For the injection upgrade of the $\Phi$ factory $\mathrm{DA}\Phi \mathrm{NE}$, new fast stripline kickers have been designed. They can operate with very short pulse generators to perturb only the injected bunch and the two stored adjacent ones. The design is based on tapering the striplines to simultaneously obtain low beam coupling and transfer impedances, excellent uniformity of the deflecting field, and better matching between the strip and the pulse generators. It has been done using 2D and 3D electromagnetic codes (Superfish and HFSS). The kickers have been constructed, tested, and installed in the collider. Measurements of the reflection coefficient at input ports and of the longitudinal and transverse beam coupling impedance have been also performed to characterize the structure and have been compared to the simulation results. A circuital model of general tapered striplines for a first order estimation of the transfer and longitudinal beam coupling impedances is also presented. Finally operational performances are described, pointing out the problems which occurred and the flexibility of the stripline structures that worked with both the short and with the previously installed long pulse generators and have been used as an additional damping kicker to improve the efficiency of the horizontal multibunch feedback system. This system is also a demonstration of the operation of fast kickers with similar characteristics as those for the International Linear Collider (ILC) damping rings (DRs).

Fast phase shifters are described that use a novel barium strontium titanate ceramic that can rapidly change its dielectric constant as an external bias voltage is changed. These phase shifters promise to reduce by $\sim 10$ times the power requirements for the rf source needed to drive an energy recovery linac (ERL). Such phase shifters will be coupled with superconducting radiofrequency cavities so as to tune them to compensate for phase instabilities, whether beam-driven or those caused by microphonics. The most promising design is presented, which was successfully cold tested and demonstrated a switching speed of $\sim 30\mathrm{ns}$ for 77 deg, corresponding to $<0.5\mathrm{ns}$ per deg of rf phase. Other crucial issues (losses, phase shift values, etc.) are discussed.

The use of electrostatic ion beam traps requires one to set many potentials on the electrodes (ten in our case), making the tuning much more difficult than with quadrupole traps. In order to obtain the best trapping conditions, an analytical formula giving the electrostatic potential inside the trap is required. In this paper, we present a general method to calculate the analytical expression of the electrostatic potential in any axisymmetric set of electrodes. We use conformal mapping to simplify the geometry of the boundary. The calculation is then performed in a space of simple geometry. We show that this method, providing good accuracy, allows one to obtain the potential on the axis as an analytic function of the potentials applied to the electrodes, thus leading to fast, accurate, and efficient calculations. We conclude by presenting stability maps depending on the potentials that enabled us to find the good trapping conditions for ${\mathrm{O}}^{4+}$ at much higher energies than what has been achieved until now.

A new method that explores turn-by-turn beam position monitor (BPM) data to calibrate lattice models of accelerators is proposed. The turn-by-turn phase space coordinates at one location of the ring are first established using data from two BPMs separated by a simple section with a known transfer matrix, such as a drift space. The phase space coordinates are then tracked with the model to predict positions at other BPMs, which can be compared to measurements. The model is adjusted to minimize the difference between the measured and predicted orbit data. BPM gains and rolls are included as fitting variables. This technique can be applied to either the entire or a section of the ring. We have tested the method experimentally on a part of the SPEAR3 ring.

When an energy-chirped bunch is undercompressed in a magnetic chicane, the compressed bunch also has an energy chirp. The chirp may be decreased by sending the bunch through bending magnets, since the largest energy loss from the wake of coherent synchrotron radiation occurs in the tail of a typical bunch. We obtain formulas for the dechirping of a rectangular bunch by short magnets, and apply this dechirping technique in a design for a free-electron laser.

