Accelerator Vacuum Systems at DESY - INSPIRE HEPinspirehep.net/record/788516/files/jpcs_114_1_012003.pdf · bellows. Initially integrated sputter ion pumps have been used inside the

Accelerator Vacuum Systems at DESY

K Zapfe1

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg

Email: [email protected]

Abstract. The research center DESY in Germany is one of the leading accelerator centers worldwide. At the facilities located in Hamburg more than 3000 scientists from all over the world do research with photons and in the field of particle physics. Since 1992 the 6-km-long HERA storage ring was used for high energy collisions of electrons/positrons and protons. It consists of two rings. The one for the 27.5 GeV electrons/positrons uses normal conducting magnets. The other one bends the up to 920 GeV protons with superconducting magnets. Data taking at HERA has been terminated only recently. Synchrotron light for 36 experimental stations is generated by the 4.5 GeV storage ring DORIS. The 2.3 km long storage ring PETRA is presently rebuilt into PETRA III, one of the most brilliant X-ray sources worldwide, to start user operation in 2009. Therefore the vacuum system is completely replaced. The construction of the European X-ray Free Electron Laser XFEL, a new international research facility, just has started next to DESY. Its extremely intense X-ray laser flashes with tunable wavelengths down to 0.1 nm will open up completely new experimental possibilities for nearly all fields of natural sciences. The basic process adopted to generate the X-ray pulses is SASE (Self-Amplified Spontaneous Emission). Therefore electron bunches are brought to high energy of about 20 GeV through a superconducting linear accelerator, and conveyed to up to 250 m long undulators where the X-rays are generated. The beam vacuum system of this 3.4 km long straight facility contains sections operated at room temperature as well as at 2 K in the areas of the superconducting accelerating structures. In addition to standard UHV requirements the vacuum system needs to preserve the particle cleanliness of the superconducting cavity surfaces. Further challenges are the undulator vacuum chambers filling more than 750 m with extreme requirements to the surface quality. Unique research opportunities worldwide are offered already now by the 250 m long free-electron laser FLASH, the prototype for the XFEL, which is under operation since several years as a user facility. The vacuum systems of the various DESY accelerator facilities will be discussed in this paper in more detail.

1. Introduction The Deutsche Elektronen-Synchrotron DESY was founded as national research center in 1959 in Hamburg/Germany, having a second location in Zeuthen/Brandenburg since 1992. It is one of the leading accelerator centers worldwide. Financed by public funding its mission is to perform basic research in natural science with special emphasis on the development, construction and operation of accelerator facilities for particle physics and research with photons. More than 3000 scientists from all over the world are using the facilities located in Hamburg.

An overview of the operating accelerators at DESY and some relevant parameters are given in table 1. These facilities are operated 24 h per day, 7 days a week with 1 to 2 months shutdown each

1 Correspondence to be addressed to [email protected]

International Symposium on “Vacuum Science and Technology” (IVS 2007) IOP PublishingJournal of Physics: Conference Series 114 (2008) 012003 doi:10.1088/1742-6596/114/1/012003

c© 2008 IOP Publishing Ltd 1

year for maintenance and modifications or upgrades. Also listed are the new facilities PETRA III and XFEL, which are presently under construction. In addition to the accelerators listed below a chain of pre-accelerators is in use.

Table 1. Overview of the operating accelerators at DESY and new facilities under construction with its type, size, particles and energy. In addition some information on the application and operational period are given.

