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Universität Hamburg, Diss., 2005; 159 pp., (2005). doi:10.3204/DESY-THESIS-2005-012, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

TESLA Reports 2005 9 pp. (2005)., The paper includes a description of predicted functionalities to be implemented in a universal motherboard (MB) for the next generation of LLRF control system for TESLA. The motherboard bases on a number of quasi-autonomous embedded executive modules. The modules are implemented in a few FPGA chips featured by the MB. The paper presents a practical design of the MB. The initial (basic) solution of the MB has the Cyclone as the chip where the board management is embedded. The board features communication modules – VME and micro, single chip PC with Ethernet. The board provides power supply for the FPGA chips. The board has fast internal communication between particular modules.

The TESLA Test Facility (TTF) Injector II photocathode preparation system is in opera-tion since spring 1998. High quantum efficiency tellurium and alkali metals based pho-toemissive films are routinely produced at Milano with typical 10% quantum efficiency (QE). Photocathodes are then successfully transported with no QE degradation, using a handy ultra high vacuum (UHV) system, to DESY and here transferred to the RF gun. The main characteristics of the system and the future developments are here discussed.

3 pp. (2000)., To ensure overlap between the photon beam and electron beam at the SASE-FEL at the TESLA Test Facility [1], several position-sensitive diagnostics components are installed along the beamline of the FEL. For the undulator part, a new type of waveguide beam position monitors (BPMs) is designed, tested, and installed inside the beam pipe of one undulator module. This paper proposes a method to calibrate these monitors with beam-based measurements

2 pp. (1999).

5 pp. (2000)., Sub-picosecond electron bunches are required for the operation of future VUV and X-ray Free Electron Lasers. A streak camera, a Martin–Puplett interferometer and a longitudinal phase space rotation method have been applied at the TESLA Test Facility linac to measure electron bunch lengths.

Physical review accelerators and beams 3(9), 092001 (2000). doi:10.1103/PhysRevSTAB.3.092001, 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 > 5E+9. 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 = 5E+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 = 5E+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., Published by American Physical Society, College Park, MD

6 pp. (2000)., Three vacuum chambers for the VUV SASE FEL undulator sections at the TESLA Test Facility (TTF) were designed, built, tested and installed. Each chamber is 4.5 m long and of 11.5 mm thick. The inner diameter of the beam pipe is 9.5 mm. The rectangular chamber profile with a width of 128 mm is used to integrate beam position monitors and steerers. This is needed to provide a good overlap between the electron and the photon beam over the entire undulator length. The chambers are built in an aluminum extrusion technology developed for the insertion device vacuum chambers of the Advanced Photon Source. After manufacturing, special processing was performed to reach low outgassing rates (

5 pp. (1999)., During the run 1998/1999, the new injector based on a laser driven RF gun was brought into operation at the TESLA Test Facility Linac (TTFL) at DESY. A key element of the injector is the laser system to illuminate the RF gun cathode to produce short (ps) electron bunches of high charge (nC). This electron beam is used to perform various experiments for the future TESLA linear collider, and to drive the free electron laser TTF-FEL. The laser design is challenged by the unusual requirement of providing synchronized ps UV pulses in 0.8 ms long trains with ambitious stability requirements. The design was also driven by the requirement to have an operational system with a high reliability. The system is based on a mode locked solid-state (Nd:YLF) pulse train oscillator followed by a linear amplifier chain. In a first phase, a laser pulse rate of 1 MHz within the train has been realized, 2.25 MHz and 9 are in preparation. Performance and running experiences with the laser system during the last TTF run are reported.

TESLA-FEL Reports 6 pp. (1999).

1999 Particle Accelerator Conference, PAC'99, New York City, United States, 29 Mar 1999 - 2 Apr 1999, In this talk I’ll briefly review the design challenges of a high energy, high luminosity e+e- linear collider and discuss the layout and performance of various technical options. I’ll then present the status of the R&D effort and review the performance of the integrated system tests now underway at several laboratories.

TESLA-FEL Reports 9 pp. (1999)., The Free Electron Laser at the TESLA Test Facility (TTF FEL) is based on the principle of the so-called self amplified spontaneous emission, which requires an electron beam with very high phase space density. In order to meet the requirements an rf gun is under test at DESY. In this paper the emittance of the electron beam as function of the charge is investigated by means of PARMELA simulations. The effect of solenoid offset and of beam offsets at the cathode onto the beam emittance is discussed. The emittance growth due to field unbalance in the gun is mentioned and the frequency difference between π-mode and 0-mode as function of the field balance is presented.

