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Linear colliders are an attractive platform to explore high-precision physics of newly discovered particles. The recent significant progress in advanced accelerator technologies has motivated their applications to colliders which has been discussed in the {\sc alegro} workshop. In this paper we discuss one promising scheme, collinear wakefield acceleration. We especially discuss available drive and witness beam sources based on L and S-band radiofrequency technology, and also summarize available and forthcoming longitudinal shaping techniques to improve the overall acceleration efficiency via the transformer ratio.

Journal of Instrumentation 17(05), P05036 (2022). doi:10.1088/1748-0221/17/05/P05036, Linear colliders are an attractive platform to explore high-precision physics of newly discovered particles. The recent significant progress in advanced accelerator technologies has motivated their applications to colliders which has been discussed in the alegro workshop. In this paper we discuss structure wakefield acceleration, namely collinear wakefield acceleration and two-beam acceleration. We especially discuss available drive and witness beam sources based on L and S-band radiofrequency technology, and also summarize available and forthcoming longitudinal shaping techniques to improve the overall acceleration efficiency via the transformer ratio., Published by Inst. of Physics, London

Narrow X-ray lines from helium-like argon emitted from a dedicated ECR source have been used to determine the response function of a Bragg crystal spectrometer equipped with large area spherically bent silicon (111) or quartz (10$\bar{1}$) crystals. The measured spectra are compared with simulated ones created by a ray-tracing code based on the expected theoretical crystal's rocking curve and the geometry of the experimental set-up., Version acceptee (NIM)

TESLA Reports 2003 15 pp. (2003)., Numerical prediction of the performance of charged particle accelera- tors is essential for the design and understanding of these machines. Meth- ods to calculate the self-fields of accelerated particles, the so-called space- charge forces, become increasingly important as the demand for high-quality bunches increases.We report on our development of a new 3D space-charge routine in the General Particle Tracer (GPT) code. It scales linearly with the number of particles in terms of CPU time, allowing detailed design studies with over a million sample particles on a normal PC. The model is based on a non- equidistant multigrid Poisson solver that has been constructed to solve the electrostatic fields in the rest frame of the bunch on meshes with large aspect ratio. Theoretical and numerical investigations of the behaviour of SOR re- laxation and PCG method on non-equidistant grids emphasize the advantages of the multigrid algorithm with adaptive coarsening.Numerical investigations have been performed with a selected range of cylindrically shaped bunches (from very long to very short) spanning a wide range of recent applications. The application to the simulation of the photoin- jector at the Eindhoven University of Technology demonstrates the power of the new 3D routine.

29 pp. (2006)., This paper details electromagnetical, thermal and structural 3D Finite Element Analyses (FEA) for normal conducting RF photoinjector gun cavities. The simulation methods are described extensively. Achieved results are presented.

We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

73 pp. (2005)., This report summarises the status of the work in the seven scientific Work Packages of EUROTeV as presented during the ILC-European Regional Meeting at Royal Holloway in June 2005. The purpose of the meeting was to monitor the progress and to contrast the developments inside EUROTeV with the worldwide developments of the GDE. The presentations of the entire meeting are available from http://www.pp.rhul.ac.uk/workshop/.

Universität Hamburg, Diss., 2005; 123 pp., (2005). doi:10.3204/DESY-THESIS-2005-045, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

7 pp. (2005)., The present paper discusses the possibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.

The fast calculation of space-charge fields of bunches of charged particles in three dimensional space is a demanding problem in accelerator design. Since particles of equal chargerepel each other due to space-charge forces, it is difficult to pack a high charge in a small volume. For this reason, the calculation of space-charge forces is an important part of thesimulation of the behaviour of charged particles in these machines. As the quality of the charged particle bunches increases, so do the requirements for the numerical space-chargecalculations. In this paper we develop a new fast summation algorithm for the determination of the electric field generated by N charged particles. Applying the nonequidistant FastFourier Transform (NFFT) the fast summation requires only O(NlogN) operations. The numerical test cases confirm this behaviour.

