Gas Target Experiments Research Articles

Collimation of target induced halo following MAGIX at MESA

The Mainz Energy-recovering Superconducting Accelerator (MESA) will be an electron accelerator allowing operation in energy-recovery linac (ERL) mode. It provides the opportunity to operate scattering experiments at energies of ~ 100 MeV with thin gas-targets. The MESA Internal Gas Target Experiment (MAGIX) aims to operate windowless jet targets and different gases up to Xenon to search for possible dark photon interactions, to precisely measure the magnetic proton radius and astrophysical S-factors. Investigations on the impact of the target on beam dynamics and beam losses are required for machine safety and to examine limits to ERL operation. The goal of this work is to understand target induced halo in the different experimental setups, track halo particles through downstream sections to examine beam losses and include a suitable collimation system and shielding into the accelerator layout to protect the machine from direct and indirect damage through beam losses and radiation. The present status of the investigations is presented.

Electron Energy Distribution in a Divertor Simulating Device with an RF Source

Electron energy distribution measurement with oscillating plasma potential compensation was performed in the radio-frequency plasma device, DT-ALPHA. Electrons near the plasma production region are confirmed to have Maxwellian distribution. The radial profile of the electron energy distribution in the high neutral pressure region, which is maintained by secondary helium gas puffing, was also investigated. Whereas the electrons still have Maxwellian distribution, the electron temperature in the outer region of the plasma column is lower compared with the inner region. This indicates that the volumetric recombination is enhanced at the periphery of the gas target experiment in the DT-ALPHA device.

ISOSPIN SYMMETRY BREAKING AND BRANCHING RATIO IN THE DEUTERON REACTIONS AT VERY LOW ENERGIES

The target-material dependence of the neutron-proton branching ratio and breaking of the isospin symmetry in the the 2H(d, n)3He and 2H(d, p)3H reactions at very low deuteron energies have been investigated. Angular distributions and total cross sections of the proton and neutron mirror channels have been measured for nuclear reactions taking place in different metallic environments. For Sr , Li , Na targets, we have found a first evidence for an alteration of the neutron-proton branching ratio and angular anisotropy of the neutron channel. We discuss various theoretical approaches explaining isospin mixing effects both in gas and metallic target experiments including a deuteron polarization in the crystal lattice. Direct reaction contribution has been calculated within the zero range distorted wave Born approximation (DWBA).

Study of the 15N(p,γ)16O reaction at the LUNA accelerator with a BGO detector

The 15N(p,γ)16O reaction has been intensively studied by the LUNA collaboration. In this contribution the measurements performed using the same BGO detector and two different setups, with gas and solid target, are described in details. The measurement of the cross section for this reaction allows to determine the astrophysical S-factor. The results of the gas target experiment will be discussed while the analysis of the solid target data is still in progress.

Measurement of the enhanced screening effect of the d + d reactions in metals

The investigation of the d+d fusion reactions in metallic environments at sub-Coulomb energies demands especially adapted techniques beyond standard procedures in nuclear physics. The measurements which were performed with an electrostatic accelerator at different self-implanted metallic target materials show an enhancement of the reaction cross-section compared to the gas target experiments. The resulting electron screening energy values are about one order of magnitude larger relative to the gas target experiments and exceed significantly the theoretical predictions. The measurements on deuterium inside metals are heavily affected by the interference of two peculiarities of this system: the possibly very high mobility of deuterium in solids and the formation of surface contamination layers under ion beam irradiation in high vacuum systems. Thorough investigations of these processes show their crucial influence on the interpretation of the experimental raw data. The differential data acquisition and analysis method employed to it is outlined. Non observance of these problems by using standard procedures results in fatal errors for the extraction of the screening energies.

Evidence for a host-material dependence of the n/p branching ratio of low-energy d+d reactions within metallic environments

Angular distributions and the neutron-proton branching ratio of the mirror reactions 2H(d, p)3H and 2H(d, n)3He have been investigated using different self-implanted deuterized metallic targets at projectile energies between 5 and 60 keV. Whereas the experimental results obtained for the transition metals Zr, Pd, Ta and also Al do not differ from those known from gas-target experiments, an enhancement of the angular anisotropy in the neutron channel and an attenuation of the neutron-proton branching ratio have been observed for the (earth)alkaline metals Li, Sr and Na at deuteron energies below 20 keV. Experimental results are discussed with consideration of the special problems arising from the properties of these chemically very reactive target materials. A first theoretical effort explaining simultaneously both n/p asymmetry effects based on an induced polarization of the reacting deuterons within the crystal lattice is presented.

Review of absolute doubly differential cross-section experiments and cross-section ratios for electron bremsstrahlung from rare gas atom and thin-film targets

We discuss doubly differential cross-section experiments for electron bremsstrahlung from free gas atom and thin-film targets for electron energies of 100 keV or less. We compare cross-section ratios for different target atoms with two theoretical models: ordinary bremsstrahlung and total bremsstrahlung calculated in the stripping approximation. Ratios of cross sections have been used to improve the comparison between experiment and theory when only relative cross sections are available or when the error in the absolute cross section is large. We also discuss additional background processes that may be more important in gas target experiments.

Experimental techniques for the investigation of the electron screening effect for d+d fusion reactions in metallic environments

Experimental studies of the fusion reactions 2H(d,p) 3H and 2H(d,n) 3He have shown that the reaction rates on deuterons implanted into metals (Al,Zr,Ta,Pd) are strongly enhanced compared to gas target experiments. The deduced screening energy values are about one order of magnitude larger and exceed significantly the theoretical predictions. The development of the implantation density and the deposition of carbon and oxide layers on the target surface are of crucial importance in order to investigate the screening effect correctly.

