Showing papers in "Physical review accelerators and beams in 2017"

Generation of high-energy electron-positron pairs in the collision of a laser-accelerated electron beam with a multipetawatt laser

Abstract: Generation of electron-positron pairs via the multiphoton Breit-Wheeler process in an all-optical scheme will be made possible on forthcoming high-power laser facilities through the collision of wakefield-accelerated GeV electrons with a counter-propagating laser pulse of 1022–1023 W cm-2 peak intensity. By means of integrated 3D particle-in-cell simulations, we show that the production of high-density sources of ultrarelativistic electron-positron pairs is within the reach of soon-to-be-available laser systems. Under physical conditions accessible to the dual-beam CILEX-Apollon facility, we find that the generated positrons can carry a total charge of 0.05–1 nC, with a mean energy of 100–400 MeV and an angular divergence of 0.01–0.1 rad. The variations of the positron source’s properties with respect to the laser parameters are also examined.

Optimizing density down-ramp injection for beam-driven plasma wakefield accelerators

Abstract: Density down-ramp (DDR) injection is a promising concept in beam-driven plasma wakefield accelerators for the generation of high-quality witness beams. We review and complement the theoretical principles of the method and employ particle-in-cell (PIC) simulations in order to determine constrains on the geometry of the density ramp and the current of the drive beam, regarding the applicability of DDR injection. Furthermore, PIC simulations are utilized to find optimized conditions for the production of high-quality beams. We find and explain the intriguing result that the injection of an increased charge by means of a steepened ramp favors the generation of beams with lower emittance. Exploiting this fact enables the production of beams with high charge (∼140 pC), low normalized emittance (∼200 nm) and low uncorrelated energy spread (0.3%) in sufficiently steep ramps even for drive beams with moderate peak current (∼2.5 kA).

Nonuniform discharge currents in active plasma lenses

Abstract: Author(s): Van Tilborg, J; Barber, SK; Tsai, HE; Swanson, KK; Steinke, S; Geddes, CGR; Gonsalves, AJ; Schroeder, CB; Esarey, E; Bulanov, SS; Bobrova, NA; Sasorov, PV; Leemans, WP | Abstract: Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations.

Control of tunable, monoenergetic laser-plasma-accelerated electron beams using a shock-induced density downramp injector

Abstract: Author(s): Swanson, KK; Tsai, HE; Barber, SK; Lehe, R; Mao, HS; Steinke, S; Van Tilborg, J; Nakamura, K; Geddes, CGR; Schroeder, CB; Esarey, E; Leemans, WP | Abstract: Control of the properties of laser-plasma-accelerated electron beams that were injected along a shock-induced density downramp through precision tailoring of the density profile was demonstrated using a 1.8 J, 45 fs laser interacting with a mm-scale gas jet. The effects on the beam spatial profile, steering, and absolute energy spread of the density region before the shock and tilt of the shock were investigated experimentally and with particle-in-cell simulations. By adjusting these density parameters, the electron beam quality was controlled and improved while the energy (30-180 MeV) and energy spread (2-11 MeV) were independently tuned. Simple models that are in good agreement with the experimental results are proposed to explain these relationships, advancing the understanding of downramp injection. This technique allows for high-quality electron beams with percent-level energy spread to be tailored based on the application.

High quality electron bunch generation using a longitudinal density-tailored plasma-based accelerator in the three-dimensional blowout regime

Abstract: Plasma-based acceleration in density down ramps is proposed to generate electron beams with unprecedented combinations of brightness and energy spread, which can drive a new class of compact free-electron-lasers and linear colliders.

Performance in the vertical test of the 832 nine-cell 1.3 GHz cavities for the European X-ray Free Electron Laser

Abstract: Comprehensive description of the fabrication, surface treatment, and performance of all superconducting cavities for the European X-ray Free Electron Laser project.

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Abstract: Spectroscopic measurements of plasma density, temperature, and plasma closure velocities are preparing the path to scaled-up pulsed power drivers for future research.

APS : LHC optics commissioning : A journey towards 1% optics control

Abstract: Since 2015 the LHC has been operating at 6.5 TeV. In 2016 the β-functions at the interaction points of ATLAS and CMS were squeezed to 0.4 m. This is below the design β 1⁄4 0.55 m at 7 TeV, and has been instrumental to surpass the design luminosity of 10 cm−2 s−1. Achieving a lower than nominal β has been possible thanks to the extraordinary performance of the LHC, in which the control of the optics has played a fundamental role. Even though the β-beating for the virgin machine was above 100%, corrections reduced the rms β-beating below 1% at the two main experiments and below 2% rms around the ring. This guarantees a safe operation as well as providing equal amount of luminosity for the two experiments. In this article we describe the recent improvements to the measurement, correction algorithms and technical equipment which allowed this unprecedented control of the optics for a high-energy hadron collider.

