Proton Driver Research Articles

Elevating electron energy gain and betatron x-ray emission in proton-driven wakefield acceleration

The long proton beams present at CERN have the potential to evolve into a train of microbunches through the self-modulation instability process. The resonant wakefield generated by a periodic train of proton microbunches can establish a high acceleration field within the plasma, facilitating electron acceleration. This paper investigates the impact of plasma density on resonant wakefield excitation, thus influencing the acceleration of a witness electron bunch and its corresponding betatron radiation within the wakefield. Various scenarios involving different plasma densities are explored through particle-in-cell simulations. The peak wakefield in each scenario is calculated by considering a long pre-modulated proton driver with a fixed peak current. Subsequently, the study delves into the witness beam acceleration in the peak wakefield and its radiation emission. Elevated plasma density increases both the number of microbunches and the accelerating gradient of each microbunch, consequently resulting in heightened resonant wakefield. Nevertheless, the scaling is disrupted by the saturation of the resonant wakefield due to the nonlinearities. The simulation results reveal that at high plasma densities, an intense and broadband radiation spectrum extending into the domain of the hard x-rays and gamma rays is generated. Furthermore, in such instances, the energy gain of the witness beam is significantly enhanced. The impact of wakefield on the witness energy gain and the corresponding radiation spectrum is clearly evident at elevated densities.

Linear and nonlinear beam dynamics of vertical fixed-field accelerators

Vertical fixed-field accelerators (vFFAs) feature a magnetic field that increases exponentially in the vertical direction, resulting in vertically stacked nonplanar orbits. Their magnetic field is highly nonlinear, and their solenoid and quadrupolar components induce strongly coupled optics. The detailed study of their beam dynamics must account for the transverse motion linear and nonlinear coupling. Specifically, the study of linear beam dynamics requires adequate coupling parametrizations, and the study of nonlinear beam dynamics, including the characterization of the dynamic aperture (DA), must be performed in the full 4D phase space. The ray-tracing code is ideally suited to study the vFFA transverse dynamics, as it can perform step-by-step particle tracking in vFFA complex geometry and magnetic fields. This paper provides an in-depth study of the vFFA prototype ring designed under the ISIS-II proton driver prototype project to accelerate proton beams from 3 to 12 MeV. The magnets of this vFFA ring exhibit slow magnetic field falloffs, resulting in a significant influence of the neighboring cells on the optical lattice parameters. The determination of stable orbits and tunes requires superimposing 3D magnetic field maps in to account for the neighboring cell residual fields. The study of nonlinear beam dynamics revealed the appearance of fourth-order stability islands. A complete characterization of the DA in the 4D phase space was conducted to give a measure of the stability domain and characterize the performance and limitations of this lattice. This study paves the way for further validation studies with experimental data and field maps. Published by the American Physical Society 2024

Modeling and implementation of vertical excursion FFA in the Zgoubi ray-tracing code

Vertical Fixed Field Accelerators (vFFAs) feature complex and highly non-linear magnetic fields, which require simulation codes allowing step-wise particle tracking. Methods to model the 3D magnetic field of scaling vFFAs have been developed in the ray-tracing code Zgoubi. The field modeling and particle tracking methods include the field non-linearities, the fringe fields, and the field superposition of neighboring magnets. The procedure implements the vFFA analytical field expressions, allowing design studies and parameter optimizations using the Zgoubi built-in fit method. The vFFA procedure has been applied to a ten-fold symmetry ring with a triplet focusing structure designed to accelerate protons from 3 MeV to 12 MeV and studied under the ISIS-II proton driver prototype project. Results from particle tracking in externally generated 3D semi-analytical field maps and the developed vFFA analytical model are shown to be in excellent agreement.

