Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasma.

We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufficient initial amplitude [≥(4.1±0.4) MV/m], the phase of the modulation along the bunch is reproducible from event to event, with 3%-7% (of 2π) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated.

Proton Bunch Self-Modulation in Plasma with Density Gradient.

We study experimentally the effect of linear plasma density gradients on the self-modulation of a 400 GeV proton bunch. Results show that a positive or negative gradient increases or decreases the number of microbunches and the relative charge per microbunch observed after 10 m of plasma. The measured modulation frequency also increases or decreases. With the largest positive gradient we observe two frequencies in the modulation power spectrum. Results are consistent with changes in wakefields' phase velocity due to plasma density gradients adding to the slow wakefields' phase velocity during self-modulation growth predicted by linear theory.

Proton-driven plasma wakefield acceleration in AWAKE.

In this article, we briefly summarize the experiments performed during the first run of the Advanced Wakefield Experiment, AWAKE, at CERN (European Organization for Nuclear Research). The final goal of AWAKE Run 1 (2013-2018) was to demonstrate that 10-20 MeV electrons can be accelerated to GeV energies in a plasma wakefield driven by a highly relativistic self-modulated proton bunch. We describe the experiment, outline the measurement concept and present first results. Last, we outline our plans for the future. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Experimental Observation of Proton Bunch Modulation in a Plasma at Varying Plasma Densities.

We give direct experimental evidence for the observation of the full transverse self-modulation of a long, relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a periodic density modulation resulting from radial wakefield effects. We show that the modulation is seeded by a relativistic ionization front created using an intense laser pulse copropagating with the proton bunch. The modulation extends over the length of the proton bunch following the seed point. By varying the plasma density over one order of magnitude, we show that the modulation frequency scales with the expected dependence on the plasma density, i.e., it is equal to the plasma frequency, as expected from theory.

Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch.

We measure the effects of transverse wakefields driven by a relativistic proton bunch in plasma with densities of 2.1×10^{14} and 7.7×10^{14} electrons/cm^{3}. We show that these wakefields periodically defocus the proton bunch itself, consistently with the development of the seeded self-modulation process. We show that the defocusing increases both along the bunch and along the plasma by using time resolved and time-integrated measurements of the proton bunch transverse distribution. We evaluate the transverse wakefield amplitudes and show that they exceed their seed value (<15 MV/m) and reach over 300 MV/m. All these results confirm the development of the seeded self-modulation process, a necessary condition for external injection of low energy and acceleration of electrons to multi-GeV energy levels.

A novel simulation and analysis algorithm for high resolution optical transition radiation imaging.

The use of optical transition radiation (OTR) for charged particle beam imaging is a well-established and commonly used technique. As such, simulations of the images expected from an arbitrary transverse beam profile are important in both the design of such OTR imaging systems and the analysis of the data. However OTR image simulations of high-energy, low-emittance particle beams, that are becoming commonplace within accelerator physics, can be extremely challenging to produce and limited in their account of practical factors. In this paper we systematically show how high-energy OTR image simulations can be carried out using low-energy parameters, whilst providing little deviation in the resulting transverse beam profiles. Simulations require significantly less resources and can be combined with further analysis techniques, which would otherwise be too costly to be practically viable. Using this methodology as a basis for OTR simulations, we present a new method of analyzing OTR transverse beam profile data for high-energy, low-emittance beams. In contrast to previous work, this algorithm includes the effects of a finite bandwidth and directly allows the inclusion of optical effects, such as chromatic aberration.

Acceleration of electrons in the plasma wakefield of a proton bunch.

