A linear radio frequency plasma reactor for potential and current mapping in a magnetized plasma.

Langmuir probe measurements in front of high power ion cyclotron resonant frequency antennas are not possible or simply too noisy to be analyzed properly. A linear experiment is a radio frequency (RF) magnetized plasma discharge reactor designed to probe the rectified potential in front of such antennas but at low power level (1 kW) to next improve antenna design and mitigate sheath effects. The maximum magnetic field is 0.1 T, and the RF amplifier can work between 10 kHz and 250 MHz allowing ion cyclotron resonances for argon or helium. The first measurements with no magnetic field are presented here, especially 2D potential maps extracted from the RF compensated probe measurements yield ni ≈ 10(15) m(-3) and Te ≈ 2 eV for RF power lower than 100 W. Series resonances in the chamber are highlighted and allow to deduce the plasma parameters from a simple equivalent impedance model of the plasma in helium gas. Next studies will be focused on magnetized plasmas and especially magnetized RF sheaths.

Spectroscopic interpretation and velocimetry analysis of fluctuations in a cylindrical plasma recorded by a fast camera.

Fast visible imaging is used on a cylindrical magnetized argon plasma produced by thermionic discharge in the Mirabelle device. To link the information collected with the camera to a physical quantity, fast camera movies of plasma structures are compared to Langmuir probe measurements. High correlation is found between light fluctuations and plasma density fluctuations. Contributions from neutral argon and ionized argon to the overall light intensity are separated by using interference filters and a light intensifier. Light emitting transitions are shown to involve a metastable neutral argon state that can be excited by thermal plasma electrons, thus explaining the good correlation between light and density fluctuations. The propagation velocity of plasma structures is calculated by adapting velocimetry methods to the fast camera movies. The resulting estimates of instantaneous propagation velocity are in agreement with former experiments. The computation of mean velocities is discussed.

Indication of a deeply bound and compact K- pp state formed in the pp- -> pLambdaK+ reaction at 2.85 GeV.

We have analyzed data of the DISTO experiment on the exclusive pp --> pLambdaK+ reaction at 2.85 GeV to search for a strongly bound compact K- pp(approximately = X) state to be formed in the pp --> K+ + X reaction. The observed spectra of the K+ missing mass and the pLambda invariant-mass with high transverse momenta of p and K+ revealed a broad distinct peak of 26-sigma confidence with a mass M(X)=2267+/-3(stat)+/-5(syst) MeV/c2 and a width Gamma(X)=118+/-8(stat)+/-10(syst) MeV. The enormously large cross section indicates formation of a compact K- pp with a large binding energy of B(K)=103 MeV, which can be a possible gateway toward cold and dense kaonic nuclear matter.

Transitions to spatiotemporal chaos and turbulence of flute instabilities in a magnetized plasma.

The spatiotemporal transition scenario of flute instabilities from a regular to a turbulent state is experimentally investigated in the plasma column of a thermionic discharge. The same transition scenario, i.e., the Ruelle-Takens route to turbulence, is found for both the Kelvin-Helmholtz and the Rayleigh-Taylor instabilities. It is demonstrated that the transition can be more or less smooth, according to the discharge mode. In both cases, a strong radial dependence is observed, which is linked to the velocity shear layer in the case of the Kelvin-Helmholtz instability.

Motions induced by asymmetric vibrations. The solid/solid case.

We discuss theoretically the motions of a coin on a horizontally vibrating plate, with dry friction between the coin and the plate. As first noticed by Daniel and Chaudhury in a different situation (droplets on a plate), when the periodic acceleration gamma(t) imposed by the plate is unsymmetrical, the coin can move macroscopically with a certain drift velocity V. We analyse here: (a) the vibration threshold below which V=0, and the generic behavior expected just above threshold; (b) the limiting behavior at very high amplitudes, where V should become independent of the amplitude; (c) the complications due to small, macroscopic inhomogeneities on the supporting plate.

Rho(0) meson production in the pp-->pppi(+)pi(-) reaction at 3.67 GeV/c.

Total and differential cross sections for the exclusive reaction pp-->pp rho observed via the pi(+)pi(-) decay channel have been measured at p(beam)=3.67 GeV/c. The observed total meson production cross section is determined to be (23.4+/-0.8+/-8) mu b and is significantly lower than typical cross sections used in model calculations for heavy-ion collisions. The differential cross sections measured indicate a strong anisotropy (approximately cos(theta(CM)(rho)) in the rho(0) meson production.

Exclusive measurements of light fragment production at forward angles in Ne-Pb and Ne-NaF collisions at E/A=400 MeV and 800 MeV.

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.

Calibration curves for size-exclusion chromatography: description of HPLC gels in terms of porous fractals.

We have tested the proposition that porous media used in protein size exclusion chromatography are surface fractals. The data obtained in the calibration of classical gels (Sephacryl and Sepharose) and of HPLC gels (TSK SW and PW) using a wide range of protein sizes, have been analyzed within the framework of this theory. While the model does not apply to classical gels, it seems that HPLC gels can be described as fractals in the range of protein sizes. This finding has interesting implications for the calibration procedure.

Nuclear collective flow and charged-pion emission in Ne-nucleus collisions at E/A = 800 MeV.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.

Proton-proton correlations at small relative momentum in neon-nucleus collisions at E/A=400 and 800 MeV.

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.

Exclusive measurements of mean pion multiplicities in 4He-nucleus reactions from 200 to 800 MeV/nucleon.

Mean multiplicities of pi+ and pi- in 4He collisions with C, Cu, and Pb at 200, 600, and 800 MeV/u, and with C and Pb at 400 MeV/u have been measured using the large solid angle detector Diogene. The independence of pion multiplicity on projectile incident energy, target mass and proton multiplicity is studied in comparison with intra-nuclear cascade predictions. The discrepancy between experimental results and theory is pointed out and discussed.

The Diogene 4 pi detector at Saturne.

Diogene, an electronic 4 pi detector, has been built and installed at the Saturne synchrotron in Saclay. The forward angular range (0 degree-6 degrees) is covered by 48 time-of-flight scintillator telescopes that provide charge identification. The trajectories of fragments emitted at larger angles are recorded in a cylindrical 0.4-m3 Pictorial Drift Chamber (PDC) surrounding the target. The PDC is inside a 1-T magnetic field; the axis of the PDC cylinder and the magnetic field are parallel to the beam. Good identification has been obtained for both positive and negative pi mesons and for hydrogen and helium isotopes. Multiplicities in relativistic nucleus-nucleus reactions up to 40 have been detected, limited mainly by the present electronics.