name type length part. energy application operation

operating facilities

p 40-920 GeV User operation 1992-2007

HERA storage ring

6,300 m

e-/e+ 12-27.5 GeV

high energy physics electron/positron - proton collider

DORIS storage ring

289 m e-/e+ 4.5 GeV 2nd generation light source

dedicated �’s since 1993

TTF/FLASH linear accelerator

250 m e- 1.0 GeV prototype 4th generation light source

1. beam 1997 users since 2002

facilities under construction

PETRA III storage ring

2,300 m e-/e+ 6.0 GeV 3rd generation light source

users start in 2009

XFEL linear accelerator

3,400 m e- 20 GeV 4th generation light source

users start in 2014

2. HERA The high energy electron/positron – proton collider HERA was used for fundamental research in particle physics. The 6.3 km long storage ring is a combination of two accelerators using different technologies. While warm magnets bend the 27.5 GeV electrons/positrons, superconducting magnets are used for the much heavier protons of 920 GeV. Figure 1 shows a view into the HERA tunnel with the two accelerators on top of each other. First collisions started in 1991. The two experiments H1 and ZEUS used the colliding beams, while HERMES and HERA-B installed fixed targets in one of the two beam lines. Last collisions occurred in summer 2007. While all systems are shut down now, no dismantling is foreseen for the coming years to keep the systems intact to keep the option of further usage.

The vacuum system for the electrons/positrons [1] has a rather uniform structure. It has to cope with huge load of synchrotron radiation which is continuously absorbed by the water cooled copper vacuum chambers shown in figure 2. In addition copper absorbers protect critical components like bellows. Initially integrated sputter ion pumps have been used inside the long dipole magnets. Due to problems with dust particles produced by these pumps, which disturbed the operating with electrons by unacceptable reductions of the beam life time [2], they have later been replaced by NEG strips. Lumped sputter ion pumps, which are also used for pressure information, support the distributed pumps.


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Figure 1. View into the HERA tunnel with the normal conducting electron ring and the superconducting proton ring on top.

Figure 2. Profile of the copper electron beam vacuum chamber with the channels for water cooling (left) and pumping (right).

The major part of the proton ring is filled by the superconducting magnets, where the vacuum tube

inside the superconducting bending dipole and quadrupole magnets is cooled to temperatures of 4.2 K. The vacuum chambers therefore work as an ideal cryo pump resulting in a pressure below 10-10 mbar [3]. In the cryostats an insulating vacuum of 10-6 mbar is maintained. In the straight sections, the vacuum system is at room temperature. Here a pressure of 10-10 mbar is reached in the stainless steel chambers using lumped sputter ion and titanium sublimation pumps [4].

3. DORIS The 290 m long storage ring DORIS is operated as dedicated synchrotron radiation facility using positrons at 4.5 GeV since 1993. Initially built as electron – positron collider in 1974, first parasitic use of synchrotron radiation started in 1981. Today nine insertion devices serve 36 experimental stations. The beam vacuum system is mainly built from copper vacuum chambers similar to the HERA electron beam vacuum chamber manufactured with brazing technology. The system is pumped by integrated sputter ion pumps in the arcs and combinations of lumped titanium sublimation and sputter ion pumps. The average dynamic pressure is about 10-9 mbar at 144 mA beam current, resulting in a beam lifetime of 15 to 25 hours.

4. PETRA III Since summer 2007 the 2.3 km long storage ring PETRA II is rebuilt into one of the most brilliant X-ray sources of the 3rd generation worldwide (PETRA III) [5]. The large bending radius and the use of damping wigglers allow achieving small beam emittance and extremely brilliant X-ray beams. Therefore the vacuum system is completely replaced [6]. It consists of seven standard arc sections, where the existing magnets will be reused. The experimental octant will be completely new containing eight insertion devices to be filled with undulators for 13 high brilliance beam lines. First beam operation is expected for the beginning of 2009 and first user operation is foreseen for summer 2009.

The vacuum system is designed to guarantee a beam life time due to vacuum effects of larger than 50 h. Taking into account losses due to inelastic scattering and bremsstrahlung the required average dynamic pressure results in pavg ≤ 2 �10-9 mbar assuming a gas composition of 75 % H2 and 25 % CO.

Because of the long length of the system a cost effective and simple solution had to be found, especially for the standard arcs and straight sections. Here the synchrotron radiation will be continuously absorbed by the water cooled vacuum chambers. Inside the dipole magnets the chambers are made from extruded aluminum profiles. Explosion bonded aluminum-stainless steel transitions are used to connect stainless steel ConFlat® flanges. The quadrupole and sextupole chambers are fabricated from stainless steel, containing massive blocks for the beam position monitors (BPM). NEG strips in all chambers will provide distributed pumping, supported by lumped sputter ion pumps. For the two 80 m long damping wiggler sections, NEG coated aluminum profiles are used inside the


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wiggler magnets. The synchrotron radiation will be absorbed by optimized water cooled copper blocks here.

