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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.
arXiv: Accelerator Physics, 2013
Understanding the effects of RF breakdown in high-gradient accelerator structures on the accelerated beam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) and is one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN. During a RF breakdown large electro-magnetic fields are generated and produce parasitic magnetic fields which interact with the accelerated beam affecting its orbit and energy. We discuss here measurements of such effects observed on an electron beam accelerated in a CLIC prototype structure. Measurements of the trajectory of bunch-trains on a nanosecond time-scale showed fast changes in correspondence of breakdown which we compare with measurements of the relative beam spots on a scintillating screen. We identify different breakdown scenarios for which we offer an explanation based also on measurements of the power at the input and output ports of the accelerator structure. Finally we pre...
Physical Review Special Topics - Accelerators and Beams, 2013
Understanding the effects of RF breakdown in high-gradient accelerator structures on the accelerated beam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) and is one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN. During a RF breakdown high currents are generated causing parasitic magnetic fields which interact with the accelerated beam affecting its orbit. The beam energy is also affected because the power is partly reflected and partly absorbed thus reducing the available energy to accelerate the beam. We discuss here measurements of such effects observed on an electron beam accelerated in a CLIC prototype structure. Measurements of the trajectory of bunch-trains on a nanosecond time-scale showed fast changes in correspondence of breakdown which we compare with measurements of the relative beam spots on a scintillating screen. We identify different breakdown scenarios for which we offer an explanation based also on measurements of the power at the input and output ports of the accelerator structure. Finally we present the distribution of the magnitude of the observed changes in the beam position and we discuss its correlation with RF power and breakdown location in the accelerator structure.
2017
The RF breakdown rate is crucial for the luminosity performance of the CLIC linear collider. The required breakdown rate at the design gradient of 100 MV/m has been demonstrated, without beam presence, in a number of 12GHzCLIC prototype structures. Nevertheless, the beam-loading at CLIC significantly changes the field profile inside the structures, and the behaviour with beam needs to be understood. A dedicated experiment in the CLIC Test Facility CTF3 to determine the effect of beam on the breakdown rate has been collecting breakdown data throughout the year 2016. The complete results of the experiment and the effect of the beam-loading on the breakdown rate are presented.
2011
The CLEX building in the CTF3 facility is the place where essential experiments are performed to validate the Two-Beam Acceleration scheme upon which the CLIC project relies. The Drive Beam enters the CLEX hall after being recombined in the Delay loop and the Combiner Ring in intense beam trains of 24 A -120 MeV lasting 140 ns and bunched at 12 GHz, although other beam parameters are also accessible. This beam is then decelerated in dedicated structures installed in the Test Beam 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 high accelerating gradient of 100 MV/m in specially designed accelerating structures. To assess the performances of these structures a probe beam is used, produced by a second Linac. We report here various experiments conducted in the TBTS making use of the versatility of the probe beam and of dedicated diagnostics.
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.
Within the framework of the research on high-gradient accelerating structures for future linear colliders, diagnostics of radio-frequency (RF) breakdowns is of great importance to support the understanding of the vacuum breakdown process. Measurements of RF and electron and ion currents emitted during and after a breakdown can be used to calculate the properties of any objects responsible for such power reflection and charge emission. Possible breakdown models, breakdown localization and a time-scale of the process are here discussed and compared to dedicated measurements. First results are presented.
Abstract The CLEX building in the CTF3 facility is the place where essential experiments are performed to validate the Two-Beam Acceleration scheme upon which the CLIC project relies. The Drive Beam enters the CLEX hall after being recombined in the Delay loop and the Combiner Ring in intense beam trains of 24 A–120 MeV lasting 140 ns and bunched at 12 GHz, although other beam parameters are also accessible.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
A e + e − collider of several TeV energy will be needed for the precision studies of any new physics discovered at the LHC collider at CERN. One promising candidate is CLIC, a linear collider which is based on a two-beam acceleration scheme that efficiently solves the problem of power distribution to the acceleration structures. The phenomenon that currently prevents achieving high accelerating gradients in high energy accelerators such as the CLIC is the electrical breakdown at very high electrical field. The ongoing experimental work within the CLIC collaboration is trying to benchmark the theoretical models focusing on the physics of vacuum breakdown which is responsible for the discharges. In order to validate the feasibility of accelerating structures and observe the characteristics of the vacuum discharges and their eroding effects on the structure two dedicated spectrometers are now commissioned at the high-power test-stands at CERN. First, the so called Flashbox has opened up a possibility for non-invasive studies of the emitted breakdown currents during two-beam acceleration experiments. It gives an unique possibility to measure the energy of electrons and ions in combination with the arrival time spectra and to put that in context with accelerated beam, which is not possible at any of the other existing test-stands. The second instrument, a spectrometer for detection of the dark and breakdown currents, is operated at one of the 12 GHz stand-alone test-stands at CERN. Built for high repetition rate operation it can measure the spatial and energy distributions of the electrons emitted from the acceleration structure during a single RF pulse. Two new analysis tools: discharge impedance tracking and tomographic image reconstruction, applied to the data from the spectrometer make possible for the first time to obtain the location of the breakdown inside the structure both in the transversal and longitudinal direction thus giving a more complete picture of the vacuum breakdown phenomenon.
