Testing the Properties of Beam-Dose Monitors for VHEE-FLASH Radiation Therapy

Very High Energy Electrons (VHEE) of 50 - 250 MeV are an attractive choice for FLASH radiation therapy (RT). Before VHEE-FLASH RT can be considered for clinical use, a reliable dosimetric and beam monitoring system needs to be developed, able to measure the dose delivered to the patient in real-time and cut off the beam in the event of a machine fault to prevent overdosing the patient. Ionisation chambers are the standard monitors in conventional RT; however, their response saturates at the high dose rates required for FLASH. Therefore, a new dosimetry method is needed that can provide reliable measurements of the delivered dose in these conditions. Experiments using 200 MeV electrons were done at the CLEAR facility at CERN to investigate the properties of detectors such as diamond beam loss detectors, GEM foil detectors, and Timepix3 ASIC chips. From the tests, the GEM foil proved to be the most promising

The Compact Linear Collider (CLIC) - 2018 Summary Report

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years

Intensity-dependent effects in the Accelerator Test Facility 2 and extrapolation to future electron-positron linear colliders

The high energy physics community considers electron-positron linear colliders in order to complement the results obtained at the Large Hadron Collider. In order to achieve the design luminosity above 1034 cm-2s-1, these linear colliders require a nanometer beam size at the Interaction Point (IP). The electron and positron beams are transported inside the Beam Delivery Systems (BDS) from the linear accelerators (LINACS) to the IP. The beam is focused by two strong quadrupoles in the Final Focus System (FFS) where chromatic effects and aberrations are corrected thanks to a local chromaticity correction scheme. Two projects are being studied now, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). Their FFS and the local chromaticity correction are being tested at the Accelerator Test Facility 2 (ATF2) at KEK in Japan. This test facility has been studying this matter for more than 20 years, achieving two of its main goals: obtaining a stable beam size around 37 nm at the IP and an orbit stabilisation with a nanometer precision at the IP. However, these goals were achieved at 10% of the nominal beam intensity. Indeed, when increasing the beam intensity, the beam becomes more unstable and its size grows. This is mainly due to wakefields in the ATF2 extraction line. Ultra-relativistic electrons going through the beam pipe interact with the surrounding structure and create an electromagnetic field, the wakefield. This field interacts with electrons inside the same bunch (short-range wakefield) but also with electrons in the following bunches (long-range wakefield). In ATF2, one considers that bellows, flanges and cavity BPMs are the main sources of wakefield. This effect results in increasing significantly the beam size at the IP. This thesis will show the impact of these intensity-dependent effects inside ATF2 and how to mitigate them. It will also show the impact of the same intensity-dependent effects in future electron-positron linear colliders, the ILC and CLIC.</p

Intensity dependent effects in the ILC BDS

The International Linear Collider (ILC) is an electron-positron collider being considered for the post-LHC era. Its Beam Delivery System (BDS) receives the beam from the main linac. This beam is then focused to the nanometer scale after going through collimators, beam diagnostic systems, strong magnets, etc. Effects such as wakefields due to resistive-wall, BPMs and collimators make the system very sensitive to the beam intensity. Understanding these effects is crucial in order to demonstrate that the nominal beam size at the Interaction Point (IP) can be reached in realistic scenarios. In this paper, results of the intensity dependence effects in the ILC BDS, simulated with PLACET, are presented

Consolidation and future upgrades to the CLEAR user facility at CERN

The CERN Linear Electron Accelerator for Research (CLEAR) at CERN has been operating since 2017 as a dedicated user facility providing beams for a varied range of experiments. CLEAR consists of a 20 m long linear accelerator (linac), able to produce beams from a Cs₂Te photocathode and accelerate them to energies of between 60 MeV and 220 MeV. Following the linac, an experimental beamline is located, in which irradiation tests, wakefield and impedances tudies, plasma lens experiments, beam diagnostics development, and terahertz (THz) emission studies, are performed. In this paper, we present recent upgrades to the entire beamline, as well as the design of future upgrades, such as a dogleg section connecting to an additional proposed experimental beamline. The gain in performance due to these upgrades is presented with a full range of available beam properties documented

Consolidation and future upgrades to the CLEAR user facility at CERN

The CERN Linear Electron Accelerator for Research (CLEAR) at CERN has been operating since 2017 as a dedicated user facility providing beams for a varied range of experiments. CLEAR consists of a 20 m long linear accelerator (linac), able to produce beams from a Cs₂Te photocathode and accelerate them to energies of between 60 MeV and 220 MeV. Following the linac, an experimental beamline is located, in which irradiation tests, wakefield and impedances tudies, plasma lens experiments, beam diagnostics development, and terahertz (THz) emission studies, are performed. In this paper, we present recent upgrades to the entire beamline, as well as the design of future upgrades, such as a dogleg section connecting to an additional proposed experimental beamline. The gain in performance due to these upgrades is presented with a full range of available beam properties documented

The design of a second beamline for the CLEAR user facility at CERN

The CERN Linear Electron Accelerator for Research (CLEAR) has been operating as a general user facility since 2017 providing beams for a wide range of user experiments. However, with its current optical layout, the beams available to users are not able to cover every request. To overcome this, a second experimental beamline has been proposed. In this paper we discuss the potential optics of the new line as well as detailing the hardware required for its construction. Branching from the current beamline, via a dogleg chicane that could be used for bunch compression, the new beamline would provide an additional in-air test stand to be available to users. The beamline before the test stand would utilise large aperture quadrupoles to allow the irradiation of large target areas or strong focussing of beams onto a target. In addition to this there would also be further in-vacuum space to install experiments

Wakefield effects and mitigation techniques for nanobeam production at the KEK Accelerator Test Facility 2

The ATF2 beamline at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $$10% of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of 10 10 e − . We present studies of the impact of wakefields on the production of `nanobeams’ at the ATF2. Wake potentials were evaluated for the ATF2 beamline elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and BPM resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and IP tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity-dependence of the beam size