Recently, a novel technique to perform multiturn extraction from a circular particle accelerator was proposed. It is based on beam splitting and trapping, induced by a slow crossing of a nonlinear resonance, inside stable islands of transverse phase space. Experiments at the CERN Proton Synchrotron started in 2002 and evidence of beam splitting was obtained by summer 2004. In this paper, the measurement results achieved with both a low- and a high-intensity, single-bunch proton beam are presented.

The development of modern accelerator and free-electron laser projects often requires one to consider wakefields of very short bunches in arbitrary three-dimensional structures. To obtain the wake numerically by direct integration of fields is difficult, since it can take a long time for fields scattered off the structure to catch up to the short bunch. On the other hand, no general algorithm for indirect wakefield integration exists in the literature. In this report we review the known indirect methods to compute wake potentials in rotationally symmetric and cavitylike three-dimensional structures. We present several extensions to the existing techniques and then derive a new general indirect method for arbitrary three-dimensional structures. Finally, the new method is numerically tested and applied to the problem of a rectangular collimator.

We study how the critical gradient depends on the coil layout in a superconducting quadrupole for particle accelerators. We show that the results relative to a simple sector coil are well representative of the coil layouts that have been used to build several quadrupoles in the past 30 years. Using a semianalytical approach, we derive a formula that gives the critical gradient as a function of the coil cross-sectional area, of the magnet aperture, and of the superconducting cable parameters. This formula is used to evaluate the efficiency of several types of coil layouts (shell, racetrack, block, open midplane).

Challenging beam-induced energy deposition issues are addressed for the next generation of the LHC high-luminosity interaction regions based on ${\mathrm{Nb}}_3\mathrm{Sn}$ quadrupoles. Detailed mars15 Monte Carlo energy deposition calculations are performed for various coil diameters, thicknesses, and materials of the inner absorber at a field gradient of $200\mathrm{T}/\mathrm{m}$. It is shown that using the inner absorber made of tungsten-based materials can make the final focus superconducting quadrupoles compatible with a luminosity of ${10}^{35}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$.

The new trend is to operate storage ring based light sources in a “chromatic mode” with a distributed dispersive function in the straight sections for low emittance. The electron bunch heating induced by a storage ring free electron laser (FEL) has been investigated for such optics, and exhibits a more complex saturation process as compared to a usual achromatic mode of operation without dispersion in the straight sections. The correlated measured FEL power is then interpreted in terms of the electron bunch heating and compared to theoretical expectations. Experiments performed at UVSOR-II are here reported. The theoretical interpretation of the new saturation phenomenon is then discussed.

We consider the means to damp the wakefield left behind ultrarelativistic charges. In particular, we focus on a pair of traveling wave accelerators operating at an $X$-band frequency of 11.424 GHz. In order to maximize the efficiency of acceleration, in the context of a linear collider, multiple bunches of charged particles are accelerated within a given pulse of the electromagnetic field. The wakefield left behind successive bunches, if left unchecked, can seriously disturb the progress of trailing bunches and can lead to an appreciable dilution in the emittance of the beam. We report on a method to minimize the influence of the wakefield on trailing bunches. This method entails detuning the characteristic mode frequencies which make up the electromagnetic field, damping the wakefield, and interleaving the frequencies of adjacent accelerating structures. Theoretical predictions of the wakefield and modes, based on a circuit model, are compared with experimental measurements of the wakefield conducted within the ASSET facility at SLAC. Very good agreement is obtained between theory and experiment and this allows us to have some confidence in designing the damping of wakefields in a future linear collider consisting of several thousand of these accelerating structures.

We propose a novel gamma source suitable for generating a polarized positron beam for the next generation of electron-positron colliders, such as the International Linear Collider (ILC), and the Compact Linear Collider (CLIC). This 30-MeV polarized gamma source is based on Compton scattering inside a picosecond ${\mathrm{CO}}_2$ laser cavity generated from electron bunches produced by a 4-GeV linac. We identified and experimentally verified the optimum conditions for obtaining at least one gamma photon per electron. After multiplication at several consecutive interaction points, the circularly polarized gamma rays are stopped on a target, thereby creating copious numbers of polarized positrons. We address the practicality of having an intracavity Compton-polarized positron source as the injector for these new colliders.

The VUV and soft x-ray free electron laser FLASH (former VUV-FEL) is a user facility at DESY (Hamburg). In order to optimize the performance of the facility, an accurate characterization of the electron beam properties is essential. The transverse projected emittance, one of the important parameters characterizing the quality of an electron beam, is measured using a four monitor method with optical transition radiation monitors. A normalized rms emittance below 2 mm mrad for a 1 nC beam has been measured. In this paper we describe the experimental setup, data analysis methods, and present experimental results.

Electron storage rings of GeV energy with laser pulse stacking cavities are promising intense sources of polarized hard photons which, via pair production, can be used to generate polarized positron beams. In this paper, the dynamics of electron bunches circulating in a storage ring and interacting with high-power laser pulses is studied both analytically and by simulation. Both the common features and the differences in the behavior of bunches interacting with an extremely high power laser pulse and with a moderate pulse are discussed. Also considerations on particular lattice designs for Compton gamma rings are presented.