The octant containing the beam lines to the experiments consists of nine DBA cells using short dipole magnets. Figure 3 shows schematically one of these cells. In this section the vacuum system is optimized for the insertion devices with its high load on synchrotron radiation and the required high thermal stability with respect to magnets and BPM's. Inside the magnets keyhole type stainless steel chambers equipped with NEG strips will be placed as shown in figure 4. The synchrotron radiation is guided in a separate channel to the high power absorbers made out of massive copper blocks (see figure 5). These absorbers are equipped with titanium sublimation and sputter ion pumps for local pumping. Rectangular flanges with flat aluminum seals are used in this section.

Due to the very limited space for the insertion devices, the beam position monitors, requiring an extreme mechanical stability of less than 0.5 �m, had to be integrated into the undulator vacuum chambers without any bellows. The vacuum chambers, fabricated from extruded aluminum profiles with the flat beam ellipse of 57 x 7 mm2 and a pump channel for two NEG strips, will therefore be fixed to massive support bars. In total 13 undulators of various types and lengths including one in-vacuum undulator are foreseen. Thus different solutions for the vacuum chambers are required.

Presently the existing PETRA tunnel has been completely cleared up. The first dipole magnets with vacuum chambers have been installed and the installation of the vacuum system is scheduled to be finished in summer 2008.

Figure 3. Schematic layout of the DBA cell with two short undulators in the middle. Indicated are the various pump types – NEG strips, titanium sublimation (TSP) and sputter ion pumps (SIP).

Figure 4. Keyhole shaped stainless steel chamber inside a quadrupole magnet with the channels for the NEG strip (left) and the synchrotron light (right).

Figure 5. Copper absorber block with wire eroded beam channel and port for pumping.


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5. FLASH All accelerators discussed so far are of the storage ring type. In addition there are linear accelerators in use at DESY. The 250 m long TTF/FLASH facility produces light pulses by a SASE (Self Amplifying Spontaneous Emission) Free Electron Laser (FEL).

Using the TESLA technology electrons are accelerated by superconducting cavities to energies of up to 1 GeV. The high intense light pulses are produced in undulators thereafter. The wavelength of the light can be varied in the nm range by changing the electron beam energy. A schematic layout of FLASH is shown in figure 6. The electrons are produced in a laser-driven RF-gun and accelerated by several modules containing the superconducting cavities. The bunch compression and collimator sections are used for beam formation before the beam pulses enter the undulators. Finally the electrons are disposed of in a beam dump, while the photons are guided to the experimental stations.

Figure 6. Schematic layout of the SASE FEL FLASH with the laser driven RF-source, superconducting linear accelerator, undulators and experimental stations.

This facility has initially been built as a prototype of a superconducting linear accelerator to

develop and establish successfully the operation of high gradient superconducting cavities [7]. In addition the first experiments to produce high intense FEL light pulses in the nm range by SASE have been performed here [8]. Due to this success the facility has been turned into the user facility FLASH in 2005. Presently it is the only operating user facility worldwide offering SASE FEL light pulses [9]. Adding a sixth accelerating module the design energy of 1 GeV as well as the design wavelength of 6.5 nm have been reached recently [10].

5.1. The Vacuum Systems of the Superconducting Linear Accelerator The beam vacuum system of this facility contains sections operated at room temperature as well as at 2 K in the areas of the superconducting accelerating structures. A detailed description is given in [11]. In the accelerating linac the cold beam vacuum is formed by 12 m long strings, which consists of eight superconducting cavities, a superconducting magnet and a beam position monitor closed off by manual valves at both ends. The components of the strings are cleaned and assembled in a class 10 clean room. Thereafter the strings are assembled to the cold mass and finally inserted into the large insulating vacuum tank of a module. In-between two modules short interconnections with a pump port are installed. Figure 7 shows a view into a superconducting module of FLASH. The CAD model in figure 8 shows the layout of the accelerator modules with the three vacuum systems involved: The beam vacuum system operated at 2 K, thus forming a huge cryo pump, the room temperature vacuum system of the high power couplers and the vacuum to insulate the cold components against ambient air.

