Beam dynamics studies and emittance optimization in the CTF3 linac at CERN

Small transverse beam emittances and well-known lattice functions are crucial for the 30 GHz power production in the Power Extraction and Transfer Structure (PETS) and for the commissioning of the Delay Loop of the CLIC Test Facility 3 (CTF3). Following beam dynamics simulation results, two additional solenoids were installed in the CTF3 injector in order to improve the emittance. During the runs in 2005 and 2006, an intensive measurement campaign to determine Twiss parameters and beam sizes was launched. The results obtained by means of quadrupole scans for different modes of operation suggest emittances well below the nominal .n,rms = 100 ?Î?Êm and a good agreement with PARMELA simulations

Efficient long-pulse fully-loaded CTF3 linac operation

An efficient RF to beam energy transfer in the accelerating structures of the drive beam is one of the key points of the Compact Linear Collider (CLIC) RF power source. For this, the structures are fully beam-loaded, i.e. the accelerating gradient is nearly zero at the downstream end of each structure. In this way, about 96 % of the RF energy can be transferred to the beam. To demonstrate this mode of operation, 1.5 ..s long beam pulses are accelerated in six fully loaded structures in the CLIC Test Facility (CTF3) Linac. The final beam energy is compared to the input RF power of the structures, proving the efficient energy transfer

Commissioning Status of the CTF3 Delay Loop

The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the linear collider by 2010. In particular, one of the main goals is to study the generation of high-current electron pulses by interleaving bunch trains in delay lines and rings using transverse RF deflectors. This will be done in the 42 m long delay loop, built under the responsibility of INFN/LNF, and the 84 m long combiner ring that will follow it. The delay loop installation was completed and its commissioning started at the end of 2005. In this paper the commissioning results are presented, including the first tests of beam recombination

Time resolved spectrometry on the CLIC Test Facility 3

The high charge (>6ìC) electron beam produced in the CLIC Test Facility 3 (CTF3) is accelerated in fully beam loaded cavities. To be able to measure the resulting strong transient effects, the time evolution of the beam energy and its energy spread must be determined with at least 50MHz bandwidth. Three spectrometer lines are installed along the linac in order to control and tune the beam. The electrons are deflected by dipole magnets onto Optical Transition Radiation (OTR) screens which are observed by CCD cameras. The measured horizontal beam size is then directly related to the energy spread. In order to provide time-resolved energy spectra, a fraction of the OTR photons is sent onto a multi-channel photomultiplier. The overall setup is described, special focus is given to the design of the OTR screen with its synchrotron radiation shielding. The performance of the time-resolved measurements are discussed in detail. Finally, the limitations of the system, mainly due to radiation problems are discussed

Longitudinal beam profile measurements at CTF3 using a streak camera

The proposed Compact Linear Collider (CLIC) is a multi-TeV electron-positron collider for particle physics based on an innovative two-beam acceleration concept. A high-intensity drive beam powers the main beam of a high-frequency (30 GHz) linac with a gradient of 150 MV/m, by means of transfer structure sections. The aim of the CLIC Test Facility (CTF3) is to make exhaustive tests of the main CLIC parameters and to prove the technical feasibility. One of the points of particular interest is the demonstration of bunch train compression and combination in the Delay Loop and in the Combiner Ring. Thus, detailed knowledge about the longitudinal beam structure is of utmost importance and puts high demands on the diagnostic equipment. Among others, measurements with a streak camera have been performed on the linac part of the CTF3 as well as on the newly installed Delay Loop. This allowed e.g. monitoring of the longitudinal structure of individual bunches, the RF combination of the beam, the behavior during phase shifts and the influence of the installed wiggler. This article first gives an overview of the CTF3 facility, then describes in detail the layout of the long optical lines required for observation of either optical transition radiation or synchrotron radiation, and finally shows first results obtained during the last machine run this year

Beam Dynamics and First Operation of the Sub-Harmonic Bunching System in the CTF3 Injector

The CLIC Test Facility 3 (CTF3), built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme by 2010. The CTF3 drive beam generation scheme relies on the use of a fast phase switch of a sub-harmonic bunching system in order to phase-code the bunches. The amount of charge in unwanted satellite bunches is an important quantity, which must be minimized. Beam dynamic simulations have been used to study the problem, showing the limitation of the present CTF3 design and the gain of potential upgrades. In this paper the results are discussed and compared with beam measurements taken during the first operation of the system

A high-gradient test of a 30 GHz copper accelerating structure

The CLIC study is investigating a number of different materials at different frequencies in order to find ways to increase achievable accelerating gradient and to understand what are the important parameters for high-gradient operation. So far a series of rf tests have been made with a set of identical-geometry 30 GHz and X-band structures in copper, tungsten and molybdenum. A new test of a 30 GHz copper accelerating structure has been completed in CTF3 with pulse lengths up to 70 ns. The new results are presented and compared to the previous structures to determine dependencies of quantities such accelerating gradient, material, frequency, pulse length, conditioning rate, breakdown rate and surface damage

