Two Beam Test Stand Experiments in the CTF3 Facility

Physical Review Special …, 2011

MOEPPB01, these …

The measurement of the effects of RF-breakdown on the beam in CLIC prototype accelerator structures is one of the key aspects of the CLIC two-beam acceleration scheme being addressed at the Two-beam Test Stand (TBTS) at CTF3. RF-breakdown can randomly cause energy loss and transverse kicks to the beam. Transverse kicks have been measured by means of a screen intercepting the beam after the accelerator structure. In correspondence of a RF-breakdown we detect a double beam spot which we interpret as a sudden change of the beam trajectory within a single beam pulse. To time-resolve such effect, the TBTS has been equipped with five inductive Beam Position Monitors (BPMs) and a spectrometer line to measure both relative changes of the beam trajectory and energy losses. Here we discuss the methodology used and we present the latest results of such measurements.

Conf. Proc., 2012

The feasibility of the CLIC novel scheme of two-beam acceleration was extensively tested in the CTF3 facility over the last few years. In particular, efficient full beam loading acceleration, isochronous ring operation, beam recombination by transverse RF deflectors have been fully proven. 12 GHz RF power production by highcurrent drive beam is now part of CTF3 routine operation, and two-beam acceleration up to 150 MV/m has been achieved. Drive beam deceleration tests were carried out as well. In this paper we summarize the main results obtained, including the more recent ones. We also outline and discuss the future experimental program, both in CTF3 and in other beam facilities, as well as the path to a possible facility needed in the initial stage of the CLIC project, CLIC0.

Proc. EPAC, 2004

The aim of the CLIC (Compact Linear Collider) Study is to investigate the feasibility of a high luminosity, multi-TeV linear e+e-collider. CLIC is based on a two-beam method, in which a high current drive beam is decelerated to produce 30 GHz RF power needed for high-gradient acceleration of the main beam running parallel to it. To demonstrate the outstanding feasibility issues of the scheme a new CLIC Test Facility, CTF3, is being constructed at CERN by an international collaboration. In its final configuration CTF3 will consist of a 150 MeV drive beam linac followed by a 42 m long delay loop and an 84 m combiner ring. The installation will include a 30 GHz high power test stand, a representative CLIC module and a test decelerator. The first part of the linac was installed and commissioned with beam in 2003. The first issue addressed was the generation and acceleration of a high-current drive beam in the "full beam loading" condition where RF power is converted into beam power with an efficiency of more than 90 %. The full beam loading operation was successfully demonstrated with the nominal beam current of 3.5 A. A variety of beam measurements have been performed, showing good agreement with expectations.

2008

The CLIC project based on the innovative Two Beams Acceleration concept is currently under study at CTF3 where the acceleration of a probe beam will be demonstrated. This paper will describe in details the status of the probe beam linac called CALIFES. This linac (170 MeV, 0.9 A) is developed by CEA Saclay, LAL Orsay and CERN. It has been installed in the new experimental area of CTF3 to deliver short bunches (1.8 ps) with a charge of 0.6 nC to the CLIC 12 GHz accelerating structures. We report new results of beam dynamic and RF simulations considering the new CLIC parameters. The construction of CALIFES in the CLEX building is presented. Recent measurements from the laser system are discussed. Details about the HV modulator tests and the power phase shifter fabrication will be described and the start of commissioning will be also reported.

2001

In the framework of the CLIC (Compact Linear Collider) RF power source studies, the scheme of electron pulse compression and bunch frequency multiplication, using injection by RF deflectors into an isochronous ring, will be tested, at low charge, during the preliminary phase of the new CLIC Test Facility (CTF3) at CERN. In this paper, we describe the beam dynamics studies made in order to assess the feasibility of the bunch combination experiment, as well as the related beam measurements performed on the LEP Pre-Injector complex (LPI) before its transformation into CTF3.

2013

The CLEX building in the CTF3 facility is the placewhere essential experiments are performed to validate theTwo-Beam Acceleration scheme upon which the CLICproject relies. The Drive Beam enters the CLEX hall afterbeing recombined in the Delay loop and the CombinerRing in intense beam trains of 24 A – 120 MeV lasting140 ns and bunched at 12 GHz, although other beamparameters are also accessible. This beam is thendecelerated in dedicated structures installed in the TestBeam Line (TBL) and in the Two-Beam Test Stand(TBTS) aimed at delivering bursts of 12 GHz RF power.In the TBTS this power is used to generate a highaccelerating gradient of 100 MV/m in specially designedaccelerating structures. To assess the performances ofthese structures a probe beam is used, produced by asecond Linac. We report here various experimentsconducted in the TBTS making use of the versatility ofthe probe beam and of dedicated diagnostics.

2014

The CLIC Test Facility CTF3 has been built at CERN by the Compact Linear Collider (CLIC) International Collaboration, in order to prove the main feasibilit y issues of the two-beam acceleration technology on which the collider is based. After the successful completion of its initial task, CTF3 is continuing its experimental prog ram in order to give further indications on cost and performance issues, to act as a test bed for the CLIC technology, and to conduct beam experiments aimed at mitigating technological risks. In this paper we di scuss the status of the ongoing experiments and present the more recent results, including improvements in beam quality and stability .