TESLA-FEL Reports 12 pp. (1999)., An electron beam with a small energy spread (0.1%) and a small normalized emittance (2 mm.mrad) is required to drive a Free Electron Laser at the TESLA Test Facility (TTF) at DESY. During FEL operations, the longitudinal and transverse wakefields which are generated by vacuum components, principally by RF cavities, bellows and valves, will induce an additional energy spread and emittance growth, respectively. This paper presents the wakefields and its induced correlated energy spread and emittance growth at the TTF FEL of phase I and II.

TESLA Reports 12 pp. (1999).

21st International Conference on Free Electron Laser and 6th FEL Applications Workshop, FEL'99, Hamburg, Germany, 23 Aug 1999 - 28 Aug 1999; TESLA-FEL Reports 25-29 (1999). doi:10.3204/PUBDB-2018-04085

5 pp. (1999)., For shorter bunches and narrower undulator gaps the interaction between the electrons in the bunch and the wake fields becomes so large that the FEL amplification is affected. For a typical vacuum chamber of an X-ray or VUV Free Electron Laser three major sources of wake fields exist: a resistance of the beam pipe, a change in the geometric aperture and the surface roughness of the beam pipe. The generated wake fields, which move along with the electrons, change the electron energy and momentum, depending on the electron longitudinal and transverse position. In particular, the accumulated energy modulation shifts the electrons away from the resonance condition. Based on an analytic model the energy loss by the wake fields has been incorporated into the time-dependent FEL simulation code GENESIS 1.3. For the parameters of the TESLA Test Facility the influence of the bunch length, beam pipe diameter and surface roughness has been studied. The results are presented in this paper.

TESLA Reports 26 pp. (1999).

2 pp. (1999).

2 pp. (1999).

5 pp. (1999)., 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.

2 pp. (1999).

Universität Hamburg, Diss., 1999; 182 pp. (1999). = Universität Hamburg, Diss., 1999

7 pp. (1999)., In this contribution, the requirements on undulators for linac driven SASE FELs will be discussed. Differences between long and short wavelength SASE FELs will be worked out. The problematic influencing the choice of minimum gap and undulator peak field which are special for SASE FELs driven by multi GeV electron beams with sub picosecond pulses, peak currents of several kiloamperes will be pointed out. Special attention is given to the magnetic design of combined strong focusing undulators as are needed for VUV FELs. As an example results will be presented of the undulator for the VUV-FEL at the TESLA Test Facilty which has just been completed.

4 pp. (1999)., A highly desirable measurement in Free Electron Laser (FEL) experiments is the dependency of the radiation power along the undulator. Most designs of undulators prohibit detection of the radiation power within the undulator or extracting the electron beam at arbitrary positions. Transport of both, the radiation field and the electron beam, through the entire undulator, and thus an ongoing FEL interaction, is unavoidable. If there are many correction magnets distributed along the beam pipe, one can think of exciting a large orbit distortion downstream from any of these correctors. For a gain length comparable to or larger than the beta function this excitation of a coherent betatron oscillation might degrade the FEL amplification to a level, for which the radiation power does not further grow over the remaining length of the undulator. This paper presents the efficiency of this method for the parameters of the VUV FEL at the TESLA Test Facility.

TESLA-FEL Reports 24 pp. (1998).

TESLA-FEL Reports 8 pp. (1998).

TESLA Reports 15 pp. (1998).

