Showing papers on "Linear particle accelerator published in 2018"

High dose-per-pulse electron beam dosimetry: Commissioning of the Oriatron eRT6 prototype linear accelerator for preclinical use.

Abstract: The Oriatron eRT6 is an experimental high dose-per-pulse linear accelerator (linac) which was designed to deliver an electron beam with variable dose-rates, ranging from a few Gy/min up to hundreds of Gy/s. It was built to study the radiobiological effects of high dose-per-pulse/dose-rate electron beam irradiation, in the context of preclinical and cognitive studies. In this work, we report on the commissioning and beam monitoring of the Oriatron eRT6 prototype linac. The beam was characterized in different steps. The output stability was studied by performing repeated measurements over a period of 20 months. The relative output variations caused by changing beam parameters, such as the temporal electron pulse width, the pulse repetition frequency and the pulse amplitude were also analyzed. Finally, depth dose curves and field sizes were measured for two different beam settings, resulting in one beam with a conventional radiotherapy dose-rate and one with a much higher dose-rate. Measurements were performed with Gafchromic EBT3 films and with a PTW Advanced Markus ionization chamber. In addition, we developed a beam current monitoring system based on the signals from an induction torus positioned at the beam exit of the waveguide and from a graphite beam collimator. The stability of the output over repeated measurements was found to be good, with a standard deviation smaller than 1%. However, non-negligible day-to-day variations of the beam output were observed. Those output variations showed different trends depending on the dose-rate. The analysis of the relative output variation as a function of various beam parameters showed that in a given configuration, the dose-rate could be reliably varied over three orders of magnitude. Interdependence effects on the output variation between the parameters were also observed. The beam energy and field size were found to be slightly dose-rate-dependent and suitable mainly for small animal irradiation. The beam monitoring system was able to measure in a reproducible way the total charge of electrons that exit the machine, as long as the electron pulse amplitude remains above a given threshold. Furthermore, we were able to relate the charge measured with the monitoring system to the absorbed dose in a solid water phantom. The Oriatron eRT6 was successfully commissioned for preclinical use and is currently in full operation, with studies being performed on the radiobiological effects of high dose-per-pulse irradiation.

Plasma wakefield acceleration experiments at FACET II

Abstract: During the past two decades of research, the ultra-relativistic beam-driven plasma wakefield accelerator (PWFA) concept has achieved many significant milestones. These include the demonstration of ultra-high gradient acceleration of electrons over meter-scale plasma accelerator structures, efficient acceleration of a narrow energy spread electron bunch at high-gradients, positron acceleration using wakes in uniform plasmas and in hollow plasma channels, and demonstrating that highly nonlinear wakes in the 'blow-out regime' have the electric field structure necessary for preserving the emittance of the accelerating bunch. A new 10 GeV electron beam facility, Facilities for Accelerator Science and Experimental Test (FACET) II, is currently under construction at SLAC National Accelerator Laboratory for the next generation of PWFA research and development. The FACET II beams will enable the simultaneous demonstration of substantial energy gain of a small emittance electron bunch while demonstrating an efficient transfer of energy from the drive to the trailing bunch. In this paper we first describe the capabilities of the FACET II facility. We then describe a series of PWFA experiments supported by numerical and particle-in-cell simulations designed to demonstrate plasma wake generation where the drive beam is nearly depleted of its energy, high efficiency acceleration of the trailing bunch while doubling its energy and ultimately, quantifying the emittance growth in a single stage of a PWFA that has optimally designed matching sections. We then briefly discuss other FACET II plasma-based experiments including in situ positron generation and acceleration, and several schemes that are promising for generating sub-micron emittance bunches that will ultimately be needed for both an early application of a PWFA and for a plasma-based future linear collider.

A soft X‐ray free‐electron laser beamline at SACLA: the light source, photon beamline and experimental station

Abstract: The design and performance of a soft X-ray free-electron laser (FEL) beamline of the SPring-8 Compact free-electron LAser (SACLA) are described. The SPring-8 Compact SASE Source test accelerator, a prototype machine of SACLA, was relocated to the SACLA undulator hall for dedicated use for the soft X-ray FEL beamline. Since the accelerator is operated independently of the SACLA main linac that drives the two hard X-ray beamlines, it is possible to produce both soft and hard X-ray FEL simultaneously. The FEL pulse energy reached 110 µJ at a wavelength of 12.4 nm (i.e. photon energy of 100 eV) with an electron beam energy of 780 MeV.