The high power couplers at each cavity have two ceramic windows, one at a temperature of 70 K and one at room temperature. This design enables the cavity to be closed off completely by mounting the coupler up to the first window during string assembly in the clean room. A common pump line connects the eight couplers of each module. Using a titanium sublimation and sputter ion pump a pressure of 10-10 mbar is usually reached during operation of the cavities.

The pressure needs for the insulating vacuum are relaxed; about 10-3 mbar are required before cool down. This is achieved using roughing and turbomolecular pumps, although pump down times might


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be quite long due to the large amount of components and super insulating foil installed into the insulating vacuum tank. Once the system is cold a pressure of 10-6 mbar is maintained.

Figure 7. View into the superconducting module of the FLASH facility. The large central tube is the helium return pipe. In the lower part the manual valve closing off the beam vacuum is seen.

Figure 8. CAD model showing the three vacuum systems of the superconducting linac.

5.2. Vacuum Requirements The beam vacuum system itself has to be made such as to avoid any effects causing significant beam losses or deterioration of the beam quality. In contrast to storage ring type light sources, here the beam particles pass the straight accelerator only once. Therefore the pressure requirements with respect to losses due to scattering on the residual gas are relaxed. An average pressure of 10-7 mbar is acceptable. Effects like emittance growth, fast ion instabilities or dynamic pressure increase due to synchrotron radiation are negligible. Deterioration of the beam quality by RF losses however is an issue due to the very short and intense bunches. Thus proper shielding of bellows, pump ports, gate valves etc. are necessary in most parts of the system.

The vacuum system also needs to avoid effects causing deterioration of the superconducting cavity performance. Particles can act as field emitters and thus limit the performance of the cavities [12]. Any kind of particles must be avoided for operating the cavities at high accelerating gradients. Therefore the cavities are cleaned and finally assembled in clean rooms under conditions similar to the semiconductor industry. Although the cavities are forming the major part of the cold beam pipe itself, the remaining vacuum needs to preserve the particle cleanliness of the superconducting cavity surfaces by applying similar cleaning and assembly procedures to the vacuum components of the cold system. In addition, strong gas condensation from neighboring room temperature sections onto the cold surfaces needs to be avoided requiring a pressure level of 10-10 mbar in those areas. This will be accomplished using combinations of titanium sublimation and sputter ion pumps for part of the facility. A fast shutter next to the last cold section should protect the sensitive part of the beam vacuum system in case of a sudden vacuum break in the room temperature sections.

Following standard UHV-cleaning procedures the preparation of all vacuum components of this linear accelerator includes cleaning steps in a special clean room containing various facilities to remove particles [13], and installing them into the accelerator using local clean rooms. Components for the photon beam lines are treated similarly to avoid contamination of e.g. mirrors with dust particles. Oil free pump stations are used for initial pump down. In addition, special care is taken during pump down and venting to avoid any particle transport inside the beam pipe into critical areas during these processes.


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6. XFEL The European X-Ray Free Electron Laser XFEL [14] is a 4th generation synchrotron radiation facility to be built next to DESY. The purpose of this new international scientific infrastructure is to generate extremely brilliant and ultra short pulses of spatially coherent X-rays in a wavelength regime from 0.1 nm to 5 nm, and to exploit them for exciting and benchmarking scientific experiments at various disciplines spanning e.g. physics, chemistry, material science and biology. The peak brilliance will be more than 100 million times higher than at present day 3rd synchrotron radiation sources. The basic process adopted to generate the intense X-ray pulses is SASE.

The XFEL has a strong link to the running FLASH linear accelerator, which in nearly all respects is a pilot facility for this future project [9]. It comprises the necessary accelerator technologies, FEL process and photon beam lines. As a running user facility it provides lots of experience with FEL operation for user experiments. For example, for many of the vacuum components and procedures needed for the XFEL up to 10 years operational experience exists. In addition FLASH also is an ideal test bed for technical developments specifically required for the XFEL.

