The statistics of FEL spontaneous emission power detected with a detector integration time much larger than the slippage time has been measured in many previous works at high frequencies. In such cases the quantum (shot) noise generated in the detection process is dominant. We have measured spontaneous emission in the Israeli electrostatic accelerator FEL (EA-FEL) operating in the mm-wave lengths. In this regime the detector is based on a diode rectifier for which the detector quantum noise is negligible. The measurements were repeated numerous times in order to create a sample space with sufficient data enabling evaluation of the statistical features of the radiated power. The probability density function of the radiated power was found and its moments were calculated. The results of analytical and numerical models are compared to those obtained in experimental measurements.

The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) was commissioned in October 2007, and successfully accomplished 3 GeV acceleration on October 31. Six run cycles through February 2008 were dedicated to commissioning the RCS, for which the initial machine parameter tuning and various underlying beam studies were completed. Then since May 2008 the RCS beam has been delivered to the downstream facilities for their beam commissioning. In this paper we describe beam tuning and study results following our beam commissioning scenario and a beam performance and operational experience obtained in the first commissioning phase through June 2008.

The 3 GeV Rapid Cycling Synchrotron (RCS) at Japan Proton Accelerator Research Complex is nearly at the operational stage with regard to the beam commissioning aspects. Recently, the design painting injection study has been commenced with the aim of high output beam power at the extraction. In order to observe the phase space footprint of the painting injection, a method was developed utilizing a beam position monitor (BPM) in the so-called single pass mode. The turn-by-turn phase space coordinates of the circulating beam directly measured using a pair of BPMs entirely positioned in drift space, and the calculated transfer matrices from the injection point to the pair of BPMs with several successive turns were used together in order to obtain the phase space footprint of the painting injection. There are two such pairs of BPMs placed in two different locations in the RCS, the results from which both agreed and were quite consistent with what was expected.

Pulsed laser deposition (PLD) has been proposed several years ago as a suitable technique to deposit a pure Mg film over a radio frequency (rf) gun Cu backflange in order to obtain a high efficiency photocathode surface for the generation of high brightness electron beams. In this paper we report preliminary experimental results on the emission properties of a PLD grown Mg film within the high electric field gradients of a rf gun showing the effects of the rf conditioning process on the cathode surface. Even though a laser cleaning process should be performed on the sample surface in order to remove contaminated layers, the results presented here are very promising for the realization of a final Mg-based photocathode.

The head-tail modes are described for the space charge tune shift significantly exceeding the synchrotron tune. A general equation for the modes is derived. The spatial shapes of the modes, their frequencies, and coherent growth rates are explored. The Landau damping rates are also found. The suppression of the transverse mode coupling instability by the space charge is explained.

Observations of strongly enhanced optical transition radiation (OTR) following significant bunch compression of photoinjector beams by a chicane have been reported during the commissioning of the Linac Coherent Light Source accelerator and recently at the Advanced Photon Source (APS) linac. These localized transverse spatial features involve signal enhancements of nearly a factor of 10 and 100 in the APS case at the 150-MeV and 375-MeV OTR stations, respectively. They are consistent with a coherent process seeded by noise and may be evidence of a longitudinal space charge microbunching instability which leads to coherent OTR emissions. Additionally, we suggest that localized transverse structure in the previous self-amplified spontaneous emission (SASE) free-electron laser (FEL) data at APS in the visible regime as reported at FEL02 may be attributed to such beam structure entering the FEL undulators and inducing the SASE startup at those “prebunched” structures. Separate beam structures 120 microns apart in $x$ and 2.9 nm apart in wavelength were reported. The details of these observations and operational parameters will be presented.

The Spallation Neutron Source ring extraction Lambertson septum magnet contains a strong skew quadrupole term, which has been identified as the source of causing a beam profile distortion on the target. We have performed 3D computer simulations to study the magnetic field quality in the magnet. The skew quad term is computed with different methods in simulations and is compared to measurement data. The origin of the large skew quad term is thoroughly investigated. The remedy for minimizing the skew quad term by modifying the magnet is proposed. Particle tracking is performed to verify the beam profile evolution through the existing and modified septum. The magnetic interference to the septum performance from an adjacent quadrupole is also assessed.

We use the ponderomotive potential of the rf field to accurately describe the motion of ions in an rf gun. We apply the method to the BNL $1/2$-cell superconducting radio-frequency photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, we propose simple mitigation techniques that can reduce the rate of ion bombardment.

