Jet Target Research Articles

Observation of Raman scattering and hard X-rays in short pulse laser interaction with high density hydrogen gas

Backward and forward Raman scattering has been experimentally investigated in a high density hydrogen gas jet target at electron densities up to 0.2 n c, well above the density of previously reported studies. Stokes shifted radiation from both backward and forward scattering is observed with a peak wavelength which is consistent with the frequency matching condition for a cold plasma. Strong up-shifted spectra are observed in the forward direction which cannot be simply attributed to anti-Stokes shifted Raman light. Hard X-ray emission is also observed and its onset together with a saturation in the backscatter signal coincide with the predicted threshold for relativistic self-focusing of the laser in the gas. The results also show a correlation between the generation of hard X-rays and the forward Raman scattering as the laser power is varied.

Higher-order effects studied for K-shell excitation of high-Z projectiles

The study of projectile excitation of high-Z ions in collisions with light target atoms is a powerful tool for the investigation of magnetic and higher-order effects occurring in relativistic collisions. Very first investigations performed for bismuth ions were recently extended at the ESR storage ring by using He-like uranium ions in collisions with gaseous targets. At the ESR jet target, the absence of solid-state effects (e.g., multiple collisions) allows one to study higher order processes, such as excitation and ionization or excitation and capture, occurring in single collisions.

Observation of bound-state β− decay of bare 187Re using magnetic analysis

We observed the bound-state β − decay of fully ionized 187Re-nuclei circulating in the experimental storage ring ESR at GSI. 187Re ions were accelerated in the GSI accelerator complex to a final energy of 347 MeV/u, fully stripped and injected into the ESR. During storage times of up to four hours, several hundred 187Os 75+ ions were produced via bound-state β − decay of 187Re 75+ ions and circulating on almost the same orbit. To separate the 187Os ions from their mother nuclei, an internal Ar gas jet target was used to strip off the last electron and produce 187Os 76+. As a result of the higher charge state the 187Os ions now were stronger deflected by the following dipole magnet, and detected in a position sensitive microstrip-gas-counter. The determined half-life is T 1 2 = 31.2 −2.5 +3.0 yr . With the now measured 187Re half-life the 187 Re 187 Os cosmochronometer can be recalibrated. By taking into account the β − decay enhancement in stellar interiors, this ‘clock’ will lead to a more accurate estimation of the Galactic age.

Pionic Fusion Study of the halo analogue state6Li

The isobaric analogue state of the ground state of the halo nucleus6He,6Li* has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala, Sweden. This was the first of two proposed experiments with the aim to study the high momentum part of the wave functions of the halo nuclei6He and6Li (0+, T=1). The Li nuclei were produced in inverse kinematics reactions with alpha particles incident on a deuterium cluster jet target. The6Li ions were detected in a zero-degree spectrometer situated in the fourth quadrant of the CELSIUS ring. The measurement was done for three different beam energies corresponding to 5.4, 2.2 and 1.5 MeV above threshold in the c.m. The cross-sections slowly increase with beam energy from 95 nb at the lowest energy to about 250 nb at 5.4 MeV above threshold.

Onset of relativistic self-focusing in high density gas jet targets

Optical investigations are reported of the interaction of $0.3$ TW, 250 fs Ti:sapphire laser pulses with underdense plasmas created from high density gas jet targets. Time resolved shadowgraphy using a $2\ensuremath{\omega}$ probe pulse, images of the transmitted radiation and images of $1\ensuremath{\omega}$ and $2\ensuremath{\omega}$ side radiation are presented for various gases. The experimental results and their analysis based on a simple numerical Gaussian beam model show that ionization-induced refraction dominates the interaction process for all gases except hydrogen. The numerical modeling also shows that for a given laser power there exists only a narrow density range in which self-focusing can be expected to occur. In the case of hydrogen for electron densities greater than $\ensuremath{\sim}{10}^{20}{\mathrm{cm}}^{\ensuremath{-}3}$, the onset of channeling expected at the critical power for relativistic self-focusing is experimentally observed. X-ray and forward stimulated Raman scattering measurements were also conducted to verify the onset of high intensity relativistic interactions and the onset of fast electron generation.

Half-life measurement of the bound state beta decay of 187Re 75+

Whereas neutral 187Re has a half-life of ≈ 4 · 10 10 yr, one expects for fully stripped 187Re 75+ a half-life of < 100 yr, as it can decay into bound electronic states of the first excited state of the daughter isotope, 187Os 75+. The latter decay occurs in hot stellar plasmas and must therefore be known if one wishes to infer from the 187Re 187Os ratio found in meteorites the age of the material in our solar system. This decay was measured for the first time in an experiment performed at the heavy ion storage ring ESR of GSI. 187Re 75+ ions were produced by stripping in a thick copper target after acceleration to 350 MeV per nucleon in the heavy ion synchrotron SIS. Up to 1.7 · 10 8 ions were stored in the ESR ring at a time. After different storage times (up to 5h), the hydrogen-like decay products were stripped in an internal argon gas jet target. The number of stripped 187Os 76+ ions was determined in two independent experiments. In the first one the osmium ions were counted in a microstrip gas counter. In the second experiment, the 187Os 76+ ions were still circulating in the storage ring and their number was determined non-destructively by Schottky spectroscopy. In both cases, a separation of the beta decay products from nuclear fragments produced either in the rest gas or the internal target was possible. One can safely exclude that a major fraction of the 187Os ions were produced by n-p exchange reactions. Rates for stripping in the gas jet and the relevant particle loss rates were determined independently.