Positron annihilation lifetime and Doppler broadening spectroscopy at the ELBE facility

Abstract: The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA with bunch charges up to 120 pC. The electron beam is employed to produce several secondary beams including X-rays from bremsstrahlung production, coherent IR light in a Free Electron Laser, superradiant THz radiation, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films. Bulk materials, fluids, gases, and even radioactive samples can be studied at the unique Gamma-induced Positron Source (GiPS) where an intense bremsstrahlung source generates positrons directly inside the material under study. A 22Na-based monoenergetic positron beam serves for offline experiments and additional depth-resolved Doppler-broadening studies complementing both accelerator-based sources.

RF Properties of Periodic Accelerating Structures for Linear Colliders

Abstract: With the advent of the SLAC electron-positron linear collider (SLC) in the 100 GeV center-of-mass energy range, research and development work on even higher energy machines of this type has started in several laboratories in the United States, Europe, the Soviet Union and Japan. These linear colliders appear to provide the only promising approach to studying e/sup /plus//e/sup /minus// physics at center-of-mass energies approaching 1 TeV. This thesis concerns itself with the study of radio frequency properties of periodic accelerating structures for linear colliders and their interaction with bunched beams. The topics that have been investigated are: experimental measurements of the energy loss of single bunches to longitudinal modes in two types of structures, using an equivalent signal on a coaxial wire to simulate the beam; a method of canceling the energy spread created within a single bunch by longitudinal wakefields, through appropriate shaping of the longitudinal charge distribution of the bunch; derivation of the complete transient beam-loading equation for a train of bunches passing through a constant-gradient accelerator section, with application to the calculation and minimization of multi-bunch energy spread; detailed study of field emission and radio frequency breakdown in disk-loaded structures at S-, C- and X-band frequencies under more » extremely high-gradient conditions, with special attention to thermal effects, radiation, sparking, emission of gases, surface damage through explosive emission and its possible control through RF-gas processing. 53 refs., 49 figs., 9 tabs. « less

First heavy ion beam tests with a superconducting multigap CH cavity

Abstract: Very compact accelerating-focusing structures, as well as short focusing periods, high accelerating gradients and short drift spaces are strongly required for superconducting (sc) accelerator sections operating at low and medium energies for continuous wave (cw) heavy ion beams. To keep the GSI-super heavy element (SHE) program competitive on a high level and even beyond, a standalone sc cw linac (Helmholtz linear accelerator) in combination with the GSI high charge state injector (HLI), upgraded for cw operation, is envisaged. Recently the first linac section (financed by Helmholtz Institute Mainz (HIM) and GSI) as a demonstration of the capability of 217 MHz multigap crossbar H-mode structures (CH) has been commissioned and extensively tested with heavy ion beam from the HLI. The demonstrator setup reached acceleration of heavy ions up to the design beam energy. The required acceleration gain was achieved with heavy ion beams even above the design mass to charge ratio at high beam intensity and full beam transmission. This paper presents systematic beam measurements with varying rf amplitudes and phases of the CH cavity, as well as phase space measurements for heavy ion beams with different mass to charge ratio. The worldwide first and successful beam test with a superconducting multigap CH cavity is a milestone of the R work of HIM and GSI in collaboration with IAP in preparation of the HELIAC project and other cw-ion beam applications.

Bremsstrahlung hard x-ray source driven by an electron beam from a self-modulated laser wakefield accelerator

Abstract: An x-ray source generated by an electron beam produced using a Self-Modulated Laser Wakefield Accelerator (SM-LWFA) is explored for use in high energy density science facilities. By colliding the electron beam, with a maximum energy of 380MeV, total charge of >10 nC and a divergence of 64× 100 mrad, from a SM-LWFA driven by a 1 ps 120 J laser, into a high-Z foil, an x/gamma-ray source was generated. A broadband bremsstrahlung energy spectrum with temperatures ranging from 0.8 to 2MeV was measured with an almost 2 orders of magnitude flux increase when compared with other schemes using LWFA. GEANT4 simulations were done to calculate the source size and divergence.