Future facilities at PSI, the High-Intensity Muon Beams (HIMB) project

Currently, PSI delivers the most intense continuous muon beam in the world with up to a few 108 µ+/s. The High-Intensity Muon Beams (HIMB) project is developing a new target station and muon beamlines able to deliver 1010 µ+/s, with a huge impact for low-energy, high-precision muon experiments. While the next generation of proton drivers with beam powers in excess of the currently achieved 1.4 MW still require significant research and development, the focus of HIMB is to improve the surface muon yield with a new target geometry and to increase capture and transmission with a solenoid-based beamline in order to reach a total efficiency of approximately 10 %. We present the current status of the HIMB project.

Proton-beam driver transport in the fast ignition of proton–boron-11 fuel plasma

The invention of Chirped Pulse Amplification lasers along with the development of fast ignition methods have made fuels such as proton–boron-11 seem promising nuclear fusion energy sources because of their lack of high-energy neutrons and abundance of constituent isotopes. This paper investigates the transport of charged particles in proton–boron-11 fuel. In this study, the confinement parameter has been estimated as [Formula: see text] g/cm2 with the help of a proton driver in the fast ignition method for proton–boron-11 fuel pellets, with a ratio of boron-11 to proton [Formula: see text]. Subsequently, using the Li–Petrasso stopping-power model, the energy deposition coefficients of the accelerated proton-beam driver were calculated by the Target Normal Sheath Acceleration method with 1 MeV energy. The obtained results show that at a temperature of about 65 keV, the proton-beam driver with 1 MeV energy deposits about 85% of its energy in the hot spot area of 2.5 [Formula: see text]m depth from the surface of the fuel pellet to ignite the proton–boron-11 fuel pellet.

New Technologies for Particle Accelerators

The article proposes to consider two fundamentally new ways of accelerating charged particles: linear acceleration (LA) of protons on a backward wave (Professor Bogomolov’s Accelerator) and wake acceleration of electrons using a proton driver in the Large Hadron Collider (AWAKE project).

Remote handling systems for the Selective Production of Exotic Species (SPES) facility

The SPES (Selective Production of Exotic Species) facility, currently under development at Legnaro National Laboratories of INFN, aims at the production of intense RIB (Radioactive Ion Beams) employing the Isotope Separation On-Line (ISOL) technique for interdisciplinary research. The radioactive isotopes of interest are produced by the interaction of a multi-foil uranium carbide target with a 40 MeV 200 μA proton beam generated by a cyclotron proton driver. The Target Ion Source (TIS) is the core of the SPES project, here the radioactive nuclei, mainly neutron-rich isotopes, are stopped, extracted, ionized, separated, accelerated and delivered to specific experimental areas. Due to efficiency reasons, the TIS unit needs to be replaced periodically during operation. In this highly radioactive environment, the employment of autonomous systems allows the manipulation, transport, and storage of the TIS unit without the need for human intervention. A dedicated remote handling infrastructure is therefore under development to fulfill the functional and safety requirement of the project. This contribution describes the layout of the SPES target area, where all the remote handling systems operate to grant the smooth operation of the facility avoiding personnel exposure to a high dose rate or contamination issues.

Possible solution for the integer resonance crossing problem of GeV-class isochronous Fixed-Field Alternating Gradient accelerators

Fixed-Field Alternating Gradient accelerators (FFAG, also known as FFA) are promising candidates for next-generation GeV-class proton driver with average beam power of several megawatts. In isochronous accelerators, radial tunes are approximately increasing with beam energy in a linear way, and thus the integer resonance crossing problem becomes the major bottleneck of GeV-class isochronous FFAG design. In 2019, China Institute of Atomic Energy (CIAE) proposed an isochronous FFAG conceptual design with capability of producing 2GeV/6MW continuous wave (CW) proton beam. However, this conceptual design shows that the beam size is blown up at high energy region due to the third harmonic magnetic field caused by imperfections. The reason is that the integer resonance vr=3 causes a large coherent oscillation, and this large amplitude is not compatible with the following third order intrinsic resonance 3vr=10. In order to correct the large coherent motion before reaching the 3vr=10 resonance, we propose an idea of integer resonance suppressor (IRS) which intentionally introduces the third harmonic magnetic field. Our calculation shows that third harmonic field of 10Gs is acceptable with proper IRS settings, meaning that the requirements of magnet manufacture and installation can be relaxed. The increased imperfection tolerances will make magnet manufacture and installation much easier.

