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Real time monitoring of hadrontherapy beam intensity and profile is a critical issue for the optimisation of dose delivery to carcinogenic tissue, patient safety and operation of the accelerator complex. For this purpose an innovative beam monitor, SLIM (secondary electron emission for low interception monitoring) is being developed in the framework of the EC-funded SUCIMA (silicon ultra-fast cameras for electrons and gamma sources in medical application) project The detector system is based on the secondary emission of electrons by a non-perturbative, sub-micron thick Al foil placed directly in the extracted beam path. The secondary electrons, accelerated by an electrostatic focusing system, are detected by a monolithic silicon position-sensitive sensor, which provides the beam intensity and its position with a precision of 1 mm at a 10 kHz frame rate. The results of the laboratory tests of the first system prototype with thermoionic electrons emitted from a hot Tungsten wire are presented together with the measurements performed on a low intensity hadron beam at the Cyclotron of the Joint Research Centre in Ispra.

In this paper the Fokker-Planck equation, which takes into account the medium absorption and the Maxwellian behavior of the field particles at low energy for Coulomb interactions is obtained. The analytical solution of the stationary distribution function is obtained in both angle and velocity variables. In particular the electron distribution for electron-ion collisions has been obtained using this diffusion approximation for beam and isotropic sources. If the absorption is neglected the solution recovers the classical stationary Maxwell distribution. For low absorption rates the solution shows a typical slowing down spectrum for high energy and a Maxwellian-like distribution at thermal energy. For moderate and high absorption rates the test particles do not reach the thermal equilibrium and the Maxwell distribution at low energies does not appear.

The Large Hadron Collider (LHC) nominal luminosity is 10 34 cm −2 s −1 , but special runs at 10 28 cm −2 s −1 are also foreseen. In order to cover a luminosity dynamic range of six orders of magnitude, we have studied a new concept of luminosity monitor based on a double mode detector, working as a secondary emission counter at the highest luminosity and as an ionisation chamber at lower levels. We present the description of the device and the results obtained during tests at the CERN PS and SPS beams.

To prepare dense bunches of lead ions for the LHC it has been proposed to accumulate the 4.2 MeV/u linac beam in a storage ring with electron cooling. A series of experiments is being performed in the low-energy ring LEAR to test this technique. First results were already reported at the Beam Crystallisation Workshop in Erice in November 1995. Two more recent runs to complement these investigations were concerned with: further study of the beam lifetime; the dependence of the cooling time on optical settings of the storage ring and on neutralization of the electron beam; and tests in view of multiturn injection. New results obtained in these two runs in December 1995 and in April 1996 will be discussed in this contribution.

This report presents results of experiments performed between 1994 and 1996 by a CERN/JINR collaboration, aimed to study the problem of the generation of intense electron beams whose space charge is neutralised by the residual gas ions. The problem is related to the development of electron cooling methods. The large space charge potential for high density electron beams is a significant drawback for the cooling process. In order to reduce this effect, an electron beam neutralisation system has been implemented on the LEAR cooler and the JINR test bench. In this paper we briefly discuss the physics of the neutralisation process, technological aspects of neutralisation, the measurement techniques and the results.

A large space-charge is detrimental to the cooling process of a dense beam. Generation of a neutralised electron beam is restricted by beam-drift instability. To suppress this instability, active methods are used: a kicker with a transverse electric field (shaker) and longitudinal electrodes placed in the vacuum chamber and in the gun region expel secondary electrons. Results of experiments dedicated to the development of beam stabilisation on the JINR test bench and in the electron cooling system at LEAR are discussed.

A proposal for benchmark problems to test electromagnetic optimization methods, relevant to multiobjective optimization of a solenoidal superconducting magnetic energy storage with active and passive shielding is presented. The system has been optimized by means of different optimization procedures based on the global search algorithm, evolution strategies, simulated annealing and the conjugate gradient method, all coupled to integral or finite element codes. A comparison of results is performed and the features of the problem as a test of optimization procedures are discussed.

The plasma generated in a spherical pinch device consists of a linear discharge along the diameter of a spherical vessel and of an implosion that compresses the linear plasma. Because the linear di...