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The aim of the TESLA Free Electron Laser (FEL) is to develop and realize an Angstrom wavelength, high gain FEL in parallel with the TESLA superconducting e$^+$e$^-$ linear collider. As a first step, an FEL for the VUV wavelength regime is now under construction at DESY, making use of the TESLA Test Facility (TTF). The VUV FEL at the TTF comes in two phases, which are both approved. The paper describes the over-all layout of each phase and the status of components.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The klystrons at the S-band test facility at DESY require high voltage pulses of 550kV at a flat top pulse duration of 3$\mu$s, at a current of 700A and a repetition frequency of 50Hz. Two HV pulse modulators with a nominal power of 375MW were built. The design and results of the commissioning of the first system were described in [1]. The second system came into operation and was operated at an output power up to 475MW (610kV, 780A). In addition it was modified to investigate capacitor charging power supplies, which might be used in a linear collider tunnel. This type of power supply promises a better efficiency than the conventional resonant charging method and also saves space in the linear collider tunnel. This paper describes the operation experience with the HV modulators at the test facility especially with the second system. It reports the modifications, which were required to operate the modulator with the new type of HV power supply and presents results of the operation.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The design goal of the 1.3 GHz 9-cell superconducting RF cavities for the Tesla Test Facility (TTF) is a gradient Eacc $\geq$ 15 MV/m at a quality factor of Qo $\geq$ 3$\centerdot$ 10$^9$. The cavities are operated in pulsed mode: 0.8 ms constant gradient with 10 Hz repetition rate.After the vertical acceptance test and prior to the assembly in the linac the cavities are tested in a horizontal cryostat fully equipped with helium vessel, high power input coupler, higher order modes coupler and tuning system. After installing module 1 the first 120 MeV beam has been delivered successfully.We report about the measured results in vertical and horizontal tests, the processing of the superconducting cavity system in the first module and the performance of the cavity system before, during and after operating the linac.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The rf control system for the TESLA Test Facility employs a digital feedback system to provide flexibility in the choice of feedback algorithms and extensive diagnostics for rf system operation and exception handling. The control algorithm makes use of the state space formalism where the state describes the real and imaginary part of the cavity voltage (vector of the accelerating field) and the cavity detuning. The cavity detuning - which is time dependent due to the dynamics of lorentz-force-detuning in a pulsed cavity - can not be measured directly. Knowledge about the time-varying cavity detuning and other rf system parameters such as beam phase are derived by application of system identification to the uncalibrated measured cavity field and incident and reflected wave. In this process the calibrations for incident and reflected wave are determined which includes compensation for the finite directivity of the directional couplers.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The status of the layout of the linear collider project, TESLA, which employs superconducting accelerating structures, will be presented. Latest results from the R&D program on 1.3 GHz superconducting cavities, the accelerating gradients and quality factors which were achieved will be shown as well as the performance of the TESLA Test Facility linear accelerator.

Universität Hamburg, Diss., 1998; 104 pp., (1998). doi:10.3204/PUBDB-2016-02636

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., During the winter shutdown 1997/98, the injection system of the H$^-$-Linac III was upgraded. At present two different kinds of H$^-$-sources are operated at DESY. The new cesium-free rf ion source is planned to operate parallel to the magnetron ion source.In addition a new MEBT (Medium Energy Beam Transport line) between two distinct RFQ accelerators and the Alvarez accelerator of Linac III was installed to match the beam of each ion source to the Alvarez acceptance. This scheme makes it possible to operate either H$^-$-source with the Alvarez linac with a miniumum of effort to switch from one to the other. The design of the transport line also facilitates the development and tests of newly proposed ion sources, for example deuterium and polarized proton sources.After assembly of the RFQs and ion sources as well as the new components for the MEBT, a relatively easy commissioning could be demonstrated, although the ions have to be transported on a long distance from the RFQ to the Alvarez linac. First results of measurements will be presented.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., In the rf system for the TESLA Test Facility each klystron will supply rf power to up to 32 cavities. The superconducting cavities are operated in pulsed mode and at high accelerating gradients. The control of significant Lorentz force detuning and precise calibration and measurement of the vector sum are the main issues to be solved. Presently installed are 8 cavities in the first cryomodule of the linac which have been in operation since June 97. Initial commissioning has been conducted in a very short time due to the extensive diagnostics available in the digital the rf control system. The paper describes commissioning of the rf system with emphasis on the calibration of the vector-sum, adaptive feedforward, and the various diagnostic tools available. RF control performance and plans for the control of 24 cavities are also presented.

