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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 III damping wiggler section operation are presented.

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.

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 110°C 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.

Among the different approaches towards a next generation 500 GeV e + e − linear collider, the TESLA design uses superconducting accelerating structures operating at 1.3 GHz with a gradient of 25 MV/m. Presently, the TESLA test facility, which includes a prototype linear accelerator with superconducting cavities, is build up at DESY/Hamburg to serve as an R&D tool. First, electrons have been accelerated in spring 1997. In the present state of the project two cryomodules, each containing eight solid niobium cavities are installed. One of the major objectives for the beam vacuum system is to preserve the cleanliness of the superconducting cavity surfaces and thus the operation at high gradients and high Q. Contamination by any sort of dust or condensation of gases during assembly and operation has to be absolutely avoided. Thus all vacuum components are carefully cleaned in clean rooms to make them particle free. Local clean rooms are used for installation of the components into the linac. A description of the linac vacuum system, the running experience and the present status of the project is given.

DESY pursues a luminosity upgrade project for the HERA electron–proton collider that foresees an increase of the luminosity by nearly a factor of 5. This is achieved mainly by a completely new layout of the interaction region. The new scheme involves a very early separation of the colliding beams by means of superconducting magnets that are installed inside the experimental detectors. The early beam separation allows the final focus quadrupoles to be located closer to the interaction point (IP), which in turn leads to smaller beam spot-sizes and higher luminosity. The HERA upgrade requires the whole vacuum system in the interaction regions of the machine to be rebuilt. This amounts to about 400 m length of new electron, proton and common vacuum system. The requirements for the vacuum quality were raised in comparison to the present machine, because electrons that lost energy due to beam–gas interactions will be mainly deflected into the detector beam pipes by the superconducting separation magnets. At all possible locations we have foreseen to install NEG pumps. Another critical point is the safe handling of about 30 kW synchrotron radiation power, produced by the separation magnets in the detectors. An overview on the project is presented and some critical issues are discussed with emphasis.

During the run 1998/1999 a new injector based on a laser-driven RF gun was brought in operation at the TESLA Test Facility (TTF) linac at DESY, in order to produce the beam structure and quality required either by TeV collider and SASE FEL experiments. High quantum efficiency cesium telluride photocathodes, prepared at Milano and transferred to DESY, have been successfully operated in the RF gun. A bunch charge of 50 nC, only limited by space charge effects, was achieved. The photocathodes have shown an operative lifetime of several months. A new cathode surface finishing has showed a promising decrease of the photocathode dark current. Measurements of dark current, quantum efficiency and lifetime are reported.

The HERMES experiment is investigating the spin structure of the proton and neutron via deep-inelastic scattering of polarized positrons from polarized nuclear targets. The polarized positrons are provided by the HERA positron storage ring at DESY, Hamburg, Germany. The targets are pure internal gas targets. Data acquisition began in 1995, utilizing a polarized 3 He internal gas target to study the spin structure of the neutron. The target gas was polarized using the metastability-exchange optical-pumping technique and then injected into a cryogenically cooled target cell. The target was designed to operate with either longitudinal or transverse directions of polarization. Operating conditions included polarizations of up to 54% and target thicknesses of 1×10 15 nucleons/cm 2 . In this paper the HERMES polarized 3 He internal gas target is described in detail.

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1n(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023

A high-density target of polarized atomic hydrogen gas for applications in storage rings was produced by injecting atoms from an atomic beam source into a T-shaped storage cell. The influence of the internal gas target on electron-cooled beams of 27 MeV α-particles and 23 MeV protons in the Heidelberg Test Storage Ring has been studied in detail. Target polarization and target thickness were measured by means of 27 MeV α-particles. For hyperfine states 1 + 2 a target thickness of n = (0.96±0.04) × 1014H→/cm2 was achieved with the cell walls cooled to 100 K. Working with a weak magnetic holding field (≈5 G) the maximum target polarization was PT = 0.84±0.02 when state 1 and PT = 0.46±0.01 when states 1 + 2 were injected. The target polarization was found to be constant over a period of 3 months with a net charge of Q ≈ 100C passing the storage cell.

A pair of spin rotators has been installed in the electron ring of HERA. Longitudinal spin polarizations up to 65% have been reached reproducibly during dedicated measurement time. This is the first time that longitudinal spin polarization has been produced in a high energy electron storage ring.

The FILTEX/HERMES atomic beam source (ABS) for polarized hydrogen is described. Recent improvements concern mainly the optimization of the beam forming system and a new design of the sextupole magnet system. For a precise measurement (error 5%) of the output flow a calibrated compression tube was installed. The output flow of 0.81×1017 H atoms per second in two hyperfine substates was constant within 2% in a long-term measurement over 16 h. At the FILTEX test experiment, the target density in the storage cell fed by the ABS was constant within the experimental error of 4% over a period of four months.

This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described.

The nuclear polarization of spin-polarized hydrogen gas targets can be measured using the spin coupling of electron and nucleus in the hydrogen atom. The polarized target atoms are excited by electron impact at low energy. Due to fine and hyperfine interaction the spin polarization of electron and proton is partially transferred to circular polarization of the emitted Hα-light. In a weak magnetic field the light polarization is proportional to the initial nuclear polarization with a measured analyzing power of 0.33 ± 0.03. The simple principle allows a compact polarimeter setup. It can be used as target polarization monitor, e.g., for targets at low energy storage rings where weak guide fields at the target are required.

A polarized hydrogen gas target for use in storage rings has been developed. One application may be the production of a stored polarized antiproton beam via spin dependent attenuation which would allow a study of the spin-dependence of antiproton-proton interactions. In order to increase the target thickness compared to jet targets the polarized hydrogen atoms are injected into a T-shaped storage cell. Polarization and density of the target have been measured in a test experiment by elastic scattering of an α-beam from the Heidelberg MP-tandem accelerator. The target polarization amounts to 83±8% of the maximum possible value. The target areal density of n = (2.6±0.1±0.2) × 10 13 H / cm 2 is consistent with the density calculated from the measured H beam intensity.