Industrialization of the nitrogen-doping preparation for SRF cavities for LCLS-II

Abstract: The Linac Coherent Light Source II (LCLS-II) is a new state-of-the-art coherent X-ray source being constructed at SLAC National Accelerator Laboratory. It employs 280 superconducting radio frequency (SRF) cavities in order operate in continuous wave (CW) mode. To reduce the overall cryogenic cost of such a large accelerator, nitrogen-doping of the SRF cavities is being used. Nitrogen-doping has consistently been shown to increase the efficiency of SRF cavities operating in the 2.0 K regime and at medium fields (15–20 MV/m) in vertical cavity tests and horizontal cryomodule tests. While nitrogen-doping’s efficacy for improvement of cavity performance was demonstrated at three independent labs, Fermilab, Jefferson Lab, and Cornell University, transfer of the technology to industry for LCLS-II production was not without challenges. Here we present results from the beginning of LCLS-II cavity production. We discuss qualification of the cavity vendors and the first cavities from each vendor. Finally, we demonstrate that nitrogen-doping has been successfully transferred to SRF cavity vendors, resulting in consistent production of cavities with better cryogenic efficiency than has ever been achieved for a large-scale accelerator.

Development of Carbon-Ion Radiotherapy Facilities at NIRS

Abstract: Radiotherapy using high-energy carbon beams from the Heavy Ion Medical Accelerator in Chiba has been carried out at the National Institute of Radiological Sciences (NIRS) since June 1994, and more than 10 000 patients have been treated to date. With the prospective clinical results for the first ten years, we designed a compact accelerator facility for carbon-ion radiotherapy (CIRT), and performed related Research and Development (RD two of them have both horizontal and vertical fixed-irradiation-ports, and the other is a rotating-gantry port. For all ports, fast three-dimensional raster-scanning irradiation technology is employed. The rotating gantry equips ten combined-function superconducting magnets, and can deliver carbon ions having the energy of between E = 430 and 50 MeV/ u to an isocenter with irradiation angles of over ±180°. Construction as well as installation of the superconducting gantry was completed by the end of September 2015, and treatments using the gantry began since May 2015. Presently, we are further designing a next-generation compact facility as a future project; superconducting and laser technologies are to be used for accelerator design. In this paper, we report development of carbon-ion accelerator facilities as well as the future project.

TES X-ray Spectrometer at SLAC LCLS-II

Abstract: We are building a transition edge sensor (TES) X-ray spectrometer for the Linac Coherent Light Source (LCLS-II) at SLAC National Accelerator Laboratory (SLAC) to coincide with new upgrades for this free electron laser facility. This new X-ray spectrometer will have 1000 TES pixels with 0.5 eV energy resolution for soft X-rays below 1 keV. Multiplexing will be done with microwave SQUID resonators and new specialized electronic hardware developed at SLAC. This spectrometer will use a dilution refrigerator to achieve lower operating temperatures than previous TES spectrometers and will be coupled to the liquid jet endstation at LCLS-II. The spectrometer is designed to operate at much higher count rates than previous TES X-ray spectrometers to take advantage of the high repetition rate of the LCLS-II. Science applications will utilize the high photon collection efficiency and throughput, high energy resolution, as well as its ability to simultaneously measure its full calibrated energy range.

FemtoMAX – an X-ray beamline for structural dynamics at the short-pulse facility of MAX IV

Abstract: The FemtoMAX beamline facilitates studies of the structural dynamics of materials. Such studies are of fundamental importance for key scientific problems related to programming materials using light, enabling new storage media and new manufacturing techniques, obtaining sustainable energy by mimicking photosynthesis, and gleaning insights into chemical and biological functional dynamics. The FemtoMAX beamline utilizes the MAX IV linear accelerator as an electron source. The photon bursts have a pulse length of 100 fs, which is on the timescale of molecular vibrations, and have wavelengths matching interatomic distances (A). The uniqueness of the beamline has called for special beamline components. This paper presents the beamline design including ultrasensitive X-ray beam-position monitors based on thin Ce:YAG screens, efficient harmonic separators and novel timing tools.