Trapping of particles in nonlinear resonances in the presence of space charge and synchrotron motion may be a source of beam halo generation and beam loss in high intensity synchrotrons, in particular for extended storage times at the injection plateau as planned for the SIS100 synchrotron of the FAIR project. Although extensive simulation studies have theoretically demonstrated this mechanism, experimental evidence was so far limited to demonstration experiments at the CERN Proton Synchrotron (PS) in 2002–2003 using an octupolar resonance. Here we describe new experiments at the SIS18 synchrotron at GSI, where the resonance is driven by a sextupolar field error and horizontal static tune scans are taken across the resonance stop band. The new data significantly extend the previous observations by a complete set of measurements comparing beams with and without rf, both at low and high intensity. The correlation between transverse beam loss and simultaneous bunch length shortening provides strong evidence that the measured emittance and the loss in intensity are indeed caused by periodic resonance crossing, leading to the main effect of scattering but also to a lesser extent to the trapping of particles due to the combined effect of the nonlinear resonance and the space charge.

The scaling of the two important figures of merit, the transformer ratio $T$ and the longitudinal electric field $E_z$, with the peak drive-bunch current $I_p$, in a nonlinear plasma wakefield accelerator is presented for the first time. The longitudinal field scales as $I_P^{0.623\pm 0.007}$, in good agreement with nonlinear wakefield theory ($\sim I_P^{0.5}$), while the unloaded transformer ratio is shown to be greater than unity and scales weakly with the bunch current. The effect of bunch head erosion on both parameters is also discussed.

Longitudinal space charge (LSC) driven microbunching instability in electron beam formation systems of x-ray free-electron lasers (FELs) is a recently discovered effect hampering beam instrumentation and FEL operation. The instability was observed in different facilities in infrared and visible wavelength ranges. In this paper we propose to use such an instability for generation of vacuum ultraviolet (VUV) and x-ray radiation. A typical longitudinal space charge amplifier (LSCA) consists of few amplification cascades (drift space plus chicane) with a short undulator behind the last cascade. If the amplifier starts up from the shot noise, the amplified density modulation has a wide band, on the order of unity. The bandwidth of the radiation within the central cone is given by an inverse number of undulator periods. A wavelength compression could be an attractive option for LSCA since the process is broadband, and a high compression stability is not required. LSCA can be used as a cheap addition to the existing or planned short-wavelength FELs. In particular, it can produce the second color for a pump-probe experiment. It is also possible to generate attosecond pulses in the VUV and x-ray regimes. Some user experiments can profit from a relatively large bandwidth of the radiation, and this is easy to obtain in the LSCA scheme. Finally, since the amplification mechanism is broadband and robust, LSCA can be an interesting alternative to the self-amplified spontaneous emission free-electron laser (SASE FEL) in the case of using laser-plasma accelerators as drivers of light sources.

Head-tail modes in bunches with space charge are studied using particle tracking simulations. The eigenfrequencies and eigenfunctions of transverse coherent oscillations in a Gaussian bunch are determined and compared with theories. A model for an airbag distribution in a barrier potential gives good predictions for the head-tail spectrum and for eigenfunctions in bunches with space charge. Using numerical simulations, space-charge induced Landau damping in a bunch is demonstrated. The damping rates are quantified for different modes and space-charge tune shifts. Finally, the head-tail instability with space charge is studied for the resistive-wall impedance below the mode coupling threshold. Results demonstrate that space-charge induced damping can suppress the instability for moderately strong space charge; instability growth rates saturate at strong space charge, in agreement with theoretical predictions.

In this paper, a simplified theoretical model that allows prediction of the final stationary state attained by an initially mismatched beam is presented. The proposed stationary state has a core-halo distribution. Based on the incompressibility of the Vlasov phase-space dynamics, the core behaves as a completely degenerate Fermi gas, where the particles occupy the lowest possible energy states accessible to them. On the other hand, the halo is given by a tenuous uniform distribution that extends up to a maximum energy determined by the core-particle resonance. This leads to a self-consistent model in which the beam density and self-fields can be determined analytically. The theory allows one to estimate the emittance growth and the fraction of particles that evaporate to the halo in the relaxation process. Self-consistent $N$-particle simulation results are also presented and are used to verify the theory.