High-gradient breakdown studies of an X -band Compact Linear Collider prototype structure

Abstract: A Compact Linear Collider prototype traveling-wave accelerator structure fabricated at Tsinghua University was recently high-gradient tested at the High Energy Accelerator Research Organization (KEK). This $X$-band structure showed good high-gradient performance of up to $100\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ and obtained a breakdown rate of $1.27\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ per pulse per meter at a pulse length of 250 ns. This performance was similar to that of previous structures tested at KEK and the test facility at the European Organization for Nuclear Research (CERN), thereby validating the assembly and bonding of the fabricated structure. Phenomena related to vacuum breakdown were investigated and are discussed in the present study. Evaluation of the breakdown timing revealed a special type of breakdown occurring in the immediately succeeding pulse after a usual breakdown. These breakdowns tended to occur at the beginning of the rf pulse, whereas usual breakdowns were uniformly distributed in the rf pulse. The high-gradient test was conducted under the international collaboration research program among Tsinghua University, CERN, and KEK.

Spectral and spatial shaping of a laser-produced ion beam for radiation-biology experiments

Abstract: The study of radiation biology on laser-based accelerators is most interesting due to the unique irradiation conditions they can produce, in terms of peak current and duration of the irradiation. In this paper we present the implementation of a beam transport system to transport and shape the proton beam generated by laser-target interaction for in vitro irradiation of biological samples. A set of four permanent magnet quadrupoles is used to transport and focus the beam, efficiently shaping the spectrum and providing a large and relatively uniform irradiation surface. Real time, absolutely calibrated, dosimetry is installed on the beam line, to enable shot-to-shot control of dose deposition in the irradiated volume. Preliminary results of cell sample irradiation are presented to validate the robustness of the full system.

Review of linear optics measurement and correction for charged particle accelerators

Abstract: Linear optics measurements and correction for charged particle beams are reviewed, including the historical path, recent trends, and a comparison of different approaches, providing a valuable reference for years to come

Large Hadron Collider momentum calibration and accuracy

Abstract: As a result of the excellent quality of the Large Hadron Collider (LHC) experimental detectors and the accurate calibration of the luminosity at the LHC, uncertainties on the LHC beam energy may contribute significantly to the measurement errors on certain observables unless the relative uncertainty is well below 1%. Direct measurements of the beam energy using the revolution frequency difference of proton and lead beams combined with the magnetic model errors are used to provide the energy uncertainty of the LHC beams. Above injection energy the relative uncertainty on the beam energy is determined to be $\ifmmode\pm\else\textpm\fi{}0.1%$. The energy values as reconstructed and distributed online to the LHC experiments do not require any correction above injection energy. At injection a correction of $+0.31\text{ }\text{ }\mathrm{GeV}/\mathrm{c}$ must be applied to the online energy values.

First accelerator test of vacuum components with laser-engineered surfaces for electron-cloud mitigation

Abstract: Electron cloud mitigation is an essential requirement for high-intensity proton circular accelerators. Among other solutions, laser engineered surface structures (LESS) present the advantages of having potentially a very low secondary electron yield (SEY) and allowing simple scalability for mass production. Two copper liners with LESS have been manufactured and successfully tested by monitoring the electron cloud current in a dipole magnet in the SPS accelerator at CERN during the 2016 run. In this paper we report on these results as well as the detailed experiments carried out on samples—such as the SEYand topography studies—which led to an optimized treatment in view of the SPS test and future possible use in the HL-LHC.

First operation of a harmonic lasing self-seeded free electron laser

Abstract: First experimental observation of harmonic lasing self-seeded free electron laser demonstrates shorter saturation length, narrower bandwidth, and improved taper efficiency.

Start-to-end simulation of the shot-noise driven microbunching instability experiment at the Linac Coherent Light Source

Abstract: The shot-noise driven microbunching instability can significantly degrade electron beam quality in x-ray free electron laser light sources. Experiments were carried out at the Linac Coherent Light Source (LCLS) to study this instability. In this paper, we present start-to-end simulations of the shot-noise driven microbunching instability experiment at the LCLS using the real number of electrons. The simulation results reproduce the measurements quite well. A microbunching self-heating mechanism is also illustrated in the simulation, which helps explain the experimental observation.