The magnetic spectrometer and charged particle tracking system used in Fermilab experiment 687 to study the photoproduction and decay of charm particles are described in detail. The photons are produced by a wideband electron beam which can operate at energies up to 600 GeV/ c . The spectrometer consists of a high resolution silicon microstrip detector, a large aperture dipole magnet, proportional chambers, a second large aperture dipole, and more proportional chambers. Three multi-cell threshold Cherenkov counters provide charged particle identification. The tracking system is capable of resolving the secondary decay vertices of charm and beauty mesons and baryons from the primary interaction vertex. It also determines the invariant mass of the multibody final states of particles containing heavy quarks with excellent resolution. The particle identification system allows one to identify kaons and protons present in these final states clearly. This collection of detectors produces very clean signals for charm particles and permits one to make many cross checks of the apparatus. The performance is illustrated for a variety of charm signals. Of particular interest is a description of the tracking through the silicon microstrip detector and its use in isolating downstream decay vertices. Two complementary approaches to the reconstruction of secondary decay vertices are presented and insight is gained by comparing their strengths and weaknesses.

The present paper describes a direct method of obtaining are expression of the distribution function of charged particles which diffuse in a plasma. The distribution function in velocity, angle and time is presented starting from the Fokker-Planck equation. Temperature, average velocity and energy of charged particles (electron or ions) have also been calculated as functions of time. © 1992 Società Italiana di Fisica.

The nitrogen pulsed laser monitoring system for the outer electromagnetic calorimeter of the E687 photoproduction experiment, investigating charm and beauty states at the Fermilab Tevatron, is described. The system is reliable, economical and allows a photomultipliers gain stability control as good as 1%.

C. Santoni, coll. Atlas, To be published in the proceeding of the conference.; During the construction of the LHC main dipoles, 12 cases of short circuits between the cables of the superconducting coils have been detected. Some of them appeared only under the press, making impossible their localization after disassembly. In this paper we describe a method to locate electrical shorts through the use of room temperature magnetic measurements. An example case is discussed in detail to illustrate the features of the approach, and a statistic of the cases met during the production of more that 70% of the dipole total quantity is presented.

The LHC ring will contain 1232 main dipole and 382 main quadrupole twin aperture magnets. All main magnets are superconducting and employ NbTi/Cu Rutherford type cables operated at 1.9 K. The dipole production has reached the equivalent of almost three octants of cold masses and nearly four octants of collared coils. The quadrupole production has reached 75 cold masses and over 150 bare magnets. The ramping up of large scale magnet production has posed several challenges which will be discussed, like: the coil size uniformity, coil pre-stress control, cold mass welding technique and the geometrical shape issues. The magnetic measurement results at warm will be presented together with their usage for the quality control in the production. The common features and differences of the three dipole producers will be discussed. Finally the latest version of the production schedule will be presented.

Real time monitoring of hadrontherapy beam intensity and profile is a critical issue for the optimization of dose delivery to carcinogenic tissue, patient safety and operation of the accelerator complex. For this purpose an innovative beam monitor, secondary electron emission for low interception monitoring (SLIM) is being developed in the framework of the EC-funded silicon ultra-fast cameras for electrons and gamma sources in medical application (SUCIMA) project. The detector system is based on the secondary emission of electrons by a nonperturbative, sub-micron thick Al foil placed directly in the extracted beam path. The secondary electrons, accelerated by an electrostatic focusing system, are detected by a monolithic silicon position-sensitive sensor, which provides the beam intensity and its position with a precision of 1 mm at a 10 kHz frame rate. The results of the laboratory tests of the first system prototype with thermoionic electrons emitted from a hot Tungsten wire are presented together with the measurements performed on a low intensity hadron beam at the Cyclotron of the Joint Research Centre in Ispra.

The LEAR electron cooler uses dense electron beams. Because of this high density the large space-charge potential induces significant drawbacks for the cooling process itself. As a consequence a space-charge neutralisation system has been implemented on the cooler. It consists of two positively polarised pairs of electrodes, placed on the outside of the drift space, which aim to store the ionised positive ions of charge Z. The major difficulty arises in the neutralisation instabilities. This paper reports on the technological aspects, the measurement techniques and the results.

Aim of this work is to extend the results obtained in a previous study on the magnetic confinement and stability of a quantum degenerate non-neutral fermion plasma. This extension consists in the inclusion in the previously set up model of the effects of the exchange forces, and generalises the Thomas-Fermi (TF) approach used in the referenced work towards a Thomas-Fermi-Dirac (TFD) statistical description. The TF model has not only been used extensively and with success in these years to study atomic, nuclear and molecular properties, or to evaluate features of matter in extreme conditions such as low temperatures and/or high densities typical of astrophysics and inertial confinement fusion experiments, but also to found hydrodynamic theories for the diffusion and stability of fermion plasmas, one component non-neutral degenerate fluids, plasmas etc. In this paper an equation for density profiles in cylindrical symmetry is found, from the semiclassical kinetic theory of quantum gases, which takes into ac...

