A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing-wave linac and rf photoinjector powered by a single ultrastable rf transmitter at X-band rf frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire accelerator is approximately 1 meter long and produces hard x rays tunable over a wide range of photon energies. The colliding laser is a $\mathrm{Yb}:\mathrm{YAG}$ solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is $5\times 10^{11}\mathrm{photons}/\mathrm{second}$ in a 5% bandwidth and the brilliance is $2\times 10^{12}\mathrm{photons}/(\sec {\mathrm{mm}}^2{\mathrm{mrad}}^{2}0.1\%)$ in pulses with rms pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.

Beam lines using echo-enabled harmonic generation can be designed to have extremely low sensitivity to energy chirps in the electron beam, as shown through theory and detailed simulations. These designs would allow stable and coherent radiation to be produced even when using electron beams with a large amount of shot-to-shot jitter in the longitudinal profile.

Most hadron synchrotrons rely on lattice nonlinearities for Landau damping of impedance driven coherent modes of oscillation. However, in a collider, the presence of beam-beam interactions strongly modifies the transverse amplitude detuning and therefore the resulting stability diagram. A numerical tool to evaluate the effect of beam-beam on the stability diagram has been developed and is used to discuss observations during different phases of the operational cycle of the Large Hadron Collider during the 2012 proton run. In particular, we show the evolution of the stability diagram when the strength of long range beam-beam interactions is increased, during the betatron squeeze. Also, we investigate the stability of beams colliding with a small transverse offset and compare to observations of instabilities when bringing the beams into collision and while leveling the luminosity.

We have developed, at the SPARC test facility, a procedure for a real time self-amplified spontaneous emission free electron laser (FEL) device performance control. We describe an actual FEL, including electron and optical beam transport, through a set of analytical formulas, allowing a fast and reliable on-line “simulation” of the experiment. The system is designed in such a way that the characteristics of the transport elements and the laser intensity are measured and adjusted, via a real time computation, during the experimental run, to obtain an on-line feedback of the laser performances. The detail of the procedure and the relevant experimental results are discussed.

In a linear nonscaling fixed field alternating gradient accelerator, the large natural chromaticity of the machine results in a betatron tune that varies by several integers over the momentum range. Orbit correction is complicated by the consequent variation of the phase advance between lattice elements. Here we investigate how the correction of multiple closed orbit harmonics allows correction of both the closed orbit distortion and the accelerated orbit distortion over the momentum range.

The effects of space charge play a significant role in modern-day accelerators, frequently constraining the beam parameters attainable in an accelerator or in an accelerator chain. They also can limit the luminosity of hadron colliders operating either at low energies or with sub-TeV high-brightness hadron beams. The latter is applied for strongly cooled proton and ion beams in eRHIC—the proposed future electron-ion collider at Brookhaven National Laboratory. Several schemes were proposed to compensate for space-charge effects in a coasting (e.g., continuous) hadron beam, and some have been tested. Using an appropriate transverse profile of the electron beam (or plasma column) for a coasting beam would compensate both the tune shift and the tune spread in the hadron beam. But none of these methods address the issue of compensating space-charge induced tune spread in a bunched hadron beam, i.e., the dependence of the particle’s tune shift on its longitudinal position inside the bunch. In this paper we propose and evaluate a novel idea of using a copropagating electron bunch with mismatched longitudinal velocity to compensate the space-charge induced tune shift and tune spread. We present several practical examples of such a system.

We describe herein for the first time a full circuit model for electromagnetic pulse transmission in the Primary Test Stand (PTS)—the first TW class pulsed power driver in China. The PTS is designed to generate 8–10 MA current into a $z$-pinch load in nearly 90 ns rise time for inertial confinement fusion and other high energy density physics research. The PTS facility has four conical magnetic insulation transmission lines, in which electron current loss exists during the establishment of magnetic insulation. At the same time, equivalent resistance of switches and equivalent inductance of pinch changes with time. However, none of these models are included in a commercially developed circuit code so far. Therefore, in order to characterize the electromagnetic transmission process in the PTS, a full circuit model, in which switch resistance, magnetic insulation transmission line current loss and a time-dependent load can be taken into account, was developed. Circuit topology and an equivalent circuit model of the facility were introduced. Pulse transmission calculation of shot 0057 was demonstrated with the corresponding code FAST (full-circuit analysis and simulation tool) by setting controllable parameters the same as in the experiment. Preliminary full circuit simulation results for electromagnetic pulse transmission to the load are presented. Although divergences exist between calculated and experimentally obtained waveforms before the vacuum section, consistency with load current is satisfactory, especially at the rising edge.

