Hosing of a Long Relativistic Particle Bunch in Plasma.

Experimental results show that hosing of a long particle bunch in plasma can be induced by wakefields driven by a short, misaligned preceding bunch. Hosing develops in the plane of misalignment, self-modulation in the perpendicular plane, at frequencies close to the plasma electron frequency, and are reproducible. Development of hosing depends on misalignment direction, its growth on misalignment extent and on proton bunch charge. Results have the main characteristics of a theoretical model, are relevant to other plasma-based accelerators and represent the first characterization of hosing.

Controlled Growth of the Self-Modulation of a Relativistic Proton Bunch in Plasma.

A long, narrow, relativistic charged particle bunch propagating in plasma is subject to the self-modulation (SM) instability. We show that SM of a proton bunch can be seeded by the wakefields driven by a preceding electron bunch. SM timing reproducibility and control are at the level of a small fraction of the modulation period. With this seeding method, we independently control the amplitude of the seed wakefields with the charge of the electron bunch and the growth rate of SM with the charge of the proton bunch. Seeding leads to larger growth of the wakefields than in the instability case.

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.

Filamentation of a relativistic proton bunch in plasma.

We show in experiments that a long, underdense, relativistic proton bunch propagating in plasma undergoes the oblique instability, which we observe as filamentation. We determine a threshold value for the ratio between the bunch transverse size and plasma skin depth for the instability to occur. At the threshold, the outcome of the experiment alternates between filamentation and self-modulation instability (evidenced by longitudinal modulation into microbunches). Time-resolved images of the bunch density distribution reveal that filamentation grows to an observable level late along the bunch, confirming the spatiotemporal nature of the instability. We provide a rough estimate of the amplitude of the magnetic field generated in the plasma by the instability and show that the associated magnetic energy increases with plasma density.

Simultaneous ionization and excitation of molecules by positron impact.

Cross sections for ionization excitation of molecules by positron impact have been measured for the first time by scattering a positron beam from CO2 and N2. The cross sections have been observed to exceed those for electron impact by up to a factor of approximately 3 for CO2 and approximately 5 for N2. The enhancement arises primarily via positronium formation. The cross sections account for up to approximately 12% and 20% of the total cross sections for positron scattering from N2 and CO2, respectively.

Double hit reconstruction in large area multiplexed detectors.

A novel approach is presented to unfold particle hit positions in tracking detectors with multiplexed readout representing an underdetermined system of linear equations. The method does not use any prior information about the hit positions, and the only assumption in the procedure is that single strip charge values on consecutive detector strips follow a smooth distribution. Ambiguities introduced by charge sharing from multiplexing are reduced by using a regularization technique. We have tested this method on a multiplexed 50 × 50 cm2 Micromegas detector with 1037 strips and only 61 readout channels, using cosmic rays, and we have found that single and double clusters of hits can be reconstructed with high efficiency. In addition, simulations show that the algorithm is capable of reconstructing isolated hits in events with larger multiplicity.

Pancreatitis and palindromic arthropathy with effusions associated with sodium stibogluconate treatment in a renal transplant recipient.

We report the occurrence of two side effects, pancreatitis and palindromic arthropathy with effusions, associated with injections of sodium stibogluconate used in the treatment of kala-azar. No clear mechanism to account for the problems was identified despite extensive investigation. We suggest that when abdominal pain is experienced during treatment with antimonial drugs pancreatitis should be borne in mind as a possible cause.

Hepatic perfusion index and the evolution of liver metastases.

A total of 150 patients with primary carcinoma of the gastrointestinal tract had first-pass technetium colloid scintigraphy to estimate the hepatic perfusion index (HPI). Postoperative follow-up over 2-4 years shows that the HPI remains a sensitive method of detecting hepatic metastases, even in patients whose liver appeared normal at laparotomy. HPI was elevated in 94% of patients with liver metastases found at laparotomy; 87% of patients with occult metastases which became overt within 3 years of surgery had elevated HPI; and 91% of all patients who have to date developed hepatic metastases had elevated HPI at presentation. Of all patients with elevated HPI, 82% had metastases which were either apparent at surgery or became detectable by other means within 3 years.

The supine pneumothorax.

The consequences of an undiagnosed pneumothorax can be life-threatening, particularly in patients with trauma to the head or multiple injury and in those requiring mechanical ventilation. Yet it is these patients, whose films will be assessed initially by the surgeon, who are more likely to have a chest X-ray taken in the supine position. The features of supine pneumothoraces are described and discussed together with radiological techniques used to confirm the diagnosis, including computed tomography (CT) which may be of particular importance in patients with associated cranial trauma.

The Relationship Between Population Density of Heterodera schachtii, Soil Temperature, and Sugarbeet Yields.

In two glasshouse experiments, relations between sugarbeet root dry weight (y, expressed as a percentage of the maximum dry root weight), and preplanting populations of Heterodera schachtii (P(i)) were described by the equation y = 100(Z)(P(i)-T), in which Z = a constant slightly smaller than 1, and T = the tolerance limit (the value of P(i) below which damage was not measureable). T varied with temperature; it was 65 eggs/100 g soil at 23 and 27 C and 430 eggs/100 g soil at 19 C. At 15 and 31 C there was no loss of root dry weight up to the maximum preplanting populations tested. In a field experiment in the Imperial Valley the relation between root yield (y) and P(i) was y = 100 (0.99886)(P(i) ) - 100, and the tolerance limit was 100 eggs/100 g soil.

Excited-state positronium formation from helium, argon, and xenon.

The cross sections for the formation of positronium in the 2P state in collisions of positrons with He, Ar, and Xe atoms have been determined by measuring coincidences between the remnant ion and the Lyman-alpha photon from positronium. The maximum fractional contributions of these to the total Ps formation cross sections increase from approximately 0.06+/-0.01 in He to 0.12+/-0.04 in Ar and 0.26+/-0.09 in Xe. In the case of He, good agreement is found with a coupled-state calculation; for Ar and Xe, measurements are compared with a distorted-wave Born approximation.