Characterization and Optimization of the Photoneutron Flux Emitted by a 6- or 9-MeV Electron Accelerator for Neutron Interrogation Measurements

Abstract: Active neutron interrogation is a nondestructive active method that consists in inducing fission reactions on actinides (e.g., 235U and 239Pu) and then in detecting prompt and delayed particles emitted further to these reactions. This method is required in various application fields such as radiological characterization of nuclear waste packages and homeland security. Neutron sources traditionally used in neutron interrogation facilities are deuterium–tritium neutron generators. However, a linear electron accelerator (LINAC) can also be used as a photoneutron generator. When accelerating electrons with energy lower than 10 MeV, the use of a secondary target such as heavy water is of interest to convert bremsstrahlung photons to neutrons and to improve neutron production. In this paper, we characterize the photoneutron flux emitted by a Linatron-M9 VARIAN LINAC and the photoneutron flux emitted by a secondary target made of heavy water. We show that operating the LINAC at 9 MeV, the average emission intensity reaches $1.08 \times 10^{10}$ neutrons per second, which is on the order of $10{\times}$ higher than the maximum average emission intensity delivered by a traditional deuterium–tritium neutron generator. Then, we carry out neutron interrogation measurements on uranium samples using the Linatron-M9 LINAC and a secondary target made of different volumes of heavy water. We show that prompt neutron signals were enhanced when using 16 kg of heavy water and operating the LINAC at 9 MeV. Performances of the setup were then assessed by carrying out measurements on a mockup of nuclear waste drum containing different types of matrices. Considering a 0.22-g/cm3 iron matrix and a uranium sample at the center of the drum, 44 mg of 235U can be detected in 5 min of irradiation time using a single detection block housing five 150NH100 3He detectors.

H− extraction systems for CERN’s Linac4 H− ion source

Abstract: Linac4 is a 160 MeV linear H − accelerator at CERN. It is an essential part of the beam luminosity upgrade of the Large Hadron Collider (LHC) and will be the primary injector into the chain of circular accelerators. It aims at increasing the beam brightness by a factor of 2, when compared to the currently used 50 MeV linear proton accelerator, Linac2. Linac4’s ion source is a cesiated RF-plasma H − ion source. Several beam extraction systems were designed for H − beams of 45 keV energy, 50 mA intensity and an electron to H − ratio smaller than 5. The goal was to extract a beam with an rms-emittance of 0 . 25 π mm mrad. One of the main challenges in designing an H − extraction system is dumping of the co-extracted electrons. Separating the electrons from the negative ions as early as possible reduces space-charge induced emittance-growth. However, a strong magnetic field close to the extraction might cause unnecessary strong deflection in a region of low beam energy. For this purpose a novel magnetic configuration was designed using a magnetic shield between the magnetic fields of the source and the electron dump, which conserves the filter field strength to keep the electron to H − ratio low and effectively dumps the co-extracted electrons. Magnetic configuration and beam trajectories were calculated using the TOSCA Opera 3D code and IBSimu, respectively. Three extraction systems will be discussed in terms of electron dumping efficiency, emittance and transport through the extraction system and LEBT to the RFQ and compared to the simulations. An improved emittance conservation through the extraction system and LEBT is predicted and further design improvements are proposed. Measurements show that the novel electron dump successfully traps the co-extracted electrons.

Design of a 5 GeV Laser Plasma Accelerating Module in the Quasi-linear Regime

Abstract: Multi-GeV-class laser–plasma accelerating modules are key components of laser–plasma accelerators, because they can be used as a booster of an upstream plasma or conventional injector or as modular acceleration sections of a multi-staged high energy plasma linac. Such a plasma module, operating in the quasi-linear regime, has been designed for the 5 GeV laser–plasma accelerator stage (LPAS) of the EuPRAXIA project. The laser pulse ( ∼ 150 TW, ∼ 15 J) is quasi-matched into a plasma channel ( n p = 1 . 5 × 1 0 17 cm−3, L ∼ 30 cm) and the bi-Gaussian electron beam is externally injected into the wakefield. The beam emittance is preserved through the acceleration by matching the beam size to the transverse focusing fields. And a final energy spread of 1% has been achieved by optimizing the beam loading effect. Several methods have been proposed to reduce the slice energy spread and are found to be effective. The simulations were conducted with the 3D PIC code Warp in the Lorentz boosted frame.