We have developed a relativistic-fluid model of the flow-electron plasma in a steady-state one-dimensional magnetically insulated transmission line (MITL). The model assumes that the electrons are collisional and, as a result, drift toward the anode. The model predicts that in the limit of fully developed collisional flow, the relation between the voltage $V_a$, anode current $I_a$, cathode current $I_k$, and geometric impedance $Z_0$ of a 1D planar MITL can be expressed as $V_a=I_a{Z}_{0}h(\chi )$, where $h(\chi )\equiv [(\chi +1)/4(\chi -1){]}^{1/2}-\ln \lfloor \chi +({\chi }^2-1{)}^{1/2}\rfloor /2\chi (\chi -1)$ and $\chi \equiv I_a/I_k$. The relation is valid when $V_a\gtrsim 1\mathrm{MV}$. In the minimally insulated limit, the anode current $I_{a,\min }=1.78V_a/Z_0$, the electron-flow current $I_{f,\min }=1.25V_a/Z_0$, and the flow impedance $Z_{f,\min }=0.588Z_0$. {The electron-flow current $I_f\equiv I_a-I_k$. Following Mendel and Rosenthal [Phys. Plasmas 2, 1332 (1995)], we define the flow impedance $Z_f$ as $V_a/(I_a^2-I_k^2{)}^{1/2}$.} In the well-insulated limit (i.e., when $I_a\gg I_{a,\min }$), the electron-flow current $I_f=9V_a^2/8I_a{Z}_0^2$ and the flow impedance $Z_f=2Z_0/3$. Similar results are obtained for a 1D collisional MITL with coaxial cylindrical electrodes, when the inner conductor is at a negative potential with respect to the outer, and $Z_0\lesssim 40\Omega$. We compare the predictions of the collisional model to those of several MITL models that assume the flow electrons are collisionless. We find that at given values of $V_a$ and $Z_0$, collisions can significantly increase both $I_{a,\min }$ and $I_{f,\min }$ above the values predicted by the collisionless models, and decrease $Z_{f,\min }$. When $I_a\gg I_{a,\min }$, we find that, at given values of $V_a$, $Z_0$, and $I_a$, collisions can significantly increase $I_f$ and decrease $Z_f$. Since the steady-state collisional model is valid only when the drift of electrons toward the anode has had sufficient time to establish fully developed collisional flow, and collisionless models assume there is no net electron drift toward the anode, we expect these two types of models to provide theoretical bounds on $I_a$, $I_f$, and $Z_f$.

Obtaining very short bunches in an electron storage ring is one of the frontiers of the accelerator physics. The strong rf focusing (SRFF) is a way to have short bunches at a given position in the ring, thanks to the principle of the bunch length modulation. Until now, the bunch length modulation has been studied only in the limit of zero current; in this paper we present the results of a simulation code suitable to study the effects of coherent synchrotron radiation and vacuum chamber wakefields on the single bunch longitudinal dynamics in the SRFF regime . The code has been applied to three different lattices that can be realized in the Frascati ${\mathrm{e}}^{+}/{\mathrm{e}}^{-}$ collider DAΦNE for a possible experiment on bunch length modulation.

The concepts of the laser-plasma based accelerator and injector are discussed here. The recent tests done at LOA as well as design studies of high-quality GeV electron beam production with low energy spread (1%) are presented. These laser-produced particle beams have a number of interesting properties and could lend themselves to applications in many fields, including medicine (radiotherapy), chemistry (radiolysis), and accelerator physics. They could be used as a source for the production of $\gamma$ ray beams for nondestructive material inspection by radiography, or for future compact X-free electron laser machines.

In an electron storage ring, coupling between dipole and quadrupole Robinson oscillations modifies the spectrum of longitudinal beam oscillations driven by radio-frequency (rf) generator phase noise. In addition to the main peak at the resonant frequency of the coupled dipole Robinson mode, another peak occurs at the resonant frequency of the coupled quadrupole mode. To describe these peaks analytically for a quadratic synchrotron potential, we include the dipole and quadrupole modes when calculating the beam response to generator noise. We thereby obtain the transfer function from generator-noise phase modulation to beam phase modulation with and without phase feedback. For Robinson-stable bunches confined in a synchrotron potential with a single minimum, the calculated transfer function agrees with measurements at the Aladdin 800-MeV electron storage ring. The transfer function is useful in evaluating phase feedback that suppresses Robinson oscillations in order to obtain quiet operation of an infrared beam line.

We have used coherent Smith-Purcell radiation in order to investigate the longitudinal (temporal) profile of the electron bunch at the FELIX facility. Detection of the far-infrared radiation was achieved by a simple and compact experimental arrangement, consisting of an array of 11 room-temperature pyroelectric detectors. Accurate determination of the background radiation, use of high quality optical filters, and an efficient light collection system are essential for this type of experiment. The radiated power is in good agreement with the predictions of the surface current description of this process. It is concluded that 90% of the bunch particles are contained within 5.5 ps, with a temporal profile that could be approximately triangular in shape.