Coherent synchrotron radiation can severely limit the performance of accelerators designed for high brightness and short bunch length. Examples include light sources based on energy recovery LINAC or free-electron lasers, and bunch compressors for linear colliders. In order to better simulate coherent synchrotron radiation, a one-dimensional formalism due to Saldin, Schneidmiller, and Yurkov has been implemented in the general beam dynamics code Bmad. Wide vacuum chambers are simulated by means of vertical image charges. Results from Bmad are here compared to analytical approximations, to numerical solutions of the Maxwell equations, and to the simulation code elegant and the code of Agoh and Yokoya.

Usual treatments of resistive wall effects in accelerators are limited to the normal skin effect regime of electrical conductivity in metals. Therefore they do not generally apply to the situations when beam-exposed metallic surfaces of the vacuum chamber are held at cryogenic temperatures, where simple metals exhibit anomalous skin effect behavior. These situations occasionally occur in accelerators with cold-bore devices, such as small-gap superconducting undulators. The amount of anomalous resistivity material can be substantial to significantly influence beam dynamics. To accurately estimate these effects, we expand the conventional treatment of resistive wall in accelerators into the extreme anomalous skin effect region. Starting with the surface impedance expressions, we derive resistive wall related quantities commonly used in accelerator physics, such as wake functions, wake potentials, loss factor, etc. in the extreme anomalous skin effect region. We follow with examples for resistive wall generated heat and transverse mode-coupling instability.

Numerical simulations of ${\mathrm{H}}^{-}$ stripping losses from blackbody radiation, electromagnetic fields, and residual gas have been implemented into the beam dynamics code TRACK. Estimates of the stripping losses along two high-intensity ${\mathrm{H}}^{-}$ linacs are presented: the Spallation Neutron Source linac currently being operated at Oak Ridge National Laboratory and an 8 GeV superconducting linac currently being designed at Fermi National Accelerator Laboratory.

A superconducting linear accelerator based on niobium quarter wave resonators has recently become operational to boost the energy of the heavy ion beams available from the existing 15 UD (unit doubled) Pelletron accelerator. The niobium resonators typically performed at an accelerating field of $3–6\mathrm{MV}/\mathrm{m}$ at 6 watts of input power in the test cryostat. When they were tested in the linac cryostat, the accelerating fields were drastically reduced and a number of other problems were also encountered. At present, all the problems have been diagnosed and solved. Many design modifications, e.g., in power coupler, mechanical tuner, helium cooling system, etc. were incorporated to solve the problems. A novel method of vibration damping was also implemented to reduce the effect of microphonics on the resonators. Finally, the accelerated beam through linac was delivered to conduct experiments.

In an undulator, magnetic field errors limit the quality of the emitted photon beam. In an ideal undulator, the sinusoidal motion of the electron beam and the emitted photons are in phase along the whole trajectory. Small variations in the magnetic field from period to period can produce phase errors and have to be corrected. This procedure is called shimming. Recently, a new scheme for superconductive undulators based on Faraday’s law of induction in a type-II superconductor was proposed in which these errors are automatically minimized. The field errors create currents and therefore magnetic fields in an array of coupled high temperature superconductor loops which minimize the field errors. In this paper the first experimental results of a test of this new concept are described.

We report a universal beam envelope equation that governs the transverse linear dynamics of high-intensity and high-brightness relativistic beams under constant acceleration in axisymmetric linear accelerators. This dimensionless and almost parameter-free nonlinear equation is useful for understanding scaling properties and for investigating nonlinear behaviors that are beyond analytical analysis. Particularly, we explore emittance compensation in high-brightness beams evolving from the space-charge regime to the thermal-emittance regime, a transition that commonly occurs during acceleration but is not well studied. A new formula is given for correctly computing the rms bunch emittance from slice envelopes, which is different from the commonly used quadratic sum of the thermal emittance and the rms emittance in the envelope phase space.

At SLAC, a five-cell, normal-conducting, $L$-band (1.3 GHz), standing-wave (SW) cavity was built as a prototype positron capture accelerator for the ILC. The structure met the ILC gradient goal but required extensive rf processing. When rf breakdowns occurred, a large variation was observed in the decay rate of the stored energy in the cavity after the input power was shut off. It appeared that the breakdowns were isolating sections of the cavity, and that the trapped energy in those sections was then partitioned among its natural modes, producing a distinct beating pattern during the decay. To explore this phenomenon further, an equivalent circuit model of cavity was created that reproduces well its normal operating characteristics. The model was then used to compute the spectra of trapped energy for different numbers of isolated cells. The resulting modal patterns agree well with those of the breakdown data, and thus such a comparison appears to provide a means of identifying the irises on which the breakdowns occurred.