High gradient linac for proton therapy

Abstract: Proposed for the first time almost 30 years ago, the research on radio frequency linacs for hadron therapy experienced a sparkling interest in the past decade. The different projects found a common ground on a relatively high rf operating frequency of 3 GHz, taking advantage of the availability of affordable and reliable commercial klystrons at this frequency. This article presents for the first time the design of a proton therapy linac, called TULIP all-linac, from the source up to 230 MeV. In the first part, we will review the rationale of linacs for hadron therapy. We then divided this paper in two main sections: first, we will discuss the rf design of the different accelerating structures that compose TULIP; second, we will present the beam dynamics design of the different linac sections.

Statistical analysis of laser driven protons using a high-repetition-rate tape drive target system

Abstract: One of the challenges for laser-driven proton beams for many potential applications is their stability and reproducibility. We investigate the stability of the laser driven proton beams through statistical analysis of the data obtained by employing a high repetition rate tape driven target system. The characterization of the target system shows the positioning of the target within $\ensuremath{\sim}15\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ in the focal plane of an off-axis parabola, with less than a micron variation in surface flatness. By employing this stable target system, we study the stability of the proton beams driven by ultrashort and intense laser pulses. Protons with maximum energies of $\ensuremath{\sim}6\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\mathrm{MeV}$ were accelerated for a large number of laser shots taken at a rate of 0.2 Hz with a stability of less than 5% variations in cutoff energy. The development of high repetition rate target system may provide a platform to understand the dynamics of laser driven proton beams at the rate required for future applications.

Delivering the world's most intense muon beam

Abstract: A new muon beam line, the muon science innovative channel, was set up at the Research Center for Nuclear Physics, Osaka University, in Osaka, Japan, using the 392 MeV proton beam impinging on a target. The production of an intense muon beam relies on the efficient capture of pions, which subsequently decay to muons, using a novel superconducting solenoid magnet system. After the pion-capture solenoid, the first 36° of the curved muon transport line was commissioned and the muon flux was measured. In order to detect muons, a target of either copper or magnesium was placed to stop muons at the end of the muon beam line. Two stations of plastic scintillators located upstream and downstream from the muon target were used to reconstruct the decay spectrum of muons. In a complementary method to detect negatively charged muons, the x-ray spectrum yielded by muonic atoms in the target was measured in a germanium detector. Measurements, at a proton beam current of 6 pA, yielded ( 10.4 ± 2.7 ) × 1 0 5 muons per watt of proton beam power ( μ + and μ − ), far in excess of other facilities. At full beam power (400 W), this implies a rate of muons of ( 4.2 ± 1.1 ) × 1 0 8 muons s − 1 , among the highest in the world. The number of μ − measured was about a factor of 10 lower, again by far the most efficient muon beam produced. The setup is a prototype for future experiments requiring a high-intensity muon beam, such as a muon collider or neutrino factory, or the search for rare muon decays which would be a signature for phenomena beyond the Standard Model of particle physics. Such a muon beam can also be used in other branches of physics, nuclear and condensed matter, as well as other areas of scientific research.

Design of the Compact Linear Collider main linac accelerating structure made from two halves

Abstract: Milling on two longitudinally split halves is one method to manufacture accelerating structures. This method is simple and allows one to avoid electromagnetic fields at bonding joints, making it attractive in manufacturing high-gradient accelerating structures. An X-band structure design with strong wakefield damping based on this manufacturing approach is studied in this work as an alternative design for the Compact Linear Collider (CLIC) main linac accelerating structures. The geometry of the structure is optimized to greatly reduce the surface fields, improve the efficiency, and suppress the wakefield. This structure features the baseline design of the CLIC main linac with additional advantages. This study may serve as a reference for designing other high frequency-band corrugated structures.

