522 research outputs found
Matching small functions using centroid jitter and two beam position monitors
Matching to small beta functions is required to preserve emittance in plasma
accelerators. The plasma wake provides strong focusing fields, which typically
require beta functions on the mm-scale, comparable to those found in the final
focusing of a linear collider. Such beams can be time consuming to
experimentally produce and diagnose. We present a simple, fast, and noninvasive
method to measure Twiss parameters in a linac using two beam position monitors
only, relying on the similarity of the beam phase space and the jitter phase
space. By benchmarking against conventional quadrupole scans, the viability of
this technique was experimentally demonstrated at the FLASHForward
plasma-accelerator facility.Comment: 8 pages, 7 figure
Wakefield-Induced Ionization injection in beam-driven plasma accelerators
We present a detailed analysis of the features and capabilities of
Wakefield-Induced Ionization (WII) injection in the blowout regime of beam
driven plasma accelerators. This mechanism exploits the electric wakefields to
ionize electrons from a dopant gas and trap them in a well-defined region of
the accelerating and focusing wake phase, leading to the formation of
high-quality witness-bunches [Martinez de la Ossa et al., Phys. Rev. Lett. 111,
245003 (2013)]. The electron-beam drivers must feature high-peak currents
() and a duration comparable to the plasma
wavelength to excite plasma waves in the blowout regime and enable WII
injection. In this regime, the disparity of the magnitude of the electric field
in the driver region and the electric field in the rear of the ion cavity
allows for the selective ionization and subsequent trapping from a narrow phase
interval. The witness bunches generated in this manner feature a short duration
and small values of the normalized transverse emittance (). In addition, we show that the amount of injected
charge can be adjusted by tuning the concentration of the dopant gas species,
which allows for controlled beam loading and leads to a reduction of the total
energy spread of the witness beams. Electron bunches, produced in this way,
fulfil the requirements to drive blowout regime plasma wakes at a higher
density and to trigger WII injection in a second stage. This suggests a
promising new concept of self-similar staging of WII injection in steps with
increasing plasma density, giving rise to the potential of producing electron
beams with unprecedented energy and brilliance from plasma-wakefield
accelerators
Self-stabilizing positron acceleration in a plasma column
Plasma accelerators sustain extreme field gradients, and potentially enable
future compact linear colliders. Although tremendous progress has been achieved
in accelerating electron beams in a plasma accelerator, positron acceleration
with collider-relevant parameters is challenging. A recently proposed positron
acceleration scheme relying on the wake generated by an electron drive beam in
a plasma column has been shown to be able to accelerate positron witness beams
with low emittance and low energy spread. However, since this scheme relies on
cylindrical symmetry, it is possibly prone to transverse instabilities that
could lead, ultimately, to beam break-up. In this article, we show that the
witness beam itself is subject to various damping mechanisms and, therefore,
this positron acceleration scheme is inherently stable towards misalignment of
the drive and witness beams. This enables stable, high-quality plasma-based
positron acceleration
Young adults with mild traumatic brain injury--the influence of alcohol consumption--a retrospective analysis
PURPOSE: Alcohol abuse has been associated with aggressive behavior and interpersonal violence. Aim of the study was to investigate the role of alcohol consumption in a population of young adults with mild traumatic brain injuries and the attendant epidemiological circumstances of the trauma.
SUBJECTS AND METHODS: All cases of mild traumatic brain injury among young adults under 30 with an injury severity score <16 who were treated as inpatients between 2009 and 2012 at our trauma center were analyzed with regard to the influence of alcohol consumption by multiple regression analysis.
RESULTS: 793 patients, 560 men, and 233 women were included. The age median was 23 (range 14-30). Alcohol consumption was present in 302 cases. Most common trauma mechanism was interpersonal violence followed by simple falls on even ground. Alcohol consumption was present more often in men, unemployed men, patients who had interpersonal violence as a trauma mechanism, and in patients who were admitted to the hospital at weekends or during night time. It also increased the odds ratio to suffer concomitant injuries, open wounds, or fractures independently from the trauma mechanism. Length of hospital stay or incapacity to work did not increase with alcohol consumption.
CONCLUSIONS: Among young adults men and unemployed men have a higher statistical probability to have consumed alcohol prior to suffering mild traumatic brain injury. The most common trauma mechanism in this age group is interpersonal violence and occurs more often in patients who have consumed alcohol. Alcohol consumption and interpersonal violence increase the odds ratio for concomitant injuries, open wounds, and fractures independently from another
Chirp mitigation of plasma-accelerated beams using a modulated plasma density
Plasma-based accelerators offer the possibility to drive future compact light
sources and high-energy physics applications. Achieving good beam quality,
especially a small beam energy spread, is still one of the major challenges.
For stable transport, the beam is located in the focusing region of the
wakefield which covers only the slope of the accelerating field. This, however,
imprints a longitudinal energy correlation (chirp) along the bunch. Here, we
propose an alternating focusing scheme in the plasma to mitigate the
development of this chirp and thus maintain a small energy spread
Status Report on the Hydrodynamic Simulations of a Tapered Plasma Lens for Optical Matching at the ILC Source
The International Linear Collider is a planned electron-positron linear
collider with its positron source producing positrons by aiming undulator
radiation onto a rotating target. The resulting, highly divergent positron beam
requires immediate optical matching to improve the luminosity and therefore the
success of the intended collision experiments. Here, optical matching refers to
the process of capturing particles and making them available for downstream
beamline elements like accelerators. In the past, this has been done with
sophisticated coils, but more recently the usage of a current-carrying plasma,
a so-called plasma lens, has been proposed as an alternative. For the
International Linear Collider idealised particle tracking simulations have
already been done with the purpose of finding the optimal plasma lens design
with respect to the captured positron yield. The proposed design is
characterised by a linearly widened radius in beam direction. Now further
research and development of this design is required, including both experiments
with a prototype set-up as well as corresponding simulations modelling the
hydrodynamics of the current-carrying plasma and the resulting magnetic field.