Characterization of a Novel Revolving Radiation Collimator.

Abstract: Introduction The ZAP-X is a novel self-contained and first-of-its-kind self-shielded therapeutic radiation device dedicated to brain and head and neck radiosurgery By utilizing a 27-MV linear accelerator and incorporating a design in which a beam stop and major mechanical elements serve a radiation shielding function, the Zap-X does not typically require a radiation bunker The unique collimator design of the Zap-X is especially critical to the performance of the overall system The collimator consists of a shielded tungsten wheel oriented with its rotational axis perpendicular to the beam's central axis; the goal of this design is to minimize radiation leakage Beam selection is accomplished by rotating the wheel within its tungsten-shielded housing We investigated radiation leakage from the Zap-X collimator to determine its compliance with internationally accepted standards using direct radiation measurements Materials and methods To measure collimator leakage in the plane of the patient, equidistant measurement stations were defined in a plane perpendicular to the central beam axis (cax) 1 m from this axis (1 m from the radiation focal spot) To measure leakage alongside and adjacent to the accelerator, equidistant measurement stations were located 1 m from the cax along a line parallel to the cax in the plane of the collimator wheel and along a line parallel to the cax 90 degrees offset from the first line of stations Results Radiation leakage emanating from the collimating head of the linear accelerator in the patient plane ranged between 40 and 104 mR Radiation along the linear accelerator (1000 R delivered in the primary beam) varied between 17 and 68 mR and constituted between 000017% to 000068% of the primary beam The former radiation originated from X-ray target leakage, while the latter is produced directly by the linear accelerator and both contributed to the overall leakage radiation that would reach a patient Discussion Due to the large diameter of the Zap-X tungsten collimator wheel and the massive Zap-X tungsten cylindrical collimator shield, the overall patient leakage is 000104% of the primary beam at a 1-m distance from the beam central axis in the patient plane Leakage radiation in the patient plane is limited by the International Electrotechnical Commission (IEC) to 01% of the total primary radiation Radiation leakage along the linear accelerator and the collimator housing was determined to be 000068% of primary radiation intensity This leakage value is lower than the 01% leakage limit stipulated by IEC by more than a factor of 100 Conclusions Typically, an MV radiation therapy system minimizes exposure by utilizing a combination of device and structural shielding However, the Zap-X has been uniquely designed to minimize the need for structural shielding Our results indicate radiation leakage from the collimator meets internationally accepted standards as defined by the IEC

First muon acceleration using a radio-frequency accelerator

Abstract: Muons have been accelerated by using a radio frequency accelerator for the first time. Negative muonium atoms (Mu$^-$), which are bound states of positive muons ($\mu^+$) and two electrons, are generated from $\mu^+$'s through the electron capture process in an aluminum degrader. The generated Mu$^-$'s are initially electrostatically accelerated and injected into a radio frequency quadrupole linac (RFQ). In the RFQ, the Mu$^-$'s are accelerated to 89 keV. The accelerated Mu$^-$'s are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

Femtosecond profiling of shaped x-ray pulses

Abstract: Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future x-ray pulse shaping techniques.

Longitudinal Phase Space Reconstruction Simulation Studies using a Novel X-Band Transverse Deflecting Structure at the SINBAD Facility at DESY

Abstract: A transverse deflecting structure (TDS) is a well-known device for characterizing the longitudinal properties of an electron bunch in a linear accelerator The standard use of such a cavity involves streaking the bunch along a transverse axis and analysing the image on a screen downstream to find the bunch length and slice properties along the other transverse axis A novel X-band deflecting structure, which will allow the polarization of the deflecting field to be adjusted, is currently being designed as part of a collaboration between CERN, DESY and PSI This new design will allow bunches to be streaked at any transverse angle within the cavity, which will open up the possibility of new measurement techniques, which could be combined to characterize the 6D phase space distribution of bunches In this paper, a method is presented for reconstructing the longitudinal phase space distribution of bunches by using the TDS in combination with a dipole Simulations of this technique for the SINBAD-ARES beamline are presented and the key limitations related to temporal resolution and induced energy spread are discussed