High brilliance uranium beams for the GSI FAIR

Abstract: The 40 years old GSI-UNILAC (Universal Linear Accelerator) as well as the heavy ion synchrotron SIS18 will serve as a high current heavy ion injector for the new FAIR (Facility for Antiproton and Ion Research) synchrotron SIS100 In the context of an advanced machine investigation program in combination with the ongoing UNILAC upgrade program, a new uranium beam intensity record (115 emA, ${\mathrm{U}}^{29+}$) at very high beam brilliance was achieved recently in a machine experiment campaign This is an important step paving the way to fulfill the FAIR heavy ion high intensity beam requirements Results of high current uranium beam measurements applying a newly developed pulsed hydrogen gas stripper (at $14\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$) will be presented in detail

Statistics of vacuum breakdown in the high-gradient and low-rate regime

Abstract: In an increasing number of high-gradient linear accelerator applications, accelerating structures must operate with both high surface electric fields and low breakdown rates. Understanding the statistical properties of breakdown occurrence in such a regime is of practical importance for optimizing accelerator conditioning and operation algorithms, as well as of interest for efforts to understand the physical processes which underlie the breakdown phenomenon. Experimental data of breakdown has been collected in two distinct high-gradient experimental set-ups: A prototype linear accelerating structure operated in the Compact Linear Collider Xbox 12 GHz test stands, and a parallel plate electrode system operated with pulsed DC in the kV range. Collected data is presented, analyzed and compared. The two systems show similar, distinctive, two-part distributions of number of pulses between breakdowns, with each part corresponding to a specific, constant event rate. The correlation between distance and number of pulses between breakdown indicates that the two parts of the distribution, and their corresponding event rates, represent independent primary and induced follow-up breakdowns. The similarity of results from pulsed DC to 12 GHz rf indicates a similar vacuum arc triggering mechanism over the range of conditions covered by the experiments.

Achievement of a low-loss 1-MW beam operation in the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Abstract: The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) is now in the final beam commissioning phase, aiming for a design output beam power of 1 MW. With a series of injector linac upgrades in 2013 and 2014, RCS developed a high-intensity beam test, and launched 1-MW beam tuning in October 2014. The most important issues in realizing such a high-power continuous beam operation are to control and minimize beam loss for maintaining machine activations within permissible levels. In RCS, numerical simulation was successfully utilized along with experimental approaches to isolate the mechanism of beam loss and find its solution. By iteratively performing actual beam experiments and numerical simulations, and also by several hardware improvements, we have recently established a 1-MW beam operation with very low fractional beam loss of a couple of 10-3. In this paper, our recent efforts toward realizing such a low-loss high-intensity beam acceleration are presented as a follow-up of our previous article, H. Hotchi et al. Phys. Rev. ST Accel. Beams 12, 040402 (2009)PRABFM1098-440210.1103/PhysRevSTAB.12.040402, in which the initial beam commissioning status of RCS has been reported.

Development and operation of a Pr 2 Fe 14 B based cryogenic permanent magnet undulator for a high spatial resolution x-ray beam line

Abstract: Short period, high field undulators are used to produce hard x-rays on synchrotron radiation based storage ring facilities of intermediate energy and enable short wavelength free electron laser. Cryogenic permanent magnet undulators take benefit from improved magnetic properties of ${\mathrm{RE}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ (Rare Earth based magnets) at low temperatures for achieving short period, high magnetic field and high coercivity. Using ${\mathrm{Pr}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ instead of ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$, which is generally employed for undulators, avoids the limitation caused by the spin reorientation transition phenomenon, and simplifies the cooling system by allowing the working temperature of the undulator to be directly at the liquid nitrogen one (77 K). We describe here the development of a full scale (2 m), 18 mm period ${\mathrm{Pr}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ cryogenic permanent magnet undulator (U18). The design, construction and optimization, as well as magnetic measurements and shimming at low temperature are presented. The commissioning and operation of the undulator with the electron beam and spectrum measurement using the Nanoscopmium beamline at SOLEIL are also reported.

Spin tune mapping as a novel tool to probe the spin dynamics in storage rings

Abstract: Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ult ...

Upper limit for the accelerating gradient in the collinear wakefield accelerator as a function of the transformer ratio

Abstract: The interrelation between the accelerating gradient and the transformer ratio in the collinear wakefield accelerator has been analyzed. It has been shown that the high transformer ratio and the high efficiency of the energy transfer from the drive bunch to the witness bunch can only be achieved at the expense of the accelerating gradient. Rigorous proof is given that in best cases of meticulously shaped charge density distributions in the drive bunch, the maximum accelerating gradient falls proportionally to the gain in the transformer ratio. Conclusions are verified using several representative examples.

