Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the 'Cosmics Leaving Outdoor Droplets' chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products' saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.

At LABEC (the INFN ion beam laboratory of nuclear techniques for environment and cultural heritage, located in Florence), a novel transportable accelerator for in-situ ion-beam analysis measurements of cultural heritage materials, MACHINA, has been constructed as part of an international collaboration between the INFN and the CERN. Here we present the most recent developments regarding this project, consisting in the design, construction, and testing of the hardware/software of a data acquisition system for prompt photons of characteristic energies emitted following the interaction between charged particles and matter to construct elemental maps, i.e., grayscale digital images showing the spatial distribution of elements in a material of interest wherein the brightness of each individual pixel correlates to the abundance of a given element.

Aerosol particles have an important role in Earth's radiation balance and climate, both directly and indirectly through aerosol-cloud interactions. Most aerosol particles in the atmosphere are weakly charged, affecting both their collision rates with ions and neutral molecules, as well as the rates by which they are scavenged by other aerosol particles and cloud droplets. The rate coefficients between ions and aerosol particles are important since they determine the growth rates and lifetimes of ions and charged aerosol particles, and so they may influence cloud microphysics, dynamics, and aerosol processing. However, despite their importance, very few experimental measurements exist of charged aerosol collision rates under atmospheric conditions, where galactic cosmic rays in the lower troposphere give rise to ion pair concentrations of around 1000 cm(-3). Here we present measurements in the CERN CLOUD chamber of the rate coefficients between ions and small (< 10 nm) aerosol particles containing up to 9 elementary charges, e. We find the rate coefficient of a singly charged ion with an oppositely charged particle increases from 2.0 (0.4-4.4) x 10(-6) cm(3) s(-1) to 30.6 (24.9-45.1) x 10(-6) cm(3) s(-1) for particles with charges of 1 to 9 e, respectively, where the parentheses indicate the +/- 1 sigma uncertainty interval. Our measurements are compatible with theoretical predictions and show excellent agreement with the model of Gatti and Kortshagen (2008).

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1-4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles-comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3-H2SO4-NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN) 1 – 4 . However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region 5 , 6 . Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO 3 –H 2 SO 4 –NH 3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.

Faster than expected Iodine species are one of only a handful of atmospheric vapors known to make new aerosol particles, which play a central role in controlling the radiative forcing of climate. He et al. report experimental evidence from the CERN Cosmics Leaving Outdoor Droplets, or CLOUD, chamber demonstrating that iodic acid and iodous acid rapidly form new particles and can compete with sulfuric acid in pristine regions. Science , this issue p. 589

New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid–base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres.

The Cosmics Leaving OUtdoor Droplets (CLOUD) experiment at the European Organization for Nuclear Research (CERN) is investigating the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. The experiment comprises an ultraclean 26 m 3 chamber and its associated systems (the CLOUD facility) together with a suite of around 50 advanced instruments attached to the chamber via sampling probes to analyze its contents. The set of instruments changes for each experimental campaign according to the scientific goals. The central function of the CLOUD DAQ (data acquisition) system is to combine the data from these autonomous and inhomogeneous instruments into a single, integrated CLOUD experiment database. The DAQ system needs to be highly adaptable to allow a fast setup over a single installation week at the start of each campaign when the instruments are brought to CERN and installed at the CLOUD chamber. Each campaign requires high flexibility and fast response to changes in instrument configuration or experimental parameters. The experiments require online monitoring of the physical and chemical measurements with delays of only a few seconds. In addition, the raw data, the monitoring databases, and the processed data must be archived and provided to the international collaboration for both real-time and later analyses. We will describe the various components of the CLOUD DAQ and computing infrastructure, together with the reasons for the chosen solutions.

