Bulk-viscosity-driven freeze-out in heavy ion collision

We give a review on the HBT puzzle, and argue that its resolution requires the introduction of new physics close to the phase transition scale. We argue that a candidate for this new physics is bulk viscosity, recently postulated to peak, and even diverge, close to the phase transition temperature. We show that such a viscosity peak can force the system created in heavy ion collisions to become unstable, and filament into fragments whose size is weakly dependent on the global size of the system, thereby triggering freeze-out.     

Bremsstrahlung pair production in relativistic heavy ion collision

We calculate production of electron- and muon-pairs by the bremsstrahlung process in hadron collisions and compare it with the dominant two-photon process. Results for the total cross section are given for proton-proton and heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). Received: 4 March 1997 / Revised version: 8 July 1997 / Published online: 20 February 1998     

The TMX heavy ion beam probe

A heavy ion beam probe has been used to measure the radial space potential distribution in the central cell of TMX. This was the first beam probe system to utilize computer control, CAMAC instrumentation, and fast time response for broadband fluctuation capabilities. The fast time response was obtained using off-line processing of the energy analyzer detector signals and wideband transimpedance amplifiers. The on-axis space potential was found to be 300-400 V, with φ_e/T_ec~8. The radial potential profile is parabolic when gas box fueling is used. The frequency of observed fluctuations was found to agree with the E×B plasma rotation frequency during the discharge. The measured Tl⁺⁺ secondary ion current level is consistent with calculations, given reasonable assumptions for beam attenuation     

Deposition of molecular probes in heavy ion tracks

By using polarized fluorescence techniques the physical properties of heavy ion tracks such as the dielectric number, molecular alignment and track radius can be traced by molecular fluorescence probes. Foils of poly(ethylene terephthalate) (PET) were used as a matrix for the ion tracks wherein fluorescence probes such as aminostyryl-derivatives can be incorporated using a suitable solvent, e.g. N,N′-dimethylformamide (DMF) as transport medium. The high sensitivity of fluorescence methods allowed the comparison of the probe properties in ion tracks with the virgin material. From the fluorescence Stokes shift the dielectric constants could be calculated, describing the dielectric surroundings of the molecular probes. The lower dielectric constant in the tracks gives clear evidence that there is no higher accomodation of the highly polar solvent DMF in the tracks compared with the virgin material. Otherwise the dielectric constant in the tracks should be higher than in the virgin material. The orientation of the molecular probes was examined by polarized fluorescence spectroscopy. It is shown that deposited molecular probes witha high aspect ratio have a preferential orientation parallel to the ion track axis.     

The heavy ion beam diagnostic for the tokamak ISTTOK

In this paper we describe the heavy ion beam diagnostic for the tokamak ISTTOK, which has been designed to determine the temporal evolution of the plasma density, poloidal magnetic field and plasma potential profiles. This diagnostic makes use of a new type of high density caesium plasma source, a multiple cell detector and a fast data acquisition system. We describe the numerical code for trajectory and beam attenuation simulations, a method for the experimental determination of the poloidal field profile, the ion gun and the detection, control and data acquisition systems. Calibration tests and the first experimental results are presented     

Nucleon spectra in heavy ion collision prior to equilibrium

Energy spectra and angular distribution of nucleons emitted in intermediate energy heavy ion collisions prior to equilibrium are calculated. The spectra have two components: (a) promptly emitted particles (PEPS) or Fermi jets; (b) emission from a localized excited region at the interface of the two colliding ions. The results obtained with this model have been compared with experiment and the agreement is good.     

The Ψ′ in the relativistic heavy ion collision

We have investigated the temperature influence on the hadronic decay width of Ψ′. Contrary to the divergence of the decay width ofρ-meson,π-meson at critical temperature as suggested in some papers, we find that the decay width of Ψ′ decreases with increasing temperature. Thus the leptonic decay can be used to measure the number of produced Ψ′ at finite temperature just as at zero temperature.     

Perturbed stationary state approach to nuclear heavy ion collision

In order to treat the nuclear heavy ion collision at low energy, the perturbed stationary state method developed in the atomic collision is extended so as to include the coupling between the internal state and the angular part of the relative motion. It is shown that this method provides a simple interpretation for the molecular resonances observed in the scatterings of ¹²C + ¹²C, ¹²C + ¹⁶O and ¹⁶O + ¹⁶O, and for the induced rotation mechanism during the collision between heavy ions. Also given is the detailed study for the applicability of the perturbation treatment of this method.     

Heat diffusion in heavy ion beam irradiation

For heavy ion beam irradiation in water, a model that simulates heat diffusion following measurement indicating heat diffusion is proposed as a first step. This heat is generated near the incident ion path. The model proposed here should be useful for ion-beam cancer therapy as well as the analysis of this measurement. Further, many molecules quickly migrate in the target simultaneously with heat diffusion, and this migration is expected to greatly damage DNA, that is, to create cluster DNA damage.     

Development of heavy ion beam probe diagnostics

The results of the activity of the Kharkov and Moscow HIBP groups during recent years are presented in this paper. This is a review of papers published in the USSR and also contains extracts of some unpublished reports. The mathematical aspects of the diagnostics including the problems of the planning and design of an experiment along with the problems of the interpretation of the experimental data for plasma density and current determination are reviewed. The probing apparatus used in the experiment for plasma potential and density measurements are described. Some results of measurements are discussed and the trends to spread the use of HIBP in modern research are noted     

Development of exploding wire ion source for intense pulsed heavy ion beam accelerator

A Novel exploding wire type ion source device is proposed as a metallic ion source of intense pulsed heavy ion beam (PHIB) accelerator. In the device, multiple shot operations are realized without breaking the vacuum. The basic characteristics of the device are evaluated experimentally with an aluminum wire of diameter 0.2 mm and length 25 mm. A capacitor bank of capacitance 3 μF and a charging voltage of 30 kV was used, and the wire was successfully exploded by a discharge current of 15 kA with a rise time of 5.3 μs. Plasma flux of ion current density around 70 A/cm² was obtained at 150 mm downstream from the device. The drift velocity of ions evaluated by a time-of-flight method was 2.7×10⁴ m/ s, which corresponds to the kinetic energy of 100 eV for aluminum ions. From the measurement of the ion current density distribution, the ion flow is found to be concentrated toward the direction where the ion acceleration gap is placed. From the experiment, the device is found to be acceptable for applying the PHIB accelerator.     