Analysis of Dose Distribution According to the Initial Electron Beam of the Linear Accelerator: A Monte Carlo Study

Abstract: Background: Monte Carlo (MC) simulation is the most accurate for calculating radiation dose distribution and determining patient dose. In MC simulations of the therapeutic accelerator, the characteristics of the initial electron must be precisely determined in order to achieve accurate simulations. However, It has been computation-, labor-, and time-intensive to predict the beam characteristics through predominantly empirical approach. The aim of this study was to analyze the relationships between electron beam parameters and dose distribution, with the goal of simplifying the MC commissioning process.

First saturation of 14.5 keV free electron laser at PAL-XFEL

Abstract: The hard X-ray free electron laser at the Pohang Accelerator Laboratory (PAL-XFEL) in the Republic of Korea achieved a saturation of free electron laser (FEL) beam at 14.5 keV with an unprecedented intensity of 2.8E+11 photons per pulse. Successfully maintaining a very small emittance electron beam along the 700-m long linac, maximizing the spectral overlap of undulator radiation along the undulator line by the undulator radiation spectrum analysis, and optimal matching between the electron beam and photon beam through the 100-m long undulator line have allowed saturation and reliable operation of a 14.5 keV FEL beam.

EuPRAXIA@SPARC_LAB: The high-brightness RF photo-injector layout proposal

Abstract: At EuPRAXIA@SPARC_LAB, the unique combination of an advanced high-brightness RF injector and a plasma-based accelerator will drive a new multi-disciplinary user-facility. The facility, that is currently under study at INFN-LNF Laboratories (Frascati, Italy) in synergy with the EuPRAXIA collaboration, will operate the plasma-based accelerator in the external injection configuration. Since in this configuration the stability and reproducibility of the acceleration process in the plasma stage is strongly influenced by the RF-generated electron beam, the main challenge for the RF injector design is related to generating and handling high quality electron beams. In the last decades of R&D activity, the crucial role of high-brightness RF photo-injectors in the fields of radiation generation and advanced acceleration schemes has been largely established, making them effective candidates to drive plasma-based accelerators as pilots for user facilities. An RF injector consisting in a high-brightness S-band photo-injector followed by an advanced X-band linac has been proposed for the EuPRAXIA@SPARC_LAB project. The electron beam dynamics in the photo-injector has been explored by means of simulations, resulting in high-brightness, ultra-short bunches with up to 3 kA peak current at the entrance of the advanced X-band linac booster. The EuPRAXIA@SPARC_LAB high-brightness photo-injector is described here together with performance optimisation and sensitivity studies aiming to actual check the robustness and reliability of the desired working point.

Multi-MW accelerator target material properties under proton irradiation at Brookhaven National Laboratory linear isotope producer

Abstract: The effects of proton beams irradiating materials considered for targets in high-power accelerator experiments have been studied using the Brookhaven National Laboratory's (BNL) 200 MeV proton linac. A wide array of materials and alloys covering a wide range of the atomic number (Z) are being scoped by the high-power accelerator community prompting the BNL studies to focus on materials representing each distinct range, i.e. low-Z, mid-Z and high-Z. The low range includes materials such as beryllium and graphite, the midrange alloys such as Ti-6Al-4V, gum metal and super-Invar and finally the high-Z range pure tungsten and tantalum. Of interest in assessing proton irradiation effects are (a) changes in physiomechanical properties which are important in maintaining high-power target functionality, (b) identification of possible limits of proton flux or fluence above which certain materials cease to maintain integrity, (c) the role of material operating temperature in inducing or maintaining radiation damage reversal, and (d) phase stability and microstructural changes. The paper presents excerpt results deduced from macroscopic and microscopic post-irradiation evaluation (PIE) following several irradiation campaigns conducted at the BNL 200 MeV linac and specifically at the isotope producer beam-line/target station. The microscopic PIE relied on high energy x-ray diffraction at the BNL NSLS X17B1 and NSLS II XPD beam lines. The studies reveal the dramatic effects of irradiation on phase stability in several of the materials, changes in physical properties and ductility loss as well as thermally induced radiation damage reversal in graphite and alloys such as super-Invar.

