In this article we present the measurement and correction of the chromatic coupling in the LHC. The transverse coupling is calculated from turn-by-turn data, exciting the beam with an ac dipole. By adjusting the momentum relative to the reference energy and repeating the measurement, we obtain the transverse coupling dependency on momentum. The measurements are compared to the predictions from the magnetic model, and show good agreement. We describe the algorithm used to calculate the corrections, which are performed using skew sextupoles in the LHC lattice. A reduction in the chromatic coupling of a factor $2.5\pm 0.4$ for beam 1 and 1.6 $\pm 0.3$ for beam 2 was obtained after applying the corrections.

The harmonic magnetic field properties due to eddy currents have been studied with respect to the geometry of the vacuum beam chamber. We derived a generalized formula enabling the precise prediction of any field harmonics generated by eddy currents in beam tubes with different cross-sectional geometries. Applying our model to study the properties of field harmonics in beam tubes with linear dipole magnetic field ramping clearly proved that the circular cross section tube generates only a dipole field from eddy currents. The elliptic tube showed noticeable magnitudes of sextupole and dipole fields. We demonstrate theoretically that it is feasible to suppress the generation of the sextupole field component by appropriately varying the tube wall thickness as a function of angle around the tube circumference. This result indicates that it is possible to design an elliptical-shaped beam tube that generates a dipole field component with zero magnitude of sextupole. In a rectangular-shaped beam tube, one of the selected harmonic fields can be prevented if an appropriate wall thickness ratio between the horizontal and vertical tube walls is properly chosen. Our generalized formalism can be used for optimization of arbitrarily complex-shaped beam tubes, with respect to suppression of detrimental field harmonics.

Heavy-ion-induced desorption of two different cryogenic targets was studied with a new experimental setup installed at the GSI High Charge State Injector. One gold-coated and one amorphous-carbon-coated copper target, bombarded under perpendicular impact with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions, were tested. Partial pressure rises of ${\mathrm{H}}_2$, CO, ${\mathrm{CO}}_2$, and ${\mathrm{CH}}_4$ and effective desorption yields were measured at 300, 77, and 8 K using continuous heavy-ion bombardment. We found that the desorption yields decrease with decreasing target temperature and measured the yield rises as a function of CO gas cryosorbed at 8 K. In this paper we describe the experimental system comprising a new cryogenic target assembly, the preparation of the targets, the test procedure, and the evaluation of the effective pumping speed of the setup. Pressure rise and gas adsorption experiments are described; the obtained results are discussed and compared with literature data.

A neutrino factory has unparalleled physics reach for the discovery and measurement of $CP$ violation in the neutrino sector. A far detector for a neutrino factory must have good charge identification with excellent background rejection and a large mass. An elegant solution is to construct a magnetized iron neutrino detector (MIND) along the lines of MINOS, where iron plates provide a toroidal magnetic field and scintillator planes provide 3D space points. In this paper, the current status of a simulation of a toroidal MIND for a neutrino factory is discussed in light of the recent measurements of large ${\theta }_{13}$. The response and performance using the 10 GeV neutrino factory configuration are presented. It is shown that this setup has equivalent ${\delta }_{CP}$ reach to a MIND with a dipole field and is sensitive to the discovery of $CP$ violation over 85% of the values of ${\delta }_{CP}$.

In this paper, we present theoretical and simulation-based analyses of a novel, normal-conducting, multiple-cell, traveling wave accelerating structure. Instead of the conventional circular apertures, we utilize asymmetric complementary split-ring resonators to couple pillbox cavities and bring the phase velocity below that of the speed of light in vacuo. We show that this architecture exhibits a low, negative, group velocity and that the 0 through $\pi$ modes decrease in order of frequency—in contrast to conventional electrically coupled structures in which the 0 mode has the lowest frequency and the $\pi$ mode the highest. We illustrate the efficacy of the proposed design via electromagnetic and particle simulation results for a four-cell structure operating around 1.9 GHz. Results are given for operation in the $\pi$, $2\pi /3$, and $\pi /3$ modes. Our design achieves accelerating gradients of around $3.3\mathrm{MV}/\mathrm{m}$ and a cavity voltage of 0.594 MV for an applied rf power of 82 kW ($\pi$ mode). The accelerating gradients achieved are up to 3.3 times that of a conventional circular aperture-coupled design with the same phase velocity, rf excitation power, operating frequency, mode type, and number of cells.

Recent applications in need of compact low-frequency deflecting and crabbing cavities have initiated the design and development of new superconducting structures operating at high gradients with low losses. Previously, ${\mathrm{TM}}_{110}$-type deflecting and crabbing cavities were developed and have also been operated successfully. However, these geometries are not favorable designs for low operating frequencies. The superconducting rf-dipole cavity is the first compact deflecting and crabbing geometry that has demonstrated high gradients and high shunt impedance. Since the fundamental operating mode is the lowest mode and is widely separated from the nearest higher order mode, the rf-dipole design is an attractive geometry for effective damping of the higher order modes in high current applications. A 400 MHz rf-dipole cavity was designed, fabricated, and tested as a proof-of-principle cavity. The cavity achieved high operating gradients, and the multipacting levels were easily processed and did not reoccur.