Atomic beam,optogalvanic and stored ion spectroscopy for radioactive isotopes

Systematic studies of the optical isotope shift and the hyperfine splitting of long chains of stable and radioactive isotopes were performed. The method applied was laser induced resonance absorption; the experimental techniques were the atomic beam method with fluorescence detection and the optogalvanic method. The theory of hyperfine splitting and isotope shift of atoms is reviewed in short with emphasis on the aspects interesting for nuclear physics and on the evaluation problem. The experimental methods are described and their key parameters sensitivity and resolution are discussed. Preliminary results on stored thorium ions are given. Sample results for the nuclear quantity δ<r ²> derived from atomic beam experiments with tin and strontium are presented.     

Dissipative processes in light heavy ion collisions

The characteristics of the dissipative processes in the collisions of light heavy ion systems at incident energies below 10 MeV/nucleon have been studied. The correlations between different experimental observables show similar trends as those known at much heavier systems and semiempirical relationships are established starting from assumptions on the nature of the microscopic mechanisms. The charge equilibration process in light systems is also studied.     

Correlations and fluctuations in high energy heavy ion collision experiments

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented. The experimental status on fluctuations and correlations has been reviewed and the outlook for research status of soft physics in LHC/ALICE has been introduced in this paper.     

Electromagnetic processes in relativistic heavy ion collisions

Electromagnetic effects in relativistic heavy ion collisions with impact parameter larger than the sum of the nuclear radii are studied using the virtual photon method. With increasing value of the relativistic parameter γ the hardness of the virtual photon spectrum increases. This leads to interesting new effects which will also have to be considered in the design of future relativistic heavy ion machines and experiments. The excitation of high-lying giant E1 and E2 multipole resonances is calculated as well as electromagnetic pion production. Coulomb bremsstrahlung is calculated and compared to the bremsstrahlung emitted in the more violent central nuclear collisions. K-shell ionization and electron-positron pair production is studied. The latter process has a very large cross section for heavy ions and contributes significantly to the stopping power of relativistic heavy ions in a dense medium.     

Correlations and fluctuations in high energy heavy ion collision experiments

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented.The experimental status on fluctuations and correlations has been reviewed and the outlook for research status of soft physics in LHC/ALICE has been introduced in this paper.     

A two-center-oscillator-basis as an alternative set for heavy ion processes

The two-center-oscillator-basis, which is constructed from harmonic oscillator wave functions developing about two different centers, suffers from numerical problems at small center separations due to the overcompleteness of the set. In order to overcome these problems we admix higher oscillator wave functions before the orthogonalization, or antisymmetrization resp. This yields a numerically stable basis set at each center separation. The results obtained for the potential energy surface are comparable with the results of more elaborate models.     

A short history of heavy ion beam probing

The author describes some aspects of research on controlled thermonuclear fusion as an energy source, starting in the late 1950s. There was a need for new diagnostic techniques for studying high temperature plasmas. The author proposed a diagnostic for measuring plasma density by probing a deuterium plasma with a deuterium beam and measuring the proton production from the D-D nuclear reaction. By the mid 1960s, it was possible to do so. After carrying out a D-D measurement, the author suggested switching over to an H₂⁺ beam and looking for an H⁺ signal. The H+ was loud and clear and that was the last of the nuclear measurements. One of the first things done using the molecular break-up of the H₂⁺ to measure the density of the hollow cathode arc plasma was a study of a coherent instability. The frequency response wasn't sufficient to measure the instability directly, so a Langmuir probe was used to detect the instability. The Langmuir probe gave a signal from a fixed spatial location but the beam probe signal was swept across the plasma giving 2D spatial resolution. This was the first detailed mapping of a plasma instability. Attempts to apply the ion beam probe to measuring the plasma current density in the ST Tokamak are described. Heavy ion beam probing measurements using hollow cathode arcs as target plasmas made it possible to measure T_e at low temperatures and to identify space potential fluctuations. Installation of a beam probe on the Laser Initiated Target Experiment are described, along with work on the ELMO Bumpy Torus, the VERSATOR Tokamak, TMX, TEXT, ISX-B, the Ergodic Magnetic Limiter and ATF     

Simulation of first order confinement transition in relativistic heavy ion collision

We have carried out numerical simulation of first order phase transition in 2+1 dimensions to study the formation and evolution of Z(3) domain walls in relativistic Heavy Ion Collision using the effective potential proposed by Pisarski for QCD where Polyakov loop is the order parameter of the weak first order phase transition. Bubbles of the QGP phase are randomly nucleated on the lattice, which grow and coalesce. The spontaneous breaking of Z(3) symmetry in QGP phase gives rise to domain walls and topological strings. We discuss P _T enhancement due to reflection of quarks from the collapsing domain walls. We also discuss enhancement of doubly strange and triply strange hadrons due to larger concentration of s quarks inside collapsing wall. The decay of the domain walls when temperature drops below T _c results in the fluctuations of energy density.