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TESLA Reports 2003 8 pp. (2003)., The paper illustrates some considerations concerning the design of RF Deflectors for TESLA Damping Ring. Scaling laws are applied to investigate the RF Deflector properties in term of length, filling time and dissipated power as a function of the iris diameter. Two optimized cells operating on the $π$ / 3 and $π$ / 2 modes are finally shown.

17th IEEE Particle Accelerator Conference, PAC 97, Vancouver, USA, 12 May 1997 - 16 May 1997; 65 pp. (1997)., For the SB-Linear-Collider project (SBLC) at DESY a redesign of the damping ring has been performed, mainly in order to optimise the dynamic aperture. The lattice of the proposed damping ring has a DBA structure, similar to the 3rd generation light sources ESRF, APS and SPRING-8. The damping ring is build up with 6 superperiods. The straight sections between these periods are used for the injection,ejection and rf-cavities. In turn, each superperiod consists of 6 DBA cells. The straight sections of these cells are used for the installation of the wigglers, which are needed for the damping. With the installation of overall 150 m of wigglers (B$_0$ = 2 T and $\lambda_0$ = 0.2 m) the equilibrium emittances are $\epsilon_{x,0}$ = 6.5 $\centerdot$ 10$^{−10}$ m $\centerdot$ rad and $\epsilon_{y,0}$ = 1.3 $\centerdot$ 10$^{−11}$ m $\centerdot$ rad (the corresponding normalised emittances are : $\epsilon_{x,n}$ = 3.8 $\centerdot$ 10$^{−6}$ m $\centerdot$ rad and $\epsilon_{y,0}$ = 7:6 $\centerdot$ 10$^{−8}$ m$\centerdot$rad . The damping time results in $\tau_y$ $\leq$ 3.4 ms. The dynamic acceptance including misalignment and magnet errors is in the range of A$_x$ $\leq$ 72 mm $\centerdot$ mrad and A$_y$ $\leq$ 80 mm $\centerdot$ mrad.

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 18 Jun 2001 - 22 Jun 2001; 3096-3098 (2001)., The exact alignment of accelerator components is of crucial importance for the production of low emittance beams. Once a beam-line section is set up, a supplementary correction of misalignments implies the knowledge of its magnitude which is difficult to determine using conventional adjusting instruments. An excellent alternative to measure existing misalignments of accelerator components is to vary machine parameters and compare the behaviour of the beam with results obtained from a simulation. It is obvious that time consuming particle tracking programmes are notappropriate to reach this aim. Regarding computing time, the on-line simulation code V is advantageous compared to other beam dynamics programmes. The theoretical basis of V-Code, the “Ensemble Model”, consists of selfconsistent equations for the ensemble parameters that arederived from the Vlasov equation. The requirement to simulate misalignments such as offsets and tilts led to the development of the ALIGNMENT UTILITY which utilizes the solver of V-Code. The new utility enabled us to investigate the beam-line alignment of the TESLA Test Facility injector.This contribution presents the theoretical background and an illustrating example of the optimization process.

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 18 Jun 2001 - 22 Jun 2001; 3771-3773 (2001)., This paper reports on recent beam measurements of higher order modes in the TESLA Test Facility (TTF) accelerating modules. Using bunch trains of about 0.5 ms with 54MHz bunch repetition and up to 90% modulated intensity, transverse higher order modes are resonantly excited when the beam is offset and their frequency on resonance with the modulation frequency. With this method, the trapped modes can be excited and their counteraction on the beam observed on a wide-band BPM downstream of the module. Scanning the modulation frequency from 0 to 27MHz allows a systematic investigation of all possible dangerous modes in the modules.

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 18 Jun 2001 - 22 Jun 2001; 2722-2724 (2001)., The TESLA linear collider incorporates an X-ray SASE FEL which demands challenging electron beam parameters (typically transverse emittance of 1.6 mm-mrd and peak current of 5 kA). For a realistic electron beam distribution at the entrance of the undulator, tracking has to be done from the cathode through the whole accelerator. Non-Gaussian beam profiles have to be taken into account as well as nonlinear effects such as space-charge, coherent synchrotron radiation field and wake fields. We have done this with several codes: Astra, for the low energy part (

