Large-scale Particle Accelerators Research Articles

Rigid waist shift: A new method for local coupling corrections in the LHC interaction regions

Successful operation of large-scale particle accelerators depends on the precise correction of magnet field or alignment errors present in the machine. In the Large Hadron Collider (LHC), transverse linear coupling has been shown to have a significant impact on the beam dynamics. However, current measurement methods are not sufficient for precise local coupling measurement at the interaction point. In this paper, an approach to determine interaction region local coupling corrections with a rigid waist shift based on correlated global variables such as the closest tune approach $|{C}^{\ensuremath{-}}|$ is presented. The validity of the method is demonstrated through simulations and experimental measurements taken during the LHC Run 3 commissioning in 2022, where determined corrections were applied and led to a measured luminosity increase of 9.7% and 3.5% at the ATLAS and CMS detectors, respectively.

Tabletop laser-driven gamma-ray source with nanostructured double-layer target

Laser-driven gamma-ray source potentially offers a compact, cost-effective, ultra-short, and ultra-bright alternative to conventional gamma-ray sources based on large-scale particle accelerators. Based on the laser-driven approach, we use multidimensional particle-in-cell simulations to demonstrate that a nanostructured double-layer target, which consists of a nanostructured foam coated on top of a metal substrate, can absorb laser energy into high-energy electrons in the nanostructured foam, and then efficiently convert it into copious gamma photons via the nonlinear Compton scattering process enabled by the solid-density substrate, which acts as a plasma mirror to reflect the laser pulse. The effects of different nanostructures in the foam target and the oblique laser incidence are presented. It is shown that the conversion efficiency of gamma photons increases when the size of nanoparticles decreases or the filling factor of nanoparticles increases in nanostructured foam target, but decreases when the laser incidence angle increases. At realistic conditions with nanostructured foam and non-normal incidence, the double-layer target still exhibits an unprecedentedly high conversion efficiency in high-energy gamma-ray production due to the laser reflection by the plasma mirror, which can be two and even three orders of magnitude higher than that of the single-layer target without the substrate using currently available lasers with intensity of 1021 .

Multistage coupling of independent laser-plasma accelerators.

Laser-plasma accelerators (LPAs) are capable of accelerating charged particles to very high energies in very compact structures. In theory, therefore, they offer advantages over conventional, large-scale particle accelerators. However, the energy gain in a single-stage LPA can be limited by laser diffraction, dephasing, electron-beam loading and laser-energy depletion. The problem of laser diffraction can be addressed by using laser-pulse guiding and preformed plasma waveguides to maintain the required laser intensity over distances of many Rayleigh lengths; dephasing can be mitigated by longitudinal tailoring of the plasma density; and beam loading can be controlled by proper shaping of the electron beam. To increase the beam energy further, it is necessary to tackle the problem of the depletion of laser energy, by sequencing the accelerator into stages, each powered by a separate laser pulse. Here, we present results from an experiment that demonstrates such staging. Two LPA stages were coupled over a short distance (as is needed to preserve the average acceleration gradient) by a plasma mirror. Stable electron beams from a first LPA were focused to a twenty-micrometre radius--by a discharge capillary-based active plasma lens--into a second LPA, such that the beams interacted with the wakefield excited by a separate laser. Staged acceleration by the wakefield of the second stage is detected via an energy gain of 100 megaelectronvolts for a subset of the electron beam. Changing the arrival time of the electron beam with respect to the second-stage laser pulse allowed us to reconstruct the temporal wakefield structure and to determine the plasma density. Our results indicate that the fundamental limitation to energy gain presented by laser depletion can be overcome by using staged acceleration, suggesting a way of reaching the electron energies required for collider applications.