The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7 degree orbit at altitudes between 320 and 390 km. A total of 2.86 * 10^6 helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of < 1.1 * 10^-6 is obtained., 18 pages, Latex, 9 .eps figures

The proton spectrum in the kinetic energy range 0.1 to 200 GeV was measured by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at an altitude of 380 km. Above the geomagnetic cutoff the observed spectrum is parameterized by a power law. Below the geomagnetic cutoff a substantial second spectrum was observed concentrated at equatorial latitudes with a flux ~ 70 m^-2 sec^-1 sr^-1. Most of these second spectrum protons follow a complicated trajectory and originate from a restricted geographic region., 19 pages, Latex, 7 .eps figures

To reach the design luminosity for lead-ions in the LHC, the present Low-Energy Antiproton Ring (LEAR) has to be converted into a Low-Energy Ion Ring (LEIR). Since the present ECR lead-ion source does not provide sufficient intensity, the main goal of LEIR is to act as a low-energy (4.2 MeV/u) accumulator where the ion beam is stacked and cooled (with the help of an electron-cooler) to reach the required intensity and emittances. An experimental program has been carried out at LEAR in recent years in order to test the cooling and stacking process with the present electron-cooler. A variety of results have been reported at previous conferences. This paper will focus on the electron-cooling aspects resulting from the afore mentioned experiments. Taking into account the experience gained, some guidelines will be given concerning the future LEIR machine and the electron-cooling device(s) that will be needed to produce cold dense electron beams.

For the preparation of dense bunches of ions for the LHC it has been proposed to accumulate in a small storage ring the beam from a linac with an ECR source. The scheme involves combined transverse and longitudinal multiturn injection and strong electron cooling to free phase space for the next injection. Successful experiments to determine the optimum parameters of a low-energy ion accumulator were performed at the Low Energy Antiproton Ring (LEAR) with Pb-ions of charge state 52+ to 55+ at an energy of 4.2 MeV/u. The reported measurements include: lifetime for different charge states as a function of the electron cooler current, cooling rates with different optical settings, efficiencies of the combined multiturn injection and results of accumulation. The transformation of LEAR into an accumulator ring for a wide range of ion species will be based on these results.

The LEAR machine is foreseen to be used as a lead ion accumulator in the injector chain for the LHC. Therefore, to test the principle of Pb54+ ion accumulation in LEAR, at 4.2 MeV/u, a number of studies and experiments have been made aimed at determining the improvements and modifications necessary to fulfill the LHC requirements. Amongst subjects studied we have investigated: a) The ion production and the injection line matching, b) The linac energy ramping in view of accumulation through combined longitudinal-transverse multi-turn injection, c) The ion beam lifetime and recombination processes, and finally d) The electron cooling time, as a function of the lattice parameters at the cooler. Recent experiments and measurements will be reported and commented in this paper. Also mentioned are some particular diagnostic methods.

The Fokker-Planck equation describing a beam of charged particles entering a homogeneous medium is solved here for a stationary case. Interactions are taken into account through Coulomb cross-section. Starting from the charged-particle distribution as a function of velocity and penetration depth, some important kinetic quantities are calculated, like mean velocity, range and the loss of energy per unit space. In such quantities the energy straggling is taken into account. This phenomenon is not considered in the continuous slowing-down approximation that is commonly used to obtain the range and the stopping power. Finally the well-known Bohr or Bethe formula is found as a first-order approximation of the Fokker-Planck equation. © 1996 Società Italiana di Fisica.

By measuring the lifetime of stored beams, the recombination of the ions with cooling electrons was investigated. Rates found are larger than expected for radiative electron capture and significantly higher for Pb53+ than for Pb54+ and Pb52+. These results are important for the design of the lead ion injection system for the Large Hadron Collider and for recombination theories.

The electron distribution function, the electron temperature and some transport parameters (electrical conductivity and energy flow coefficient) are obtained starting from the nonlinear Boltzmann equation for a plasma under the action of an external electric field. The Fokker-Planck approximation is used for electron-electron and electron-ion interactions. The effects of electron-electron collisions are studied for different values of collision frequencies and electric field.

