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The bunch length is measured at CEBAF using an invasive technique. The technique depends on applying an energy chirp for the electron bunch and imaging it through a dispersive region. The measurements are taken through Arc1 and Arc2 at CEBAF. The fundamental equations, procedure and the latest results are given.
Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be cured with more effective HOM damping or a longitudinal feedback system.
Transverse mode coupling instability of a single bunch caused by oscillating wake field is considered in the paper. The instability threshold is found at different frequencies of the wake with space charge tune shift taken into account. The wake phase advance in the bunch length from 0 up to $4\pi$ is investigated. It is shown that the space charge can push the instability threshold up or down dependent on the phase advance. Transition region is investigated thoroughly, and simple asymptotic formulas for the threshold are represented.
In this paper we present electron bunch length measurements at the Argonne Wakefield Accelerator (AWA) photoinjector facility. The AWA accelerator has a large dynamic charge density range, with electron beam charge varying between 0.1 nC - 100 nC, and laser spot size diameter at the cathode between 0.1 mm - 18 mm. The bunch length measurements were taken at different charge densities using a metallic screen and a Michelson interferometer to perform autocorrelation scans of the corresponding coherent transition radiation (CTR). A liquid helium-cooled 4K bolometer was used to register the interferometer signal. The experimental results are compared with OPAL-T numerical simulations.
We Report Progress to date in the development of a Novel Bunch Length Diagnostic which uniquely uses the spatial profile of coherent transition radiation or coherent diffraction radiation to measure the root mean square average bunch length of an electron beam produced by an accelerator. This new technique can potentially be applied to a wide variety of accelerators and is simple and straightforward to use.
Currently, Fermilab Booster accelerates ~4.5E12 protons per pulse (ppp) in 81 bunches from 400 MeV to 8 GeV at 15 Hz to provide beam to multiple HEP experiments and is being upgraded to handle higher beam intensity >6.7E12 ppp at a repetition rate of 20 Hz. In the current mode of operation, we control longitudinal coupled bunch instabilities (LCBI) using combination of passive and active dampers. The issues with LCBI are expected to worsen at higher beam intensities. Here, we would like to investigate at what time in the beam cycle a particular mode is going to originate and how much it contributes at a different time of the acceleration cycle using the collected wall current monitor data from injection to extraction. Also, measure growth rates as a function of beam intensity for some dominant modes. Finally, this paper presents results from the observed LCBI analysis for the highest available beam intensities, unexpected findings, and future plans to mitigate the LCBI at higher beam intensities
We report on our investigations into density fluctuations in electron bunches. Noise and density fluctuations in relativistic electron bunches, accelerated in a linac, are of critical importance to various Coherent Electron Cooling (CEC) [1-5] concepts as well as to free-electron lasers (FELs). For CEC, the beam noise results in additional diffusion that counteracts cooling. In SASE FELs, a micro-wave instability starts from the initial noise in the beam and eventually leads to the beam microbunching yielding coherent radiation, and the initial noise in the FEL bandwidth plays a useful role. In seeded FELs, in contrast, such noise interferes with the seed signal, so that reducing noise at the initial seed wavelength would lower the seed laser power requirement [6-8]. Status of the project will be presented.
The SNS Beam Test Facility research program is focused detailed studies of beam distributions for medium-energy ion beams, with the goal of reconstructing realistic 6D bunch distributions to enable halo prediction. For complete characterization of the initial distribution, scan time scales exponentially with scan dimension. Currently, a full 6D measurement with ~10 points across most dimensions requires 30 hours. However, measurement of the 5D distribution f(x, x’,y,y’,w) can be done very rapidly using a hybrid slit/screen method. This approach requires ~4 hours to obtain at least 32 points/dimension, with very high resolution (0.5 keV) in the energy distribution. This presentation reports on the approach and results for 5D characterization of the initial RFQ-formed bunch. This includes higher-resolution views of previously reported transverse-longitudinal dependence and additional interplane dependencies that were not previously reported.
The Mu2e experiment has a stringent requirement for extinction of the pulsed proton beam, referring to the elimination of particles between proton bunches to a relative level of 10$^-10$, which means a single out-of-time particle in the inter-pulse gaps for every 250 complete proton pulses. As the construction of the Mu2e experiment nears completion, it is crucially important to make an early measurement of the beam extinction in its current condition. Hence the upstream extinction monitor was constructed and operated to probe for problems in the proton pulse structure or a higher than expected incidence rate of out-of-time particles. The analysis in this work comes from data taken in March 2026. The long data run showed a significant presence of out-of-time particles from ghost bunches in the Delivery Ring approximately 388 ns after the centers of the main proton pulses. These are hypothesized to be the result of a combination of a RF frequency mismatch, particle space charge, and machine impedance during the rebunching sequence in the Recycler Ring, which can lead to particles leaking into adjacent buckets, but further studies and simulations are needed to confirm this
Laser pump–X-ray probe experiments require control over the X-ray pulse pattern and timing. Here, the first use of pseudo-single-bunch mode at the Advanced Light Source in picosecond time-resolved X-ray absorption experiments on solutions and solids is reported. In this mode the X-ray repetition rate is fully adjustable from single shot to 500 kHz, allowing it to be matched to typical laser excitation pulse rates. Suppressing undesired X-ray pulses considerably reduces detector noise and improves signal to noise in time-resolved experiments. In addition, dose-induced sample damage is considerably reduced, easing experimental setup and allowing the investigation of less robust samples. Single-shot X-ray exposures of a streak camera detector using a conventional non-gated charge-coupled device (CCD) camera are also demonstrated.