2 pp. (2002)., Commissioning of the TESLA X-ray FEL undulator cells will start at low electron energy and long photon wavelength (~6nm) corresponding to the bottom end of TTF phase II operation. Electron and photon diagnostic schemes will be used to monitor the beam trajectory through the various undulator segments. Furthermore, photon diagnostics has to control all undulator gaps and prove the phase tuning of adjacent segments. Using higher harmonics of the spontaneous radiation of individual undulator segments, the photon diagnostic station can cover a wide spectral range and will be able to cope with the progression towards lower SASE wavelength (~1Å). The use of variable gap undulators allows to realize the photon diagnostic section in a single device located in the photon beamline downstream of the last undulator cell.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1190-1192 (2002)., The transported dark current in a high-duty cycle accelerator as the TESLA Test Facility linac (TTF) could significately contribute to radiation damages of components along the beamline. In the past high dark currents emitted from the laser driven rf gun have been observed duringsubstantial time of linac operation. For a better understanding of the dark current transported through and lost in the entire linac, particularly in undulator magnets, numerical simulations are compared with experimental observations. In order to identify possible locations for collimators to remove the dark current, the beam and its halo have been investigated. The operation of an absorber recently installed in the dispersive section of TTF magnetic bunch compressor and its impact on the downstream collimator section is discussed.

Universität Hamburg, Diss., 2002; 58 pp., (2002). doi:10.3204/DESY-THESIS-2002-029, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1673-1675 (2002)., The rf control analysis tool consists of a set of library blocks to be used with SIMULINK. The tool allows to study the performance of a given rf control design. The library blocks include models for the superconducting cavities, the rf power source, the beam, and the rf feedback system.The rf control relevant electrical and mechanical characteristics of the cavity are described in form of timevarying state space models. Included are perturbations from Lorentz force detuning and microphonics with the appropriate parameters for several mechanical resonances. The power source is calibrated in terms of actual power and includes saturation characteristics and noise. An arbitrary time structure can be imposed on the beam current to reflect a macro-pulse structure and bunch charge fluctuations. For rf feedback several schemes can be selected: Generator driven system or self-excited loop, traditional amplitude and phase control or I/Q control. The choices for the feedback controller include analog ordigital approaches and various choices of filters for the gain stages. Feed forward can be added to further suppress repetitive errors. The results of a performance analysis of the TTF Linac rf system using these tools are presented.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 2466-2468 (2002)., For TESLA a lot of equipment will be installed inside the accelerator tunnel which is not accessible during the four week run periods. During the following maintenance day time consuming trouble shooting is not possible and equipment will be exchanged instead of being repaired in place. Therefore the equipment has to be installed in electronic racks inside a container frame. This container will have a docking system to allow a quick exchange of the whole assembly via a monorail that will be installed inside the tunnel. In the TESLA Test Facility this principle will be investigated. The magnet power supplies will be installed in the tunnel. For this purpose the container frames with the electronic racks and a special docking system for quick exchange have been designed, and prototypes are being developed. The power supplies are modified to fit in the electronic racks.

2 pp. (2002)., During the past years, the experience gained with the TESLA Test Facility FEL resulted in several changes of its design. In addition, as the FEL is developed further to become a user facility during 2003, more details of future development of the FEL and the complete experimental hall for the users is taking shape. In this contribution, some of the aspects re briefly mentioned.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1912-1914 (2002)., Laser wires will play an important role as the standard monitor for beam size measurements with micrometre resolution for the beam delivery system at any future linear collider. Some R&D work is still necessary to elevate preliminary laser wire designs to a compact, non-invasive and fast-scanning device. In this paper the latest R&D together with recent measurements and simulations are presented. Schemes to measure the beam size in a bunch train and from train-to-train are presented together with an evaluation of scanning techniques meeting these requirements. Results from simulations and measurements with a laser focus system and of a proposed Compton calorimeter are reported. Furthermore plans are outlined for the installation of a fast laser wire experiment at the PETRA accelerator at DESY.

4 pp. (2002)., The Phase-1 of the VUV Free Electron Laser at the TESLA Test Facility finishes in fall 2002. Phase-2, an extension of Phase-1 towards shorter wavelengths is under construction and will be ready for operation in 2003. A radiation wavelength as low as 6 nm will be obtained by raising the electron energy to 1 GeV. There will be only minor changes to the undulator system. Compared to Phase-1, six instead of three undulator segments will be installed. The integrated focusing system will be replaced by an electromagnetic doublet structure. We report about the changes of the undulator, the undulator vacuum system, the separated quadrupoles including a stretched wire alignment systems and the modifications to the beam diagnostic system consisting of pick up monitors and wire scanners.

