Showing papers on "Linear particle accelerator published in 2008"

RF linear accelerators

Abstract: 1. Introduction 2. RF Accelerator in Linacs 3. Periodic Accelerating Structures 4. Standard Linac Structures 5. Microwave Topics for Linacs 6. Longitudinal Particle Dynamics 7. Transverse Particle Dynamics 8. Radiofrequency Quadrupole Linac 9. Multiparticle Dynamics with Space Charge 10. Beam Loading 11. Wakefields 12. Special Linacs and Special Techniques 13. Superconducting Linacs

The 1.5 GeV harmonic double-sided microtron at Mainz University

Abstract: At the Institut fur Kernphysik of Mainz University a harmonic double-sided microtron (HDSM) has been built to extend the experimental capabilities for nuclear and particle physics experiments to higher excitation energies. This novel microtron variant accelerates the 0.855 GeV continuous wave (cw) electron beam of the established three-staged race track microtron (RTM) cascade MAMI B up to 1.5 GeV. It consists of two normal conducting linear accelerators (linacs) through which the electrons are guided up to 43 times by a pair of 90°-bending magnets at each end. For beam dynamical reasons the linacs operate at the harmonic frequencies of 4.90 and 2.45 GHz. The extended facility is called MAMI C. The relatively strong vertical defocussing due to the 45°-pole face rotations (Fig. 1) at both the entrance and exit of the segment-shaped bending magnets is compensated for all recirculations by a suitable field decay in the magnets towards higher orbits. As a consequence, the energy gain of the electrons has to decrease with increasing turn number to maintain coherent acceleration. This occurs by an appropriate phase slip of the electron bunches downwards the rf-waves during the acceleration process. In this paper the functional principle and the beam dynamical concept of the double-sided microtron (DSM) as well as the design and development of its main components are described. Finally, the results of first beam measurements taken after starting up in December 2006 are discussed.

Observations of microwave continuum emission from air shower plasmas

Abstract: We investigate a possible new technique for microwave detection of cosmic-ray extensive air showers which relies on detection of expected continuum radiation in the microwave range, caused by free-electron collisions with neutrals in the tenuous plasma left after the passage of the shower. We performed an initial experiment at the Argonne Wakefield Accelerator laboratory in 2003 and measured broadband microwave emission from air ionized via high-energy electrons and photons. A follow-up experiment at the Stanford Linear Accelerator Center in the summer of 2004 confirmed the major features of the previous Argonne Wakefield Accelerator observations with better precision. Prompted by these results we built a prototype detector using satellite television technology and have made measurements suggestive of the detection of cosmic-ray extensive air showers. The method, if confirmed by experiments now in progress, could provide a high-duty cycle complement to current nitrogen fluorescence observations.

Observation of Polarized Positrons from an Undulator-Based Source

Abstract: An experiment (E166) at the Stanford Linear Accelerator Center has demonstrated a scheme in which a multi-GeV electron beam passed through a helical undulator to generate multi-MeV, circularly polarized photons which were then converted in a thin target to produce positrons (and electrons) with longitudinal polarization above 80% at 6 MeV. The results are in agreement with GEANT4 simulations that include the dominant polarization-dependent interactions of electrons, positrons, and photons in matter.

Brightness enhancement method for a high-intensity positron beam produced by an electron accelerator

Abstract: A method for enhancing the brightness of an intense slow positron beam produced by an electron linear accelerator (LINAC) in order to obtain an intense positron microbeam was developed. The developed brightness enhancement system is simple and consists only of a few beam optics and a transmission remoderator. The slow positron beam produced by the LINAC is magnetically guided from the positron source to an experimental room. The beam is extracted from the magnetic field and is focused by a lens on the remoderator to enhance its brightness. The brightness-enhanced beam is extracted from the remoderator and focused on a sample by a lens. The beam size at the sample was 90 μm, which was two orders of magnitude smaller than that in the magnetic transport system that was about 10 mm. The efficiency of the transmission remoderator was about 5%. Adiabatic rules in the magnetic transport and the paraxial-ray equation were used to estimate the beam size that could be produced using this method.