Switching speed effect of phase shift keying in SLED for generating high power microwaves

SLAC energy doubler (SLED) type radio-frequency pulse compressors are widely used in large-scale particle accelerators for converting long-duration moderate-power input pulses into short-duration high-power output pulses. Phase shift keying (PSK) is one of the key components in SLED pulse compression systems. Performance of the PSK will influence the output characteristics of the SLED, such as the rise-time of the output pulse, maximal peak power gain, and energy efficiency. In this paper, a high power microwave source based on power combining and pulse compression of conventional klystrons is introduced. The effects of nonideal PSK with slow switching speed and PSK without power output during the switching process are investigated, and the experimental results with nonideal PSK agree well with the analytical results.

Quench Considerations and Protection Scheme of a High Field HTS Dipole Insert Coil

The large scale particle accelerators of the future in the 20 T regime are enabled by high temperature superconducting magnets. The dipole magnets needed in new high-field accelerators can be constructed with an YBCO insert and a Nb3Sn outsert. Such a configuration makes the quench analysis and magnet protection challenging because the quench behavior in both of these coils is different and there is very strong inductive coupling between the coils. The Nb3Sn coil is characterized by high energy and current and relatively fast quench propagation velocity. However, quench propagates slowly in YBCO coils because of typically wide spread large temperature margin. Currently, in the EuCARD project, a European collaboration is targeting to construct a small-scale high field YBCO-Nb3Sn hybrid magnet. In this paper, we scrutinize quench in the YBCO insert. We utilized an approach based on a solution of the heat diffusion equation with the finite element method. Additionally, we present a protection scheme for the coil.

Vacuum System for Large-Scale Particle Accelerators —In the case of KEKB B-factory—

Main features and key issues of the vacuum system for large-scale particle accelerators are presented, taking the KEKB vacuum system as an example. Other than its large scale and complexity, a distinctive difference of the accelerator vacuum system from other vacuum systems is the presence of high-energy charged-particle beams in the vacuum chamber (beam pipe). This brings troublesome but interesting problems into the system, such as the gas desorption by the synchrotron radiation from beams, the electro-magnetic interaction between beams and vacuum components and the interaction between beams and electrons or ions. These problems are more obvious on the KEKB vacuum system due to the unprecedented high stored beam current. The vacuum system will become increasingly important in future high-performance accelerators.

Evidence for non-linear BCS resistance in SRF cavities

Very powerful RF cavities are now being developed for future large-scale particle accelerators such as the International Linear Collider (ILC). The basic model for the cavity quality factor Q-slope in high gradient SRF cavities, i.e. the reduction of Q with increasing operating electric and magnetic fields, is the so-called thermal feedback model (TFBM). Most important for the agreement between the model and experimental data, however, is which different surface resistance contributions are included in the TFBM. This paper attempts to further clarify if the non-linear pair-breaking correction to the BCS resistance [A. Gurevich, in: Pushing the Limits of RF Superconductivity Workshop, ANL, September 2004; A. Gurevich, This conference.] is among those surface resistance contributions, through a comparison of TFBM calculations with experimental data from bulk Nb cavities built and tested at several different laboratories.

Dispersion structures in the energetic ion and electron spectra in the auroral regions: Their nature, properties and implication

In DOK-2 experiments onboard Interball 1,2 (Lutsenko at al., 1998) we observed ∼200 dispersion structures in energetic ion and electron spectra in the auroral zones of the Earth's magnetosphere at ILAT=67–74° (L=6.5–13.2). Some detailed analysis results for ∼40 of these dispersion events are given. Their main characteristics show that we have deal with particles, which were injected momentary onto closed magnetic field lines from the plasma sheet and experienced a gradient-curvature drift. In some cases we observed ions from one injection making several turns around the Earth, which allowed us to find accurate values of drift periods in the real magnetic field. Due to high energy and time resolutions of DOK-2 the dispersion structure analysis may give a drift start time To with an accuracy of tens of seconds and an estimation of the acceleration process duration which was ∼1 min. The time To was compared with the time history of UVI brightening in the auroral oval. The comparison can help to determine the moment of a large-scale particle acceleration in the chain of events accompanying substorm development. For several substorms source energetic particle spectra were reconstructed from our dispersion event data.