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The Caenorhabditis elegans germ line is an outstanding model system in which to study the control of cell division and differentiation. Although many of the molecules that regulate germ cell proliferation and fate decisions have been identified, how these signals interact with cellular dynamics and physical forces within the gonad remains poorly understood. We therefore developed a dynamic, 3D in silico model of the C. elegans germ line, incorporating both the mechanical interactions between cells and the decision-making processes within cells. Our model successfully reproduces key features of the germ line during development and adulthood, including a reasonable ovulation rate, correct sperm count, and appropriate organization of the germ line into stably maintained zones. The model highlights a previously overlooked way in which germ cell pressure may influence gonadogenesis, and also predicts that adult germ cells might be subject to mechanical feedback on the cell cycle akin to contact inhibition. We provide experimental data consistent with the latter hypothesis. Finally, we present cell trajectories and ancestry recorded over the course of a simulation. The novel approaches and software described here link mechanics and cellular decision-making, and are applicable to modeling other developmental and stem cell systems., Summary: A three dimensional in silico model of C. elegans predicts that adult germ cells are subject to a mechanical feedback on the cell cycle akin to contact inhibition.

This paper describes the first results of a feasibility study undertaken at CERN to determine whether a laser-produced plasma can be used as a source of intense highly charged heavy ion beams. A variety of important measurements have been made, and the results are encouraging. Furthermore, a beam of highly charged light ions produced by the laser ion source has been accelerated successfully in a radio frequency quadrupole (RFQ) structure

Laser Ion Sources (LIS) are well suited to filling synchrotron rings with highly charged ions of almost any element in a single turn injection mode. We report the first measurements of the LIS output parameters for Pb27+ ions generated by the new 100 J/1 Hz Master Oscillator - Power Amplifier CO2-laser system. A new LIS has been designed, built and tested at CERN, as an ion source for ITEP-TWAC accelerator/accumulator facility, and as a possible future source for an upgrade of the Large Hadron Collider (LHC) injector chain. The use of the LIS based on 100 J/1 Hz CO2-laser together with the new ion LINAC, as injector for ITEP-TWAC project, is discussed..

Contains fulltext : 111102.pdf (Publisher’s version ) (Closed access) UML 2004

CERN's heavy ion pre-injector has been in service since 1994, providing lead ions for fixed target collisions at 177 GeV per nucleon in the SPS. In the LHC era, heavy ion collisions require an increase in the beam brightness, compared to the present injector system of Linac 3, Proton Synchrotron Booster and the Proton Synchrotron. Stacking and cooling ions in a Low Energy Ion Ring should find the largest part of this increase. However, further improvements can be envisaged by upgrading the pre-injector and source. The performance and limitations of the present source and Linac 3 will be discussed, and options for increasing the source brightness will be presented. These options consist of upgrades of the ECR Source to higher frequencies, or its replacement with a Laser Ion Source.

The GEL LEBT provides high efficiency beam transport and matching to the RFQ acceptance in the 4-dimensional phase space. The rms emittance growth is relatively small even for 60 kV extraction voltage. The number of particles occupying the 4-D RFQ acceptance strongly depends from the beam emittance at the entrance of the GEL LEBT. In most realistic case with the input emittance equal to the measured one, which is 320 p×mm×mrad (4×rms emittance) the number of particles inside the 4-D space with the projection emittance of 200 p×mm×mrad is 38% at the entrance and 35% at the output of GEL LEBT, which means that LEBT does not practically destroy beam emittance. The experimental value of the yield to the double aperture is 35% and confirms the expected performance of the GEL LEBT.

High accelerating gradients are very interesting for future machines, and, in particular, for high-current heavy-ion linac projects like the "Inertial Fusion Driver". In order to explore the maximum field achievable in an Interdigital-H type structure (IH), an experiment has been carried out at CERN with the Lead Ion Linac (Linac3). After the 1997 run, the RF amplifiers were rearranged in order to allow the feeding of the IH Tank number 2 (1.54 m long, 28 gaps, frequency of 202.56 MHz) with up to 2 MW pulsed RF power. After two weeks of conditioning at pulse lengths varying between 200 ms and 1 ms with a constant pulse repetition rate of 0.8 Hz, the maximum effective accelerating gradient achieved was 10.7 MV/m. This corresponds to a local field maximum of 75 MV/m, and to fields in excess of 50 MV/m (3.5 times the Kilpatrick limit) on large portions of the drift tube surfaces. This paper reports the conditioning procedure used, the measurements of field emission current at different voltages and pulse lengths, the determination of the surface field enhancement factor as well as the calculation of the electric field distribution for the gap with the highest surface fields.

A Three Dimensional Bunch Shape Monitor (3D-BSM) has been developed for the CERN Proton Linac 2. A new area for beam studies at high intensities has been opened by this detector. Bunch density distributions in all three dimensions and their variations along the beam pulse can be obtained. Changing field gradients in linac quadrupoles, emittance variation along the bunch has been calculated. Measurements of beam halos become possible thanks to the large dynamic range of the device. Beam parameters at various linac settings have been measured and analysed.