One of the focuses of research and development towards the construction of a muon collider is muon beam preparation. Simulation of frictional cooling shows that it can achieve the desired emittance reduction to produce high-luminosity muon beams. We show that for positively charged particles, charge-exchange interactions necessitate significant changes to schemes previously developed for negatively charged particles. We also demonstrate that foil-based schemes are not viable for positive particles.

In this paper we present a high-gain free-electron-laser (FEL) oscillator scheme composed of two oscillators that are ideally coupled unidirectionally, with the coupled signal power flowing from the master to the amplifier oscillator. Electron bunches driving the oscillators are in perfect synchronization with the optical pulses building up within the respective cavities. The scheme is applied to a 100 MeV range superconducting energy recovery linac FEL. The computed mJ level, ultrashort pulse ($<10\mathrm{cycles}$) output in the midinfrared region indicates the potential of the proposed FEL oscillator scheme in driving up-frequency conversion processes in the x-ray region, enabling tunable, high average brightness, attosecond scale coherent soft/hard x-ray sources.

We present a new method for computing the transverse transfer matrix for superimposed axisymmetric rf and solenoid field maps. The algorithm constructs the transfer matrix directly from one-dimensional rf and solenoid field maps without computing numerical derivatives or eigenfunction expansions of the field map data. In addition, this method accurately describes the dynamics of low energy particles starting from a solenoid-immersed cathode, allowing the method to simulate transport through both rf and electrostatic guns. Comparison of particle tracking with the transfer matrix, and direct integration of the equations of motion through several field setups, shows excellent agreement between the two methods.

We demonstrate multiphoton, single shot diffraction images of x rays produced by inverse Compton scattering a high-power ${\mathrm{CO}}_2$ laser from a relativistic electron beam, creating a pulse of 8.7 keV x rays. The tightly focused, relatively high peak brightness electron beam and high photon density from the 2 J ${\mathrm{CO}}_2$ laser yielded $6\times {10}^7$ x-ray photons over the full opening angle in a single shot. Single shot x-ray diffraction is performed by passing the x rays though a vertical slit and on to a flat silicon (111) crystal. ${10}^2$ diffracted photons were detected. The spectrum of the detected x rays is compared to simulation. The diffraction and detection of ${10}^2$ x rays is a key step to a more efficient time resolved diagnostic in which the number of observed x rays might reach ${10}^4$; enabling a unique, flexible x-ray source as a sub-ps resolution diagnostic for studying the evolution of chemical reactions, lattice deformation and melting, and magnetism.

A photoinjector, PHIN (PHotoINjector), has been realized at CERN by a joint effort of several institutes within the European Coordinated Accelerator Research in Europe program. The test facility has been installed and commissioned at CERN with the aim to demonstrate the beam parameters needed for the CLIC Test Facility 3 (CTF3). This beam is unique with respect to its long bunch train and high average charge per bunch requirements. The nominal beam for CTF3 consists of 1908 bunches each having a 2.33 nC charge and a bunch frequency of 1.5 GHz. Thus, a total charge of $\sim 4.4\mu \mathrm{C}$ has to be extracted and accelerated. The stability of the intensity and the beam parameters along this exceptionally high average current train is crucial for the correct functioning of the CLIC drive beam scheme. Consequently, extensive time-resolved measurements of the transverse and longitudinal beam parameters have been developed, optimized, and performed. The shot-to-shot intensity stability has been studied in detail for the electron and the laser beams, simultaneously. The PHIN photoinjector has been commissioned between 2008 and 2010 during intermittent operations. This paper reports on the obtained results in order to demonstrate the feasibility and the stability of the required beam parameters.

The ASACUSA collaboration developed an ultraslow antiproton beam source, monoenergetic ultraslow antiproton source for high-precision investigation (MUSASHI), consisting of an electromagnetic trap with a liquid He free superconducting solenoid and a low energy antiproton beam transport line. The MUSASHI was capable of trapping and cooling more than $1\times {10}^7$ antiprotons and extracting them as an ultraslow antiproton beam with energy of 150–250 eV.