The accuracy of the latter will benefit greatly from the former. In this work,
first preliminary hydrodynamic simulations instil confidence into further
endeavours.Comment: Talk presented at the International Workshop on Future Linear
Colliders (LCWS 2023), 15-19 May 2023. C23-05-15.
A Neuromuscular Training Program Performed on Foam is Accompanied by Improved Balance and Jump Height in Recreational Runners
Purpose: To assess balance, plyometric performance, and strength of recreational runners completing a neuromuscular training (NMT) program on a novel foam surface. Methods: After baseline testing, participants (n=14) completed 22-minute exercise sessions on foam twice weekly for eight weeks, and a post-training testing battery. Testing included lower quarter Y-balance test (LQYBT), dynamic leap and balance test (DLBT), squat jump and countermovement jump tests, and isometric strength testing of the foot and ankle via handheld dynamometry (HHD). Participants were asked to maintain their normal running routines throughout the study period and report any training missed due to injury. Results: Participants demonstrated significant (pConclusion: This study supports the use of progressive NMT on foam as a feasible intervention for recreational runners as all participants maintained typical running routines and reported no injuries. While further research is needed to directly inform possible effects of NMT on foam on injury risk and running performance, the improvements in single leg dynamic balance, lower body plyometric performance, and some indices of lower extremity strength in the present study suggest the efficacy of NMT performed on foam
Mechanical testing of a device for subcutaneous internal anterior pelvic ring fixation versus external pelvic ring fixation
BACKGROUND: Although useful in the emergency treatment of pelvic ring injuries, external fixation is associated with pin tract infections, the patient’s limited mobility and a restricted surgical accessibility to the lower abdomen. In this study, the mechanical stability of a subcutaneous internal anterior fixation (SIAF) system is investigated. METHODS: A standard external fixation and a SIAF system were tested on pairs of Polyoxymethylene testing cylinders using a universal testing machine. Each specimen was subjected to a total of 2000 consecutive cyclic loadings at 1 Hz with sinusoidal lateral compression/distraction (+/−50 N) and torque (+/− 0.5 Nm) loading alternating every 200 cycles. Translational and rotational stiffness were determined at 100, 300, 500, 700 and 900 cycles. RESULTS: There was no significant difference in translational stiffness between the SIAF and the standard external fixation when compared at 500 (p = .089), 700 (p = .081), and 900 (p = .266) cycles. Rotational stiffness observed for the SIAF was about 50 percent higher than the standard external fixation at 300 (p = .005), 500 (p = .020), and 900 (p = .005) cycles. No loosening or failure of the rod-pin/rod-screw interfaces was seen. CONCLUSIONS: In comparison with the standard external fixation system, the tested device for subcutaneous internal anterior fixation (SIAF) in vitro has similar translational and superior rotational stiffness
Biomechanical comparison of different external fixation configurations for posttraumatic pelvic ring instability
Background. External fixation is useful in the primary treatment of pelvic ring injuries. The present study compared the biomechanical stability of five different configurations of an external pelvic ring fixation system. Methods. Five configurations of an anterior external pelvic ring fixation system were tested using a universal testing machine. One single connecting rod was used in group “SINGLE,” two parallel connecting rods in group “DOUBLE,” two and four rods, respectively, in a tent-like configuration in groups “SINGLE TENT” and “DOUBLE TENT,” and a rhomboid-like configuration in group “RHOMBOID.” Each specimen was subjected to a total of 2000 consecutive cyclic loadings at 1 Hz lateral compression/distraction (±50 N) and torque (±0.5 Nm) loading alternating every 200 cycles. Translational and rotational stiffness were determined at 100, 300, 500, 700, and 900 cycles. Results. The “SINGLE TENT” and “RHOMBOID” configurations already failed with a preloading of 50 N compression force. The “DOUBLE” configuration had around twice the translational stability compared with the “SINGLE” and “DOUBLE TENT” configurations. Rotational stiffness observed for the “DOUBLE” and “DOUBLE TENT” configurations was about 50% higher compared to the SINGLE configuration. Conclusion. Using two parallel connecting rods provides the highest translational and rotational stability
The FLASHForward Facility at DESY
The FLASHForward project at DESY is a pioneering plasma-wakefield
acceleration experiment that aims to produce, in a few centimetres of ionised
hydrogen, beams with energy of order GeV that are of quality sufficient to be
used in a free-electron laser. The plasma wave will be driven by high-current
density electron beams from the FLASH linear accelerator and will explore both
external and internal witness-beam injection techniques. The plasma is created
by ionising a gas in a gas cell with a multi-TW laser system, which can also be
used to provide optical diagnostics of the plasma and electron beams due to the
<30 fs synchronisation between the laser and the driving electron beam. The
operation parameters of the experiment are discussed, as well as the scientific
program.Comment: 19 pages, 9 figure
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