A schematic sketch of the XFEL facility is shown in figure 9. The electron bunches are produced in a high-brightness gun. Consisting of a 1.6 km long sequence of superconducting TESLA accelerating structures, magnets and diagnostic equipment, the electrons are accelerated to energies of up to 20 GeV. Along the accelerator, the two stages of bunch compression are located to produce the short and very dense electron bunches, which are required to achieve saturation in the SASE process. At the end of the linear accelerator follows a beam transport section with collimation and diagnostics systems. Thereafter the individual electron bunches are fed into one or the other of two electron beam lines with the up to 250 m long undulators by a beam distribution system, where the X-rays are generated. The linac and beam transport line are housed in a 2.1 km long underground tunnel. Photon beam lines guide the light to the instruments in the experimental hall. The components are distributed along an essentially linear geometry of 3.4 km length. In the initial configuration the user facility has 3 SASE FEL and two spontaneous radiation undulator beam lines with in total 10 experimental stations. The site layout permits a later extension of the facility by another 5 beam lines.

Figure 9. Schematic layout of the European XFEL facility.

The European XFEL will be an international multi-user facility, with 75% of the funding for the initial construction phase provided by Germany and 25% from other partner countries. Following the official go ahead in summer 2007 to start the construction the formation of the international XFEL GmbH is now ongoing. The first X-ray beam is scheduled for 2013, and first users will gain access to the facility by the following year. However, before the accelerator is put into operation, a wide range of technical challenges must be overcome – including the development of strategies for delivering and maintaining the appropriate vacuum conditions. More details are found in [].

Similar to FLASH the beam vacuum system contains sections operated at room temperature as well as at 2 K. The vacuum requirements are very similar to the ones described in section 5.2. For all vacuum components of the 1.6 km long main linac cleaning steps to remove particles are required. For the mass production of the modules and the installation of the beam vacuum system a set-up with


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automated procedures for pump down and venting has been developed to avoid any particle transport inside the beam pipe into critical areas during these processes [15]. Despite the similarity to FLASH several of the technical challenges and solutions for the various sections of the XFEL are much more ambitious than at the existing facility, and new solutions need to be developed.

6.1. Cold Vacuum Systems The layout of the superconducting linac is very similar to the existing one at FLASH shown in figure 7. However, for the cavity strings new types of beam position monitors and quadrupole magnets with integrated beam pipe have been developed. The short interconnections in between two modules will include a higher order mode absorber [16]. The full XFEL string is shown in figure 10. Continuous pumping of thebeam vacuum will be done by sputter ion pumps at a distance of 140 m when the system is at room temperature, while the pumps mainly act as pressure sensors when being cold.

Figure 10. 12 m long XFEL cavity string with 8 cavities, superconducting magnet, beam position monitor and manual valves as well as intermediate piece.

It is planned to do a full performance test of the more than 100 modules in a special test facility at

DESY. In addition, an RF-test of the more than 800 superconducting cavities will be performed in this facility, thus requiring appropriate vacuum installations. In contrast to the present layout of the FLASH tunnel the modules will be fixed to the ceiling of the XFEL tunnel.

6.2. Warm Vacuum System The electron gun and first injection section will be like the one at FLASH. The laser driven RF source uses a water-cooled brazed copper cavity. Complex diagnostic sections will then alternate with beam acceleration and beam formation.

Shortening of the electron bunches occur within the magnetic chicanes of the two bunch compressors, having a total length of 160 m. Here one option is to use quite wide but flat vacuum chambers inside the deflecting magnets. Following the experience from FLASH copper coated stainless steel chambers could fulfill the requirements with respect to the tight tolerances and minimizing RF losses. Alternatively, a movable chicane is presently investigated.

