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Universität Hamburg, Diss., 2003; 205 pp., (2003). doi:10.3204/DESY-THESIS-2003-043, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

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 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.

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 6 pp. (2002).

539469 5 pp. (2001)., By running the prospective high-energy $e^+e^−$ collider TESLA in the GigaZ mode on the $Z$ resonance, experiments can be performed on the basis of more than 109 $Z$ events. This will allow the measurement of the effective electroweak mixing angle to an accuracy of $\delta \sin^2 θ_{\mathrm{eff}}≈±1×10^{−5}$. The $W$ boson mass is likewise expected to be measurable with an error of $\delta M_W≈±6$ MeV near the $W^+W^−$ threshold. We review the electroweak precision tests that can be performed with these high precision measurements within the Standard Model (SM) and its minimal Supersymmetric extension (MSSM). The complementarity of direct measurements at a prospective linear $e^+e^−$ collider and indirect constraints following from the measurements performed at GigaZ is emphasized.

TESLA Reports 2001 20 pp. (2001).

TESLA Reports 2000 15 pp. (2000)., We report the development of different algorithms for the calculation of quality factors of eigenmodes in accelerating cavities, which have resonance frequencies above the cutoff frequency of the beam tubes. The analysis is based on a discretization of such cavity structures by the finite integration technique, and the radiation at the open boundaries is systematically taken into account by different approaches in time and frequency domain. Results indicate that even single cell cavities of the TESLA type show Q values of 103 and multicell cavities values in excess of 104. Thus these modes may cause considerable beam instabilities. Comparison with the conventional method of analyzing closed cavities and identifying modes with little change in frequency as a function of boundary condition shows qualitative differences. Some modes from the closed cavity model do not exist in the open structure and thus would be misinterpreted as trapped modes when only a closed cavity analysis is employed.

TESLA Reports 2000 5 pp. (2000)., In the cavities and finite cell structures, ultra short bunchesexcite very high frequency electromagnetic fields. A fraction of these fields stay in the structure for a very long time.After several reflections another part leaves the structure.The rest part is chasing the bunch. In a time, this field willcatch the bunch and take its kinetic energy. The time andthe distance, when and where the bunch is caught, is inversely proportional to the bunch length. The time and thedistance can be very long for a very short bunch. The analyses of the wake fields in this transient region is given forthe Linear Colliders accelerating structure.

5 pp. (1999)., As the constraint of a small transverse emittance becomes more severe, the higher the electron beam energy in an FEL. To compensate for the transverse and thus the longitudinal velocity spread, a compensation scheme has been proposed previously by Derbenev and Sessler et al., for Free Electron Lasers by introducing a correlation between the energy and the average betatron amplitude of each electron. This compensation scheme is based on a constant absolute value of the transverse velocity, a feature of the natural focusing of undulators, and does not include strong focusing of a superimposed quadrupole lattice. This paper focuses on the electron motion in a strong focusing lattice with a variation in the axial velocity. The resulting reduction of the compensation efficiency is analyzed using simulations. It is seen that the compensation scheme is not much affected if the lattice cell length is shorter than the gain length. For the results presented in this paper, the parameters of the proposed TESLA X-ray FEL have been used.

2 pp. (1999).

TESLA-FEL Reports 24 pp. (1998).

TESLA-FEL Reports 8 pp. (1998).

TESLA Reports 28 pp. (1998).

19th International Linear Accelerator Conference, LINAC 98, Chicago, USA, 23 Aug 1998 - 28 Aug 1998; 59 pp. (1998)., For the TESLA FEL operation very short intense bunches of electrons have to be accelerated. These bunches excite a broad spectrum of HOM (Higher Order Modes) up to frequencies of some THz. Two HOM couplers per cavity are foreseen in the present design proposal in order to extract some of the low frequency HOM from the superconducting accelerating structure. In this contribution an additional HOM broadband absorber is suggested which is to be installed between two cryogenic modules at a temperature of 70 K. Its task is to prevent that the really high frequency HOM are absorbed in the accelerator structure at the 2 K level. The absorption characteristics and the short range wake of four structures which make use of SiC as absorbing material are investigated using the MAFIA computer code. The proposed structures are easier to manufacture and better suited for the operation under vacuum conditions than the recently suggested waveguide array absorber.