Plasma wakefield acceleration beyond the dephasing limit with 400 GeV proton driver

A new regime of proton-driven plasma wakefield acceleration is discovered, in which the plasma nonlinearity increases the phase velocity of the excited wave compared to that of the protons. If the beam charge is much larger than minimally necessary to excite a nonlinear wave, there is sufficient freedom in choosing the longitudinal plasma density profile to make the wave speed close to the speed of light. This allows electrons or positrons to be accelerated to about 200 GeV with a 400 GeV proton driver.

Neutron generator based on intense lithium beam driver.

We are proposing a compact neutron generator based on a Li beam driver. The proposed neutron generator comprises a laser ion source, a radio-frequency quadrupole linear accelerator (RFQ linac), a drift tube linac, and a target containing protons. In the generator, the lithium ion is used as a projectile instead of protons to utilize the kinematic focusing technique. The technique enables us to enhance the neutron flux without increasing the beam energy, which is important to develop a clean compact neutron generator. Moreover, the combination of a laser ion source and a RFQ linac with the direct plasma injection scheme will provide several tens of mA of a fully ionized lithium beam, which is much higher than that of conventional heavy ion sources comparable with proton drivers. Neutrons are generated by the nuclear reaction of the lithium ions and protons in the beam target. In this paper, we reported the current status of the development. For RFQ, we designed the RFQ rods to accelerate 40 mA of 7Li3+. We fabricated and installed the rods into a cavity, and, as a first test, accelerated 10 mA of C6+ successfully.

Neutrino CP Violation with the European Spallation Source neutrino Super Beam project

After measuring in 2012 a relatively large value of the neutrino mixing angle θ 13, the door is now open to observe for the first time a possible CP violation in the leptonic sector. The measured value of θ 13 also privileges the 2nd oscillation maximum for the discovery of CP violation instead of the usually used 1st oscillation maximum. The sensitivity at this 2nd oscillation maximum is about three times higher than for the 1st oscillation maximum inducing a lower influence of systematic errors. Going to the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy. The world’s most intense pulsed spallation neutron source, the European Spallation Source (ESS), will have a proton linac with 5 MW power and 2 GeV energy. This linac, under construction, also has the potential to become the proton driver of the world’s most intense neutrino beam with very high potential to discover a neutrino CP violation. The physics performance of that neutrino Super Beam in conjunction with a megaton underground Water Cherenkov neutrino detector installed at a distance of about 500 km from ESS has been evaluated. In addition, the choice of such detector will extent the physics program to proton–decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrades, the accumulator ring needed for proton pulse compression, the target station optimization and the physics potential are described. In addition to neutrinos, this facility will also produce at the same time a copious number of muons which could be used by a muon collider. The ESS neutron facility will be fully ready by 2023 at which moment the upgrades for the neutrino facility could start.

The Future Prospects of Muon Colliders and Neutrino Factories

The potential of muon beams for high energy physics applications is described along with the challenges of producing high quality muon beams. Two proposed approaches for delivering high intensity muon beams, a proton driver source and a positron driver source, are described and compared. The proton driver concepts are based on the studies from the Muon Accelerator Program (MAP). The MAP effort focused on a path to deliver muon-based facilities, ranging from neutrino factories to muon colliders, that could span research needs at both the intensity and energy frontiers. The Low EMittance Muon Accelerator (LEMMA) concept, which uses a positron-driven source, provides an attractive path to very high energy lepton colliders with improved particle backgrounds. The recent study of a 14-TeV muon collider in the LHC tunnel, which could leverage the existing CERN injectors and infrastructure and provide physics reach comparable to the 100[Formula: see text]TeV FCC-hh, at lower cost and with cleaner physics conditions, is also discussed. The present status of the design and R&D efforts towards each of these sources is described. A summary of important R&D required to establish a facility path for each concept is also presented.

