Energy Compression and Stabilization of Laser-Plasma Accelerators.

Laser-plasma accelerators outperform current radio frequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from laser-plasma accelerators. Realistic start-to-end simulations demonstrate the potential of these postacceleration phase-space manipulations for simultaneously reducing an initial energy spread and energy jitter of ∼1-2% to ≲0.1%, closing the beam-quality gap to conventional acceleration schemes.

The effect of the number of active electrode poles during tined lead placement on long-term efficacy of sacral neuromodulation in patients with faecal incontinence.

AIM: There is an ongoing debate as to whether or not the efficacy of sacral neuromodulation (SNM) is optimized by maximizing the total number of active electrode poles (AEPs) during lead placement because there are more programming options. However, this is at the cost of increased operating time. The aims of this study were to establish if a higher number of AEPs improves SNM efficacy during the trial period and after permanent implantable pulse generator (IPG) placement and if there is there a correlation between number of AEPs and battery life of the first placed IPG. METHOD: This was a single centre retrospective cohort study of new patients with faecal incontinence who underwent SNM between 2000 and 2018. Exclusion criteria were sphincter defect > 30%, rectocele/enterocele Grade 3 or higher and incomplete records. RESULTS: In all, 288/456 (63%) patients (women 91%; mean age 58.5 ± 11.7 years) were eligible for analysis. The number of AEPs during lead placement was two (n = 42, 14.5%), three (n = 82, 28.5%) and four (n = 164, 57%). There was no association between the number of AEPs during tined lead placement and long-term efficacy. Neither the success rate of the trial phase nor the battery life after first placed IPG was influenced by the number of AEPs. CONCLUSION: In this study, the number of AEPs does not seem to influence long-term efficacy of SNM success rate during the trial phase or the battery life of the first placed IPG. However, we also suggest that at the very least there should be two AEPs at lead placement.

Compact Multistage Plasma-Based Accelerator Design for Correlated Energy Spread Compensation.

The extreme electromagnetic fields sustained by plasma-based accelerators could drastically reduce the size and cost of future accelerator facilities. However, they are also an inherent source of correlated energy spread in the produced beams, which severely limits the usability of these devices. We propose here to split the acceleration process into two plasma stages joined by a magnetic chicane in which the energy correlation induced in the first stage is inverted such that it can be naturally compensated in the second. Simulations of a particular 1.5-m-long setup show that 5.5 GeV beams with relative energy spreads of 1.2×10^{-3} (total) and 2.8×10^{-4} (slice) could be achieved while preserving a submicron emittance. This is at least one order of magnitude below the current state of the art and would enable applications such as compact free-electron lasers.

Hybrid LWFA-PWFA staging as a beam energy and brightness transformer: conceptual design and simulations.

We present a conceptual design for a hybrid laser-driven plasma wakefield accelerator (LWFA) to beam-driven plasma wakefield accelerator (PWFA). In this set-up, the output beams from an LWFA stage are used as input beams of a new PWFA stage. In the PWFA stage, a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations. In addition, preliminary simulation results for a proof-of-concept experiment in Helmholtz-Zentrum Dresden-Rossendorf (Germany) are shown. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Chirp Mitigation of Plasma-Accelerated Beams by 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. Here, we propose to use a periodically modulated plasma density to shape the longitudinal fields acting on an electron bunch in the linear wakefield regime. With simulations, we demonstrate an on-average flat accelerating field that maintains a small beam energy spread.

Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams.

Plasma wakefield accelerators are capable of sustaining gigavolt-per-centimeter accelerating fields, surpassing the electric breakdown threshold in state-of-the-art accelerator modules by 3-4 orders of magnitude. Beam-driven wakefields offer particularly attractive conditions for the generation and acceleration of high-quality beams. However, this scheme relies on kilometer-scale accelerators. Here, we report on the demonstration of a millimeter-scale plasma accelerator powered by laser-accelerated electron beams. We showcase the acceleration of electron beams to 128 MeV, consistent with simulations exhibiting accelerating gradients exceeding 100 GV m-1. This miniaturized accelerator is further explored by employing a controlled pair of drive and witness electron bunches, where a fraction of the driver energy is transferred to the accelerated witness through the plasma. Such a hybrid approach allows fundamental studies of beam-driven plasma accelerator concepts at widely accessible high-power laser facilities. It is anticipated to provide compact sources of energetic high-brightness electron beams for quality-demanding applications such as free-electron lasers.

Experimental demonstration of novel beam characterization using a polarizable X-band transverse deflection structure.