For the European x-ray free electron laser (XFEL) a split-and-delay unit based on geometrical wavefront beam splitting and multilayer mirrors is built which covers the range of photon energies from 5 keV up to 20 keV. Maximum delays between $\mathrm{\Delta }\tau =\pm 2.5\mathrm{ps}$ at $h\nu =20\mathrm{keV}$ and up to $\mathrm{\Delta }\tau =\pm 23\mathrm{ps}$ at $h\nu =5\mathrm{keV}$ will be possible. Time-dependent wave-optics simulations have been performed by means of Synchrotron Radiation Workshop software for XFEL pulses at $h\nu =5\mathrm{keV}$. The XFEL radiation was simulated using results of time-dependent simulations applying the self-amplified spontaneous emission code FAST. Main features of the optical layout, including diffraction on the beam splitter edge and optics imperfections measured with a nanometer optic component measuring machine slope measuring profiler, were taken into account. The impact of these effects on the characterization of the temporal properties of XFEL pulses is analyzed. An approach based on fast Fourier transformation allows for the evaluation of the temporal coherence despite large wavefront distortions caused by the optics imperfections. In this way, the fringes resulting from time-dependent two-beam interference can be filtered and evaluated yielding a coherence time of ${\tau }_c=0.187\mathrm{fs}$ (HWHM) for real, nonperfect mirrors, while for ideal mirrors a coherence time of ${\tau }_c=0.191\mathrm{fs}$ (HWHM) is expected.

The present article summarizes the results of two experiments which were performed to study the radiation properties of backward transition radiation (BTR) in the extreme ultraviolet (EUV) region. This wavelength region is of particular interest for transverse beam profile imaging, because the spatial resolution is improved as a result of the reduced contribution in the imaging process of the fundamental diffraction limit. In addition, the influence of coherent effects in the transition radiation emission process, which have been observed in the visible region, might be mitigated. The first experiment, dedicated to the investigation of the BTR angular characteristics, indicates that the radiation yield in the EUV region is higher than theoretically expected and that it is even comparable to the yield in the visible region. The second measurement was devoted to transverse beam profile imaging based on quasimonochromatic BTR, in both the EUV and the visible region, and is a proof-of-principle experiment demonstrating that EUV BTR is a suitable candidate for standard beam profile diagnostics.

Quantum diffusion effects in undulator radiation in semiclassical approximation are considered. Short-term effects on the electron beam motion are discussed and it is shown that approaches based on diffusion approximation with drift-diffusion coefficients derived from undulator or bending magnet radiation spectrum, and on Poisson statistics with radiation spectrum defined by the local beding field, all lead to similar results in terms of electron energy spread for cases of practical interest. An analytical estimate of the influence of quantum diffusion on the undulator radiation spectrum is derived.

We describe a simple technique to passively bunch non-ultra-relativistic ($\lesssim 10\mathrm{MeV}$) electron bunches produced in conventional photoinjectors. The scheme employs a dielectric-lined waveguide located downstream of the electron source to impress an energy modulation on a picosecond bunch. The energy modulation is then converted into a density modulation via ballistic bunching. The method is shown to support the generation of subpicosecond bunch trains with multi-kA peak currents. The relatively simple technique is expected to find applications in compact, accelerator-based, light sources and advanced beam-driven accelerator methods.

Wakefields and beam instabilities are important issues for a storage ring and are described by various theoretical formalisms. Direct measurements of the beam motion related to different dynamical mechanisms are a useful input to accelerator optimization. This paper reports on an experimental method based on a simplified wakefield model, where bunch-by-bunch position information were monitored during the transient injection process at the Shanghai Synchrotron Radiation Facility. Processing the bunch-by-bunch data by means of the principal component analysis allowed for immediate operational improvements—such as in situ compensation of the kicker leakage, and energy matching between the booster and the storage ring.

In this paper, a compact hard X-ray free electron lasers (FEL) design is proposed with all X-band rf acceleration and two stage bunch compression. It eliminates the need of a harmonic rf linearization section by employing optics linearization in its first stage bunch compression. Quadrupoles and sextupoles are employed in a bunch compressor one (BC1) design, in such a way that second order longitudinal dispersion of BC1 cancels the second order energy correlation in the electron beam. Start-to-end 6-D simulations are performed with all the collective effects included. Emittance growth in the horizontal plane due to coherent synchrotron radiation is investigated and minimized, to be on a similar level with the successfully operating Linac coherent light source (LCLS). At a FEL radiation wavelength of 0.15 nm, a saturation length of 40 meters can be achieved by employing an undulator with a period of 1.5 cm. Without tapering, a FEL radiation power above 10 GW is achieved with a photon pulse length of 50 fs, which is LCLS-like performance. The overall length of the accelerator plus undulator is around 250 meters which is much shorter than the LCLS length of 1230 meters. That makes it possible to build hard X-ray FEL in a laboratory with limited size.