High-energy particle accelerators have been crucial in providing a deeper understanding of fundamental particles and the forces that govern their interactions. To increase the energy of the particles or to reduce the size of the accelerator, new acceleration schemes need to be developed. Plasma wakefield acceleration1-5, in which the electrons in a plasma are excited, leading to strong electric fields (so called 'wakefields'), is one such promising acceleration technique. Experiments have shown that an intense laser pulse6-9 or electron bunch10,11 traversing a plasma can drive electric fields of tens of gigavolts per metre and above-well beyond those achieved in conventional radio-frequency accelerators (about 0.1 gigavolt per metre). However, the low stored energy of laser pulses and electron bunches means that multiple acceleration stages are needed to reach very high particle energies5,12. The use of proton bunches is compelling because they have the potential to drive wakefields and to accelerate electrons to high energy in a single acceleration stage13. Long, thin proton bunches can be used because they undergo a process called self-modulation14-16, a particle-plasma interaction that splits the bunch longitudinally into a series of high-density microbunches, which then act resonantly to create large wakefields. The Advanced Wakefield (AWAKE) experiment at CERN17-19 uses high-intensity proton bunches-in which each proton has an energy of 400 gigaelectronvolts, resulting in a total bunch energy of 19 kilojoules-to drive a wakefield in a ten-metre-long plasma. Electron bunches are then injected into this wakefield. Here we present measurements of electrons accelerated up to two gigaelectronvolts at the AWAKE experiment, in a demonstration of proton-driven plasma wakefield acceleration. Measurements were conducted under various plasma conditions and the acceleration was found to be consistent and reliable. The potential for this scheme to produce very high-energy electron bunches in a single accelerating stage20 means that our results are an important step towards the development of future high-energy particle accelerators21,22.

Body composition changes after laparoscopic adjustable gastric banding: what is the role of -174G>C interleukin-6 promoter gene polymorphism in the therapeutic strategy?

BACKGROUND: There is growing evidence that interleukin-6 (IL-6) is linked to the regulation of fat mass (FM). Our previous data define the common -174G>C IL-6 polymorphism as a marker for 'vulnerable' individuals at risk of age- and obesity-related diseases. An association between -174G>C IL-6 polymorphism and weight loss after bariatric surgery has been demonstrated. OBJECTIVE: We investigated the impact of -174G>C IL-6 polymorphism on weight loss, body composition, fluid distribution and cardiometabolic changes in obese subjects, after laparoscopic adjustable gastric banding (LAGB) surgery. DESIGN AND OUTCOME MEASURES: A total of 40 obese subjects were studied at baseline and at 6 months follow-up after LAGB surgery. Cardiometabolic and genetic assessment of -174G>C IL-6 polymorphism, anthropometric, body composition and fluid distribution analysis were performed. RESULTS: After LAGB surgery, significant reductions in weight (Δ%=-11.66 ± 7.78, P<0.001), body mass index (P<0.001), total and trunk FM (kg, %) (Δ% of total FM=-22.22 ± 12.15, P<0.01), bone mineral density (T-score) (P<0.001), resting metabolic rate (RMR) (P<0.01), and total body water and intracellular water (TBW, ICW) (P<0.05) were observed. At baseline, C(-) carriers of IL-6 polymorphism had a significantly higher RMR (P<0.05), free FM (kg), but less total and trunk FM (%), higher body cell mass (BCM), content of TBW (L) and ECW (extracellular water)/ICW ratio compared with C(+) carriers (P<0.001). After LAGB, C(+) carriers had a significantly stronger reduction of total FM (kg), but lower bone density, compared with C(-) carriers (P<0.05). CONCLUSIONS: Beyond the relationship between -174G>C IL-6 polymorphism and body composition, this study provides first evidence about the association of IL-6 variant with fluid distribution, at baseline, and FM and bone density loss in obese subjects at 6 months follow-up after LAGB surgery. LAGB was less effective if the subjects were carrying risk genotypes, C(-) carriers, for obesity, suggesting a role of genetic variations on bariatric surgery outcomes.

Drinking habits and risk of altered liver enzymes in the general population of a rural area in Southern Italy.

