF input coupler attached to each cavity has two ceramic windows, one at a temperature of 70 K and one at room temperature. This design enables closure of the cavity completely in the clean room by mounting the coupler up to the first window, thus preventing any contamination during further assembly of the module. Additionally, gas and dust are prevented from entering the cavities in case a crack in one of the ceramic windows would occur during operation. Details of the cold vacuum system are given elsewhere [5]. 3.2. Warm vacuum system for phase I Most of the vacuum chambers of the warm system for phase I were made from stainless steel (316LN) which are vacuum fired at 950 C to reduce the outgassing of H2. Cu-Conflat gaskets are used for sealing. Additional cleaning to make the vacuum components particle free as well as the assembly work has been done in clean rooms using procedures similar to the treatment of the superconducting cavities. Local clean rooms were used for the installation into the linac. Special care is given to the pump down and venting procedures like using oil-free pump stations, small apertures for pump down and venting of sections to avoid strong turbulences of the gas flow, particle filters to clean the dry nitrogen for venting, etc. [6]. In situ bake out of the system has not yet been performed. The warm vacuum system is pumped by titanium sublimation pumps in combination with small ion getter pumps, which are also used for pressure readout. The system is segmented by all metal gate valves. In addition, fast shutters are installed downstream of the last module to protect the cold cavities in case of a vacuum break in the experimental area of the machine.
215
3.3. RF-gun The cesium telluride cathodes used at the laserdriven RF-gun are prepared under vacuum in a separate UHV system installed at INFN Milano. In order to reach a high quantum efficiency and long life time of the cathodes low oxygen and hydrocarbon partial pressures are required under all circumstances including storage and transport to DESY [7]. Connecting the chamber containing the cathodes to the RF-gun is done using a loadlock system. Although the compact design of the RF-gun body does not allow for optimal pumping the running experience using cesium telluride cathodes so far showed reasonable life times in the order of months [8] under beam conditions. 3.4. Vacuum control system The vacuum control system is an integral part of the general TTF linac control system DOOCS [9]. It is built in a way to guarantee a fail safe operation of all components like pumps, valves, etc. by using programmable logic controllers (PLC) and special micro-processors. All information is accessible by computer-controlled readout via network from terminals. All components are fully remote controlled. Automatic error diagnostic tools and long ranging archive systems are available as standard tools. 3.5. Running experience during phase I Phase I of the TTF linac was completed at the end of 2002 after more than 13,000 h of beam time. Four modules have been tested successfully achieving more than 20 MV/m accelerating gradient under stable beam conditions. No degradation of the cavity performance with time in the TTF linac has been observed so far. The vacuum system has been operated without major failures with pressures below 10 10 mbar in most parts of the linac. However, leaks did show up after warming up the modules several times, e.g. at several ceramic feedthroughs and electron pick-ups as well as at a ceramic window of the coupler. While these leaks so far did not prevent
ARTICLE IN PRESS 216
K. Zapfe / Vacuum 73 (2004) 213–217
operation of the machine, handling of the cavity strings during warm-up and venting as well as repair of the broken components are sometimes complicated and further improvements on reliability like cold test of all feedthroughs before installation are necessary. The experience at TTF is compatible with other superconducting linacs operating at lower gradients, e.g. [10]. 3.6. Preparation of phase II For phase II the machine is presently substantially modified and extended to 250 m length as shown schematically in Fig. 1. Beam operation will be started at the beginning of 2004 using five modules with the option for two further modules to be inserted at a later stage. The beam formation sections in the bunch compressor sections as well as the collimation section protecting the narrow undulator vacuum chambers from being hit with beam are densely packed with magnets and beam diagnostic elements. In order to conserve the highly demanding bunch properties needed to operate the SASE FEL, proper RF shielding of components is required for phase II. On the other hand, particle production must be avoided, and new solutions had to be developed for moving components. For bellows a demountable copper insert without touching fingers is used as an RF shield as shown in Fig. 2. In sections with smaller beam pipe diameter the gap of valves is shielded by introducing a tube with a small gap on both sides. Especially downstream of the third bunch compressor, most beam tubes are copper coated or fabricated from copper tubes to enlarge the conductivity of the beam pipe walls. Several components do not allow proper particle cleaning after fabrication due to its geometry. Here the cleaning process is an integral part of the construction process and the final step is welding of cleaned parts in a clean room class 100. In order to separate the particle cleaning of vacuum components from the facilities used for the preparation of superconducting cavities a new cleaning facility has been installed. Two ultrasonic baths, an ultra pure water rinsing bath and a dryer
Fig. 2. Drawing of a bellows with demountable copper insert without touching fingers used as an RF shield.