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., The rf control system of the TESLA Test Facility regulates the vector sum of multiple superconducting cavities which are operated in pulsed mode at accelerating gradients exceeding 15 MV/m, In addition to the feed back control loop which suppresses stochastic errors, feedforward [1] is applied to reduce repetitive perturbations induced by beam loading and dynamic lorentz force detuning. In the case of TESLA repetitive errors are dominating. The feedforward algoridim first identifies the time varying state space model of the closed loop system by measurement of a step response. Next the pulse to pulse average of the measured perturbations is applied to the inverse state space model to obtain the correct feedforward table. The feed forward tables can be updated continuously to follow slow changes in the perturbation parameters. On-line system identification is transparent to routine beam operation due to the small step size used.

TESLA-FEL Reports 12 pp. (1998).

17th IEEE Particle Accelerator Conference, PAC 97, Vancouver, USA, 12 May 1997 - 16 May 1997; 65 pp. (1997)., If short bunches travel along trajectories with small bending radii a simple geometrical condition permits strong longitudinal and radial wake fields to act: electromagnetic fields emitted by a particle can ’overtake’ on a shorter straight trajectory and interact with particles ahead. Thebunch then starts to radiate coherently. The electromagnetic fields along the bunch have strong gradients and in general increase emittance. Investigations for the Tesla Test Facility Free Electron Laser have shown that the wrong choice of compressor parameters can increase the emittance by more than a factor of ten when compressing down to 50$\mu$m bunch length. We present a formalism and numerical code to calculate the resulting electromagnetic fields on a general trajectory. Shielding effects of the vacuum chamber have beenincluded. We present first results for the TTF-FEL undulator magnet and calculations of the influence of transition regions (bunch entering and leaving a homogeneous magnetic field).

14 pp. (1997).

7 pp. (1997).

17th IEEE Particle Accelerator Conference, PAC 97, Vancouver, USA, 12 May 1997 - 16 May 1997; 65 pp. (1997)., The S-Band Linear Collider Test Facility under construction at DESY serves as a test bed for the essentiell hardware to build a large scale e$^+e^-$ linear collider based on a 3GHz accelerating rf and having a center of mass energy of at least 500GeV. Besides the injection system at the beginning and a beam analysis area at the downstream end, the central part of the test facility consists of two modular units similar to those to be installed in a S-Band Linear Collider (SBLC) tunnel. The key-questions of Higher Order Mode (HOM) excitation, measurement, damping and feedback on the alignment of the accelerating structure as well as the quadrupole position have to be answered in order to manage the most crucial aspect of a 15 km linear accelerator, namely the beam stability. The final layout of this test facility and the performance of the present setup including the first accelerating section fed a 150MW klystron will be presented.

4 pp. (1997).

17th IEEE Particle Accelerator Conference, PAC 97, Vancouver, USA, 12 May 1997 - 16 May 1997; 65 pp. (1997)., Following tests of the various sub-assemblies at Saclay and Orsay, installation of the entire TESLA Test Facility Injector was completed in Hall 3 at DESY in December 1996. The first phase of operation employs a 250 kV thermionic electron source providing an 800 ms train of bunches, each containing 37 pC, and followed by a 216.7 MHz pre-bunching cavity. Subsequent bunching and acceleration is achieved using a standard 1.3 GHz superconducting 9 cell TESLA cavity operated in pulsed mode (10 Hz). Prior to injection in the main linac, the beam parameters are verified using a spectrometer consisting of a dipole magnet and SEM profile monitor. Once the beam is adjusted it is transported to the linac using an optical matching system employing two triplets. We present results of the first beam tests of the completed injector which took place early in 1997.

5 pp. (1997)., The paper presents comprehensive analysis of statistical properties of the radiation from self amplified spontaneous emission (SASE) free electron laser operating in linear mode. The investigation has been performed in a one-dimensional approximation, assuming the electron pulse length to be much larger than a coherence length of the radiation. The following statistical properties of the SASE FEL radiation have been studied: field correlations, distribution of the radiation energy after monochromator installed at the FEL amplifier exit and photoelectric counting statistics of SASE FEL radiation. It is shown that the radiation from SASE FEL operating in linear regime possesses all the features corresponding to completely chaotic polarized radiation.

TESLA-FEL Reports 15 pp. (1997).

128 pp. (1997).

9 pp. (1997).

2 pp. (1997).

19th International Conference on Free Electron Lasers, FEL'97, Beijing, China, 18 Aug 1997 - 21 Aug 1997; TESLA-FEL Reports 36-39 (1997).

TESLA-FEL Reports 20 pp. (1997).