Numerical study of a linear accelerator using laser-generated proton beams as a source

Abstract: The injection of laser-generated protons through conventional drift tube linear accelerators (linacs) has been studied numerically. For this, we used the parameters of the proton source produced by ultraintense lasers, i.e., with an intrinsic high beam quality. The numerical particle tracing code PARMELA [L. M. Young and J. H. Billen, LANL Report No. LA-UR-96-1835, 2004] is then used to inject experimentally measured laser-generated protons with energies of 7±0.1 MeV and rms un-normalized emittance of 0.180 mm mrad into one drift tube linac tank that accelerated them to more than 14 MeV. The simulations exhibit un-normalized emittance growths of 8 in x direction and 22.6 in y direction, with final emittances lower than those produced using conventional sources, allowing a potential luminosity gain for the final beam. However, the simulations also exhibit a limitation in the allowed injected proton charge as, over 0.112 mA, space charge effect worsens significantly the beam emittance.

Broadband single-shot electron spectrometer for GeV-class laser-plasma-based accelerators.

Abstract: Laser-plasma-based accelerators can provide electrons over a broad energy range and/or with large momentum spread. The electron beam energy distribution can be controlled via accurate control of laser and plasma properties, and beams with energies ranging from approximately 0.5 to 1000 MeV have been observed. Measuring these energy distributions in a single shot requires the use of a diagnostic with large momentum acceptance and, ideally, sufficient resolution to accurately measure narrow energy spread beams. Such a broadband single-shot electron magnetic spectrometer for GeV-class laser-plasma-based accelerators has been developed at Lawrence Berkeley National Laboratory. Detailed descriptions of the design concept and hardware are presented, as well as a performance evaluation of the spectrometer. The spectrometer covered electron beam energies raging from 0.01 to 1.1 GeV in a single shot, and enabled the simultaneous measurement of the laser properties at the exit of the accelerator through the use of a sufficiently large pole gap. Based on measured field maps and third-order transport analysis, a few percent-level resolution and determination of the absolute energy were achieved over the entire energy range. Laser-plasma-based accelerator experiments demonstrated the capability of the spectrometer as a diagnostic and its suitability for measuring broadband electron sources.

The free electron laser as a power source for a high‐gradient accelerating structure

Abstract: A two beam colliding linac accelerator is proposed in which one beam is intense (≊1kA), of low energy (≊MeV), and long (≊100 ns) and provides power at 1 cm wavelength through a free‐electron‐laser‐mechanism to the second beam of a few electrons (≊1011), which gain energy at the rate of 250 MeV/m in a high‐gradient accelerating structure and hence reach 375 GeV in 1.5 km. The intense beam is given energy in induction units and gains, and looses by radiation, 250 keV/m thus supplying 25 J/m to the accelerating structure. The luminosity, L, of two such linacs would be, at a repetition rate of 1 kHz, L=4. ×1032cm−2 s−1.

Efficiency of respiratory-gated delivery of synchrotron-based pulsed proton irradiation.

Abstract: Significant differences exist in respiratory-gated proton beam delivery with a synchrotron-based accelerator system when compared to photon therapy with a conventional linear accelerator. Delivery of protons with a synchrotron accelerator is governed by a magnet excitation cycle pattern. Optimal synchronization of the magnet excitation cycle pattern with the respiratory motion pattern is critical to the efficiency of respiratory-gated proton delivery. There has been little systematic analysis to optimize the accelerator's operational parameters to improve gated treatment efficiency. The goal of this study was to estimate the overall efficiency of respiratory-gated synchrotron-based proton irradiation through realistic simulation. Using 62 respiratory motion traces from 38 patients, we simulated respiratory gating for duty cycles of 30%, 20% and 10% around peak exhalation for various fixed and variable magnet excitation patterns. In each case, the time required to deliver 100 monitor units in both non-gated and gated irradiation scenarios was determined. Based on results from this study, the minimum time required to deliver 100 MU was 1.1 min for non-gated irradiation. For respiratory-gated delivery at a 30% duty cycle around peak exhalation, corresponding average delivery times were typically three times longer with a fixed magnet excitation cycle pattern. However, when a variable excitation cycle was allowed in synchrony with the patient's respiratory cycle, the treatment time only doubled. Thus, respiratory-gated delivery of synchrotron-based pulsed proton irradiation is feasible and more efficient when a variable magnet excitation cycle pattern is used.

