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.

[Contrast medium supported imaging of tumorous vessels by color Doppler and power Doppler mode in animal experiments]. / Kontrastmittelgestützte Darstellung von Tumorgefässen in Farb-Doppler- und Power-Doppler-Mode im Tierexperiment.

PURPOSE: The purpose was to determine tumor neovascularisation via colour-coded Doppler (duplex) sonography and the "power mode", both visually and quantitatively, by means of videodensitometry. MATERIAL AND METHODS: 6 VX2 tumours of 4 to 11 mm size were implanted in 4 rabbits at various sites. The colour-coded duplex sonography and the new sonographic power technique were tested before and after having injected a new contrast medium (SH U 616A). RESULTS: If no contrast medium was injected, tumour neovascularisation was identified in only 50% of the cases. Injection of contrast medium increased signal intensity three to fourfold with all examined tumors. Combined use of the sonographic method by the power technique with injection of contrast medium is outstandingly suitable for tumor vessel imaging even of small tumors, as these initial results seem to show. CONCLUSION: If these results are corroborated by further studies, contrast-medium supported sonographic technique may possibly become established as an alternative method to other imaging procedures.