TESLA Reports 2002 55 pp. (2002)., We present the calculation results for a lossless TTF cavity-coupler unit, for combination cavity-coupler units and for an 8-cavity accelerating module, at the frequency band corresponding to third dipole band of the 9-cell TTF cavity. Experimental investigations of the copper TESLA Test Facility cavity, equipped with two higher order mode couplers, are also presented, for the original and the modified (“mirrored”) downstream higher order mode couplers.Here we developed the procedure for the determination of resonant frequencies and Q-factors using the dependence of the complex transmission coefficient S$_{m,n}$(f) or the complex reflection coefficient S$_{m,m}$(f) on frequency in the frequency band under investigation. These dependencies were obtained from the numerical calculation of S- parameters of lossless TESLA Test Facility (TTF) modules in the third dipole mode frequency band and from the experimental investigation of the copper TESLA Test Facility cavity equipped with two higher order mode couplers in the first, second and third dipole mode frequency bands, second quadrupole and second monopole mode frequency band. The procedure permits us to determine resonant frequencies and Q- factors (Q$_o$, Q$_{Load}$ and Q$_{ext}$) using a large enough frequency step (∆f) with only few frequency points located on the resonance curve corresponding to the high Q-factor resonance.

TESLA Reports 2002 165 pp. (2002).

6 pp. (2002)., We report on experimental evidence that the free-electron laser at the TESLA Test Facility has reached the maximum power gain of 10 7 while operating in the Self-Amplified Spontaneous Emission mode. Following the request of the first scientific users, the TTF FEL has been tuned in the wavelength range between 80 and 120 nm (vacuum ultraviolet, VUV), and saturation has been achieved in this entire wavelength range. At saturation the FEL emits short pulses with GW peak power and a high degree of transverse coherence. Also, the paper reports on the demonstration of controlled pulse length variation between 30 and 100 fs and on detailed intensity fluctuation studies in this operation mode.

; TESLA Reports 2002 9 pp. (2002)., Model independent analysis (MIA) can be used in linear accelerators to analyse large statistical samples of orbit data in order to address questions like number of jittering variables that affect the beam, residual dispersion, and resolution of beam position monitors. We describe the application of MIA to TTF and try to answer some questions of practical interest.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1915-1917 (2002)., A measurement System for detecting dark currents, generated by the TESLA cavities is proposed. It is based on the cryogenic current comparator principle and senses dark currents in the nA range. Design issues and the application for the CHECHIA cavity test stand are discussed.

TESLA Reports 2002 11 pp. (2002)., Vertical emittance is a critical issue for future linear collider damping rings. Both NLC and TESLA specify vertical emittance of the order of a few picometers, below values currently achieved in any storage ring. Simulations show that algorithms based on correcting the closed orbit and the vertical dispersion can be effective in reducing the vertical emittance to the required levels, in the presence of a limited subset of alignment errors.

4 pp. (2002)., Two-color pump–probe experiments combining optical femtosecond lasers with short wavelength radiation from a free electron laser (FEL) are very attractive for sub-picosecond time-resolved studies. Since the synchronization between the two light sources to an accuracy of 100 fs is not yet solved, it is proposed to derive both radiation pulses from the same electron bunch. In the present work we focus on the special case where pump and probe beams are generated by the same electron bunch in the same insertion device. Specifically we propose to combine GW-level VUV FEL pulses between 150 and 90 nm wavelength and 10 MW -level third-harmonic radiation between 50 and 30 nm . This scheme does not require any special synchronization nor additional FEL hardware components since the nonlinear third-harmonic generation occurs naturally in the planar FEL undulator. Reflection optics are used for beam splitting and tunable delay, and the two harmonics are separated by using notch filters. The effect on the pulse duration is negligible.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 876-878 (2002)., In order to test the performance of a superconducting linac, the TESLA Collaboration has built and operated a 120 m long linac which includes an RF electron gun, two 12mlong superconducting accelerator modules, two bunch compressors and a 13.5 m long undulator for a VUV FEL. This linac serves as a test bench for high gradient operation of 9-cell superconducting cavities with full beam loading as required for the TESLA design. Results of recent running periods will be summarized in this paper.

TESLA Reports 2003 11 pp. (2003).

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 2481-2483 (2002)., Electrical power transmission systems produce stray magnetic fields around the lines. In a three phase AC system the sum of line currents is always zero, but the spatial arrangement of the wires create a displacement of the magnetic field. This causes interferences to adjacent systems, especially to accelerator beams with weak focusing, which require a magnetic and electrical environment with low parasitic fields. A multi coaxial line system has not this disadvantage. Therefore a coaxial gas insulated line (KOGIL) for medium and high voltage has been developed in a cooperation between DESY Hamburg and Darmstadt, University of Technology, High Voltage Laboratory. A prototype was built up for 20 kV and 25 MVA. The measurements and simulations as well as the possible applications of this new power transmission system will be presented.