Cross section data from the HARP experiment for pion production by protons from a tantalum target have been convoluted with the acceptance of the front-end channel for the proposed neutrino factory or muon collider and integrated over the full phase space measured by HARP, to determine the beam-energy dependence of the muon yield. This permits a determination of the optimal beam energy for the proton driver for these projects. The cross section data are corrected for the beam-energy dependent amplification due to the development of hadronic showers in a thick target. The conclusion is that, for constant beam power, the yield is maximum for a beam energy of about 7 GeV, but it is within 10% of this maximum for $4<T_{\mathrm{beam}}<11\mathrm{GeV}$, and within 20% of the maximum for $T_{\mathrm{beam}}$ as low as 2 GeV. This result is insensitive to which of the two HARP groups’ results are used, and to which pion generator is used to compute the thick target effects.

Accelerator performance, in particular the average accelerating field and the cavity quality factor, depends on the physical and chemical characteristics of the superconducting radio-frequency (SRF) cavity surface. Plasma based surface modification provides an excellent opportunity to eliminate nonsuperconductive pollutants in the penetration depth region and to remove the mechanically damaged surface layer, which improves the surface roughness. Here we show that the plasma treatment of bulk niobium (Nb) presents an alternative surface preparation method to the commonly used buffered chemical polishing and electropolishing methods. We have optimized the experimental conditions in the microwave glow discharge system and their influence on the Nb removal rate on flat samples. We have achieved an etching rate of $1.7\mu \mathrm{m}/\min $ using only 3% chlorine in the reactive mixture. Combining a fast etching step with a moderate one, we have improved the surface roughness without exposing the sample surface to the environment. We intend to apply the optimized experimental conditions to the preparation of single cell cavities, pursuing the improvement of their rf performance.

The Boltzmann equation for the transport of pencil beams of light ions in semi-infinite uniform media has been calculated. The equation is solved for the practically important generalized 3D case of Gaussian incident primary light ion beams of arbitrary mean square radius, mean square angular spread, and covariance. The transport of the associated fragments in three dimensions is derived based on the known transport of the primary particles, taking the mean square angular spread of their production processes, as well as their energy loss and multiple scattering, into account. The analytical pencil and broad beam depth fluence and absorbed dose distributions are accurately expressed using recently derived analytical energy and range formulas. The contributions from low and high linear energy transfer (LET) dose components were separately identified using analytical expressions. The analytical results are compared with SHIELD-HIT Monte Carlo (MC) calculations and found to be in very good agreement. The pencil beam fluence and absorbed dose distributions of the primary particles are mainly influenced by an exponential loss of the primary ions combined with an increasing lateral spread due to multiple scattering and energy loss with increasing penetration depth. The associated fluence of heavy fragments is concentrated at small radii and so is the LET and absorbed dose distribution. Their transport is also characterized by the buildup of a slowing down spectrum which is quite similar to that of the primaries but with a wider energy and angular spread at increasing penetration depths. The range of the fragments is shorter or longer depending on their nuclear mass to charge ratio relative to that of the primary ions. The absorbed dose of the heavier fragments is fairly similar to that of the primary ions and also influenced by a rapidly increasing energy loss towards the end of their ranges. The present analytical solution of the Boltzmann equation accurately accounts for the loss of primary particles as well as their energy losses and multiple scattering. At the same time these quantities for the fragments are also accurately derived as based on the generalized Gaussian solution of the primaries and compared both with Monte Carlo and experimental data. The results are useful for fast transport calculations and biologically optimized therapy planning with light ion beams.

We propose inverse Compton scattering (ICS) of coherent synchrotron radiation (CSR) from a relativistic short electron bunch in energy recovery linacs (ERL) as a high-flux subpicosecond x-ray and $\gamma$-ray source. An advantage of the CSR scheme over a conventional ICS source is that no external laser is required, and synchronization between CSR pulses and electron bunches is obtained automatically. Moreover, higher-flux x rays can be generated from the ICS of CSR in an ERL operated at a high repetition rate, 100 MHz to 1.3 GHz. Using parameters of the Compact ERL at KEK, $1\times {10}^{13–14}\mathrm{phs}/\mathrm{s}$ b.w. 10% (the number of photons ${\mathrm{pulse}}^{-1}$ bandwidth ${\mathrm{unit}}^{-1}$) x ray with a 100 fs–1 ps pulse duration can be obtained, for an energy range from 0.04 to 4 keV. In the case of a 5-GeV ERL, $\gamma$ rays with energy around tens of MeV are generated with $1\times {10}^8\mathrm{phs}/\mathrm{pulse}$ b.w. 10% at a repetition rate of several hundreds of MHz.