New program for measuring masses of silver isotopes near the N = 82 shell closure with MLLTRAP at ALTO

The ISOL facility ALTO, located at Orsay in France, provides stable ion beams from a 15 MV Tandem accelerator and neutron-rich radioactive ion beams (RIB) from the interaction of a γ-flux induced by a 50 MeV 10 μA electron beam in a uranium carbide target. A magnetic dipole mass separator and a resonance ionization laser ion source allow to select the ions of interest. New setups are under preparation to extend the fundamental properties measured at ALTO of ground and excited states of exotic nuclei. For example, high-precision mass measurements for an accurate determination of the nuclear binding energy. To perform these measurements two devices will be hosted at ALTO: a radio frequency quadrupole to cool and bunch (RFQCB) the continuous radioactive beam and the double Penning trap mass spectrometer MLLTRAP, commissioned off-line at the Maier-Leibnitz Laboratory (MLL) in Garching, Germany. The unique production mechanism using photo-fission at the ALTO facility allows for mass measurements in a neutron rich area of nuclides of major interest around 132Sn with less isobaric contamination than using proton drivers. In this context, we plan to measure neutron-rich silver isotopes (Z = 47, A > 121) to explore the possible weakening of the shell gap for Z < 50 and its impact on the A = 130 r- process nucleosynthesis. The ground-state light silver masses (A < 121), known with a precision below 20 keV, will be used for the on-line commissioning of MLLTRAP and to characterize the performance of the detection system. The status and timeline of the novel setup is presented.

High intensity cyclotrons for neutrino physics

In recent years, the interest in high intensity proton beams in excess of several milli-amperes has risen. Potential applications are in neutrino physics, materials and energy research, and isotope production. Continuous wave proton beams of five to ten milli-amperes are now in reach due to advances in accelerator technology and through improved understanding of the beam dynamics. As an example application, we present the proposed IsoDAR experiment, a search for so-called sterile neutrinos and non-standard interaction using the KamLAND detector located in Japan. We present updated sensitivities for this experiment and describe in detail the design of the high intensity proton driver that uses several novel ideas. These are: accelerating H2+ instead of protons, directly injecting beam into the cyclotron via a radio frequency quadrupole, and carefully matching the beam to achieve so-called vortex motion. The preliminary design holds up well in PIC simulation studies and the injector system is now being constructed, to be commissioned with a 1MeV/amu test cyclotron.

Emittance preservation of an electron beam in a loaded quasilinear plasma wakefield

We investigate beam loading and emittance preservation for a high-charge electron beam being accelerated in quasi-linear plasma wakefields driven by a short proton beam. The structure of the studied wakefields are similar to those of a long, modulated proton beam, such as the AWAKE proton driver. We show that by properly choosing the electron beam parameters and exploiting two well known effects, beam loading of the wakefield and full blow out of plasma electrons by the accelerated beam, the electron beam can gain large amounts of energy with a narrow final energy spread (%-level) and without significant emittance growth.

High-quality electron beam generation in a proton-driven hollow plasma wakefield accelerator

Simulations of proton-driven plasma wakefield accelerators have demonstrated substantially higher accelerating gradients compared to conventional accelerators and the viability of accelerating electrons to the energy frontier in a single plasma stage. However, due to the strong intrinsic transverse fields varying both radially and in time, the witness beam quality is still far from suitable for practical application in future colliders. Here we demonstrate efficient acceleration of electrons in proton-driven wakefields in a hollow plasma channel. In this regime, the witness bunch is positioned in the region with a strong accelerating field, free from plasma electrons and ions. We show that the electron beam carrying the charge of about 10% of 1 TeV proton driver charge can be accelerated to 0.6 TeV with preserved normalized emittance in a single channel of 700 m. This high quality and high charge beam may pave the way for the development of future plasma-based energy frontier colliders.