Universität Hamburg, Diss., 2002; 163 pp., (2002). doi:10.3204/DESY-THESIS-2002-030, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 242-244 (2002)., The TESLA Test Facility (TTF) phase II will be the second LINAC at the DESY, based on TESLA accelerator technology[1]. The goal of this machine is twofold: Test and demonstrate the performance of the technology developed for the TESLA linear collider. Furthermore, the excellent beam quality allows to drive a SASE FEL to produce soft X-rays for a 4th Generation Light Source. This paper presents the design of the diagnostic systemfor TTF II, and will give a brief overview over their variety and status.

TESLA Reports 2002 14 pp. (2002)., Linear collider damping rings are highly sensitive to magnet alignment. Emittance tuning simulations for current designs of damping rings for TESLA and NLC have given encouraging results, but depend on invasive measurements of dispersion. The frequency with which such measurements must be made is therefore an operational issue, and depends on the time stability of the alignment. In this note, we consider three effects that lead to misalignment and the need to retune the damping ring: (1) diffusive or ATL ground motion, (2) propagation of elastic ground waves leading to correlated motion of the beamline components, (3) uncorrelated motion arising from local noise sources.

TESLA Reports 2002 15 pp. (2002)., The TESLA collider[1] is a large scale project with a large amount of complex and partially innovative systems. In a project of such characteristics, the stage of test of its various parts and the commissioning of the whole facility requires a considerable amount of effort, expertise and time. Moreover, a prompt delivery of luminosity to the experiments depends strongly on a successful commissioning. Therefore, preparation of a detailed commissioning plan and schedule together with some account of the personnel resources needed is mandatory. This study should be included in the plans of the construction and installation work of the TESLA collider. A working group of the TESLA collaboration meeting held in Saclay in April 2002 started to address these problems. Neither time, personpower nor cost have been considered in detail. In principle, the commissioning of completed parts of the collider has to be adapted to the installation schedule. Nevertheless, we suggest to consider the possibility to partially change the installation schedule in order to commission some sections earlier. Moreover, some additional infrastructure is necessary to close and shield parts of the tunnel, and to dump low energy beams. The commissioning of the XFEL part has not yet been considered at this stage of the study.

TESLA Reports 2002 17 pp. (2002)., Development and test of wire scanners for the Free Electron Laser (FEL) at the Tesla Test Facility phase II are described. The design fulfills the requirements of high precision measurements, of compact and easily exchangeable and referable structures as well as user friendly implementation into the accelerator environment. The basic principle of the measurements consist in detecting the secondary particles created when the wire transverses the electron beam with a constant velocity of up to 1 m/sec. A high resolution measurement system connected with the wire determines the profile and position of the beam with high precision. A reference system connected with the wire scanner components enables the in situ determination of the absolute position of the beam within 20 - 30 $μ$m.

2 pp. (2002).

8 pp. (2002)., A collimation scheme for the protection of the undulators at the TESLA Test Facility phase 2 (TTF2) is discussed. The transverse and energy collimation, and the protection against off-energy and mis-steered bunches are proposed in a beam line which, besides the collimation elements, integrates the fast feedback system and matches the beam to the undulator entrance.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; AIP 2706-2708 (2002). doi:10.1063/1.1638357, To perform a proof of principle experiment of a SASE based Free Electron Laser operating at wavelength between 70-160 nanometer a 15 m long permanent magnet undulator has been installed in the TESLA Test Facility (TTF) linac phase 1. The type of magnets used (NdFeB) is known to be sensitive to radiation damages if exposed to high energy electrons. Already beam losses in the order of 10−6 of the nominal TTF beam current (64μA) are critical for the undulator and can cause an irreversible damage of its magnets after a few months of operation. To protect the undulator against radiation a two stage spoiler-absorber collimation system has been implemented to the beamline in front of the undulator. In this paper the design and the performance limits of the collimator system are presented., Published by AIP