PURPOSE: To assess the overall drinking habits (amount and duration of alcohol intake, as well as type of alcoholic drinks consumed) and their potential for alteration of liver enzymes in a random sample of the general population aged > or =18 years of a rural area in Southern Italy. MATERIALS AND METHODS: Of the 4000 subjects selected, 3306 (82.7%) agreed to take part in the study. Of these, 41% were teetotallers (54.4% females, 26.1% males; p<0.01). A very small proportion of subjects reported > or =4 drinks/day (11.9% males, 0.8% females; p<0.01). RESULTS: Increased aspartate aminotransferase and/or alanine aminotransferase values were observed in 148 (4.5%) subjects. Hepatitis C virus positivity alone, excessive body mass index alone and alcohol intake alone were observed in 28.6, 23.8 and 18.4% of cases, respectively. After exclusion of subjects with chronic viral hepatitis infections (hepatitis B virus and/or hepatitis C virus) and adjustment for the confounding effect of age (>50 years) and body mass index (> or =25) by multiple logistic regression analysis, subjects who reported consuming >4 drinks/day were 2.4-fold (95%CI=1.1-5.2) more likely than teetotallers to have altered liver enzyme values; subjects reporting intake below this threshold were not at risk of alterations in aspartate aminotransferase/alanine aminotransferase (OR 1.4; 95%CI=0.7-2.6). CONCLUSIONS: These findings indicate that only a small proportion of the rural population studied (particularly females) can be considered as alcohol misusers. Moreover, a mild alcohol intake (< or =4 drinks/day) is not associated with alterations in aspartate aminotransferase/alanine aminotransferase levels in the absence of other factors such as hepatitis viruses and impaired body mass index.

[Milligan-Morgan hemorrhoidectomy with a radiofrequency scalpel]. / Emorroidectomia sec. Milligan-Morgan con bisturi a radiofrequenze.

BACKGROUND: Postoperative pain has always been the main adverse effect of surgical treatment for hemorrhoids. Therefore, surgical techniques evolved mainly to solve this problem and, secondly, postoperative bleeding, recurrences and stenosis. METHODS: Two homogeneous groups of 20 patients each were investigated. Both of them were affected by fourth grade hemorrhoidal prolapse and were homogeneous for age, sex and presentation symptoms. Patients previously treated for other proctologic diseases were excluded. A group was treated with standard Milligan-Morgan hemorrhoidectomy and the other with radiofrequency scissors. Every patient underwent a follow-up protocol based on outpatient visits at 15, 30, 45 postoperative days and 3, 6 and 12 months. RESULTS: The results show a substantial similarity between these techniques. However, radiofrequency scissors further improved the simplicity of the technique and the postoperative adverse effects. In particular, the procedure lasted 7 minutes less with radiofrequency scissors. Patients treated with the radiofrequency technique had their first postoperative evacuation 24 hours before the standard technique and reduced the mean postoperative hospital stay at 2.5 days (4.5 days in the standard group). The incidence of postoperative pain was reduced in patients treated with radiofrequency scalpel and the follow-up controls in both groups didn't show any complication as stenosis or incontinence. CONCLUSIONS: The radiofrequency-performed Milligan-Morgan hemorrhoidectomy is a valuable technique that improves the classical difficulties in execution, reducing the length of hospital stay and the incidence of postoperative pain or other complications.

[Surgical treatment of hemorrhoid disease. A comparison between techniques]. / Il trattamento chirurgico della malattia emorroidaria. Tecniche a confronto.

BACKGROUND: The past years have seen the development of outpatient treatment and surgical procedures for the treatment of hemorrhoid disease in an attempt to reduce postoperative pain on the one hand and execution and hospitalisation times on the other. METHODS: This retrospective study compares the results obtained in the treatment of hemorrhoid disease using three different METHODS. Three groups of 30 patients were selected from those operated during the past 10 years using Milligan-Morgan s technique (Group A), Parks technique (Group B) and radiosurgery (Group C). All patients were matched for sex (50% males and 50% females), age (ranging between 30 and 50 years old), diagnosis (4th degree hemorrhoids not associated with another proctologic pathology such as anal fissures, fistulas, etc.) and referred symptoms. RESULTS: The results obtained allow a positive evaluation to be made of all three surgical techniques, but indicate submucous hemorrhoidectomy using radiosurgery as the method of choice for the treatment of grade III and IV hemorrhoids. CONCLUSIONS: The excellent results achieved using this approach in the authors opinion amply justify the relatively difficult execution and longer operating times.