Humboldt Universität Berlin, Diss., 2004; 152 pp., (2004). doi:10.3204/DESY-THESIS-2004-021, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

2003 Particle Accelerator Conference, PAC2003, Portland, USA, 12 May 2003 - 16 May 2003; Hamburg : DESY 34-36 (2003)., The Photo Injector Test facility at DESY Zeuthen (PITZ) was built in order to study the production of high brightness electron beams, which are substantial for the successful operation of Free Electron Lasers (FEL) and linear colliders. The photoinjector at Zeuthen is based on a 1.5-cell L-band rf cavity with coaxial rf coupler equipped with emittance compensating solenoids, a laser capable to generate long pulse trains, an UHV photo cathode exchange system, and various diagnostics tools. The current goal of PITZ is a full characterization of the electron source, which will be installed at the TESLA Test Facility Free Electron Laser (TTF2-FEL) in autumn 2003. In the running periods before the gun is delivered toTTF2-FEL, the rf performance and the beam parameters will be measured in detail. The results presented in this contribution contain the measurements of dark current, driving laser parameters, beam charge, beam size along the facility, transverse emittance, momentum and momentum spread. The electron beam measurements will be presented in comparison with beam dynamics simulations., Published by DESY, Hamburg

21 pp. (2003)., We present an experimental evidence of a bunch compression scheme that uses a traveling wave accelerating structure as a compressor. The bunch length issued from a laser-driven radio-frequency electron source was compressed by a factor >3 using an S-band traveling wave structure located immediately downstream from the electron source. Experimental data are found to be in good agreement with particle tracking simulations.

TESLA Reports 2003 11 pp. (2003)., This paper presents the behavior of the TTF2 RF gun with long RF pulses (up to 900 $μ$s), high peak power (up to 3 MW) and high repetition rate (up to 10 Hz). The experiments have been realized at the Photo Injector Test Facility of DESY Zeuthen from January to March 2003, where the RF gun has been tested prior to its installation at DESY Hamburg on the TTF2 beamline.

TESLA Reports 2003 14 pp. (2003).

Physical review accelerators and beams 6(3), 033503 (2003). doi:10.1103/PhysRevSTAB.6.033503, We present an experimental evidence of a bunch compression scheme that uses a traveling wave accelerating structure as a compressor. The bunch length issued from a laser-driven radio-frequency electron source was compressed by a factor >3 using an S-band traveling wave structure located immediately downstream from the electron source. Experimental data are found to be in good agreement with particle tracking simulations., Published by American Physical Society, College Park, MD

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.

4 pp. (2002)., In this paper we describe the regeneration of electron bunches from the RF gun by back-reflected radiation from VUV SASE FEL at the TESLA Test Facility (TTF) at DESY. The SASE FEL was running at the wavelength 96 nm with 30– 100 fs pulses, SASE pulse energy was up to 20 μJ . “Nominal” electron bunches for lasing were produced by RF gun with Cs 2 Te photocathode driven by UV quantum laser system. “Parasitic” bunches with a charge up to 1– 1.5 nC were extracted from the RF gun due to VUV FEL radiation reflected from the mirror (placed downstream of the undulator) to the cathode. Nontrivial dependence of a charge on a SASE pulse energy was found.

4 pp. (2002)., The Photo Injector Test facility at DESY Zeuthen (PITZ) was built to develop electron sources for the TESLA Test Facility Free Electron Laser and future linear colliders. The main goal is to study the production of minimum transverse emittance beams with short bunch length at medium charge (∼1 nC). The facility includes a 1.5 cell L-band cavity with coaxial RF coupler, a solenoid for space charge compensation, a laser capable to generate long pulse trains, an UHV photo cathode exchange system, and different diagnostics tools. Besides an overview of the facility, its main components and their commissioning, this contribution will concentrate on the first measurements at PITZ with photoelectrons. This will include measurements of the transverse and longitudinal laser profile, charge and quantum efficiency, momentum and momentum spread, transverse electron beam profiles at different locations and first results on transverse emittance.

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.

2 pp. (2002).

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.

In this report the conceptual design for the TESLA X-ray free-electron laser photoinjector is presented. Beam dynamics, design and operational issues are addressed.

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 18 Jun 2001 - 22 Jun 2001; 2236-2238 (2001)., The high-brightness beams demanded to drive future short-wavelength SASE FEL-based light sources result in stringent demands on the electron beam source. In the foreseen TESLA X-FEL [1], a slice emittance (over the cooperation length) of less than 1.6 mm-mrd and a rms bunch length of ∼ 25 μm (corresponding to a peak current of 5 kA) are required at the undulator entrance. In this paper, we present the conceptual design of the photoinjector system for the TESLA X-FEL including Beam Dynamics studies performed with the codes ASTRA and HOMDYN. The proposed injector can generate 1 nC bunches with mmmrd transverse emittances and longitudinal emittance of 60 keV-mm at an energy of 140 MeV.

2 pp. (2001).

7 pp. (2001).