Solid-state effects in d+d fusion reactions

The nuclear fusion reactions 2 H( d, p) 3 H and 2 H( d, n) 3 He have been measured at projectile energies between 5 and 60 keV using deuteron-implanted solid targets (C, Al, Zr and Ta). An exponential-like enhancement of the reaction cross-section compared to the bare nuclei fusion could be observed for energies below 20 keV. This effect may be interpreted as a result of the electron screening of the Coulomb barrier between reacting deuterons and described by a screening energy U e. The experimentally determined U e values show a clear target-material dependence and reach for heavier materials values being one order of magnitude larger than the value achieved in a gas target experiment and significantly larger than the theoretical predictions. Specific solid-state contributions to the enhancement of the fusion cross-sections arising from the channeling of projectiles in the crystal lattice and some other related effects will be discussed.

Simulation of plasma-neutral dynamics for radiation cooling

An advanced heat removal scenario is required to handle the highinput power of magnetic fusion reactors. The concepts of gas target and radiative divertorshave been explored. A set ofself-consistently coupled fluid equations for plasma and neutralsis suitable for this system because of the sophisticated equationsfor neutrals. The transfer of plasma momentum to neutrals, whichis crucial in understanding the plasma-neutral interface, isdescribed through the charge exchange process. Our code resultsshow good agreement with gas target experiments on the PISCES experiment anddemonstrate its superiority to the previous simulation. Thisbenchmarked code and a set of equations have been applied to aslot divertor for DEMO reactor. The slot length for the divertor can bedetermined by producing enough frictional force to overcome thethermal force which creates a backflow of impurities. A smallamount of radiating argon is enough to exhaust 40 MW of power fromthe core plasma in a 40 cm long slot for the inner divertor of DEMO.

Capture reactions at astrophysically relevant energies: extended gas target experiments and GEANT simulations

Abstract Several resonances of the capture reaction 20 Ne ( α , γ ) 24 Mg were measured using an extended windowless gas target system. Detailed GEANT simulations were performed to derive the strength and the total width of the resonances from the measured yield curve. The crucial experimental parameters, which are mainly the density profile in the gas target and the efficiency of the γ-ray detector, were analyzed by a comparison between the measured data and the corresponding simulation calculations. The excellent agreement between the experimental data and the simulations gives detailed insight into these parameters.

Gas target experiments in high heat flux plasma of the TPD-I device

Gas target experiments are performed in the TPD-I device, which produces a high density helium plasma ∼ 6 × 10 19 m −3 with an electron temperature around 10 eV. The maximum plasma heat flow is estimated to be about 20 MW/m 2. A strong reduction of electron density and temperature was observed by feeding a secondary helium gas into the plasma and a stable detached plasma is formed in front of the target plate. The radial profile of the electron temperature is changed from peaked to hollow as the gas pressure is increasing. These experimental results are compared with the plasma simulations performed with the 2D plasma fluid B2 code. Good agreement with the simulated radial profiles of the plasma parameters is found.

Electron impact dissociation of H2O: emission cross sections for OH*, OH+*, H*, and H2O+* fragments

The optical emission spectrum in the near ultraviolet and visible following electron impact on H2O was studied in a crossed-beam and a static gas-target experiment. Emissions of H*, OH*, OH+*, and H2O+* fragments were detected and absolute emission cross sections for the different fragments were determined. A nonthermal rotational population was observed for the diatomic fragments which gives insight into the dissociation process. Further conclusions on the dissociation mechanism are possible based on appearance potentials and the shape of the emission cross sections as a function of impact energy.

The excitation of the 1s? and 2p? quasimolecular radiation in Nb+Kr collisions

The absolute yields of quasimolecular (MO) radiation lying above the characteristic KX-rays emitted in the asymmetric Nb+Kr (43 MeV) and Kr+Nb (47 MeV) collisions have been determined. The comparison of the MO yields obtained in the gas and solid target experiments shows that the 2pσ MO radiation (C1) is emitted predominantly in primary collisions, whereas the 1sσ MO radiation (C2) is produced in secondary collisions.

K X-ray production by 90-360 keV Ar and Ne collisions with Si. A comparison between gas and solid target experiments

K X-ray production in the collisions Ne+, Ne++ to SiH4; Si+, Si++ to Ne and Ar++ to SiH4 has been studied in the energy range 90-360 keV. Ar(K) and Si(K) X-rays were looked for but not observed, and the production cross sections must be less than 10-26 cm2, but Ne(K) X-rays were found and the corresponding cross section increases between 10-24 and 3*10-22 in the energy range studied, which agrees with expectations according to the electron promotion model of Fano and Lichten (1965). Comparison has been made of these ion-gas target results, with the previous ion-solid target results of Brandt and Laubert (1970) and Taulbjerf et al. (1973), and comment is made on the interpretation in terms of 'solid effects'. Within the framework of the Fano-Lichten model a rotational coupling of the 2p sigma MO to levels at or near the continuum is required to explain our observation of Ne(K) X-rays.

Gas target experiments of K-shell vacancy sharing in asymmetric ion-atom collisions

K-shell vacancy sharing was measured using 200 to 500 keV Ne incident on Na, Ne, O2 and N2 gas targets. The experimental results are in good agreement with a previous theory assuming radial coupling between the 2p sigma and 1s sigma molecular orbitals.