TESLA Reports 2002 61 pp. (2002)., One of the sources of transverse emittance dilution in the superconducting e$^+$e$^−$ linear collider TESLA are transverse wakefields of higher frequency modes (HOM) excited in the accelerating cavities by long trains of intense bunches. Traditionally HOM couplers (HOMC) have been designed to damp modes from the 1$^{st}$ and 2$^{nd}$ dipole bands, however measurements have shown that modes with unexpectedly high Q-factors and R/Q values occur in the 3$^{rd}$ dipole band. The present work quantitatively analyses the fields and their damping in the frequency range of the 3$^{rd}$ dipole band (~2580 MHz). In our investigation we use an S-parameter concept. For the calculations the TESLA Test Facility (TTF) accelerating module is split into several components, such as the nine-cell cavity, different types of HOM and fundamental mode couplers, cylindrical and coaxial bellows, cold windows etc., for which the S-parameters are independently calculated using the MAFIA and Microwave Studio (MWS) codes. Using the scattering matrixes of all these components, we have the ability to calculate the scattering matrix of complex sub- systems or of complete modules. The frequency dependence of the S-parameters permits us to find resonant frequencies and Q-factors of complex devices and to study the field distribution in cavities and along waveguides for a given excitation. An understanding of the damping mechanisms in the 3$^{rd}$ dipole band was obtained and an improved design of the HOM couplers is proposed in order to suppress those 3$^{rd}$ dipole band modes with high values of R/Q.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1966-1968 (2002)., To perform a proof of principle experiment of a SASE based Free Electron Laser operating a permanent magnet undulator has been installed in the TESLA Test Facility (TTF) linac. The type of permanent magnets (NdFeB) used is known to be sensitive to irradiation. Already losses of the order of 10−6 at nominal TTF beam current can cause a degradation of the undulator magnets after a few month of operation. To protect the undulator against radiation a collimation system in front of the undulator removes the electrons with large betatron motion. To detect beam haloor dark current escaping the collimators a beam loss monitor (BLM) system based on photomultiplier has been developed. During the past two years the BLM system has been improved in its electronic components and detectors. It has become a standard tool for linac operation and is nowintegrated part of the linac protect system. In this paper the design, the operation experiences and the performance limits of the system are presented.

5 pp. (2002)., The Free-Electron Laser (FEL) at the TESLA Test Facility at DESY operates in the self-amplified spontaneous emission mode and generates sub-100-fs radiation pulses in the vacuum ultraviolet spectral region. During operation in the saturation regime, radiation pulses with GW peak power are produced. The statistical properties of the FEL radiation have been studied for different amplification regimes as well as behind a narrow-band monochromator and found to be in good agreement with the results of numerical simulations. Information about the spectral and temporal structure of the FEL radiation has been deduced from the statistical properties. The pulse duration of the FEL radiation can be varied by tailoring the electron bunch that drives the FEL.

9 pp. (2002)., In this paper we consider a possible mechanism of strong distortions of longitudinal phase space due to collective effects in an electron bunch passing a bunch compressor. Analytical expressions are derived for the case of a linear compression. Estimates for the TESLA Test Facility at DESY are presented.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 2475-2477 (2002)., Correction magnet power supplies are used to supply currents with a 17 bit precision to the superconducting correction magnets inside the TESLA linear accelerator. The required magnet current of up to 100A is achieved by a parallel connection of boards in EURO card size with an output current of 25A each. Additional cards provide redundancy in case of failures. By means of a 50kHz transformer the 325V DC input voltage is galvanically isolated to the ±10V output voltage on each board. The compact design includes a new polarity changing MOSFET output rectifier with a high efficiency free wheeling path and a new frequency PWM (FPWM) steered by an ALTERA chip to minimize switching losses at low output voltages. The ALTERA FPGA includes a digital regulation. Regulation parameters, reference values, temperatures and status signals are exchanged via RS232 port with a PC which provides the power supply data to the Internet. All data will be accessible by normal net browsers.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1759-1761 (2002)., A magnetic chicane is installed at the FNAL/NICADD photo-injector. It enables the compression of 1 to 8 nC bunches with a total energy of 16-18 MeV. The energyphase correlation at the entrance of the chicane is set up by adjusting the phase of a 9-cell superconducting cavity located upstream of the chicane. This paper will report measurements of beam emittance and energy spread as a function of the 9-cell phase.

TESLA Reports 2002 155 pp. (2002).

5 pp. (2002)., Radiation damage to undulator systems made of permanent magnet materials like NdFeB or SmCo is a critical issue in SASE projects. It is of even more interest in high-duty cycle machines using superconducting accelerators such as the TESLA Test Facility (TTF), which is a prototype for the future X-FEL at TESLA. This paper reports on experience on the undulator system of the VUV-FEL of TTF-1, which ended on May 6, 2002 after nearly 3 years of operation. The radiation exposure of the undulator system was recorded continuously and meticulously over the whole installation period in the TTF linac. Results of these dosage measurements as well as magnetic measurements after de-installation are reported. A comparison with magnetic field data taken prior to installation is given.