We have performed three-dimensional simulations of beam dynamics for transverse electromagnetic mode (TEM) type rf deflectors: normal and superconducting. The compact size of these cavities as compared to the conventional ${\mathrm{TM}}_{110}$ type structures is more attractive particularly at low frequency. Highly concentrated electromagnetic fields between the parallel bars provide strong electrical stability to the beam for any mechanical disturbance. An array of six 2-cell normal conducting cavities or a single cell superconducting structure is enough to produce the required vertical displacement at the target point. Both the normal and superconducting structures show very small emittance dilution due to the vertical kick of the beam.

Several planned accelerator facilities call for hundreds of elliptical cavities operating cw with low effective beam loading, and therefore require cavities that have been mechanically optimized to operate at high $Q_L$ by minimizing $df/dp$, the sensitivity to microphonics detuning from fluctuations in helium pressure. Without such an optimization, the facilities would suffer either power costs driven up by millions of dollars or an extremely high per-cavity trip rate. ANSYS simulations used to predict $df/dp$ are presented as well as a model that illustrates factors that contribute to this parameter in elliptical cavities. For the Cornell Energy Recovery Linac (ERL) main linac cavity, $df/dp$ is found to range from 2.5 to $17.4\mathrm{Hz}/\mathrm{mbar}$, depending on the radius of the stiffening rings, with minimal $df/dp$ for very small or very large radii. For the Cornell ERL injector cavity, simulations predict a $df/dp$ of $124\mathrm{Hz}/\mathrm{mbar}$, which fits well within the range of measurements performed with the injector cryomodule. Several methods for reducing $df/dp$ are proposed, including decreasing the diameter of the tuner bellows and increasing the stiffness of the enddishes and the tuner. Using measurements from a Tesla Test Facility cavity as the baseline, if both of these measures were implemented and the stiffening rings were optimized, simulations indicate that $df/dp$ would be reduced from $\sim 30\mathrm{Hz}/\mathrm{mbar}$ to just $2.9\mathrm{Hz}/\mathrm{mbar}$, and the power required to maintain the accelerating field would be reduced by an order of magnitude. Finally, other consequences of optimizing the stiffening ring radius are investigated. It is found that stiffening rings larger than 70% of the iris-equator distance make the cavity impossible to tune. Small rings, on the other hand, leave the cavity susceptible to plastic deformation during handling and have lower frequency mechanical resonances, which is undesirable for active compensation of microphonics. Additional simulations of Lorentz force detuning are discussed, and the results are compared to measurements on the ERL injector cavities.

A characterization of the transverse emittance of a 200 pC, 6 ps long electron bunch has been performed in the Fermi@Elettra Free Electron Laser (FEL) first bunch compressor area. This region includes a magnetic bunch length compressor, diagnostics, and quadrupole magnets. The beam is time compressed in one stage, without linearization of the longitudinal phase space. Some growth of the normalized emittance has been measured in the compressor area. To understand this effect, we have investigated mechanisms of emittance growth such as coherent synchrotron radiation emission, chromatic aberration, and spurious dispersion. We show that careful optics control inside the compressor is essential for emittance growth reduction. The final configuration of one-stage magnetic compression limits the emittance to values below the design goal of 2 mm mrad, up to a compression factor of about 5. This machine configuration has been adopted to optimize FEL radiation output at wavelengths in the range 30–60 nm.

Theoretical aspects of stretched wire field integral measurements are investigated. A least square approach is used for the processing of the measured signal; it can be applied to any wire trajectory and it allows numerical correction of the wire position errors. Moreover, the signal from some multipoles can be compensated for in a way comparable to the “bucked” rotating coil method. This can be used for accurate measurements of field multipole errors. A stretched wire bench has been built at the European Synchrotron Radiation Facility. This bench has been used for measuring dipole, quadrupole, and sextupole magnets. The results obtained with various wire trajectories are compared. It is demonstrated that an accuracy of a few ${10}^{-4}$ of the main multipole can be obtained.

