A record low horizontal emittance of 1 nm-rad was successfully obtained in PETRA III third generation synchrotron light source. A key system that allowed reaching such value includes 20 permanent magnet damping wigglers installed in two long straight sections. The wigglers radiate almost 1 MW at maximum current of hard X-ray radiation which issues a challenge for the design of SR absorbers and vacuum system components for the damping wiggler section. The paper describes in detail the design consideration, manufacturing and experimental performance of absorbers and vacuum system. The first experimental results of PETRA Ill damping wiggler section operation are presented. (C) 2011 Elsevier Ltd. All rights reserved.

K. Ackerstaff6, A. Airapetian36, N. Akopov36, I. Akushevich7, M. Amarian26,31,36, E.C. Aschenauer7,14,26, H. Avakian11, R. Avakian36, A. Avetissian36, B. Bains16, S. Barrow28, C. Baumgarten24, M. Beckmann13, S. Belostotski29, J.E. Belz32,33, Th. Benisch9, S. Bernreuther9, N. Bianchi11, S. Blanchard25, J. Blouw26, H. Böttcher7, A. Borissov6,15, J. Brack5, B. Bray4, S. Brauksiepe13, B. Braun9,24, St. Brons7, W. Brückner15, A. Brüll15, E.E.W. Bruins21, H.J. Bulten19,26,35, R.V. Cadman16, G.P. Capitani11, P. Carter4, P. Chumney25, E. Cisbani31, G.R. Court18, P. F. Dalpiaz10, R. De Leo3, P.P.J. Delheij33, E. De Sanctis11, D. De Schepper2,21, E. Devitsin23, P.K.A. de Witt Huberts26, P. Di Nezza11, M. Düren9, A. Dvoredsky4, J. Ely5, G. Elbakian36, J. Emerson, A. Fantoni, A. Fechtchenko, M. Ferstl, D. Fick, K. Fiedler, B.W. Filippone, H. Fischer, H.T. Fortune28, B. Fox5, S. Frabetti10, J. Franz13, S. Frullani31, M.-A. Funk6, N.D. Gagunashvili8, P. Galumian1, H. Gao2,16,21, Y. Gärber7, F. Garibaldi31, G. Gavrilov29, P. Geiger15, V. Gharibyan36, A. Golendukhin6,20,24,36, G. Graw24, O. Grebeniouk29, P.W. Green1,33, L.G. Greeniaus1,33, C. Grosshauser9, M. Guidal26, A. Gute9, V. Gyurjyan11, J.P. Haas25, W. Haeberli19, J.-O. Hansen2, D. Hasch7, O. Häusser†32,33, R. Henderson33, F.H. Heinsius13, Th. Henkes26, M. Henoch9, R. Hertenberger24, Y. Holler6, R.J. Holt16, W. Hoprich15, H. Ihssen6,26, M. Iodice31, A. Izotov29, H.E. Jackson2, A. Jgoun29, C. Jones2, R. Kaiser7,32,33, M. Kestel13, E. Kinney5, M. Kirsch9, A. Kisselev29, P. Kitching1, H. Kobayashi34, N. Koch20, K. Königsmann13, M. Kolstein26, H. Kolster24, V. Korotkov, W. Korsch, V. Kozlov, L.H. Kramer, B. Krause, V.G. Krivokhijine, M. Kückes, F. Kümmell13, M. Kurisuno34, G. Kyle25, W. Lachnit9, W. Lorenzon22,28, A. Lung4, N.C.R. Makins2,16, F.K. Martens1, J.W. Martin21, H. Marukyan36, F. Masoli10, A. Mateos21, M. Maul30, M. McAndrew18, K. McIlhany4,21, R.D. McKeown4, F. Meissner7, F. Menden13,33, D. Mercer5, A. Metz24, N. Meyners6 