The ESS neutrino facility for CP violation discovery

The comparatively large value of the neutrino mixing angle θ13 measured in 2012 by neutrino reactor experiments has opened the possibility to observe for the first time CP violation in the leptonic sector. The measured value of θ13 also privileges the 2nd oscillation maximum for the discovery of CP violation instead of the usually used 1st oscillation maximum. The sensitivity at the 2nd oscillation maximum is about three times higher than at the 1st oscillation maximum implying a significantly lower sensitivity to systematic errors. Measuring at the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy. The world’s most intense pulsed spallation neutron source, the European Spallation Source, has a proton linac with 5 MW power and 2 GeV energy. This linac also has the potential to become the proton driver of the world’s most intense neutrino beam with very high potential for the discovery of neutrino CP violation. The physics performance of that neutrino Super Beam in conjunction with a megaton Water Cherenkov neutrino detector installed ca 1000 m down in a mine at a distance of about 500 km from ESS has been evaluated. In addition, the use of such a detector will make it possible to extent the physics program to proton decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrade, the accumulator ring needed for proton pulse compression, the target station optimization and the physics potential are described. In addition to the production of neutrinos, this facility will also be a copious source of muons which could be used to feed a low energy nuSTORM facility, a future neutrino factory or a muon collider. The ESS linac, under construction, will reach full operation at 5 MW by 2023 after which the upgrades for the neutrino facility could start.

Scaling Fixed-Field Alternating-Gradient Accelerators with Reverse Bend and Spiral Edge Angle.

A novel scaling type of fixed-field alternating-gradient (FFAG) accelerator is proposed that solves the major problems of conventional scaling FFAGs. This scaling FFAG accelerator combines reverse bending magnets of the radial sector type and a spiral edge angle of the spiral sector type to ensure sufficient vertical focusing without relying on extreme values of either parameter. This new concept makes it possible to design a scaling FFAG for high energy (above GeV range) applications such as a proton driver for a spallation neutron source and an accelerator driven subcritical reactor.

Physics design of rod type proton Radio Frequency Quadrupole linac

A Radio Frequency Quadrupole (RFQ) linac delivering 800 keV, 5 mA protons has been designed. It is envisaged as first injector of the proton driver that will be used for production of proton-rich radioactive beams in the proposed ANURIB facility. The option of rod-type structure at frequency of 80 MHz has been chosen owing to ease of mechanical fabrications and to avoid detrimental nearby dipole modes present in vane type structure. Optimization of parameters has been carried out for a viable length and power of RFQ in order to avoid any infrastructural complexity. Conventional method of keeping focusing factor and vane voltage constant along the length of RFQ has been adopted. Results of detailed beam dynamics and RF structure design, space charge induced effects and corroborative particle tracking with realistic 3D fields of modulated vane has been presented.

A Multi-MW Proton/Electron Facility at KEK

The main “bottleneck” limiting the beam power in circular machines is caused by space charge effects that produce beam instabilities. To increase maximally the beam power of a “proton driver”, it is proposed to build a facility consisting solely of a 2.5 GeV injector linac (PI) and a 20 GeV pulsed superconducting linac (SCL). Such a facility could be constructed using the existing KEK accelerator infrastructure. The PI, based on the European Spallation Source (ESS) linac, would serve both as an injector to the SCL and a source of proton beams that could be used to copiously produce, e.g., muons and “cold” neutrons. Protons accelerated by the SCL would be transferred through the KEK Tristan ring in order to create neutrino, kaon and muon beams for fixed-target experiments. At a later stage, a 70 GeV proton synchrotron could be installed inside the Tristan ring. The SCL, comprising 1.3 GHz ILC-type rf cavities, could also accelerate polarized or unpolarized electron beams. After acceleration, electrons could be used to produce polarized positrons, or may traverse an XFEL undulator.