Once the electrons are accelerated to full energy, they are guided through a 200 m long section to collimate the beam pulses and to distribute them into the two undulator beam lines. Special collimators should protect the radiation sensitive undulator magnets against direct beam hits from mis-steered beams. The collimator must be able to withstand beam hits of a few bunches, as due to the short bunch distance within a bunch train, several bunches will already be on its way to the undulators once a problem is detected and the electron gun is switched off. In addition, the collimators have to absorb losses from beam halo and dark current generated by the superconducting cavities. The present collimator design follows the experience from FLASH using massive titanium blocks, which will be brazed to water cooled copper blocks. The 30 vacuum chambers for the fast kicker magnets for beam distribution will be made out of ceramics with sputtered metallic coating to reduce RF losses.

The undulators, filling about 750 m, will be built up in a modular structure. 5 m long undulators with 10 mm gap height will alternate with 1.1 m long intersections, containing a phase shifter, quadrupole magnet, beam position monitor, small absorber and a 20 l/s sputter ion pump as shown in figure 11. Without active pumping inside the undulator an average pressure of a few times 10-7 mbar is expected, assuming a conservative outgassing rate of 10-11 mbar l/s/cm2. The undulator vacuum


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chamber has a cross section of 8.8 mm x 15 mm. It will pose challenges with respect to fabrication and surface preparation. Due to their small cross section and its long length losses by wake fields could be quite significant and therefore must be minimized. Choosing aluminum a surface roughness with RMS values below 300 nm in longitudinal direction and an oxide layer thickness below 5 nm are required. A development program is ongoing to evaluate fabrication and surface preparation techniques of an extruded aluminum profile, passivating coatings using e.g. Au, and cleaning procedures to ensure that the chambers are as smooth and oxide-free as possible.

Figure 11. Intersection between the undulators with phase shifter, quadrupole magnet, beam position monitor, small absorber and a 20 l/s sputter ion pump.

The transport beam lines in-between the various undulators and from there to the beam dumps sum

up to about 1.7 km. Here a cost effective solution is required, which offers sufficient electrical conductivity to minimize losses by resistive wake field effects over the long length of the system. It is planned to use copper tubes connected to stainless steel ConFlat® flanges via inductive brazing, i.e. brazing under Argon atmosphere using locally the magnetic field of a strong coil to heat up the material.

Once the electrons complete their path through the facility, they must be disposed of safely by removing them from the beam vacuum system and delivering them to quite massive beam dumps, where their kinetic energy is absorbed. In total 6 beam dumps are foreseen at various locations of the facility in order to allow successive commissioning and to serve all beam lines. At these locations exit windows are required as barriers to the vacuum system. These windows need to withstand the passage of the short and very intense electron bunches, resulting locally in high thermal and mechanical stress. Graphite seems to be a good candidate to fulfill these requirements; however its porous structure will not act as vacuum barrier. Therefore studies are ongoing to coat the graphite using thin brazing foils. In addition this foil should be polished in order to be used as mirror for an optical transition radiation detector to monitor online the position of the electron beam on the exit window.

7. Concluding Remarks At DESY several kilometers of accelerator vacuum systems are designed, manufactured and operated since decades. The different requirements to the vacuum systems of the various facilities resulted in a wide spectrum of solutions for the vacuum chambers, absorbers and pumping systems. Quite a number of technologies have been developed for in-house manufacturing of vacuum components as e.g. welding of various materials like stainless steel, aluminum, titanium und niobium as well as (inductive) brazing. Several facilities for UHV- and particle cleaning have been set up.

Designing, building and operating the many kilometers of the HERA storage ring has been an exciting experience. For the future projects PETRA III and XFEL new and ambitious technical challenges for the vacuum systems have to be solved.