A 1.3 GHz ${\mathrm{Nb}}_3\mathrm{Sn}$ superconducting radio-frequency cavity prepared with a modified annealing step reached $B_{pk}>50\mathrm{mT}$, well above $B_{c1}=25\pm 7\mathrm{mT}$, without the strong $Q$-slope observed in previous ${\mathrm{Nb}}_3\mathrm{Sn}$ cavities. At 4.2 K, it has a $Q_0$ of approximately $1\times 10^{10}$ at $>10\mathrm{MV}/\mathrm{m}$, far outperforming Nb at useable gradients. At 2 K, quench occurred at $\sim 55\mathrm{mT}$, apparently due to a defect, so additional treatment may increase the maximum gradient. Material parameters of the coating were extracted from $Q$ vs $T$ data, including a $T_c$ of $18.0\pm 0.1\mathrm{K}$, close to the maximum literature value. High power pulses were used to reach fields far higher than in CW measurements, and near $T_c$, quench fields close to the superheating field were observed. Based on a review of previous experience with ${\mathrm{Nb}}_3\mathrm{Sn}$ cavities, a speculative mechanism involving weak link grain boundaries is presented to explain how the modified annealing step could be the cause of the absence of strong $Q$-slope. Finally, an analysis of the progress to date provides hints that the path forward for ${\mathrm{Nb}}_3\mathrm{Sn}$ cavities should focus on minimizing defects.

We analytically estimated the three-dimensional free electron laser (FEL) power gain length’s increase due to the collective effects of an ultrarelativistic electron beam, namely, geometric transverse wakefield, coherent synchrotron radiation, and microbunching instability. We showed that the gain length is affected by an increase of the electron beam projected emittance, even though the slice (local) emittance is preserved. We also proved that the minimum gain length and the maximum of output power may notably differ from the ones derived when collective effects are neglected. Finally, we demonstrated that our model may be handy for a parametric study of electron beam six-dimensional brightness and FEL performance as a function, e.g., of the bunch length compression factor, the accelerator alignment tolerances, and the optics design.

We study the dependence of the peak power of a 1.5 Å Terawatt (TW), tapered x-ray free-electron laser (FEL) on the transverse electron density distribution. Multidimensional optimization schemes for TW hard x-ray free-electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of ${\lambda }_r=1.5\AA$ using the fully three-dimensional FEL particle code genesis. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30%–70% reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian. An analysis of the transverse coherence of the radiation shows the coherence area to be much larger than the beam spotsize for all three distributions, making coherent diffraction imaging experiments possible.

The measurement of the beam orbit plays a very important role in particle accelerators. The button-type beam position monitor (BPM) was designed for the Shanghai Synchrotron Radiation Facility to reduce the impedances and to guarantee a high resolution of the measurement. Position resolution, beam impedance, higher-order mode, and impedance matching have been studied during the design based on the physical parameters of the storage ring at the Shanghai Synchrotron Radiation Facility. Meanwhile, an analytic formula of the BPM broadband impedance was derived based on a resistor-capacitor equivalent circuit. Thus, the impedance of the BPM could be analyzed quantitatively by simply measuring the capacitance of the electrode. This formula had been verified by comparing the results of the calculations of the formula and the simulations in MAFIA.

The initial modulation in the scheme for coherent electron cooling (CeC) rests on the screening of the ion charge by electrons. However, in a CeC system with a bunched electron beam, inevitably, a long-range longitudinal space charge force is introduced. For a relatively dense electron beam, its force can be comparable to, or even greater than, the attractive force from the ions. Hence, the influence of the space charge field on the modulation process could be important. If the 3D Debye lengths are much smaller than the extension of the electron bunch, the modulation induced by the ion happens locally. Then, in that case, we can approximate the long-range longitudinal space charge field as a uniform electric field across the region. As detailed in this paper, we developed an analytical model to study the dynamics of ion shielding in the presence of a uniform electric field. We solved the coupled Vlasov-Poisson equation system for infinite anisotropic electron plasma, and estimated the influences of the longitudinal space charge field to the modulation process for the experimental proof of the CeC principle at the Relativistic Heavy Ion Collider.