Monte Carlo study on a flattening filter-free 18-MV photon beam of a medical linear accelerator

Abstract: Purpose Several studies on the dosimetric properties of unflattened photon beams have shown some advantages for radiotherapy. In this study, the effect of removing the flattening filter from an 18-MV photon beam was investigated using the Monte Carlo method.

An overview on TRIUMF’s developments on ion source for radioactive beams (invited)a)

Abstract: The ISAC facility at TRIUMF utilizes up to 100μA from the 500MeV H− cyclotron to produce the radioactive ion beam (RIB) using the isotopic separation on line method. The ISAC-I facility comprised the RIB production target stations, the mass separator, and the beam delivery to low energy area and to a room temperature linear accelerator composed of a four-rod radio frequency quadrupole and an interdigital H-type structure drift tube LINAC. ISAC-I linear accelerator can provide beam from A=3to30amu with an energy range from 0.15to1.5AMeV. Since the beginning of operations target development program has been to increase proton beam currents on targets. Now we routinely operate our target at 50–85μA and recently we have operated our target at 100μA. Other developments are in place to add other ion sources, laser, force electron beam induced are discharge and electron cyclotron resonance ion source to the actual surface ion source. The last two five year plans were mainly devoted to the construction of a heavy...

Rotational total skin electron irradiation with a linear accelerator

Abstract: The rotational total skin electron irradiation (RTSEI) technique at our institution has undergone several developments over the past few years. Replacement of the formerly used linear accelerator has prompted many modifications to the previously reported technique. With the current technique, the patient is treated with a single large field while standing on a rotating platform, at a source to surface distance of 380 cm. The electron field is produced by a Varian 21EX linear accelerator using the commercially available 6 MeV high dose rate total skin electron mode, along with a custom-built flattening filter. Ionization chambers, radiochromic film, and MOSFET detectors have been used to determine the dosimetric properties of this technique. Measurements investigating the stationary beam properties, the effects of full rotation and the dose distributions to a humanoid phantom are reported. The current treatment technique and dose regimen are also described.

Observation of Coherent Optical Transition Radiation in the LCLS Linac

Abstract: The beam diagnostics in the linac for the Linac Coherent Light Source (LCLS) X-ray FEL project at SLAC includes optical transition radiation (OTR) screens for measurements of transverse and longitudinal beam properties. We report on observations of coherent light emission from the OTR screens (COTR) at visible wavelengths from the uncompressed and compressed electron beam at various stages in the accelerator.

Measurement of Two-Dimensional Photon Beam Distributions Using a Fiber-Optic Radiation Sensor for Small Field Radiation Therapy

Abstract: In this study, we fabricated a fiber-optic radiation sensor with an organic scintillator to measure the high-energy photon beam from a clinical linear accelerator, and a two-dimensional fiber-optic sensor array to measure high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light-measuring device. Two-dimensional photon beam distributions in a water phantom were measured for photon beams with different energies and field sizes. Also, percent depth dose curves for 6 and 15 MV photon beams were obtained.

Spatial resolution limits for synchrotron-based spectromicroscopy in the mid- and near-infrared.

Abstract: Spatial resolution tests were performed on beamline 1.4.4 at the Advanced Light Source in Berkeley, CA, USA, a third-generation synchrotron light source. This beamline couples the high-brightness synchrotron source to a Thermo-Electron Continumum XL infrared microscope. Two types of resolution tests were performed in both the mid-IR and near-IR. The results are compared with a diffraction-limited spot size theory. At shorter near-IR wavelengths the experimental results begin to deviate from diffraction-limited so a combined diffraction-limit and electron-beam-source-size model is employed. This description shows how the physical electron beam size of the synchrotron source begins to dominate the focused spot size at higher energies. The transition from diffraction-limited to electron-beam-size-limited performance is a function of storage-ring parameters and the optical demagnification within the beamline and microscope optics. The discussion includes how different facilities, beamlines and microscopes will affect the achievable spatial resolution. As synchrotron light sources and other next-generation accelerators such as energy-recovery LINACs and free-electron lasers achieve smaller beam emittances, beta-functions and/or energy spreads, diffraction-limited performance can continue to higher-energy beams, perhaps ultimately into the extreme ultraviolet.