LUE-75 Linear Accelerator Facility at Yerevan Physics Institute

Abstract: Owing to the growing interest in the low-energy nuclear physics, it becomes relevant to enhance the potential of the experimental facilities at Yerevan Physics Institute (YerPhI). The complex unit based on the linear electron accelerator LUE-75 (ARUS synchrotron injector) for applied and fundamental experiments with electron beams, the intensity and energy of which can vary in a wide range of 10–18–10–5 А and 10–50 MeV, has been created. In recent years, the regimes developed at LUE-75 were applied to obtain the controllable electron beams of extremely low intensity used for calibration of detectors.

ESS nBLM: Beam Loss Monitors based on Fast Neutron Detection

Abstract: A new type of Beam Loss Monitor (BLM) system is being developed for use in the European Spallation Source (ESS) linac, primarily aiming to cover the low energy part (proton energies between 3-100 MeV). In this region of the linac, typical BLM detectors based on charged particle detection (i.e. Ionization Cham-bers) are not appropriate because the expected particle fields will be dominated by neutrons and photons. Another issue is the photon background due to the RF cavities, which is mainly due to field emission from the electrons from the cavity walls, resulting in brems-strahlung photons. The idea for the ESS neutron sensi-tive BLM system (ESS nBLM) is to use Micromegas detectors specially designed to be sensitive to fast neutrons and insensitive to low energy photons (X and gammas). In addition, the detectors must be insensitive to thermal neutrons, because those neutrons may not be directly correlated to beam losses. The appropriate configuration of the Micromegas operating conditions will allow excellent timing, intrinsic photon back-ground suppression and individual neutron counting, extending thus the dynamic range to very low particle fluxes.

An Advanced NCRF Linac Concept for a High Energy e$^+$e$^-$ Linear Collider

Abstract: We have explored a concept for an advanced Normal-Conducting Radio-Frequency (NCRF) C-band linear accelerator (linac) structure to achieve a high gradient, high power e$^+$e$^-$ linear collider in the TeV class. This design study represents the first comprehensive investigation for an emerging class of distributed coupling accelerator topology exploring nominal cavity geometries, frequency and temperature of operation. The structure features internal manifolds for distributing RF power separately to each cell, permitting the full structure geometry to be designed for high shunt impedance and low breakdown. Optimized within operational constraints, we find that it is advantageous for the structure to be cooled directly by liquid nitrogen (LN), further increasing the shunt impedance. A crucial part of this design process has been cost optimization, which is largely driven by the cost of peak RF power. The first operation of a distributed coupling structure at cryogenic temperatures and the nominal operating gradient 120 MeV/m is also presented, demonstrating the feasibility of achieving high-gradient performance with a cryogenically-cooled normal-conducting accelerating structure.

Physical design of a single-amplifier-driven proton linac injector for a synchrotron-based proton-therapy system in China

Abstract: This paper describes the physical design of a 7 MeV proton linac injector for a synchrotron-based proton-therapy system, sponsored by the Chinese government under the support of the National Key Research and Development Program. The proton linac injector consists of an electron cyclotron resonance proton source, a low-energy beam transport section, a radio-frequency quadrupole (RFQ) accelerator, and an Alvarez-type drift tube linac (DTL). The peak current of the proton beam at the exit of the DTL accelerator is required to exceed 12 mA, with a normalized emittance of ⩽ 1 . 2 π mm mrad (90% particles), a repetition rate of 0.5 Hz, and a beam pulse width of 40–100 μ s . For the beam current whose momentum spread falls within ± 0.3%, the intensity must exceed 8 mA. The design of the linac injector is optimized in the principle of adopting sophisticated domestic technologies and cost control. Only one tetrode-based RF power amplifier is required after minimizing the total peak-power consumption of the RFQ and DTL accelerator, which is 378 kW. The idea of the RF power lines feeding two cavities with one amplifier is presented. To facilitate the manufacture of permanent-magnet quadrupoles and reduce the cost, the focusing strength at the end of the RFQ accelerator is optimized. Consequently, the focusing strength of all permanent-magnet quadrupoles is the same, and the DTL accelerator can be directly connected to match the RFQ accelerator without a medium-energy beam transport section between them. After construction, the 7 MeV proton linac injector is hoped to be the first homemade linac injector for a synchrotron-based proton-therapy facility in China.