2014
The Compact Linear Collider (CLIC) is an e + /e - collider based on the two-beam acceleration principle, proposed to support precision high-energy physics experiments in the energy range 0.5-3 TeV [1]. To achieve a high luminosity of up to 6x10 34 cm -2 s -1 , the transport and preservation of a low emittance beam is mandatory. A large number and great variety of beam diagnostics instruments is foreseen to verify and guarantee the required beam quality. We discuss the status of the beam diagnostics developments and experimental results accomplished at the CLIC Test Facility (CTF) and at the Cornell University CesrTA ring accelerator.
2004
With its 4kW average beam power, the CLIC test facility 3 (CTF3) is a machine where the control of beam losses is an important issue. Beam losses must be monitored all along the linac in order to keep the radiation level and the activation as low as possible. The Beam Loss Monitor (BLM) system currently under development is described. The goal of our effort is to provide quantitative beam loss measurements. An intensive simulation work has been carried out in order to estimate the e + -eshowers in a realistic accelerator environment. Based on these results, we investigate two scenarios to measure beam losses using a set of 48 detectors distributed along the machine.
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.
proc. EPAC, 2006
In CLIC, the rf power to accelerate the main beam is produced by decelerating a drive beam. The Test Beam Line (TBL) of the CLIC Test Facility (CTF3) is designed to study and validate the drive beam stability during deceleration. This is one of the R&D items required from ...
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.
2010
The CLIC study is based on the so-called two-beam acceleration concept and one of the main goals of the CLIC Test Facility 3 is to demonstrate the efficiency of the CLIC RF power production scheme. As part of this facility a Test Beam Line (TBL), presently under commissioning, is a small scale version of a CLIC decelerator. To perform as expected the beam line must show efficient and stable RF power production over 16 consecutive decelerating structures. As the high intensity electron beam is decelerated its energy spread grows by up to 60%. A novel segmented beam dump for time resolved energy measurements has been designed to match the requirements of the TBL. As a complement, a diffusive OTR screen is also installed in the same spectrometer line. The combination of these two devices will provide both a high spatial resolution measurement of both the energy and energy spread and a measurement with a few nanoseconds time response. This paper describes the design of the new segmented...
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.
In the CLIC two-beam scheme, the main beam is accel-erated by rf power provided by energy extraction from a secondary drive beam. This energy is extracted in deceler-ators, and the first prototype decelerator is the Test Beam Line in the CLIC Test Facility 3. The line is currently equipped with 12 Power Extraction and Transfer Structures (PETS), which allows for extracting up to 40 % of the beam energy. We correlate the measured deceleration with pre-dictions from the beam current and the rf power produced in the PETS. We also discuss recent bunch length measure-ments and how it influences the deceleration. Finally we look at the evolution of the transverse emittance.
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 .
2004
The CLIC test facility 3 (CTF3) provides a 3.5-A, 1.6-µs electron beam pulse of 150 MeV at the end of the linac. The average beam power is 4 kW. Beam losses will be monitored all along the linac in order to keep the radiation level as low as possible. The heavy beam loading of the linac can lead to time transients of beam position, size, and energy along the pulse. To compensate for these transients effectively, the beam loss monitor (BLM) technology must have a time response faster than a few nanoseconds. Preliminary tests have been performed in 2003 on the already existing part of the accelerator with the aim of studying the requirements for the system to be built in the future. The experimental data are compared to the results of Geant3 simulations. Based on these results, a complete beam loss detection system is currently designed for the observation of the beam transient loss and its minimization.
Physical Review Special …, 2011
1998
The second phase of the Compact LInear Collider (CLIC) Test Facility (CTF II) at CERN has demon-strated the feasibility of two-beam acceleration at 30 GHz using a high-charge drive beam, running parallel to the main beam, as the RF power source. To date accelerating gradients of 59 MV/m at 30 GHz have been achieved. In CTF II, the two beams are generated by 3 GHz RF photo-injectors and are accelerated in 3 GHz linacs, before injection into the 30 GHz modules. The drive beam linac has to accelerate a 16 ns long train of 48 bunches, each with a nominal charge of 13.4 nC. To cope with the very substantial beam-loading special accelerating structures are used (running slightly off the bunch repetition frequency). A magnetic chicane compresses the bunches to less than 5 ps fwhm, this is needed for efficient 30 GHz power generation. The 30 GHz modules are fully-engineered representative sections of CLIC, they include a 30 GHz decelerator for the drive beam, a 30 GHz accelerator for the main beam, high resolution BPM's and a wire-based active align-ment system. The performance achieved so far, as well as the operational experience with the first accelerator of this type, are reported.
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