Measurement of the neutron leakage from a dedicated intraoperative radiation therapy electron linear accelerator and a conventional linear accelerator for 9, 12, 15(16), and 18(20) MeV electron energies

Abstract: The issue of neutron leakage has recently been raised in connection with dedicated electron-only linear accelerators used for intraoperative radiation therapy (IORT) In particular, concern has been expressed about the degree of neutron production at energies of 10 MeV and higher due to the need for additional, perhaps permanent, shielding in the room in which the device is operated In particular, three mobile linear accelerators available commercially offer electron energies at or above the neutron threshold, one at 9 MeV, one at 10 MeV, and the third at 12 MeV To investigate this problem, neutron leakage has been measured around the head of two types of electron accelerators at a distance of 1 m from the target at azimuthal angles of 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees The first is a dedicated electron-only (nonmobile) machine with electron energies of 6 (not used here), 9, 12, 15, and 18 MeV and the second a conventional machine with electron energies of 6 (also not used here), 9, 12, 16, and 20 MeV Measurements were made using neutron bubble detectors and track-etch detectors For electron beams from a conventional accelerator, the neutron leakage in the forward direction in Sv/Gy is 21 x 10(-5) at 12 MeV, 13 x 10(-4) at 16 MeV, and 42 x 10(-4) at 20 MeV, assuming a quality factor (RBE) of 10 For azimuthal angles > 0 degrees, the leakage is almost angle independent [2 x 10(-6) at 12 MeV; (07-16) x 10(-5) at 16 MeV, and (16-29) x 10(-5) at 20 MeV] For the electron-only machine, the neutron leakage was lower than for the conventional linac, but also independent of azimuthal angle for angles > 0 degrees: {[0 degrees: 77 x 10(-6) at 12 MeV; 30 x 10(-5) at 15 MeV; 10 x 10(-4) at 18 MeV]; [other angles: (26-59) x 10(-7) at 12 MeV; (14-22) x 10(-6) at 15 MeV; (27-47) x 10(-6) at 18 MeV]} Using the upper limit of 6 x 10(-7) Sv/Gy at 12 MeV for the IORT machine for azimuthal angles > 0 degrees and assuming a workload of 200 Gy/wk and an inverse square factor of 10, the neutron dose equivalent is calculated to be 0012 mSv/wk For the primary beam at 12 MeV (0 degrees), the 10 x higher dose would be compensated by the attenuation of a primary beam stopper in a mobile linear accelerator These neutron radiation levels are below regulatory values (National Council on Radiation Protection and Measurements, "Limitation of exposure to ionizing radiation," NCRP Report No 116, NCRP Bethesda, MD, 1993)

Dynamic compensation of an rf cavity failure in a superconducting linac

Abstract: An accelerator driven system (ADS) for transmutation of nuclear waste typically requires a 600 MeV--1 GeV accelerator delivering a proton flux of a few mA for demonstrators, and of a few tens of mA for large industrial systems. Such a machine belongs to the category of the high-power proton accelerators, with an additional requirement for exceptional ``reliability'': because of the induced thermal stress to the subcritical core, the number of unwanted ``beam trips'' should not exceed a few per year, a specification that is several orders of magnitude above usual performance. In order to meet this extremely high reliability, the accelerator needs to implement, to the maximum possible extent, a fault-tolerance strategy that would allow beam operation in the presence of most of the envisaged faults that could occur in its beam line components, and in particular rf systems' failures. This document describes the results of the simulations performed for the analysis of the fault-tolerance capability of the XT-ADS superconducting linac in the case of an rf cavity failure. A new simulation tool, mixing transient rf behavior of the accelerating cavities with full 6D description of the beam dynamics, has been developed for this purpose. Fast fault-recovery scenarios are proposed, and required research and development is identified.