An experimental setup was designed and fabricated to study superconducting wire motion under the influence of electromagnetic force. Experiments were conducted at 4.2 K by varying the experimental conditions such as the tension to the superconducting wire and different insulating materials at the interface of the superconducting wire and head part. The insulating materials used in the experiments were polyimide film and a high strength polyethylene fiber cloth, Dyneema. Details of the experimental setup and the test results are reported in this paper.

A magnetron-driven microtron injector has been developed for a terahertz free electron laser (FEL). An internal injection system was chosen for the microtron to achieve a compact and inexpensive design. The system provides acceleration of electrons with low emittance and energy spread that is highly important for the FEL. However, the intrapulse instabilities of the accelerated current and the bunch repetition rate inherent to the injection system make problems for the FEL operation. Simulations of the beam dynamics and the transient process allow one to compute the load characteristic of the accelerating cavity and the time-dependent accelerated current. The simulation techniques also allow one to calculate time-dependent deviations of the magnetron frequency in the coupled system of the accelerating and magnetron cavities, as well as deviations in the bunch repetition rate. The computations validate proposed concepts for increasing the intrapulse current stability with appropriate time-dependent variation of the magnetron power and decreasing the bunch repetition rate instability through a simple microwave scheme utilizing the microtron accelerating cavity concurrently as an external stabilizing resonator for the magnetron. The realized concepts and optimization of the microtron regimes using the simulated phase motion of the accelerated bunch provide stable operation of the terahertz FEL, tunable in the range of 1–3 THz with extracted macropulse power up to 50 Watts at the macropulse energy of $\sim 0.2\mathrm{mJ}$.

In the rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), the longitudinal painting is important to alleviate the space-charge effects. It is known that the momentum offset injection and applying the second harmonic rf voltage improves the bunching factor, which is defined as the ratio of average and peak current. Our simulation studies show that the large-amplitude second harmonic, 80% to the fundamental, is optimum, and the second harmonic phase sweep improves the bunching factor at the beginning of the injection period. We performed the beam tests of longitudinal painting in the J-PARC RCS. We proved that the longitudinal painting with the 80% second harmonic, the momentum offset of $-0.2\%$, and the second harmonic phase sweep improved bunching factors significantly.

The present article presents a system making it possible to produce time information at spatially separate points with picosecond range precision. By using this time information, the accelerator and storage rings of the Facility for Antiproton and Ion Research (FAIR) are to be synchronized. To do this, the rf cavities of these ring accelerators have to be controlled by signals having different phases and frequencies (0.4 to 5.4 MHz). Some frequencies of the signals are variable during acceleration due to what is referred to as ramp control. To enable synchronization of all these different signals, also during acceleration, the signals for controlling the cavities are not sent directly by the timing system, but instead two clock signals of constant frequency are sent. These clock signals are produced phase synchronously at different points up to 1 km apart and represent the time information. With the help of these clock signals, it is then possible to synchronize frequency generators that produce the signals actually needed for the cavities. Because of the universal character of the time information produced, it can be used not only to control the cavities but also to synchronize other processes. To transmit the clock signals, an optical network with dense wavelength division multiplex methods is used. The delay of the clock signals is measured and with the help of the delay information a reference generator produces, at the end of each transmission line, a phase-synchronous and phase-stable time reference. Since the delays of the clock signals are not constant due to environmental influences, they must be determined regularly. Using a prototype of this system, a precision of the time information of 21.2 ps on average was achieved. The short-term jitter exhibits a standard deviation of 7.57 ps. In addition to the description of the system, detailed information on noise characteristics is provided that can also be used to optimize other optical systems for transmission of time information.

The pulse line ion accelerator (PLIA) is a promising approach to accelerating heavy ion beams to regimes of interest for the study of high energy density physics (HEDP) and warm dense matter in a cost effective way. In this paper we demonstrate a PLIA-based design for a proposed HEDP machine, the neutralized drift compression experiment II. The simulation results from the injector to the exit of the accelerator using the particle-in-cell code WARP are presented. We show how the traveling wave structure of PLIA suggests straightforward strategies in controlling the longitudinal and transverse dynamics of the ion beam.