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Acknowledgements The author would like to thank the DESY vacuum group for their excellent work and technical support of the accelerator vacuum systems described in this paper. References [1] Ballion R, Boster J, Giesske W, Hartwig H, Jagnow D, Kose R, Kouptsidis J, Schumann G and Schwartz M 1990 Vacuum 41 1887 [2] Kelly D R C 1996 The cffect of beam excitation on the HERA electron-beam lifetime disruption Proc. of the European Particle Accelerator Conference ( Sitges, Spain, 10-14 June 1996) Par.http://accelconf.web.cern.ch/accelconf/e96/PAPERS/THPG/THP041G.PDF [3] Trines D, Böhnert M, Brauer D, Hensler R, Hoppe D, Hubert D, Rehlich K, Sanok Z, Wyszogrodsky A 1993 The cold bore beam pipe vacuum system of the HERA proton storage ring Proc. XVth Intern. Conf. on High Energy Accelerators (Hamburg, Germany, 20-24 July 1992) (Int. J. Mod. Phys. A (Proc. Suppl.)) 2A 344 [4] Römer J G M and Trines D 1988 Vacuum 38 613 [5] Balewski K, Brefeld W, Decking W., Franz H, Röhlsberger and Weckert E (eds.) 2004 PETRA III: A low emittance synchrotron radiation source, Technical Design Report DESY-2004-035 [6] Böspflug R, Boster J, Giesske W, Keese D, Köhler R, Mildner N, Nagorny B, Naujoks U, Remde H, Schulz E, Seidel M, Tiessen J, Wedekind H P and Zapfe K 2008 Vacuum system design of the third generation synchrotron radiation source PETRA III Proc of the 17th International Vacuum Conference (Stockholm, Sweden, 2-6 July 2007) to be published in Jounal of Physics: Conference Series [7] Lilje L 2006 Performance limitations of TESLA cavities in the FLASH accelerator and their relation to the assembly process Proc. Linear Accelerator Conf. (Knoxville, USA, 21-25 August 2006) http://accelconf.web.cern.ch/accelconf/ [8] Andruszkow J et al. 2000 Phys. Ref. Lett. 85 3825 [9] Weise H 2006 The TTF/VUV-FEL (FLASH) as the prototype for the European XFEL project Proc. Linear Accelerator Conf. (Knoxville, USA, 21-25 August 2006) http://accelconf.web.cern.ch/accelconf/ [10] The FLASH team, to be published [11] Zapfe K 2004 Vacuum 73 213 [12] Reschke D 2003 Final cleaning and assembly Proc. of the 10th Workshop on RF Superconductivity (Tsukuba, Japan, 6-11 September 2001) KEK Proc. 2003-2 (2003) 477 http://conference.kek.jp/srf2001/ [13] Hahn U, Hesse M, Remde H and Zapfe K 2004 Vacuum 73 231Zapfe K, Hahn U, Hesse M and Remde H 2003 A cleaning facility to prepare particle free UHV-components Proc. 11th Workshop on RF Superconductivity (Travemünde, Germany, 8-12 September 2003) http://srf2003.desy.de/fap/ [14] Brinkmann R et al. (eds.) 2002 TESLA XFEL Technical Design Report - Supplement DESY-2002-167 Brinkmann R 2006 Proc. 28th Free Electron Laser Conf. (Berlin, Germany, 27 August - 1 September 2006) http://www.bessy.de/fel2006/proceedings [15] Zapfe K Böhnert M, Hensler O, Hoppe D, Mildner N, Nagorny B, Rehlich K, Remde H, Wagner A, Wohlenberg T, Wojtkiewicz J 2008 The vacuum system of the European X-ray free electron laser XFEL Proc of the 17th International Vacuum Conference (Stockholm, Sweden, 2-6 July 2007) to be published in Jounal of Physics: Conference Series [16] Zapfe K and Wojtkiewicz J 2007 Particle free pump down and venting of UHV-vacuum systems Proc. of the 13th Workshop on RF Superconductivity (Beijing, China, 15-19 October 2007) http://www.pku.edu.cn/academic/srf2007/proceeding.html [17] Mildner N, Dohlus M, Sekutowicz J and Zapfe K 2005 A beam line HOM absorber for the European XFEL linac Proc. 12th Workshop on RF Superconductivity (Ithaca, USA, 10-15 July 2005) http://www.lepp.cornell.edu/public/SRF2005/Proceedings.html


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http://accelconf.web.cern.ch/accelconf/

http://srf2003.desy.de/fap/

http://www.bessy.de/fel2006/proceedings

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Accelerator Vacuum Systems at DESY - INSPIRE HEPinspirehep.net/record/788516/files/jpcs_114_1_012003.pdf · bellows. Initially integrated sputter ion pumps have been used inside the