are available in a clean room class 100. Vacuum chambers as long as 4.8 m can be handled. More details of the facility and the improved procedures are given in [11].
4. Summary and outlook In order to prepare the TESLA 500 GeV e+e collider with integrated XFEL the TTF has been set up. During phase I the TTF linac was used to demonstrate the viability of a superconducting linear collider and a SASE FEL. For the successful operation of the superconducting cavities a high level of cleanliness of all vacuum components, especially with respect to particles, is required. Special cleaning and installation procedures under clean room conditions have been established to minimize the risk of particle and gas contamination of the superconducting cavities from other parts of the vacuum system. At present the TESLA Collaboration is extending the TTF linac to 1 GeV. The installation of the vacuum system is ongoing. The machine will turn into a VUV-FEL user facility with wavelengths down to 6 nm after commissioning in 2004.
ARTICLE IN PRESS K. Zapfe / Vacuum 73 (2004) 213–217
Based on the successful operation of the TTF linac as well as on the evaluation of the German Science Council, the XFEL project has recently been approved by the German Federal Research Minister. In view of this support for the XFEL, the TESLA Collaboration has started a careful design review of basically all components tested so far. Most of this work has large overlap with the continuing international research towards the TESLA linear collider.
Acknowledgements The TTF linac vacuum system presented here is the result of the common effort of many members of the TESLA Collaboration. My grateful thanks are due to the members of the MVP vacuum group . at DESY, especially M. Bohnert, A. Brenger, O. Hensler, D. Hoppe, K. Rehlich, H. Remde, H.-P. Wedekind and J. Wojtkiewicz for their excellent work and technical support.
References [1] TESLA TDR, TESLA Report 2001-03, DESY 2001-011, 2001.
217
[2] Weise H. Operational experience with the test facilities for TESLA, In: Proceedings of the 21st International Linear Accelerator Conference, Gyeongji, Korea, 2002, http:// linac2002.postech.ac.kr/html/proceedings.html. [3] Andruszkow J, et al. Phys Ref Lett 2000;85:3825. [4] Zapfe K, et al. A new flange design for the superconducting cavities for TESLA. In: Palmieri V, Lombardi A, editors. Proceedings of the Eighth Workshop on RF Superconductivity, Abano Terme, 1997, (INFN, LNLINFN (Rep) 133/98) p. 457. [5] Zapfe K. Vacuum 2001;60:51. . [6] Bohnert M, et al. Oil-free pump stations for pumping of the superconducting cavities of the TESLA test facility, In: Proceedings of the Tenth Workshop on RF Superconductivity, Tsukuba, 2001, http://conference.kek.jp/ srf2001/. [7] di Bona A. J Appl Phys 1996;80:3024. [8] Schreiber S, et al. On the Photocathodes used at the TTF Photoinjector, In: Proceedings of the 20th Particle Accelerator Conference, Oregon, 2003. http://warrior.lbl. gov:7778/PAC PUBLIC/search.html. [9] Grygiel G, Hensler O, Rehlich K. Experience with an object oriented control system at DESY. In: Proceedings of the Second International Workshop on Personal Computers and Particle Accelerator Controls, Tsukuba, 1999 (KEK-Proceedings 98-14). [10] Reece C. Overview of SRF-related activities at Jefferson lab. In: Proceedings of the tenth Workshop on RF Superconductivity, Tsukuba, 2001, http://conference. kek.jp/srf2001/. [11] Hahn U, et al. A new cleaning facility for particle free UHV-components, Vacuum, these proceedings. doi:10.1016/j.vacuum.2003.12.020.