The characterization of the transverse phase space of beams is a fundamental requirement for particle accelerators. We present a novel approach for measurement of transverse emittance for beams with space charge, an important quality indicator of transverse phase space. The method utilizes a lens-drift-screen setup similar to that of a quadrupole scan emittance measurement. Measurements of radius and divergence that can be obtained from beam produced radiation, e.g. optical transition, are used to calculate the cross-correlation term and therefore the rms emittance. A linear space-charge model is used in the envelope equations; hence, the errors in the measurement relate to the nonuniformity of the beam distribution. The emittance obtained with our method shows small deviation from those obtained by WARP simulations for beams with high space charge, in contrast to other techniques.

To meet the demand from the growing number of user experiments, multi-beam-line operation with a wide spectral range is seriously considered in x-ray free-electron laser facilities. In a conventional design, the beam line of low photon energies branches off from the middle of the accelerator to take out low energy electron beams. Here in this paper, a novel method is proposed to deliver bunch-to-bunch energy changed electron beams at the end of the accelerator. Since all accelerator components are operated in steady state, this method enables quasisimultaneous operation of multi-beam-line in the same undulator hall without degrading the stability and performance of the electron beam.

Autoresonance laser acceleration of electrons is theoretically investigated using circularly polarized focused Gaussian pulses. Many-particle simulations demonstrate feasibility of creating over 10-GeV electron bunches of ultrahigh quality (relative energy spread of order ${10}^{-4}$), suitable for fundamental high-energy particle physics research. The laser peak intensities and axial magnetic field strengths required are up to about ${10}^{18}\mathrm{W}/{\mathrm{cm}}^2$ (peak power $\sim 10\mathrm{PW}$) and 60 T, respectively. Gains exceeding 100 GeV are shown to be possible when weakly focused pulses from a 200-PW laser facility are used. In our parametric study of this acceleration scheme, substantial challenges still need to be dealt with, especially on the road to realizing experimentally the required high magnetic field strengths and laser powers.

We analyze the interaction between a charge and its electromagnetic field in the case of the charge moving in a waveguide and intersecting a boundary between two nondispersive media. The total work done by the field on the charge is calculated both analytically and numerically. It is shown that the work is positive under certain conditions, that is the force actuating the charge is accelerating. A physical interpretation of this phenomenon from the point of view of energy conservation is given. The kinetic energy gain per unit length and for all time of motion is analyzed as well.

An accelerator-driven subcritical system (ADS) program was launched in China in 2011, which aims to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power in multiple phases lasting about 20 years. The driver linac is defined to be 1.5 GeV in energy, 10 mA in current and in cw operation mode. To meet the extremely high reliability and availability, the linac is designed with much installed margin and fault tolerance, including hot-spare injectors and local compensation method for key element failures. The accelerator complex consists of two parallel 10-MeV injectors, a joint medium-energy beam transport line, a main linac, and a high-energy beam transport line. The superconducting acceleration structures are employed except for the radio frequency quadrupole accelerators (RFQs) which are at room temperature. The general design considerations and the beam dynamics design of the driver linac complex are presented here.

The neutrino factory is a facility for future precision studies of neutrino oscillations. A so-called near detector is essential for reaching the required precision for a neutrino oscillation analysis. The main task of the near detector is to measure the flux of the neutrino beam. Such a high intensity neutrino source like a neutrino factory provides also the opportunity for precision studies of various neutrino interaction processes in the near detector. We discuss the design concepts of such a detector. Results of simulations of a high resolution scintillating fiber tracker show that such a detector is capable of determining the neutrino flux normalization with an uncertainty of less than 1% by measuring pure leptonic interactions. Reconstruction of the neutrino energy in each event and a flux estimation based on the shapes of the neutrino energy spectra are discussed. A full setup of the near detector, consisting of a high granularity vertex detector, high resolution tracker, and muon catcher is also presented. Finally, a method to extrapolate the measured near detector flux to the far detector is shown, demonstrating that it is able to extract the correct values of ${\theta }_{13}$ and the $CP$ violation phase $\delta$ without any significant bias and with high accuracy.

Fixed field alternating gradient (FFAG) accelerators with vertical orbit excursion (VFFAGs) provide a promising alternative design for rings with fixed-field superconducting magnets. They have a vertical magnetic field component that increases with height in the vertical aperture, yielding a skew quadrupole focusing structure. Scaling-type VFFAGs are found with fixed tunes and no intrinsic limitation on momentum range. This paper presents the first multiparticle tracking of such machines. Proton driver rings to accelerate the 800 MeV beam from the ISIS synchrotron are presented, in terms of both magnet field geometry and longitudinal behavior during acceleration with space charge. The 12 GeV ring produces an output power of at least 2.18 MW. Possible applications of VFFAGs to waste transmutation, hadron therapy, and energy-recovery electron accelerators are also discussed.