We present a method to generate a flat (large horizontal to vertical emittance ratio) electron beam suitable for linear colliders. The concept is based on a round-beam rf photoinjector with finite solenoid field at the cathode together with a special beam optics adapter. Computer simulations of this new type of beam source show that the beam quality required for a linear collider may be obtainable without the need for an electron damping ring.

2 pp. (2001).

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 22 Jun 2001 - 22 Jun 2001; 2420-2422 (2001)., The first electron energy spectra obtained from a Cs$_2$Te photocathode using a Time-of-Flight (TOF) spectrometer are presented and discussed in this paper. The highresolution angle resolved TOF electron spectrometer has been developed at INFN Milano-LASA (theoretical resolution: 2 meV at 5 eV). The system has been designed for the investigation of the electron beam thermal emittance that is a key parameter for future generation FEL based high brilliance photon sources. The excitation light source is a short pulse solid-state Nd:glass laser (4$^{th}$ harmonic, $\tau$= 400 fs, $\lambda$= 264 nm). In this paper the spectrometer is presented together with first measurements on different metals and Cs$_2$Te.

The 2001 Particle Accelerator Conference, PAC2001, Chicago, USA, 18 Jun 2001 - 22 Jun 2001; 3099-3101 (2001)., The beam dynamics simulation code V [1,2], based on the Ensemble Model [3], is being developed for on-line simulations. One practical application of the V-Code is the beam-based alignment (BBA) of accelerator (TESLA Test Facility) elements. Before we started with BBA thefirst beam position monitor (BPM1), located after the RFgun cavity, showed non-zero readings. Moreover the readings depended on RF-power, RF-phase and primary and secondary solenoid currents. This effect could be explained by misalignments of the gun and the solenoids. Such beam offsets must be compensated by means of steering coils but such a procedure can be one of the sources of increased emittances. Based on the V-Code solver a dedicated utility was developed for alignment studies. The laser beam mismatch at the cathode, as well as the primary and secondary solenoid displacements were considered as probable reasons for the misalignment of the beam. A new method for the correction of these misalignments combines a sequence of measurements, simulations and the elimination of the largest imperfections. This semi-automatic method applied to the TTF RF-gun yields a centering of the beam within the accuracy of the BPM1.

The arc that occurs during RF breakdown is known to cause local heating of a copper cavity surface, with temperatures sometimes exceeding the melting point. Thermally generated acoustic shock waves [1,2] that accompany breakdowns can be easily detected on the surface of the cavity using externally mounted sensors. Acoustic emission sensors [3] have been used at the TESLA Test Facility to find RF high voltage breakdown locations in the photocathode gun system. It is not known if the acoustic signal emitted from the source (cathode) of the arc is stronger than that emitted from its terminus. The start time and root mean square amplitude of the signal from each of several sensors can be used to locate and classify the breakdown event. We report here on the use of eight sensors mounted on the TTF RF gun [4] to locate its breakdown events during operation with a pulse length of 300$μ$s and a pulse amplitude up to 35 MeV/m.

We review the current status of the R&D results and design studies on the TESLA superconducting e$^+$e$^−$ linear collider project.

2 pp. (2001).

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.

The 7th European Particle Accelerator Conference EPAC 2000, EPAC 2000, Vienna, Austria, 26 Jun 2000 - 30 Jun 2000; Hamburg : DESY 309-311 (2000)., The TESLA Test Facility Linac (TTFL) at DESY uses two modules with 8 TESLA superconducting accelerating structures each to accelerate an electron beam up to 360MeV. At present, the beam has been used to perform the proof-of-principle test of the TTF Free Electron Laser and to continue various experiments for the TESLA linear collider project. For this, an rf-gun based photoinjector was installed late 1998 and is in operation since then. It produces a 0.8 ms long train of 1 nC or optionally 8 nC bunches spaced by 1 $\mu$s with low transverse emittance. Theperformance of the injector during the last run from July 1999 to end of April 2000 is reported., Published by DESY, Hamburg

21 pp. (2000)., Experimental data on transverse emittance and beam density measurements for a variety of injector settings (photocathode drive-laser phase w.r.t. to peak electric field in the RF-gun cavity, magnetic fields settings of solenoids) are compared along with numerical simulations performed using the particle tracking code ASTRA [1].

2 pp. (1999).

22nd International Free Electron Laser Conference and 7th FEL Users Workshop, Durham, United States, 13 Aug 2000 - 18 Aug 2000; 2 pp. (2000).

2 pp. (1999).

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 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.

2 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

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.

TESLA Reports 13 pp. (1999).

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.

2 pp. (1997).

7 pp. (1997).