O. Mikloukho29, C.A. Miller1,33, M.A. Miller16, R. Milner21, V. Mitsyn8, A. Most16,22,28, R. Mozzetti11, V. Muccifora11, A. Nagaitsev8, E. Nappi3, Yu. Naryshkin29, A.M. Nathan16, F. Neunreither9, J.M. Niczyporuk16,21, W.-D. Nowak7, M. Nupieri11, P. Oelwein15, H. Ogami34, T.G. O’Neill2, R. Openshaw33, B.R. Owen16, J. Ouyang33, V. Papavassiliou25, S.F. Pate21,25, M. Pitt4, H.R. Poolman26, S. Potashov23, D.H. Potterveld2, G. Rakness5, A. Reali, R. Redwine, A.R. Reolon, R. Ristinen, K. Rith, G. Röper, P. Rossi, S. Rudnitsky, M. Ruh13, D. Ryckbosch14, Y. Sakemi34, I. Savin8, C. Scarlett22, A. Schäfer30, F. Schmidt9, H. Schmitt13, G. Schnell25, K.P. Schüler6, A. Schwind7, J. Seibert13, T.-A. Shibata34, K. Shibatani34, T. Shin21, V. Shutov8, C. Simani10, A. Simon13,25, K. Sinram6, P. Slavich10,11, W.R. Smythe5, J. Sowinski15, M. Spengos6,28, E. Steffens9, J. Stenger9, J. Stewart18, F. Stock9,15, U. Stoesslein7, M. Sutter21, H. Tallini18, S. Taroian36, A. Terkulov23, D.M. Thiessen32,33, B. Tipton21, E. Thomas11, A. Trudel33, M. Tytgat14, G.M. Urciuoli31, J.J. van Hunen26, R. van de Vyver14, J.F.J. van den Brand26,35, G. van der Steenhoven26, M.C. Vetterli32,33, V. Vikhrov29, M. Vincter33, J. Visser26, E. Volk15, W. Wander9,21, T.P. Welch27, J. Wendland32,33, S.E. Williamson16, T. Wise19, K. Woller6, S. Yoneyama, K. Zapfe, H. Zohrabian, R. Zurmühle Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada Physics Division, Argonne National Laboratory, Argonne, Illinois 60439-4843, USA Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70124 Bari, Italy W.K. Kellogg Radiation Lab, California Institute of Technology, Pasadena, California 91125, USA Nuclear Physics Laboratory, University of Colorado, Boulder, Colorado 80309-0446, USA DESY, Deutsches Elektronen Synchrotron, 22603 Hamburg, Germany DESY Zeuthen, 15738 Zeuthen, Germany Joint Institute for Nuclear Research, 141980 Dubna, Russia Physikalisches Institut, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara and Dipartimento di Fisica, Università di Ferrara, 44100 Ferrara,