About the production rates and the activation of the uranium carbide target for SPIRAL 2

Abstract: In the near future, the accelerator and experimental facilities at GANIL (Caen/France) will be extended by a new facility called SPIRAL2. It will be based on a superconducting linear accelerator which will deliver a 40-MeV deuteron beam (5 mA; 200 kW). These accelerated particles will produce a very high neutron flux with a fast spectrum (most probable neutrons energy is about 14 MeV with an extension to 40 MeV). With the neutron-induced fission of the natural uranium, intense beams of neutron-rich nuclei will be created and will become available at SPIRAL2. In this work, done with the support of SAFERIB and EURONS, we present the results of the modelling of the uranium carbide target. The modelling was mainly done with the code MCNPX26B. The target is theoretically optimised to produce a global fission rate greater than 5 × 1013 fissions s−1. In fact, the optimised target, of 2.3 kg of carbide uranium, has a calculated fission rate closer to about 6 × 1013 fissions s−1.

Femtosecond electron bunches, source and characterization

Abstract: A femtosecond electron source has been developed at the Fast Neutron Research Facility (FNRF), Chiang Mai University, Thailand. So far, it has produced electron bunches as short as σ z ∼180 fs with (1–6)×10 8 electrons per microbunch. The system consists of an RF-gun with a thermionic cathode, an alpha-magnet as a magnetic bunch compressor, and a linear accelerator as a post acceleration section. Coherent transition radiation emitted at wavelengths equal to and longer than the bunch length is used in a Michelson interferometer to determine the bunch length by autocorrelation technique. The experimental setup and results of the bunch length measurement are described.

Measurement of Electron Clouds in Large Accelerators by Microwave Dispersion

Abstract: Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.

Initial performance of a high gain, high efficiency 17 GHz traveling wave relativistic klystron for high gradient accelerator research

Abstract: We present the initial test results of a new RF source developed for high peak power 17 GHz linear accelerator applications. The immediate objective of this program was to provide a working prototype tube having a peak power output in the range of 20 to 30 MW, a saturated gain of between 60 and 70 dB, and an RF conversion efficiency of approximately 50%. The prototype tube and associated beam focusing elements were designed to match the 580 kV, 110 A, 1 μs pulse characteristics of an existing electron source at the MIT Plasma Fusion Center.

A high-brightness SRF photoelectron injector for FEL light sources

Abstract: Most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources require electron beams with an unprecedented combination of high brightness, low emittance, and high average current. In all projects photoguns will be applied: DC-photoguns, normal conducting RF-photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF-gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high average power into the gun, and, finally, the risk of beam excitation of higher-order cavity modes. In combination with SRF linacs, the SRF-guns seem to be the best solution for high average currents. Several R&D projects of SRF-gun have been launched. In this paper, we will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, the performance and the status of the Dresden Rossendorf SRF-gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. The main design parameters of this SRF-gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three TESLA-shaped cells, a specially designed half-cell where the photocathode is placed and a choke filter in order to prevent RF losses at the cathode side. The normal-conducting photocathode with a Cs2Te photoemission layer is cooled by liquid nitrogen. The SRF-gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen-cooled thermal shield and a titanium He tank with a two-phase supply tube. The 10 kW fundamental power coupler is adopted from the ELBE cryomodule. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF-gun. In a final step, the gun will be connected to the ELBE superconducting linear accelerator to deliver an improved electron beam to the user labs.

End-to-end absolute energy calibration of atmospheric fluorescence telescopes by an electron linear accelerator

Abstract: The Telescope Array (TA) is a hybrid detector composed of atmospheric fluorescence telescopes and a ground array of particle detectors for the precise energy measurement of ultra high-energy cosmic rays. We propose an end-to-end absolute energy calibration of fluorescence telescopes by using air showers induced by electron beams from a linear accelerator, which will be installed at the site of the TA experiment and will have a well-measured beam energy. We have simulated electron beam dynamics and interaction of electrons in air to evaluate the accuracy of the beam energy determination, beam currents, air showers, and detector response using a beam simulation code (PARMELA) and GEANT4. We found that the systematic error of energy measurement estimated for the TA fluorescence telescopes can be reduced from 23% to 17% by this end-to-end energy calibration. We are developing and constructing a compact linear accelerator with a maximum electron energy of 40 MeV and an intensity of 6.4 mJ/pulse. In this article, we describe the method of absolute energy calibration and the design of the accelerator.