The PolariX TDS (Polarizable X-Band Transverse Deflection Structure) is an innovative TDS-design operating in the X-band frequency-range. The design gives full control of the streaking plane, which can be tuned in order to characterize the projections of the beam distribution onto arbitrary transverse axes. This novel feature opens up new opportunities for detailed characterization of the electron beam. In this paper we present first measurements of the Polarix TDS at the FLASHForward beamline at DESY, including three-dimensional reconstruction of the charge-density distribution of the bunch and slice emittance measurements in both transverse directions. The experimental results open the path toward novel and more extensive beam characterization in the direction of multi-dimensional-beam-phase-space reconstruction.

The effect of Virtual Reality on evoked potentials following painful electrical stimuli and subjective pain.

BACKGROUND: Virtual reality (VR) has been shown to reduce pain, however outcome parameters of previous studies have primarily been of a subjective nature and susceptible to bias. This study investigated the effect of VR on cortical processing of evoked potentials (EPs) and subjectively reported pain. Additionally, we explored whether subjects' demographic and personal characteristics modulated the effect of VR analgesia. METHODS: Three VR conditions were compared in a randomized cross-over study of 30 healthy volunteers: Passive VR (i.e. no interaction possible with the virtual world), active VR (interactive virtual environment) and no VR (black screen). Subjects received noxious electrical stimuli at random intervals during all conditions. EPs, recorded at Cz, were extracted time locked to stimuli. Pain scores were reported after each condition. RESULTS: Active VR significantly decreased pain scores and amplitudes of N1 and P3. Passive VR had no analgesic effect. Age was significantly correlated to pain scores, with older subjects demonstrating larger effects of VR. Gender, game experience, and susceptibility for immersion, did not influence VR analgesia. CONCLUSION: Active VR decreases pre-perceptual and perceptual brain activity following painful electrical stimuli, corresponding with reduced pain experience. VR has potential to serve as a non-pharmacologic treatment for pain, particularly in elderly patients.

[Anorectal injury after a fall from a jet ski]. / Anorectaal letsel na een val van een waterscooter.

A 28-year-old female sustained an anorectal rupture after a fall from a jet ski. The rupture was sutured and a double-loop colostomy was created. Three months later, following a test of functional continence, the colostomy was removed. The patient recovered without complications and with preservation of faecal continence. During a fall from a jet ski at high speeds, the water behaves as a solid object that penetrates the body. The choice oftreatment depends on the anatomical location and extent of the injury, on the comorbidity, and on a possible delay in the presentation of the symptoms. Wearing ofwetsuits is proposed as a possible preventive measure.

AXSIS: Exploring the frontiers in attosecond X-ray science, imaging and spectroscopy.

X-ray crystallography is one of the main methods to determine atomic-resolution 3D images of the whole spectrum of molecules ranging from small inorganic clusters to large protein complexes consisting of hundred-thousands of atoms that constitute the macromolecular machinery of life. Life is not static, and unravelling the structure and dynamics of the most important reactions in chemistry and biology is essential to uncover their mechanism. Many of these reactions, including photosynthesis which drives our biosphere, are light induced and occur on ultrafast timescales. These have been studied with high time resolution primarily by optical spectroscopy, enabled by ultrafast laser technology, but they reduce the vast complexity of the process to a few reaction coordinates. In the AXSIS project at CFEL in Hamburg, funded by the European Research Council, we develop the new method of attosecond serial X-ray crystallography and spectroscopy, to give a full description of ultrafast processes atomically resolved in real space and on the electronic energy landscape, from co-measurement of X-ray and optical spectra, and X-ray diffraction. This technique will revolutionize our understanding of structure and function at the atomic and molecular level and thereby unravel fundamental processes in chemistry and biology like energy conversion processes. For that purpose, we develop a compact, fully coherent, THz-driven atto-second X-ray source based on coherent inverse Compton scattering off a free-electron crystal, to outrun radiation damage effects due to the necessary high X-ray irradiance required to acquire diffraction signals. This highly synergistic project starts from a completely clean slate rather than conforming to the specifications of a large free-electron laser (FEL) user facility, to optimize the entire instrumentation towards fundamental measurements of the mechanism of light absorption and excitation energy transfer. A multidisciplinary team formed by laser-, accelerator,- X-ray scientists as well as spectroscopists and biochemists optimizes X-ray pulse parameters, in tandem with sample delivery, crystal size, and advanced X-ray detectors. Ultimately, the new capability, attosecond serial X-ray crystallography and spectroscopy, will be applied to one of the most important problems in structural biology, which is to elucidate the dynamics of light reactions, electron transfer and protein structure in photosynthesis.

On the fluorometric assay of circulating lipoperoxides.

The methodology for the measurement of circulating thiobarbituric acid (TBA)-reactive products of lipid peroxidation in human plasma by means of fluorometry has been reinvestigated. The lipid precipitation of plasma with phosphotungstic acid, which step is laid down in the standard assay method, strongly increases the apparent TBA-reactivity. However, subsequent washing of the precipitate may reduce the apparent levels of lipoperoxide to values close to those obtained by using untreated plasma. Also, short-time storage of plasma at either 4 degrees C or -20 degrees C induces large day to day variations in assay results. This phenomenon may be prevented almost completely by the addition of glutathione plus EDTA. It is proposed to use untreated plasma and to perform the assay immediately after collection of plasma or to add both glutathione and EDTA before storage.