Design and simulation of a LINAC for high energy electron radiography research

Abstract: We designed an electron linear accelerator (LINAC) for High Energy Electron Radiography (HEER) studies, which consists of two different guns, either a thermionic cathode or a photocathode RF gun, for diagnosing different targets. In this paper, we present the simulation studies and optimization of the LINAC based on an S-band thermionic RF gun. The LINAC is capable of generating sub-picosecond electron pulses with low energy spread (0.13%) and large micro-bunch charge (143 pC). The beam dynamics of the LINAC is studied and optimized by different beam dynamics simulation codes. The entrance hole induced field distortion in the alpha magnet is also reported. The space charge effects are studied by the General Particle Tracer (GPT) code. The results showed that the space charge forces had a significant influence on beam dynamics in such a low energy LINAC.

Commissioning of the ECR ion source of the high intensity proton injector of the Facility for Antiproton and Ion Research (FAIR)

Abstract: The CEA at Saclay is in charge of developing and building the ion source and the low energy line of the proton linac of the FAIR (Facility for Antiproton and Ion Research) accelerator complex located at GSI (Darmstadt) in Germany. The FAIR facility will deliver stable and rare isotope beams covering a huge range of intensities and beam energies for experiments in the fields of atomic physics, plasma physics, nuclear physics, hadron physics, nuclear matter physics, material physics, and biophysics. A significant part of the experimental program at FAIR is dedicated to antiproton physics that requires an ultimate number 7 × 1010 cooled pbar/h. The high-intensity proton beam that is necessary for antiproton production will be delivered by a dedicated 75 mA/70 MeV proton linac. A 2.45 GHz microwave ion source will deliver a 100 mA H+ beam pulsed at 4 Hz with an energy of 95 keV. A 2 solenoids low energy beam transport line allows the injection of the proton beam into the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm. rms). An electrostatic chopper system located between the second solenoid and the RFQ is used to cut the beam macro-pulse from the source to inject 36 μs long beam pulses into the RFQ. At present time, a Ladder-RFQ is under construction at the University of Frankfurt. This article reports the first beam measurements obtained since mid of 2016. Proton beams have been extracted from the ECR ion source and analyzed just after the extraction column on a dedicated diagnostic chamber. Emittance measurements as well as extracted current and species proportion analysis have been performed in different configurations of ion source parameters, such as magnetic field profile, radio frequency power, gas injection, and puller electrode voltage.

Propagation of modulated electron and X-ray beams through matter and interactions with radio-frequency structures

Abstract: The generation and evolution of modulated particle beams and their interactions with resonant radiofrequency (RF) structures are of fundamental interest for both particle accelerator and vacuum electronic systems. When the constraint of propagation in a vacuum is removed, the evolution of such beams can be greatly affected by interactions with matter including scattering, absorption, generation of atmospheric plasma, and the production of multiple generations of secondary particles. Here, we study the propagation of 21 MeV and 25 MeV electron beams produced in S-band and L-band linear accelerators, and their interaction with resonant RF structures, under a number of combinations of geometry, including transmission through both air and metal. Both resonant and nonresonant interactions were observed, with the resonant interactions indicating that the RF modulation on the electron beam is at least partially preserved as the beam propagates through air and metal. When significant thicknesses of metal are placed upstream of a resonant structure, preventing any primary beam electrons from reaching the structure, RF signals could still be induced in the structures. This indicated that the RF modulation present on the electron beam was also impressed onto the x-rays generated when the primary electrons were stopped in the metal, and that this RF modulation was also present on the secondary electrons generated when the x-rays struck the resonant structures. The nature of these interactions and their sensitivities to changes in system configurations will be discussed.