Linear accelerator 4 (Linac4) is designed to accelerate negative hydrogen ions for injection into the Proton Synchrotron Booster (PSB). It will become the source of proton beams for the Large Hadron Collider (LHC) after the long shutdown in 2019–2020. Linac4 will accelerate H– ions, consisting of a hydrogen atom with an additional electron, to 160 MeV energy and then inject them into the PSB, which is part of the LHC injection chain. The new accelerator comprises an ion source and four types of accelerating structures. The particles are accelerated first to 3 MeV energy by a Radio-Frequency Quadrupole (RFQ), then to 50 MeV by three Drift Tube Linacs (DTL) tanks, then to 100 MeV by seven Cell-Coupled Drift Tube Linac (CCDTL) modules, and finally to 160 MeV by twelve Pi-Mode Structures (PIMS). A chopper line placed between the RFQ and the first DTL tank modulates the linac beam at the PSB injection frequency. Linac4 includes transfer and measurement lines up to the PSB injection, where the ions are stripped of their two electrons to leave only protons. Linac4 is 76 metres long and located 12 metres below ground. The first low-energy beams were produced in 2013 and after the commissioning of all accelerating structures the milestone energy of 160 MeV was reached in 2016. Linac4 will be connected to the PSB during the long shutdown of 2019–20, after which it will replace the 50 MeV Linac2 as source of protons for the LHC. The Linac4 is a key element in the project to increase the luminosity of the LHC during the next decade.

Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms – which drive particle nucleation and early growth – while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C20 and C15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2⚫) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene ∕ monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH⚫) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2⚫ radicals that reduce C20 formation. RO2⚫ termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.

Data presented in the manuscript "Rapid growth of new atmospheric particles by nitric acid and ammonia condensation" currently in review. The manuscript associated with this data was written using results from the CLOUD experiment at CERN, and the author list is a subset of the CLOUD collaboration.

Protons with an energy of few MeV are commonly used for Ion Beam Analysis of materials, in particular with the Proton Induced X-ray Emission technique (PIXE). Because of its non-damaging character, PIXE is used in a variety of fields, in particular for the diagnosis of cultural heritage artwork. A compact accelerator based on a high frequency RFQ (Radio Frequency Quadrupole) linac has been designed and is being built at CERN. The length of the RFQ is only one meter and it allows the acceleration of a proton beam up to an energy of 2 MeV. The complete system is conceived to be transportable, allowing PIXE analysis almost anywhere. This paper covers the RF design of the compact RFQ operating at 750 MHz. We present general accelerator parameters and the current state of the RF design, which includes RFQ geometry and coupler design, thermal simulation and first particle tracking results. INTRODUCTION The Proton Induced X-Ray Emission (PIXE) [1] is a widely used method for cultural heritage material characterization (among others). It allows for a non-damaging and highly sensitive quantitative analysis by stimulating specimen atoms using 2 to 4 MeV proton beams and measuring the emitted X-ray spectrum. Conventional electrostatic PIXE accelerators require significant space and infrastructure and are thus installed in dedicated centres. Contrarily, an RFQ operating at 750 MHz is able to provide 2 MeV protons over the length of just one meter, as proposed in [2]. The PIXE RFQ is developed within the context of the MACHINA project [3], whose aim is to build the first transportable system for in situ ion beam analysis. The RFQ design is based on the high-frequency RFQ for medical applications [2, 4, 5], adapted to the requirements of PIXE analysis. A selection of design parameters is presented in Table 1. RF DESIGN In general, all geometries are optimised to a resonant frequency of f0 = 749.48 MHz, as well as minimum surface losses expressed by a maximum Q0 factor. While a circular shape of the four quadrants would be the optimum in this ∗ This work has been sponsored by the Wolfgang Gentner Programme of the German Federal Ministry of Education and Research (grant no. 05E15CHA). † hermann.winrich.pommerenke@cern.ch Table 1: Design Parameters of the PIXE RFQ Input energy Ein 20 keV Output energy Eout 2 MeV RF frequency f0 749.48 MHz RFQ length 1072.938 mm Vane voltage V 35 kV Min. aperture 0.7 mm Vane tip radius 1.439 mm Peak current 200 nA Transmission T 30 % Max. duty cycle dmax 2.5 % regard, a planar back side surface is used to simplify the machining (Fig. 1). The cavity geometries of the two RFQ modules are slightly different to account for the changing vane modulation.