A High-Gradient Test of a 30 GHz Molybdenum-Iris Structure

The CLIC study is actively investigating a number of different materials in an effort to find ways to increase achievable accelerating gradient. So far a series of rf tests have been made with a set of identical-geometry structures: a W-iris 30 GHz structure, a Mo-iris 30 GHz structure (with pulses as long as 16 ns) and a scaled Mo-iris X-band structure. A second Mo-iris 30 GHz structure of the same geometry has now been tested in CTF3 with pulse lengths up to 350 ns. The structure was conditioned to a gradient of 140 MV/m with a 70 ns pulse length and a breakdown rate slope of 13 MV/m per decade has been measure

Measurement and Compensation of Second and Third Order Resonances at the CERN PS Booster

Space charge effects at injection are the most limiting factor for the production of high brightness beams in the CERN PS Booster. The beams for LHC, CNGS and ISOLDE feature incoherent tune spreads exceeding 0.5 at injection energy and thus cover a large area in the tune diagram. Consequently these beams experience the effects of transverse betatron resonances and efficient compensation is required. Several measurements have been performed at the PS Booster in 2003, aiming at a detailed analysis of all relevant second and third order resonances and an optimisation of the compensation schemes. Special attention was paid to the systematic 3Qv=16 resonance. To avoid this particularly dangerous resonance an alternative working point was tested. A comparison of resonance driving terms and compensation settings for both working points was made and important differences in the strengths of the resonances were found. The peculiarities when measuring third order coupling resonance driving terms are also mentioned

Measurement and compensation of betatron resonances at the CERN PS booster synchrotron

Zsfassung in dt. SpracheDas CERN PS Booster Synchrotron ist der erste Kreisbeschleuniger in der Proton-Injektorkette des zukünftigen Large Hadron Colliders und verbindet den Linearbschleuniger mit dem Proton Synchrotron. Während der Injektion in den PS Booster und der frühen Beschleunigungsphase erfahren die einzelnen Teilchen im Strahl eine raumladungsbedingte Tune-Verschiebung, infolgedessen ein großer Bereich des ``Tunediagramms'' abgedeckt ist. Die Protonen verspüren daher die Wirkung zahlreicher Betatronresonanzen, die eine Vergrößerung der Schwingungsamplitude der Teilchen und in letzter Konsequenz Teilchenverluste, zur Folge hat. Um dies zu verhindern, ist eine effiziente Resonanzkompensation erforderlich. Die ständig steigende Nachfrage an Hochintensitätsstrahlen, machte eine eingehende Analyse aller relevanten Betatronresonanzen wünschenswert. Die Kombination aus schneller Elektronik, leistungsstarken Rechnern und der Normal Form Technik, ermöglicht die Bestimmung von Stärke und Phase transversaler Resonanzen auf der Basis von Strahlpositionsmessungen über viele aufeinanderfolgende Umläufe. Zu diesem Zweck wurde ein neues Meßsystem installiert. Das durchgeführte Meßprogramm gliedert sich im Wesentlichen in zwei Teile. Im Ersten wurden alle für die Standardoperation des PS Boosters relevanten Resonanzen zweiter und dritter Ordnung vermessen.Mit Kenntnis der intrinsischen Resonanzstärken wurden die entsprechenden Kompensationsströme errechnet und eine effiziente Resonanzkompensation erzielt. Im zweiten Teil des Meßprogramms wurde die Leistungsfähigkeit des neuen Meßsystems ausgenutzt, um einen neuen Arbeitspunkt für den PS Booster zu analysieren. Die in diesem neuen Arbeitsbereich durchgeführten Messungen zeigten eine deutlich kleinere inhärente Resonanzanregung. Aufgrund dieser Resultate wurde der PS Booster 2004 mit dem neuen Arbeitspunkt gestartet und ein neues Kompensationsschema für diesen Arbeitspunkt entwickelt.The CERN PS Booster Synchrotron is the first circular accelerator in the proton injector chain of the future Large Hadron Collider and links the linear accelerator with the Proton Synchrotron.Throughout injection into the PS Booster and early acceleration, the individual particles in the beam "see" large, fluctuating incoherent space-charge tune shifts, consequently sweeping a large area in the tune diagram and covering many resonances. Thus, the beam suffers amplitude blow-up from transverse betatron resonances and an efficient compensation is required to avoid subsequent particle losses. With the increasing demands for higher intensities and higher brightness beams, a revision of the existing working point with a general analysis of all relevant betatron resonances was needed. Modern methods allow to extract resonance driving terms from turn-by-turn beam position data. For this a new multi-turn acquisition system was installed. All second and third order resonances relevant for the operation were analysed in the PS Booster. With the knowledge of the bare machine driving terms, compensation settings for all resonances were calculated, resulting in an efficient resonance compensation. Furthermore a new, alternative working point was tested. It was found that the driving terms are significantly smaller in this area of the tune diagram than for the standard working point. The results obtained had the direct consequence of restarting the PS Booster in 2004 with the new working point. The final part of the thesis was to establish the resonance compensation scheme for this new working point.10