Trace-space reconstruction of low-emittance electron beams through betatron radiation in laser-plasma accelerators

Abstract: A new methodology able to model and reconstruct the transverse trace space of low-emittance electron beams accelerated in the bubble regime of laser-plasma interaction is presented. The single-shot measurement of both the electron energy spectrum and the betatron radiation spectrum is shown to allow a complete measurement of the transverse emittance, including the correlation term. A novel technique to directly measure the betatron oscillation amplitude distribution is described and tested at the SPARC-LAB test facility through the interaction of the ultrashort ultraintense Ti:Sa laser FLAME with a He gas-jet target. Via the exposed technique the beam transverse profile is also retrieved. From the study of the electron transverse dynamics inside the plasma bubble, the nonlinear correlation between the betatron amplitude and the divergence, i.e. the angle with respect the acceleration axis, is found. The angular distribution of the electron beam inside the bubble is retrieved. The knowledge of the trace-space density allows a more accurate measurement of the transverse emittance with respect to previous paradigms.

Development and operating experience of a 1.1-m-long superconducting undulator at the Advanced Photon Source

Abstract: Development of superconducting undulators continues at the Advanced Photon Source (APS). Two years after successful installation and commissioning of the first relatively short superconducting undulator ``SCU0'' in Sector 6 of the APS storage ring, the second 1.1-m-long superconducting undulator ``SCU1'' was installed in Sector 1 of the APS. The device has been in user operation since its commissioning in May 2015. This paper describes the magnetic and cryogenic design of the SCU1 together with the results of stand-alone cold tests. The SCU1's magnetic and cryogenic performance as well as its operating experience in the APS storage ring are also presented.

Challenges of in-vacuum and cryogenic permanent magnet undulator technologies

Abstract: An in-vacuum undulator (IVU) provides a means to reach high-brilliance x rays in medium energy storage rings. The development of short period undulators with low phase errors creates the opportunity for an unprecedented brilliant light source in a storage ring. Since the spectral quality from cryogenic permanent magnet undulators (CPMUs) has surpassed that of IVUs, NdFeB or PrFeB CPMUs have been proposed for many new advanced storage rings to reach high brilliance x-ray photon beams. In a low emittance ring, not only the performance of the undulator but also the choice of the lattice functions are important design considerations. Optimum betatron functions and a zero-dispersion function shall be provided in the straight sections for IVU/CPMUs. In this paper, relevant factors and design issues for IVUs and CPMUs are discussed together with many technological challenges in short period undulators associated with beam induced--heat load, phase errors, and the deformation of support girders.

Beam dynamics analysis of dielectric laser acceleration using a fast 6D tracking scheme

Abstract: An important step toward high fidelity beam-transport codes for dielectric laser accelerators is presented with the long-term goal of building an entire microchip-sized laser-driven accelerator.

Coherent resonance stop bands in alternating gradient beam transport

Abstract: An extensive experimental study is performed to confirm fundamental resonance bands of an intense hadron beam propagating through an alternating gradient linear transport channel. The present work focuses on the most common lattice geometry called ``FODO'' or ``doublet'' that consists of two quadrupoles of opposite polarities. The tabletop ion-trap system ``S-POD'' (Simulator of Particle Orbit Dynamics) developed at Hiroshima University is employed to clarify the parameter-dependence of coherent beam instability. S-POD can provide a non-neutral plasma physically equivalent to a charged-particle beam in a periodic focusing potential. In contrast with conventional experimental approaches relying on large-scale machines, it is straightforward in S-POD to control the doublet geometry characterized by the quadrupole filling factor and drift-space ratio. We verify that the resonance feature does not essentially change depending on these geometric factors. A few clear stop bands of low-order resonances always appear in the same pattern as previously found with the sinusoidal focusing model. All stop bands become widened and shift to the higher-tune side as the beam density is increased. In the space-charge-dominated regime, the most dangerous stop band is located at the bare betatron phase advance slightly above 90 degrees. Experimental data from S-POD suggest that this severe resonance is driven mainly by the linear self-field potential rather than by nonlinear external imperfections and, therefore, unavoidable at high beam density. The instability of the third-order coherent mode generates relatively weak but noticeable stop bands near the phase advances of 60 and 120 degrees. The latter sextupole stop band is considerably enhanced by lattice imperfections. In a strongly asymmetric focusing channel, extra attention may have to be paid to some coupling resonance lines induced by the Coulomb potential. Our interpretations of experimental data are supported by theoretical predictions and systematic multiparticle simulations.