Using a diamond-based detector, the electron beam halo in a high-energy accelerator can be measured with a lower detection limit than that using other instruments, such as a core monitor, a dose meter, or an optical fiber. We have successfully measured an electron beam halo using diamond-based detectors operating in the ionization mode, which were installed in the beam duct to measure the intensity of the beam halo directly. Pulse-by-pulse measurements were adopted to suppress the background noise efficiently. Feasibility tests on the diamond-based detector and beam halo monitor were performed in the beam dump area of the 8 GeV SPring-8 synchrotron booster and at the 250 MeV SPring-8 Compact SASE Source test accelerator for the SPring-8 Angstrom Compact free electron LAser (SACLA), respectively. We achieved a lower detection limit of $2\times {10}^3\mathrm{electrons}/\mathrm{pulse}$ for single-shot measurement, which corresponds to a ratio of about ${10}^{-6}$ relative to the typical charge of the beam core of 0.3 pC. We also confirmed the feasibility of the electron beam halo monitor for use as an interlock sensor to protect undulator permanent magnets used in SACLA from radiation damage.

The presence of microbunching instabilities due to the compression of high-brightness electron beams at existing and future x-ray free-electron lasers (FELs) results in restrictions on the attainable lasing performance and renders beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e., heating the electron beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of advanced FEL schemes such as seeding. In this paper, we present a reversible electron beam heating system based on two transverse deflecting radio-frequency structures (TDSs) upstream and downstream of a magnetic bunch compressor chicane. The additional energy spread is introduced in the first TDS, which suppresses the microbunching instability, and then is eliminated in the second TDS. We show the feasibility of the microbunching gain suppression based on calculations and simulations including the effects of coherent synchrotron radiation. Acceptable electron beam and radio-frequency jitter are identified, and inherent options for diagnostics and on-line monitoring of the electron beam’s longitudinal phase space are discussed.

We demonstrate a sharp density transition for electron injection in laser wakefield acceleration through numerical study. This density transition is generated by a detached shock wave induced by a cylinder inserted into a supersonic helium gas flow. In a Mach 1.5 flow, the scale length of the density transition $L_{\mathrm{grad}}$ can approximately equal to plasma wavelength ${\lambda }_p$ at the shock front, and can be further reduced with an increase of the flow Mach number. A density down ramp with $L_{\mathrm{grad}}\ge {\lambda }_p$ can reduce the phase velocity of the wakefield and lower the energy threshold for the electrons to be trapped. Moreover, the quality of the accelerated beam may be greatly improved by precisely controlling of $L_{\mathrm{grad}}$ to be one ${\lambda }_p$. For an even sharper density down ramp with $L_{\mathrm{grad}}\ll {\lambda }_p$, the oscillating electrons in the plasma wave will up shift their phase when crossing the ramp, therefore a fraction of the electrons are injected into the accelerating field. For this injection mechanism, there is no threshold requirement for the pump laser intensity to reach wave breaking, which is a big advantage as compared with other injection mechanisms.

Simulation of x-ray generation from bombardment of various solid targets by quasimonoenergetic electrons is considered. The electron bunches are accelerated in a plasma produced by interaction of 500 mJ, 30 femtosecond laser pulses with a helium gas jet. These relativistic electrons propagate in the ion channel generated in the wake of the laser pulse. A beam of MeV electrons can interact with targets to generate x-ray radiation with keV energy. The MCNP-4C code based on Monte Carlo simulation is employed to compare the production of bremsstrahlung and characteristic x rays between 10 and 100 keV by using two quasi-Maxwellian and quasimonoenergetic energy distributions of electrons. For a specific electron spectrum and a definite sample, the maximum x-ray flux varies with the target thickness. Besides, by increasing the target atomic number, the maximum x-ray flux is increased and shifted towards a higher energy level. It is shown that by using the quasimonoenergetic electron profile, a more intense x ray can be produced relative to the quasi-Maxwellian profile (with the same total energy), representing up to 77% flux enhancement at $K_{\alpha }$ energy.