From mid-2012, the Two Beam Test Stand (TBTS) in the CTF3 Experimental Facility is hosting 2 high gradient accelerating structures powered by a single power extraction and transfer structure in a scheme very close to the CLIC basic cell. We report here about the results obtained with this configuration as: energy gain and energy spread in relation with RF phases and power, octupolar transverse beam effects compared with modelling predictions, breakdown rate and breakdown locations within the structures. These structures are the first to be fitted with Wake Field Monitors (WFM) that have been extensively tested and used to further improve the structures alignment on the beam line. These results show the unique capabilities of this test stand to conduct experiments with real beams.

1996

In order to study the principle of the Compact Linear Collider (CLIC) based on the Two Beam Acceleration (TBA) scheme at high frequency, a CLIC Test Facility (CTF) has been set-up at CERN. After four years of successful running, the experimental programme is now fully completed and all its objectives reached, particularly the generation of a high intensity drive beam with short bunches by a photo-injector, the production of 30 GHz RF power and the acceleration of a probe beam by 30 GHz structures. A summary of the CTF results and their impact on linear collider design is given. This covers 30 GHz high power testing, study of intense, short single bunches; as well as RF-Gun, photocathode and beam diagnostic developments. A second phase of the test facility (CTF2) is presently being installed to demonstrate the feasibility of the TBA scheme by constructing a fully engineered, 10 m long, test section very similar to the CLIC drive and main linacs, producing up to 480 MW of peak RF power at 30 GHz and accelerating the beam up to 320 MeV. The present status of CTF2 is reported.

RF breakdown is a key issue for the multi-TeV highluminosity e+e-Compact Linear Collider (CLIC). Breakdowns in the high-gradient accelerator structures can deflect the beam and decrease the desired luminosity. The limitations of the accelerating structures due to breakdowns have been studied so far without a beam present in the structure. The presence of the beam modifies the distribution of the electrical and magnetic field distributions, which determine the breakdown rate. Therefore an experiment has been designed for high power testing a CLIC prototype accelerating structure with a beam present in the CLIC Test Facility (CTF3). A special beam line allows extracting a beam with nominal CLIC beam current and duration from the CTF3 linac. The paper describes the beam optics design for this experimental beam line and the commissioning of the experiment with beam.

Physical Review Special Topics - Accelerators and Beams, 2011

We discuss X-band rf power production and deceleration in the two-beam test stand of the CLIC test facility at CERN. The rf power is extracted from an electron drive beam by a specially designed power extraction structure. In order to test the structures at high-power levels, part of the generated power is recirculated to an input port, thus allowing for increased deceleration and power levels within the structure. The degree of recirculation is controlled by a splitter and phase shifter. We present a model that describes the system and validate it with measurements over a wide range of parameters. Moreover, by correlating rf power measurements with the energy lost by the electron beam, as measured in a spectrometer placed after the power extraction structure, we are able to identify system parameters, including the form factor of the electron beam. The quality of the agreement between model and reality gives us confidence to extrapolate the results found in the present test facility towards the parameter regime of CLIC.

2009

Abstract The two-beam acceleration scheme foreseen for CLIC and the associated radio-frequency (RF) components will be tested in the Two-beam Test Stand (TBTS) at CTF3, CERN. Of special interest is the performance of the power extraction structures (PETS) and the acceleration structures as well as the stability of the beams in the respective structures. After the recent completion of the TBTS, the first 12 GHz PETS has been tested with beam, using so-called recirculation of the RF power inside the PETS.

2016

The CLIC Test Facility CTF3 was build, commissioned and operated at CERN by an international collaboration, with the aim of validating the CLIC two beam acceleration scheme, in which the RF power used to accelerate e+/ebeams is extracted from a high intensity electron beam. In the past years themain issues of such a schemewere assessed, demonstrating its feasibility. The CTF3 experimental program is complementing these results by addressing cost and performance subjects, mainly using the CALIFES test beam injector and a full scale two-beam module. In this paper we document the present status and give an outlook to the 2016 run, when the experimental program should be completed. CONTROL OF THE BEAMS AND MACHINE DEVELOPMENT In the last experimental runs, a large fraction of beam time has been dedicated to improvements of the drive beam performance, in terms of stability, availability and control of emittance growth. Apart from enabling a better exploitation of the beam by the users, t...

2014

The Compact Linear Collider (CLIC) project aims to accelerate and collide electrons and positrons up to 3 TeV center-of-mass energy using a novel two-beam acceleration concept. To prove the feasibility of this technology the CLIC Test Facility CTF3 has been operated during the last years. CALIFES (Concept d’Accelerateur Lineaire pour Faisceau d’Electron Sonde) is an electron linac hosted in the CTF3 complex, which provides a flexible electron beam and the necessary equipment to probe both the two-beam acceleration concept and novel instrumentation to be used in the future CLIC collider. In this paper we describe the CALIFES Linac and its beam characteristics, present recent test results, outline its future program on two-beam module testing and finally discuss about possible future applications as a multi-purpose accelerator technology test facility.