Measurements of the photonuclear neutron yield of 15 MV medical linear accelerator

Abstract: High energy medical linear accelerators (>10 MV) are increasingly used in radiotherapy. At such high photon energies neutron production via photonuclear reactions in the heavy elements which compose the linac head is inevitable. Neutrons from linacs can contribute to an additional dose to staff, patients and the general public. Our intention is two-fold; to provide shielding against the neutron contamination and to establish the depthdose curve of thermal neutrons within human tissue, with an aim to utilise linacs in boron neuron capture therapy (BNCT). In our studies neutron measurements were undertaken, with a Varian Clinac 2100C/D linear accelerator operating at 15 MV nominal energy, by irradiating 18 cm thick 30×30 cm2 block of tissue equivalent material. Measurements were taken using indium and aluminum activation foil at the centre of the block. Our results show that by leaving the linac jaws open neutron production is increased compared to the case when these are shut, for one minute exposure at 400MU. In this work we present a comparison between our results and existing literature and attempt to explore some sharp contrasts.

Source of polarised deuterons - (JINR accelerator complex)

Abstract: The proposed project assumes the development of a universal high-intensity source of polarized deuterons (protons) using a charge-exchange plasma ionizer. The design output current of the source will be up to 10mA for ↑ D+(↑ H+) and polarization will be up to 90% of the maximal vector (±1) and tensor (+1,−2) polarization. The project is based on the equipment which was supplied within the framework of an agreement between JINR and IUCF (Bloomington, USA). The project will be realized in close cooperation with INR (Moscow, Russia). The source will be installed in the linac hall (LU-20) and polarization of beams will be measured at the output of LU-20. The main purpose of the project is to increase the intensity of the accelerated polarized beams at the JINR Accelerator Complex up to 1010 d/pulse. Calculations and first accelerator runs have shown that the depolarization resonances are absent for the deuteron beam in the entire energy range of the NUCLOTRON. The source could be transformed into a source of polarized negative ions if necessary. The period of reliable operation without participation of the personnel should be within 1000 hours. The project should be implemented within two to two and a half years from the start of funding.

Potential Uses of ERL-Based $\gamma$ -Ray Sources

Abstract: We expand upon the idea of using gamma-rays for nuclear photoflssion of 238U at the giant dipole resonance to generate rare neutron-reach nuclei. The SPIRAL II project proposes the employment of 10-20-MeV Bremsstrahlung gamma-rays generated by a 45-MeV electron beam /http://ganinfo.in2p3.fr/research/ developments/ spiral2/ index.html/. In this paper, we explore the possibility of using a Compton gamma-ray source for such a process. The Collider Accelerator Department at Brookhaven National Laboratory is developing high-current (up to 1 A), high-brightness (down to 1-mm ldr mrad normalized emittance), and high-energy energy-recovery linacs (up to 20-GeV electron beam energy for eRHIC). These electron beams are perfectly suited for generating photon beams with tremendous average power, approaching the megawatt level. The range of photon's energy extends from subelectronvolts from free-electron lasers to 10 GeV from the Compton process. In this paper, we focus on a gamma-ray source for producing rare isotopes.

The Radiofrequency Quadrupole Accelerator for the Linac4

Abstract: The first stage of acceleration in Linac4, the new 160 MeV CERN H injector, is a 352 MHz, 3-m long Radiofrequency Quadrupole (RFQ) Accelerator. The RFQ will capture a 70 mA, 45 keV beam from the RF source and accelerate it to 3 MeV, an energy suitable for chopping and injecting the beam in a conventional Drift Tube Linac. Although the RFQ will be initially operated at low duty cycle (0.1%), its design is compatible with higher duty cycle (10%) as the front-end for a possible high-intensity upgrade of the CERN linac facility. The RFQ will be of brazed-copper construction and will be built and assembled at CERN. Beam dynamics design allows for a compact structure made of a single resonant unit. Field symmetry is ensured by fixed tuners placed along the structure. In this paper we present the RF and mechanical design, the beam dynamics and the sensitivity to fabrication and to RF errors.