[Quantitative evaluation of film-screen combinations for x-ray diagnosis]. / Quantitative Bewertung von Film-Folien-Kombinationen für die Röntgendiagnostik.

The properties of screen/film combinations for radiographs set a lower limit for the x-ray exposure of the patient and an upper limit for the quality of the x-ray picture. Sensitivity, slope and resolution of different screen/film combinations were determined using a measuring phantom which was developed in the PTB. For all screens used the measurements show the same relation between screen sensitivity and resolution. This allows quantitative evaluation of image quality. A classification scheme derived from these results facilitates the selection of screen/film combinations for practical use. In addition for quality assurance gross differences in material properties and conditions of film development can be detected with the aid of the measuring phantom.

Measurements of radiation near an atomic spectral line from the interaction of a 30 GeV electron beam and a long plasma.

Emissions produced or initiated by a 30-GeV electron beam propagating through a approximately 1-m long heat pipe oven containing neutral and partially ionized vapor have been measured near atomic spectral lines in a beam-plasma wakefield experiment. The Cerenkov spatial profile has been studied as a function of oven temperature and pressure, observation wavelength, and ionizing laser intensity and delay. The Cerenkov peak angle is affected by the creation of plasma, and estimates of neutral and plasma density have been extracted. Increases in visible background radiation, consistent with increased plasma recombination emissions due to dissipation of wakefields, were simultaneously measured.

A video-angiometer for simultaneous and continuous measurement of inner and outer vessel diameters. Technical report.

A system is described for continuously measuring vessel diameters. It bases on the evaluation of video signal differences of a video camera which are induced by light intensity differences (grey levels) caused by the vascular wall structures. The system is electronically linear, automatically measuring and in addition eyeball controlled by the human sensor: the inaccuracy does not exceed the 5% level.

Intravital measurement of arteriolar pressure and tangential wall stress in normotensive and spontaneously hypertensive rats (established hypertension).

Under intravital conditions, intravascular pressures of mesenteric resistance vessels were measured in normotensive (NR, mean blood pressure 92 mm Hg) and spontaneously hypertensive rats (SHR, 161 mm Hg) being elevated over all by about 75%; the tangential wall stress (sigma = p.r/h; p represents the intravascular pressure and r/h the ratio of internal radius to wall thickness) was found to be increased by 120-140% in SHR.

Structural differences in the mesentery microcirculation between normotensive and spontaneously hypertensive rats.

The mesentery preparation of normotensive rats (NR) (Pcarotis97 +/- 4 mm Hg) and of spontaneously hypertensive rats (SHR) (161 +/- 2 mm Hg) of comparable age (20 +/- 3 weeks) was used to study morphological changes of the microvasculature in established hypertension. The arterioles, classified according to their branching order, had an increased inner diameter in SHR (by 20%). The smooth muscle hypertrophy decreased with smaller vessel size. Pre- and postcapillary vessels were shorter in SHR than in NR by 17 to 35%. The number of these vessels related to the number of the feeding terminal arterioles was found to be reduced by nearly 50% in SHR. The data suggest a lowered arteriolar flow resistance in individual vessels of the hypertensive group concomitant with a gradually disappearing smooth muscle hypertrophy towards the capillary bed. The elevation of the resistance to blood flow in the hypertensive rats is obviously caused by a reduced number of resistance vessels, as seen in the mesentery vascular bed. Similar results were obtained in the true capillaries, which showed greater inner diameters (SHR vs NR:7.2 micron vs 6.4 micron), shortened lengths (141 vs 170 micron) and a reduced number (50 vs 70). Red cell velocity in true capillaries did not differ (0.51 mm/s vs 0.49 mm/s). Arterio-venous shunt vessels were described with an average inner diameter of 11 micron. In SHR these vessels were shorter (424 vs 654 micron) and increased in number. The 'hydraulic hindrance' of AV-shunt vessels and true capillaries together was decreased in SHR; the surface area did not differ between SHR (55.7 . 10(3) micron2) and NR (50.1 . 10(3) micron2) suggesting no major variation in the exchange functions.

Spectrophotometric correction for bile pigments in the thiobarbituric acid test for malondialdehyde-like substances in plasma.

A simple method is proposed to improve specificity when estimating malondialdehyde-like components of plasma thiobarbituric acid-reactivity, especially with regard to the considerable contribution of bilirubin. The spectrophotometric method comprises measurement of A485, A532 and A560 instead of only A532. A correction formula is then applied to calculate the portion of the A532 which originates from malondialdehyde-like substances. Using this method, normal values for malondialdehyde average 0.84 mumol/l.