The nonlinear threshold phenomena of particle reflection and capture of electrons in the induced Compton process that have previously been revealed in the case of plane monochromatic counterpropagating waves, take place also with the actual nonplane laser pulses of ultrashort duration and lead to particle acceleration. In contrast to analogous phenomena in the induced Cherenkov and undulator processes, the Compton reflection-capture mechanism with laser pulses of relativistic intensities practically may be realized for arbitrary initial energies of particles. The acceleration effect for particles initially in rest is explored numerically, taking into account the significance of this case connected with the relativistic electron bunches of high densities, which currently may be realized by relativistic lasers on the ultrathin solid foils where the electrons initially are almost in rest.

In self-consistent modeling of many-particle systems it is convenient to solve the Maxwell equations for self-fields in coordinates based in the laboratory with time as the evolution variable, but conventional and also convenient to follow particle motion in Frenet-Serret coordinates referred to a reference orbit, with arclength along that orbit as the evolution variable. We refer to these two pictures as the laboratory system and beam system descriptions, while emphasizing that a Lorentz transformation is not involved; it is only a matter of two alternative descriptions of motion in one inertial frame. The problem then arises of how to express the laboratory system charge/current density for the Maxwell equations in terms of the phase space density described in the beam system. We find the exact expression, then make justified approximations to put the formula in a simple and practical form. Incidentally, we derive exact and approximate equations of motion in the different coordinates, without the use of the canonical formalism. The results have been applied in a study of coherent synchrotron radiation in bunch compressors.

We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy $>100\mathrm{MeV}$) was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense materials that are placed at a large distance from the source. We report radiographic imaging of steel with submillimeter resolution.

The Large Hadron Collider rf station-beam interaction strongly influences the longitudinal beam dynamics, both single-bunch and collective effects. Nonlinearities and noise generated within the radio frequency (rf) accelerating system interact with the beam and contribute to beam motion and longitudinal emittance blowup. Thus, the noise power spectrum of the rf accelerating voltage strongly affects the longitudinal beam distribution. Furthermore, the coupled-bunch instabilities are also directly affected by the rf components and the configuration of the low level rf (LLRF) feedback loops. In this work we present a formalism relating the longitudinal beam dynamics with the rf system configurations, an estimation of collective effects stability margins, and an evaluation of longitudinal sensitivity to various LLRF parameters and configurations.

We use a Vlasov-Fokker-Planck program and a linearized Vlasov solver to study the microwave instability threshold of impedance models: (1) a $Q=1$ resonator and (2) shielded coherent synchrotron radiation (CSR), and find the results of the two programs agree well. For shielded CSR we show that only two dimensionless parameters, the shielding parameter $\Pi$ and the strength parameter $S_{\mathrm{csr}}$, are needed to describe the system. We further show that there is a strong instability associated with CSR, and that the threshold, to good approximation, is given by $(S_{\mathrm{csr}}{)}_{\mathrm{th}}=0.5+0.12\Pi$. In particular, this means that shielding has little effect in stabilizing the beam for $\Pi \lesssim 2$; for larger $\Pi$ it is effective, with threshold current depending on shielding aperture as $h^{-3/2}$. We, in addition, find another instability in the vicinity of $\Pi =0.7$ with a lower threshold, $(S_{\mathrm{csr}}{)}_{\mathrm{th}}\approx 0.2$. We find that the threshold to this instability depends strongly on damping time, $(S_{\mathrm{csr}}{)}_{\mathrm{th}}\sim {\tau }_p^{-1/2}$, and that the tune spread at threshold is small—both hallmarks of a weak instability.