For particle free vacuum systems, as e.g. systems containing superconducting cavities to be operated at high gradients, special care needs to be taken during pump down and venting. Neither should be particles introduced into the vacuum system, nor should particles already present within the system be moved. A series of measurements to study the movement of particles in long tubes during pump down and venting using an in-situ vacuum particle counter has been performed. Based on these measurements a set-up using flow controllers, diffuser and pressure gauges has been developed to avoid introducing particles into the vacuum system as well as moving existing particles during pump down and venting. This set-up can be operated manually as well as via a control unit. The electronics unit is an in- house development at DESY. It is usually connected to an oil free pump station. This set-up allows automated pump-down and venting of critical vacuum systems in a reliable and reproducible way, being faster than the procedures used so far.

The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of Eacc ≥ 25 MV/m at a quality factor Q0 ≥ 5 · 10 . The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of Eacc ≥ 15 MV/m. In a first series of 27 industrially produced TTF cavities the average gradient at Q0 = 5 · 10 9 was measured to be 20.1 ± 6.2 MV/m, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities additional quality control measures were introduced, in particular an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electron-beam welds. The average gradient of these cavities at Q0 = 5·10 9 amounts to 25.0±3.2 MV/m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing R&D towards higher gradients is briefly addressed.

The European X-ray Free Electron Laser XFEL, a new international research facility, will be built at DESY/Hamburg. The XFEL will generate extremely brilliant and ultra short pulses of spatially coherent X-rays with tuneable wavelengths down to 0.1 nm, and exploit them for revolutionary scientific experiments at various disciplines. The basic process adopted to produce the X-ray pulses is SASE (Self-Amplified Spontaneous Emission). Therefore electron bunches are produced in a high-brightness gun, brought to high energy of about 20 GeV through a superconducting linear accelerator, and transported to up to 250 m long undulators, where the X-rays are generated. The beam vacuum system of the accelerator contains sections operated at room temperature as well as at 2 K in the areas of the superconducting accelerating structures, thus requiring an insulating vacuum system. In addition to standard UHV requirements, the vacuum system for this facility needs to preserve the cleanliness of the superconducting cavity surfaces. Therefore the preparation of all vacuum components for the 1.6 km long main linac includes cleaning of the components in a clean room to remove particles, installation into the accelerator in local clean rooms, and special procedures for pump down and venting. Further challenges are the undulator vacuum chambers filling more than 700 m, where a high surface quality with respect to surface roughness and thickness of oxide layers is mandatory to reduce wake field effects, and the vacuum systems for the various beam dumps, where exit windows acting as vacuum barriers of sufficient reliability need to be developed. In addition, a large amount of about 1.7 km of transport beam lines is required. The layout of the various vacuum sections as well as experience with prototype components will be described.

Within the next two years the 2.3 km long storage ring PETRA will be rebuild into one of the most brilliant x-ray sources worldwide (PETRA III). The large bending radius and the use of damping wigglers allow to achieve small beam emittances and extremely brilliant x-ray beams. In this paper we describe the design and the expected performance of the vacuum system for the storage ring. It consists of standard arc sections, an experimental octant which is equipped with undulators and several straight sections that include the damping wigglers. Because of the long length of the storage ring a cost effective solution had to be found. Besides the requirement to quickly provide acceptable residual gas pressures the technical challenges of the system include the provision of high thermal stability with respect to magnets and BPM's, and the design of thin walled insertion device chambers as well as high power synchrotron radiation absorbers.

For particle free vacuum systems, as e.g. systems containing superconducting cavities to be operated at high gradients, special care needs to be taken during pump down and venting. Neither should be particles introduced into the vacuum system, nor should particles already present within the system be moved. A series of measurements to study the movement of particles in long tubes during pump down and venting using an in-situ vacuum particle counter has been performed. Based on these measurements a set-up using flow controllers, diffuser and pressure gauges has been developed to avoid introducing particles into the vacuum system as well as moving existing particles during pump down and venting. This set-up can be operated manually as well as via a control unit. The electronics unit is an inhouse development at DESY. It is usually connected to an oil free pump station. This set-up allows automated pump-down and venting of critical vacuum systems in a reliable and reproducible way, being faster than the procedures used so far.

We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 µJ for individual pulses, and the average energy per pulse reached 70 µJ. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.

A high resolution Beam Position Monitor (BPM) is necessary for the beam‐based alignment systems of high energy and low emittance electron linacs. Such a monitor is developed in the framework of the European CARE/SRF programme, in a close collaboration between DESY and CEA/DSM/DAPNIA. This monitor is a radiofrequency re‐entrant cavity, which can be used either at room or cryogenic temperature, in an environment where dust particle contamination has to be avoided, such as superconducting cavities in a cryomodule. A first prototype of a re‐entrant BPM has already delivered measurements at 2K. inside the first cryomodule (ACC1) on the TESLA Test Facility 2 (TTF2). The performances of this BPM are analyzed both experimentally and theoretically, and the limitations of this existing system clearly identified. A new cavity and new electronics have been designed in order to improve the position resolution down to 1 μm and the damping time down to 10 ns.

Many scientific disciplines ranging from physics, chemistry and biology to material sciences, geophysics and medical diagnostics need a powerful X-ray source with pulse lengths in the femtosecond range [1-4]. This would allow, for example, time-resolved observation of chemical reactions with atomic resolution. Such radiation of extreme intensity, and tunable over a wide range of wavelengths, can be accomplished using high-gain free-electron lasers (FEL) [5-10]. Here we present results of the first successful operation of an FEL at a wavelength of 32 nm, with ultra-short pulses (25 fs FWHM), a peak power at the Gigawatt level, and a high degree of transverse and longitudinal coherence. The experimental data are in full agreement with theory. This is the shortest wavelength achieved with an FEL to date and an important milestone towards a user facility designed for wavelengths down to 6 nm. With a peak brilliance exceeding the state-of-the-art of synchrotron radiation sources [4] by seven orders of magnitude, this device opens a new field of experiments, and it paves the way towards sources with even shorter wavelengths, such as the Linac Coherent Light Source [3] at Stanford, USA, and the European X-ray Free Electron Laser Facility [4] in Hamburg, Germany.