The proton-induced x-ray emission (PIXE) is the most commonly used ion beam analysis technique. It allows for nondestructive quantitative elemental characterization and is used in a variety of fields, particularly for the diagnosis of cultural heritage artwork. To provide mobile access to PIXE, a compact transportable radio frequency quadrupole (RFQ) linac has been designed and is being built at CERN. The PIXE RFQ has a length of only one meter and accelerates a proton beam to an energy of 2 MeV. This paper covers various rf design studies for the RFQ operating at 750 MHz. We show simulation results regarding cavity, equipment, and coupler geometry. Thermomechanical and beam dynamics studies are presented as well. The paper concludes with a conceptual study on dipole mode detuning by means of length adjustment.

Significance Aerosol particles can form and grow by gas-to-particle conversion and eventually act as seeds for cloud droplets, influencing global climate. Volatile organic compounds emitted from plants are oxidized in the atmosphere, and the resulting products drive particle growth. We measure particle growth by oxidized biogenic vapors with a well-controlled laboratory setup over a wide range of tropospheric temperatures. While higher temperatures lead to increased reaction rates and concentrations of highly oxidized molecules, lower temperatures allow additional, but less oxidized, species to condense. We measure rapid growth over the full temperature range of our study, indicating that organics play an important role in aerosol growth throughout the troposphere. Our finding will help to sharpen the predictions of global aerosol models.

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO x ) and sulfur oxides (SO x ) from fossil fuel combustion, as well as ammonia (NH 3 ) from livestock and fertilizers. Here, we show how NO x suppresses particle formation, while HOMs, sulfuric acid, and NH 3 have a synergistic enhancing effect on particle formation. We postulate a novel mechanism, involving HOMs, sulfuric acid, and ammonia, which is able to closely reproduce observations of particle formation and growth in daytime boreal forest and similar environments. The findings elucidate the complex interactions between biogenic and anthropogenic vapors in the atmospheric aerosol system.

ADAM (Application of Detectors and Accelerators to Medicine), a CERN spin-off company, is developing the Linac for Image Guided Hadron Therapy, LIGHT, which will accelerate proton beams up to 230 MeV. The design of the linac will allow fast intensity and energy modulation for pencil-beam scanning during cancer treatment. The linac consists of a 40 keV Proton Injector; a 750 MHz Radio Frequency Quadrupole (RFQ) accelerating the proton beam up to 5 MeV; a 3 GHz Side Coupled Drift Tube Linac (SCDTL) up to 37.5 MeV; and a 3 GHz Cell Coupled Linac (CCL) section up to 230 MeV. A prototype of LIGHT is being commissioned progressively with the installation of the accelerating structures at a CERN site. The beam commissioning of the RFQ, which was designed and built by CERN, was completed in 2017 using a movable beam diagnostic test bench with various instruments. This paper reports on the RFQ commissioning strategy and the results of the beam measurements. INTRODUCTION LIGHT is a normal conducting 230 MeV medical proton linear accelerator being constructed by ADAM. The linac structures up to 70 MeV are being installed in the ADAM test facility, at a CERN site, and being commissioned progressively with the increasing beam energy [1, 2]. The first accelerating structure of the LIGHT prototype, a 750 MHz Radio Frequency Quadrupole (RFQ) [3-5], which was designed and produced by CERN, accelerates the proton beam from 40 keV to 5 MeV in only 2 meters. The RFQ is being used as an injector to the subsequent 3 GHz linac section which has strict input requirements in terms of transverse and longitudinal beam emittance. Therefore, it was crucial to determine the RF amplitude set point of the RFQ within the tolerances and measure the output beam properties to ensure high injection efficiency from 750 MHz to 3 GHz. MEASUREMENT SETUP Figure 1 shows the layout of the linac during the beam commissioning of the RFQ at 5 MeV. As it can be seen from the figure, the diagnostic test bench was installed downstream of the Medium Energy Beam Transport (MEBT) where the RFQ and MEBT could be commissioned together. The MEBT houses two permanent magnet quadrupoles, two steering magnets, a beam position monitor (BPM) and an AC beam current transformer. Along with the diagnostic devices on the movable test bench, the permanent diagnostics on the MEBT were also used for the beam commissioning. Figure 1: Layout of the LIGHT structures during the beam commissioning at 5 MeV. Figure 2 shows the movable diagnostic test bench [6] and its components used for the beam commissioning. Each diagnostic box (Dbox) has vertical and horizontal slits followed by a Faraday Cup (FC) for beam profile and beam current measurements. The two Dboxes can be used together for transverse emittance measurements. The spectrometer line of the bench can be used for average energy and energy spread measurements (together with the electromagnetic quadrupoles). In addition, on the straight section of the test bench there are two BPMs, and three phase probes for the time of flight (ToF) measurements. Figure 2: Diagnostic test bench with measurement instruments. RFQ INPUT BEAM AND SIMULATIONS The properties of the beam at the end of the Low Energy Beam Transport (LEBT) section was fully characterized during the source commissioning in 2016. The transverse emittance of the beam was measured 1 cm away ___________________________________________ † veliko.dimov@avo-adam.com 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-TUPAF002