We show that the difference resonance driven by the space charge pseudo-octupole of high intensity beams not only couples the beam core emittances; it can also lead to emittance exchange in the beam halo, which is of relevance for beam loss in high intensity accelerators. With reference to linear accelerators the “main resonance” $k_z/k_{x,y}=1$ (corresponding to the Montague resonance $2Q_x-2Q_y=0$ in circular accelerators) may lead to such a coupling and transfer of halo between planes. Coupling of transverse halo into the longitudinal plane—or vice versa—can occur even if the core (rms) emittances are exactly or nearly equal. This halo argument justifies additional caution in linac design including consideration of avoiding an equipartitioned design. At the same time, however, this mechanism may also qualify as an active dynamical halo cleaning scheme by coupling a halo from the longitudinal plane into the transverse plane, where local scraping is accessible. We present semianalytical emittance coupling rates and show that previously developed linac stability charts for the core can be extended—using the longitudinal to transverse halo emittance ratio—to indicate additional regions where halo coupling could be of importance.

Thermionic electron guns are capable of operating at high average currents in a variety of vacuum electronic applications, including conventional microwave tubes, but have been replaced by laser photocathode injectors for most applications requiring high-brightness electron beams. However, while laser photocathode guns are capable of providing the very high-brightness beams, they provide an increased level of system complexity and do not extrapolate well to injectors for high average current applications requiring high beam quality. We are developing a 714 MHz injector based on a gridded thermionic electron gun for these applications. This paper presents an experimental study, computer simulations, and analysis of the performance of an existing gridded thermionic electron gun as an injector prototype, and a design concept for an improved injector configuration based on these results.

In the 3 GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, significant losses were observed at the branching of the ${\mathrm{H}}^0$ dump line and the beam position monitor that was inserted downstream of the ${\mathrm{H}}^0$ dump branch duct. These losses were caused by the large-angle scattering of the injection and circulating beams at the charge-exchange foil. To realize high-power operation, these losses must be mitigated. Therefore, a new collimation system was developed and installed in October 2011. To efficiently optimize this system, the behavior of particles scattered by the foil and produced by the absorber were simulated, and the optimal position and angle of the absorber were investigated. During this process, an angle regulation method for the absorber was devised. An outline of this system, the angle regulation method for the absorber, and the performance of this new collimation system are described.

X-ray free-electron lasers (FELs) require a very high electron beam quality in terms of emittance and energy spread. Since 2004 high quality electrons produced by laser-wakefield accelerators have been demonstrated, but the electron quality up to now did not allow the operation of a compact x-ray FEL using these electrons. Maier et al. [Phys. Rev. X 2, 031019 (2012)] suggested a concept for a proof-of-principle experiment allowing FEL operation in the vacuum ultraviolet range based on an optimized undulator and bunch decompression using electron bunches from a laser-plasma accelerator as currently available. In this paper we discuss in more detail how a chicane can be used as a bunch stretcher instead of a bunch compressor to allow the operation of a laser-wakefield accelerator driven FEL using currently available electrons. A scaling characterizing the impact of bunch decompression on the gain length is derived and the feasibility of the concept is tested numerically in a demanding scenario.

Coulombian diffusion determines a dilution of bunching coefficients in free electron laser seeded devices. From the mathematical point of view the effect can be modeled through a heat-type equation, which can be merged with the ordinary Liouville equation, ruling the evolution of the longitudinal phase space beam distribution. We will show that the use of analytical tools like the generalized Bessel functions and algebraic techniques for the solution of evolution problems may provide a useful method of analysis and shine further light on the physical aspects of the underlying mechanisms.

A new scheme for accelerating positively charged particles in a plasma-wakefield accelerator is proposed. If the proton drive beam propagates in a hollow plasma channel, and the beam radius is of order of the channel width, the space charge force of the driver causes charge separation at the channel wall, which helps to focus the positively charged witness bunch propagating along the beam axis. In the channel, the acceleration buckets for positively charged particles are much larger than in the blowout regime of the uniform plasma, and stable acceleration over long distances is possible. In addition, phasing of the witness with respect to the wave can be tuned by changing the radius of the channel to ensure the acceleration is optimal. Two-dimensional simulations suggest that, for proton drivers likely available in future, positively charged particles can be stably accelerated over 1 km with the average acceleration gradient of $1.3\mathrm{GeV}/\mathrm{m}$.

The Single Bunch Selector (SBS) will be used on the Spiral2 linear accelerator to reduce the rate of high energy bunches reaching the target with, in principle, no residual particles from the suppressed bunches. For this purpose, a pulsed electromagnetic wave will travel along the $100\Omega$ microstrip meander line electrode of the SBS. In this work we describe the broadband accurate characterization of the electrode electromagnetic features. The method applied here leads to the analytical determination of complex characteristic impedance, propagation constant, and group velocity from a measurement of the $50\Omega$ scattering parameters on the meander transmission line. Particular care is given to the de-embedding phase of the transitions required to connect the meander electrode to the measurement device.