A new cleaning facility has been installed at Deutsches Elektronen-Synchrotron DESY in Hamburg to prepare UHV components hydrocarbon and particle free. Both requirements are important for, accelerators using superconducting accelerating structures with high gradients as well as for optical components like mirrors used for the transport of intense photon beams in synchrotron radiation beamlines.The goal of this facility is to combine standard cleaning techniques with latest clean room technology in a manageable way. Thus the new cleaning facility is installed in a clean room which fulfils class 10,000 and in its central part class 100 specifications.(1) The cleaning process following the standard UHV cleaning steps consists of a fine degreasing of the components in an ultrasonic bath. For rinsing ultra pure water(2) is used. Finally the components are dried using up to 110degreesC hot filtered air (according to clean room class 100 requirements). Comparable cleaning results for small components are achieved using a dishwasher, which is loaded from outside the clean room. Vacuum chambers of up to 4.8 m length can be treated.A small preassembly area equipped with an oil free pumping station for leak detection and residual gas analysis completes the facility. (C) 2004 Elsevier Ltd. All rights reserved.

After three years of preparation, two superstructures, each made of two superconducting 7-cell weakly coupled subunits, have been installed in the TESLA Test Facility linac (TTF) for the cold- and beam test. The energy stability, the HOMs damping, the frequency and the field adjustment methods were tested. The measured results confirmed expectation on the superstructure performance and proved that alternative layout for the 800 GeV upgrade of the TESLA collider, as it was proposed in TDR, is feasible. We report on the test and give here an overview of its results which are commented in more detail elsewhere in these Proceedings.

Superstructures, chains of superconducting multi-cell cavities (subunits) connected by e/2 long tube(s) have been proposed as an alternative layout for the TESLA main accelerator [1]. After three years of preparation, two superstructures, each made of two weakly coupled superconducting 7-cell subunits driven by a single Fundamental Power Coupler (FPC), have been installed in the Tesla Test Facility linac for beam tests. Energy stability, HOM damping, frequency and field adjustment methods were tested. The measured results confirmeSuperstructures, chains of superconducting multi-cell cavities (subunits) connected by e/2 long tube(s) have been proposed as an alternative layout for the TESLA main accelerator [1]. After three years of preparation, two superstructures, each made of two weakly coupled superconducting 7-cell subunits driven by a single Fundamental Power Coupler (FPC), have been installed in the Tesla Test Facility linac for beam tests. Energy stability, HOM damping, frequency and field adjustment methods were tested. The measured results confirmed expectation on the superstructure performance and proved that an alternative layout for the 800 GeV upgrade of the TESLA collider is feasible. We report on the test and give here an overview of its results. The tests confirmed very good damping of HOMs in superstructures and thus has openedmore » a possible new application of this concept to high current energy recovery machines. We have built two 1.5 GHz copper models of two superstructures: 2x5-cells and 2x2-cells to prove further improvement of HOM damping. This contribution presents also measured results on these models. d expectations on the superstructure performance and proved that an alternative layout for the 800 GeV upgrade of the TESLA collider is feasible. We report on the test and give here an overview of its results.« less

Experimental results are presented from vacuum-ultraviolet free-electron laser (FEL) operating in the self-amplified spontaneous emission (SASE) mode. The generation of ultrashort radiation pulses became possible due to specific tailoring of the bunch charge distribution. A complete characterization of the linear and nonlinear modes of the SASE FEL operation was performed. At saturation the FEL produces ultrashort pulses (30-100 fs FWHM) with a peak radiation power in the GW level and with full transverse coherence. The wavelength was tuned in the range of 95-105 nm.

We present experimental evidence that the free-electron laser at the TESLA Test Facility has reached the maximum power gain of 107 in the vacuum ultraviolet (VUV) region at wavelengths between 80 and 120 nm. At saturation the FEL emits short pulses with GW peak power and a high degree of transverse coherence. The radiation pulse length can be adjusted between 30 fs and 100 fs. Radiation spectra and fluctuation properties agree with the theory of high gain, single-pass free-electron lasers starting from shot noise.

For the long term successful operation of the superconducting TESLA accelerator it is essential to avoid any accidental contamination of the accelerating cavities. We discuss several failure scenarios of the beam vacuum system that could potentially result in such contaminations. The risk of individual failure situations is evaluated as well as preventive measures to avoid them.