We report the Advanced Light Source Upgrade (ALS-U) is a 4th generation diffraction-limited soft x-ray radiation source, consisting of a new accumulator ring (AR) and a new storage ring (SR). In both rings coupling-impedance driven instabilities need careful evaluation to ensure meeting the machine’s high-performance goals. This paper presents the workflow followed in building the impedance models and the beam-stability analysis based on those models. We follow the commonly accepted approach of separating the resistive-wall and the geometric parts of the impedance; the former is obtained by analytical formulas, the latter by numerical electro-magnetic codes (primarily CST Studio software) with perfectly-conducting boundary conditions. Impedance budgets are established and pseudo-Green functions calculated to be used in beam dynamics studies. We also present various ways to cross-check simulation results for reliable impedance modeling. Finally, the crucial single-bunch instability current thresholds for various operation modes are determined and discussed.
Wet-ground empty fruit bunches (EFBs), dry-ground EFB, and pelletized EFB were gasified in a laboratory-scale updraft fixed-bed reactor at differing temperatures and equivalent ratios (ERs) between 0.19 and 0.78 to evaluate the performance and quality of the syngas under autothermal operating conditions. In addition, the theoretical estimation of the key performance indicator of the ashes on the performance of the gasification process was obtained. The results show that for ERs > 0.4 the autothermal operating condition was achieved for pretreatments with pelletized and dry-ground EFBs, with reactor operating temperatures T > 700 °C. With wet EFB, this condition is achieved at any ER value. The average composition of the syngas from pelletized EFB presented the best average concentrations of the combustible species CO, H2, and CH4 when the ER values were between 0.25 and 0.40. The highest hot and cold thermal efficiency values were obtained for the gasification of EFB pellets with ER values between 0.25 and 0.40. For ground EFB, increases in the ER value led to improvements in hot thermal efficiency. Finally, during the EFB pellet gasification tests, no agglomeration and sintering problems were evidenced in comparison with wet-ground and dry-ground EFBs that showed slag formation, especially at ER < 0.46.
In this letter, we propose a mechanism to extend the spectral range of a waveguided free electron laser (FEL) oscillator driven by a rf LINAC toward significantly longer wavelengths without changing the undulator or accelerator design parameters. This mechanism involves selective amplification of a lower-frequency branch supported in a FEL due to the waveguide dispersion. Based on simulations performed for the terahertz FEL under construction at the Radboud University Nijmegen, we conclude that these long wavelengths can be efficiently amplified via stimulated super-radiance as the electron bunches are shorter than the radiation wavelength.
Generation and propagation of attosecond electron bunches along a cone-and-channel target are investigated by particle-in-cell simulation. The target electrons are pulled out by the oscillating electric field of an intense laser pulse irradiating a cone target and accelerated forward along the cone walls. It is shown that the energetic electrons can be further guided and confined by a channel attached to the cone tip. The propagation of these electrons along the channel induces a strong quasistatic magnetic field as well as a sheath electric field since a part of the energetic electrons expands into the surrounding vacuum. The electromagnetic field in turn confines the surface currents. With the cone-and-channel target the energetic electrons can be much better collimated and propagate much farther than that from the classical cone target.
The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile.
We develop a formalism for tunable coherent terahertz radiation generation from a relativistic electron beam, modulated by two laser beams, as it passes through a magnetic wiggler of wave vector k{sub w}z-caret. The lasers exert a beat frequency ponderomotive force on beam electrons, and modulate their velocity. In the drift space, velocity modulation translates into density modulation. As the beam bunches pass through the wiggler, they acquire a transverse velocity, constituting a transverse current that acts as an antenna to produce coherent THz radiation, when {omega}{sub 1}-{omega}{sub 2}=k{sub w}c/(cos{theta}-v{sub 0b}/c), where {omega}{sub 1}, {omega}{sub 2} are the frequencies of the lasers, v{sub 0b}z-caret is the beam velocity, and {theta} is the direction of maximum radiated intensity with respect to the direction of propagation of the beam.
The development of self-modulation instability (SMI) is investigated numerically for the 1 nC electron bunch available at Accelerator Test Facility (ATF) of Brookhaven National Laboratory (BNL). Possible experiment based on the simulation results is proposed. All the simulations are performed with the 2D-cylindrically symmetric particle-in-cell code.
For routine operation of Beijing Electron Positron Collider II (BEPCII) linac, many factors may affect the beam bunching process directly or indirectly. We present the measurements and analyses of the gun timing jitter, gun high voltage jitter, and beam energy at the exit of the standard acceleration section of the linac quantitatively. Almost 80 mV and more than 200 ps of gun high voltage and time jitters have ever been measured, respectively. It was analyzed that the gun timing jitter produced severe effects on beam energy than the gun high voltage jitter, if the timing jitter exceeded 100 ps which eventually deteriorates both the beam performance and the injection rate to the storage ring.