A cathode readout MWPC for the high-density projection chamber (HPC) of the DELPHI experiment at LEP has been built and tested. In order to decouple both electrically and mechanically the drift volume of the HPC from the readout region, the segmented cathodes are made of brass U profiles, with a 100 μm diameter wire wound around the profile with a 2 mm pitch.

The problem of the accurate computation of thermo-electromagnetic stresses in a toroidal field coil for Tokamak machines will be an important task in the design of future high field Tokamak machines. The high value of flux density, and the pulsed current operation of these machines, imply critical working conditions and require a correct modelling of the thermal and electrical diffusion phenomena. In this paper are presented the thermo-electromagnetic model developed for this aim and the results obtained by implementing this model in the code COMPELL. These results are then used to derive input data for the structural analysis code, ANSYS, thus providing the means for a rather detailed analysis of the structure.

This paper deals with some aspects of quantistic effects in a partially ionized plasma. A simplified Boltzmann-Vlasov equation is obtained, by taking into account the Pauli exclusion principle. Then two problems are analysed: the dispersion of electrostatic waves and the electrical conductivity.

The study of impurity particles motion in a dielectric fluid under the action of an electric field can be of interest in the analysis of conduction and breakdown processes, especially in order to assess the changes in impurity concentrations. To this aim, rather sophisticated models of particle motion are required. In this paper, on the basis of a theory of electro-dielectrophoretic forces previously developed by the authors for spherical particles, a simulation algorithm of impurity particles motion is implemented by proposing models of the charge exchange mechanism at the particle-electrode contact. Experimental identification procedures of some model parameters are outlined and performed, and simulations of particle trajectories under a.c. and d.c. voltages for a sphere plane geometry, in the case of both conducting and dielectric particles in n-hexane, are compared with experimental results obtained by high-speed movie.

The present paper deals with electron oscillations in the field of a monochromatic wave having large phase velocity. The aim of this work is to extend to the hot-plasma case, by taking into account also the collision effects, the results obtained in the framework of the cold-plasma approximation. The expressions of the electron densities, as functions of space and time, are given for the two cases of a progressive and a stationary excited longitudinal wave.

The problem of the spatial variation of thermal-neutron fluxes is investigated in the framework of energy-dependent diffusion theory. Neutron flux is expanded here in terms of Laguerre polynomials in energy, weighted with a local Maxwellian distribution in which the neutron temperature depends on the space variable. The method proposed is applied to the diffusion of thermal neutrons in moderating systems with a nonuniform temperature profile. 3 figures.

A large system of wire proportional chambers is being constructed for the readout of the High-Density Projection Chamber of the DELPHI experiment at the Large Electron-Positron (LEP) storage ring. The system consists of 144 chambers, each 0.3-m/sup 2/, and read out via cathode pads. located at the end of the HPC drift volume. The authors discuss the design of the readout chamber; the chamber construction, the mechanical tolerances and gain uniformity, and the performance. >

In this paper the usefulness of a multiformulational approach to the numerical computation of electromagnetic fields of technical interest, including coupled problems, is discussed. Several field computation problems arising from various application areas are presented to sample some of the many formulations required to face the existing computational needs. The problems are solved by means of a code designed for a multiformulational management of field computation, and the versatility of the approach and the obtained results are discussed.

Electrooptical studies of the streamer initiation process using high magnification are performed to determine streamer shapes and dimensions. Using this information, the local electrical field is computed by means of a sophisticated computer code, named COMPELL. A detailed description of several plausible primary streamer models and the numerical results obtained from the local field computations are reported. The results obtained show that the electric field in the immediate vicinity of the streamer tip is much higher than has been calculated or estimated earlier. The influence of the different shapes and dimensions of the modeled streamers on the electric field are shown and discussed. >

The aim of the paper is the analysis of some aspects of the theoretical models used for the description of the Bremsstrahlung emission from non-Maxwellian plasmas, more precisely when quantum weak degeneracy effects come into play. Referring to the standard Sommerfeld Parameter ρ as a measure of the degree of degeneracy, we considered some reference physical environments, as Inertial Confinement Fusion experiments or the first stage of LIBS, characterized by high densities (even higher than solid state values) and relatively low temperatures (tens of eV). We investigated the relevance of the first order in ρ analytical corrections into the Born and Kramers approximations for the Gaunt factors calculations due to the evaluated non-Maxwellian electron distribution function for the weakly degenerate plasma. The shown results suggest that the degeneracy effects produce up to a 20% correction to the classical values for the Gaunt factors that should be taken into account to properly validate Bremsstrahlung spectra resulting from experiments.