TESLA Reports (1999). doi:10.1103/PhysRevSTAB.2.062001, We discuss a new layout of a cavity chain (called superstructure) allowing, we hope, a significant cost reduction due to a simplification of the rf system of the TESLA linear collider. The proposed scheme increases the fill factor and thus makes an effective gradient of the accelerator higher. In this paper computations and preliminary measurements on existing copper models of the TESLA Test Facility accelerating structures are presented. A new copper model of the scheme has been ordered, made of four 7-cell standing wave cavities, which according to the results of computations and measurements seems to be the most promising version. Experiments with a beam will be necessary to prove that the proposed layout can be used for the acceleration.

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)., In this contribution the mode matching technique is applied to compute the absorption characteristics of a twodimensional array of rectangular waveguides. This analysis is motivated by a proposal of a broadband absorber for TESLA. Outside the waveguide array the so-called Rayleigh expansion is used which represents the electromagnetic field in terms of space harmonics whereas the complete modal spectrum of eigenmodes is taken into account inside the waveguides. In the case of normal incidence the validity of the presented method is confirmed by MAFIA computations. The absorption characteristics for various angles of incidence are calculated for a broad frequency range. The accuracy of the results is checked by a study of convergence. It is shown that the Rayleigh expansion has to be modified if the waveguide array is excited by an ultra-relativistic beam instead of an incoming plane wave. Numerical results for the beam parameters are presented for an array of parallel-plate waveguides and compared with those obtained by other methods.

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).

TESLA Reports 26 pp. (1997).

17th IEEE Particle Accelerator Conference, PAC 97, Vancouver, USA, 12 May 1997 - 16 May 1997; 65 pp. (1997)., Integration of an X-Ray Free Electron Laser facility is planned in the TESLA design for a future $e^+e^−$ Linear Collider. In the present scheme, the FEL drive beam is transported to a central user facility in a several km long beamline. In this paper we present how the longitudinal wakefield effect for short bunches in combination with a special beamline magnetic lattice can be used to obtain compression down to an rms-bunch length in the range of a few $\mu$m. Peak current of more than 50 kA would enable the X-Ray FEL facility to generate photon wave lengths in the sub-Angstrom regime.

4 pp. (1997).

TESLA-FEL Reports 15 pp. (1997).

128 pp. (1997).

9 pp. (1997).

Universität Hamburg, Diss., 1997; 117 pp. (1997). = Universität Hamburg, Diss., 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).

6 pp. (1997)., The paper presents analysis of statistical properties of the radiation from self-amplified spontaneous emission (SASE) free-electron laser operating in nonlinear mode. The present approach allows one to calculate the following statistical properties of the SASE FEL radiation: time and spectral field correlation functions, distribution of the fluctuations of the instantaneous radiation power, distribution of the energy in the electron bunch, distribution of the radiation energy after monochromator installed at the FEL amplifier exit and the radiation spectrum. It has been observed that the statistics of the instantaneous radiation power from SASE FEL operating in the nonlinear regime changes significantly with respect to the linear regime.

7 pp. (1997)., The bunch compression system in the TTF-FEL decreases the bunch length in order to achieve the high peak currents needed for the SASE FEL process. Along the curved trajectories in the bunch compressor magnet chicanes, these short bunches will start to radiate coherently. In this paper, a numerical calculation of the characteristics of this radiation is presented. One-dimensional bunch models are not sufficient for near-field effects, in particular, cannot completely explain the power flow to the EM field, but they can be used to estimate the radiation in the far region. For the calculation of the power flow, in presence of shielding by horizontal conducting planes, and of the far field, a two-dimensional bunch with time-dependent shape was simulated.

4 pp. (1997).

TESLA Reports 18 pp. (1997).

TESLA Reports 23 pp. (1996).

TESLA Reports 16 pp. (1996)., We describe a very fast kicker with unique combination of high repetition rate and short pulse width. Constructionally, the device is a counter traveling wave strip-line kicker fed by semiconductor high-voltage pulse generator. Experimentally tested kicker has a full pulse width of about 7 ns, 1.4 MHz repetition rate and maximum kick strength of the order of 3 G m. Recent achievements in high-voltage semiconductor field-effect-transistors (FET) technology and goal-specific optimization of the kicker parameters allow many-fold increase of the strength, and the kicker can be a very useful tool for bunch-by-bunch injection/extraction and other accelerator applications.

TESLA Reports 10 pp. (1996).

TESLA Reports (1995).

Technische Universität Darmstadt, Diss., 1995; 148 pp. (1995). = Technische Universität Darmstadt, Diss., 1995