Fundamental questions remain about the origin of newly formed atmospheric aerosol particles because data from laboratory measurements have been insufficient to build global models. In contrast, gas-phase chemistry models have been based on laboratory kinetics measurements for decades. We built a global model of aerosol formation by using extensive laboratory measurements of rates of nucleation involving sulfuric acid, ammonia, ions, and organic compounds conducted in the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber. The simulations and a comparison with atmospheric observations show that nearly all nucleation throughout the present-day atmosphere involves ammonia or biogenic organic compounds, in addition to sulfuric acid. A considerable fraction of nucleation involves ions, but the relatively weak dependence on ion concentrations indicates that for the processes studied, variations in cosmic ray intensity do not appreciably affect climate through nucleation in the present-day atmosphere.

In the frame of a new program for medical applications, CERN has designed and is presently constructing a compact 750 MHz Radio Frequency Quadrupole to be used as injector for hadron therapy linacs. The RFQ reaches an energy of 5 MeV in only 2 meters; it is divided into four standardized modules of 500 mm, each equipped with 12 tuner ports and one RF input. The inner quadrant radius is 46 mm and the RFQ has an outer diameter of 134 mm; its total weight is only 220 kg. The beam dynamics and RF design have been optimized for reduced length and minimum RF power consumption; conventional construction technologies have been adopted, to favour a future industrial production. The multiple RF ports are foreseen for using either 4 solidstate units or 4 IOT’s as RF power sources. Although hadron therapy requires only a low duty cycle, the RFQ has been designed for 5% duty cycle in view of other uses. This extremely compact and economical RFQ design opens several new perspectives for medical applications, in particular for PET isotopes production in hospitals with two coupled high-frequency RFQs reaching 10 MeV and for Technetium production for SPECT tomography with two RFQs followed by a DTL.

Quite often Monte Carlo simulation studies require a multi phase-space optimization, a complicated task, heavily relying on the operator experience and judgment. Examples of such calculations are shielding calculations with stringent conditions in the cost, in residual dose, material properties and space available, or in the medical field optimizing the dose delivered to a patient under a hadron treatment. The present paper describes our implementation inside flair[1] the advanced user interface of FLUKA[2,3] of a multi-objective Genetic Algorithm[Erreur ! Source du renvoi introuvable .] to facilitate the search for the optimum solution.

The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 26 m3 CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber at 20 and up to 210 L min−1, respectively. During steady-state calibration runs between −70 and +20 °C, the air temperature uniformity is better than ±0.06 °C in the radial direction and ±0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is ±0.04 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in temperature differences of ±1.5 °C in the vertical direction and ±1 °C in the horizontal direction, while the air returns to its equilibrium temperature with a time constant of about 200 s.