Heavy ion drivers for warm dense matter and heavy ion fusion applications use intense charge bunches which must undergo transverse and longitudinal compression in order to meet the requisite high current densities and short pulse durations desired at the target. The neutralized drift compression experiment (NDCX) at the Lawrence Berkeley National Laboratory is used to study the longitudinal neutralized drift compression of a space-charge-dominated ion beam, which occurs due to an imposed longitudinal velocity tilt and subsequent neutralization of the beam’s space charge by background plasma. Reduced theoretical models have been used in order to describe the realistic propagation of an intense charge bunch through the NDCX device. A warm-fluid model is presented as a tractable computational tool for investigating the nonideal effects associated with the experimental acceleration gap geometry and voltage waveform of the induction module, which acts as a means to pulse shape both the velocity and line density profiles. Self-similar drift compression solutions can be realized in order to transversely focus the entire charge bunch to the same focal plane in upcoming simultaneous transverse and longitudinal focusing experiments. A kinetic formalism based on the Vlasov equation has been employed in order to show that the peaks in the experimental current profiles are a result of the fact that only the central portion of the beam contributes effectively to the main compressed pulse. Significant portions of the charge bunch reside in the nonlinearly compressing part of the ion beam because of deviations between the experimental and ideal velocity tilts. Those regions form a pedestal of current around the central peak, thereby decreasing the amount of achievable longitudinal compression and increasing the pulse durations achieved at the focal plane. A hybrid fluid-Vlasov model which retains the advantages of both the fluid and kinetic approaches has been implemented to describe the formation of pedestals in the current profiles. The comparison between the experimental measurements and the various theoretical models is excellent.

We investigate the quantum regime of a high-gain free-electron laser starting from noise. In the first part, we neglect the radiation propagation and we formulate a quantum linear theory of the $N$-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion. Quantum effects such as frequency shift, line narrowing, quantum limitation for bunching and energy spread, and minimum uncertainty states are described. Using a second-quantization formalism, we demonstrate quantum entanglement between the recoiling electrons and the radiation field. In the second part, we describe the field classically but we include propagation effects (i.e. slippage) and we demonstrate the novel regime of quantum SASE with high temporal coherence and discrete spectrum. Furthermore, we describe “quantum purification” of SASE: the classical chaotic spiking behavior disappears and the spectrum becomes a series of discrete very narrow lines which correspond to transitions between discrete momentum eigenstates (which originate high temporal coherence).

A one-dimensional, quasistatic model of a capillary discharge plasma has been developed. Such a plasma is useful as a medium to generate plasma waves for acceleration of electrons via processes such as laser wakefield acceleration or plasma wakefield acceleration. Another important characteristic of the plasma is its intrinsic parabolic density distribution near the center of the capillary, which can channel a laser beam along the capillary. The model is intended to be a design tool to aid in the selection of the capillary parameters in order to obtain desired plasma characteristics, e.g., plasma density and matched laser beam radius for guiding. An optional external axial magnetic field can be included, which improves the laser-channeling effect in some cases. The model also enables a measure of the potential for laser damage of the capillary wall. Results are presented for the design of a gas-filled capillary that will be tested during the staged electron laser acceleration–laser wakefield (STELLA-LW) experiment.

The dynamics of coupled betatron motion in a circular accelerator has been studied by the Hamilton perturbation theory or the transfer matrix formalism separately. In order to incorporate the theories with each other, we develop the transfer matrix formulation on the Hamilton perturbation theory. With the help of the Hamilton perturbation theory, we can analytically solve the equation of the coupled betatron motion in the vicinity of a difference resonance. Using the solution, we can construct the transfer matrix for the coupled motion. The matrix is shown to be symplectic and then transformed to the block diagonal form which consists of two normal modes and the coupling matrix. Thus, we derive the analytical representation for the normal mode parametrization of the transfer matrix describing the coupled betatron motion. Using the formalism, we investigate the two-dimensional beam ellipse in an electron storage ring.

This work presents technologies of copper accelerating structure diffusion joints. The formation conditions of copper diffusion joint with the minimal residual plastic strain are determined experimentally.

Electron bunch lengthening due to space-charge forces in state-of-the-art rf photoinjectors limits the minimum bunch length attainable to several hundreds of femtoseconds. Although this can be alleviated by increasing the transverse dimension of the electron bunch, a larger initial radius causes path-length differences in both the rf cavity and in downstream focusing elements. In this paper we show that a curved cathode virtually eliminates these undesired effects. Detailed numerical simulations confirm that significantly shorter bunches are produced by an rf photogun with a curved cathode compared to a flat cathode device. The proposed novel method will be used to provide 100 fs duration electron bunches for injection into a laser-driven plasma wakefield accelerator.