4 pp. (2002)., This paper presents an overview of the electron beam diagnostics for the upgrade of the TELSA Test Facility (TTF II). Beside of a program for testing components, especially superconducting accelerating structures, for the linear collider project TESLA, TTF II will serve as SASE FEL 4th generation synchrotron radiation user facility.

TESLA Reports 2002 6 pp. (2002).

5 pp. (2002)., This paper presents the progress of the Self-Amplified Spontaneous Emission and Regenerative Amplifier Free Electron Laser experiments at the TESLA Test Facility (TTF). In the second part, the layout of the soft X-ray user facility TTF2 and the status of construction work is described.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1804-1806 (2002)., The RF gun based photoinjector of the TTF Free Electron Laser (TTF-FEL) at DESY has been optimized to improve the gain of the VUV free electron laser. With the new settings, saturation has been achieved. The actual injector performance in terms of longitudinal and transverse phase space is described.

11 pp. (2002)., A large X-ray FEL lab is under consideration within the TESLA project and is supposed to be operated in parallel with the TESLA linear collider. There will be five SASE FELs and five conventional spontaneous undulators. A conceptual design study has been made for the undulator systems for these X-FELs. It includes segmentation into 6.1 m long undulator ‘cells’. Each consists of a 5 m long undulator ‘segment’, a separate quadrupole, one horizontal and one vertical corrector, and a phase shifter. These items are presented and discussed.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 1473-1475 (2002)., Measurements in the TESLA Test Facility (TTF) have shown that modes with unexpectedly high Q-factors and R/Q values occur in the third dipole band. The present work quantitatively analyses the fields and their damping in the frequency range of the third dipole band (~2.5 GHz). In our investigation we use a scattering (S)-parameter concept. For the calculations the TTF accelerating module is split into several components, forwhich the S-parameters are independently calculated. Using the S-matrices of all these components, we have the ability to calculate the S-matrix of complex systems or of complete modules. The frequency dependence of the Sparameters permits us to find resonant frequencies and Qfactors of complex devices. An understanding of the damping mechanisms in the third dipole band was obtained and an improved design of the higher order mode (HOM) couplers was proposed in order to suppress those third dipole band modes with high values of R/Q.

9 pp. (2002)., An X-ray diagnostic station will be installed for each of the XFEL undulator beamlines at TESLA. Primary purpose of the X-ray diagnostics is to provide an additional tool for alignment and commissioning of the numerous undulator cells along an XFEL beamline independently from electron-beam-based alignment procedures. Both methods will complement one another. The X-ray diagnostic station will be a sensitive instrument generating essential input for the undulator control system. The diagnostic station will be located about 120 m downstream from the last undulator cell. Total flux measurements will verify the XFEL's gain. Analysis of the spectral and spatial distribution of the spontaneous radiation of individual or several consecutive undulator segments will be used to optimize angle and position of the electron beam trajectory, to verify the magnetic gap, and to adjust the phase match between two undulator segments. The two latter purposes cannot be served by electron-beam-based alignment.

The 8th European Particle Accelerator Conference, EPAC2002, Paris, France, 3 Jun 2002 - 7 Jun 2002; 221-223 (2002)., We present experimental evidence that the free-electron laser (FEL) 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. Both FEL results and related accelerator physics issues studied at TTF will be presented.

4 pp. (2002)., Electron bunch lengths and time jitters have been measured with sub-ps resolution at the TESLA Test Facility at DESY. Synchrotron radiation emitted from a dipole magnet reflects the longitudinal charge distribution of the electron bunch and can also be used as a timing reference of the radiation pulses produced by the free-electron laser. For sub-ps time resolution, dispersion effects of the spectrally broad-band synchrotron radiation have to be suppressed. The phase stability of the FEL pulses with respect to the radio-frequency master oscillator has been studied with a streak camera operating in synchroscan mode.

TESLA Reports 2002 4 pp. (2002)., The shape of TESLA accelerating structure can be improved to decrease maximal surface magnetic field by sacrificing and increasing maximal surface electric field. This sacrifice may be necessary because the magnetic field is a hard limit but electric field emission can be decreased by processing. For the case of superconducting cavities RF magnetic strength should be of a more concern.

Universität Hamburg, Diss., 2001; 85 pp. (2001). = Universität Hamburg, Diss., 2001