We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by $v_{\perp }/v_{\parallel }$, the measured spectrum $\gamma$, and the transverse electron bunch size in the bubble $r_{\perp }$. The latter is obtained via the measurement of the source size of the x rays emitted by the accelerating electron bunch in the bubble. We measure a normalized rms beam transverse emittance $<0.5\pi \mathrm{mm}\mathrm{mrad}$ as an upper limit for a spatially Gaussian, spectrally quasimonoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.

A scaling law for the time dependence of the dynamic aperture, i.e., the region of phase space where stable motion occurs, has been proposed in previous papers [M. Giovannozzi, W. Scandale, E. Todescoand , Part. Accel. 56, 195 (1996); M. Giovannozzi, W. Scandale, and E. Todesco, in Proceedings of the 1997 Particle Accelerator Conference, edited by M. Comyn, M. K. Craddock, M. Reiser, and J. Thomson (IEEE Service Center, Piscataway, NJ, 1997), p. 1445; M. Giovannozzi, W. Scandale, and E. Todesco, Phys. Rev. E 57, 3432 (1998)]. This law, based on the analysis of numerical simulations data, is not entirely phenomenological, but motivated by some fundamental theorems of the theory of dynamical systems and indicates that the dynamic aperture has a logarithmic dependence on time. This result is used in turn as a basis for deriving a scaling law for the intensity evolution in hadron storage rings. This relationship is presented and discussed in detail in this paper. Furthermore, experimental data were compared to the predictions of this law and showed a remarkable agreement.

Resonant photonuclear isotope detection (RPID) is a nondestructive detection/assay of nuclear isotopes by measuring $\gamma$ rays following photonuclear reaction products. Medium-energy wideband photons of $E_{\gamma }=12–16\mathrm{MeV}$ are used for the photonuclear $(\gamma ,n)$ reactions and $\gamma$ rays characteristic of the reaction products are measured by means of high-sensitivity Ge detectors. Impurities of stable and radioactive isotopes of the orders of $\mu \mathrm{gr}—\mathrm{ngr}$ and ppm—ppb are investigated. RPID is used to study nuclear isotopes of astronuclear and particle physics interests and those of geological and historical interests. It is used to identify radioactive isotopes of fission products as well.

Postcouplers (PCs) are devices used in order to reduce the effect of perturbations on the operating mode of a drift tube linac (DTL), using the resonant coupling stabilization method. In this article an equivalent circuit for a DTL equipped with PCs is presented, together with a 3D simulation analysis, which can explain the principle of postcoupler stabilization and define a new tuning strategy for DTL cavities. The PC tuning procedure based on the equivalent circuit and on frequency measurements has been tested and validated with measurements on the Linac4 DTL aluminum model, present at CERN.

${\mathrm{H}}^{-}$ stripping injection into the Fermilab recycler ring, combined with a beam phase painting technique, has been considered. The multiparticle three-dimensional beam dynamics with space charge has been studied numerically, using STRUCT and ORBIT codes, for different painting scenarios. In order to achieve a uniform (quasi-KV) phase-space distribution and to reduce the foil heating, the following parameters were investigated: the number of turns, strengths and temporal forms of kicker magnets, and foil geometry. Performance of the stripping foil is a crucial parameter of the whole injection scheme, so that the latter has been designed to minimize the hit number on the foil. The temperature regime has been evaluated both semianalytically and numerically using Monte Carlo codes MARS and MCNPX, with radiation cooling and transport of $\delta$ electrons taken into account. That all results agreed well proves the consistency of the models. It has been shown that the stripping foil can survive during injection with the parameters chosen for Project X at Fermilab.