Low energy proton-proton scattering near the interference minimum using a windowless gas jet target

In the energy region around 380 keV (lab.) and at detection angles near 45° (lab.) the cross section of proton-proton scattering exhibits a deep minimum, since the Coulomb amplitude and the nuclear amplitude almost cancel each other out, resulting in a pronounced deviation from pure Mott scattering. A new set of precise data in the-energy range between 300 and 407 keV was recorded using the accelerator of the IKP Münster by employing a thin gas jet target with an areal density smaller than 8 × 10 14cm −2. For the first time p-p scattering near the interference minimum was studied under single scattering conditions using a high quality ion beam (energy spread <40 eV). Since the energy smearing was two orders of magnitude lower than that of the former measurements, a more detailed evaluation of the data was feasible, resulting in differential cross sections near the minimum which are smaller than published before. The measured values cannot be explained by the interference of the Coulomb and the nuclear amplitude alone but suggest the need for vacuum polarization or other additional effects. The position of the minimum was determined to be (382.8 ± 0.1) keV.

A cryocondensation pump for a high-density atomic hydrogen jet target

A large cryocondensation pump for an intense atomic hydrogen beam was designed, fabricated, and tested; its compact design allowed a total copper cryopanel area of about 15 m 2. The cryopanels operated at about 2.6 K. For an atomic hydrogen beam of up to 3.2 × 10 18 atoms s −1, the measured pumping speed was about 1.2 × 10 7 l s −1, which is 4.2 × 10 26 atoms Torr −1 s −1.

Proton-antiproton annihilation into neutral strange mesons

In a search for gluonic hadrons, the formation channels p̄p → K s K s , p̄p → ηη, p̄p → π 0 η and p̄p → π 0 π 0 were studied in the mass range from 2.1 to 2.4 GeV using the Jetset (PS202) detector and an internal molecular hydrogen cluster jet target installed in the Low Energy Antiproton Ring (LEAR) at CERN. Cross sections for p̄p → K s K s have been obtained and limits are set on the non-observation of the ξ(2230). Conversely, we find evidence for a narrow signal in a preliminary analysis of our p̄p → ηη data consistent with a narrow ξ(2230).

A high resolution 4π multi-electron spectrometer for soft electrons

Electrons emerging form ionizing collisions of any projectiles (ions, photons, electrons) with the particles in a supersonic jet target (atoms, clusters, molecules) are projected onto three large-area, multi-hit capable position sensitive detectors applying well controlled electric and solenoidal magnetic fields. Up to three electrons with an energy bandwidth for each between 0 eV ≤ E e ≤ 1 keV are detected simultaneously with a solid angle close to 4π. Each momentum vector (three spatial components p ei) is calculated from the measured hitting positions and time-of-flights with a resolution of Δ p ei < 2 × 10 −2 a.u.. Thus, the complete final many-electron momentum space (up to 9 momentum components) is visualized. The theoretical limits in resolution achievable with such a method is in the neV-regime. In addition, the recoil-ion momentum vector is determined simultaneously applying “conventional” recoil-ion momentum spectroscopy.

Internal gas jet target for the formation of antihydrogen atoms in \barp-nucleus interactions

The use of a gas jet internal target in an antiproton storage ring provides a unique source of antiproton-nucleus interaction. This has made possible for the experiment PS210 to measure for the first time the formation of antihydrogen (\overlineH) atoms. This contribution describes the characteristics of the target of the PS210 and E835/E862 experiments.

Schottky mass spectrometry at the heavy ion storage ring ESR

Schottky mass spectrometry is a novel method of precision nuclear mass spectrometry based on the measurement of the revolution frequencies of cooled ions in storage rings performed by non-destructive frequency analysis of the beam noise, the well-established Schottky diagnosis technique. The method was applied for the first time at the Experimental Storage Ring ESR at GSI observing electron cooled highly charged ions up to bare nuclei at relativistic energies around several hundred MeV/u. To demonstrate the performance and feasibility of the method at the ESR, experimental tests have been carried out using beams of nuclear fragments produced in the ring itself by the interaction of different primary beams with the internal gas jet target. Futhermore, first Schottky mass measurements of secondary nuclear beams produced by projectile fragmentation of Au and Bi primary beams in a thick Be-target were carried out in order to determine the masses for numerous heavy neutron deficient nuclei which had not been measured before. Relative accuracies for the measured mass values in the order of 1×10−6 and below can be achieved. The method is briefly discussed and some early results are presented.

Neutron irradiation characteristics in international fusion materials irradiation facility

Neutron field and damage parameters for the planned international fusion materials irradiation facility (IFMIF) were estimated for use in developing an irradiation configuration plan using this facility. The facility generates fusion-like neutrons using d—Li reactions with 30–40 MeV and two 125 mA deuteron beams with an angle of 10°, and with a Li jet target with a square beam spot of 50 mm × 200 mm in typical size. The analysis was performed for four standard sample loading models, consisting of Fe or SiC for test materials and NaK or He for coolant. The calculation was carried out by the Monte Carlo code GMVP with the HILO/86-J3 library with the external source obtained from an analytical model. The flux—volume relation was obtained together with the relation of the dpa rate—volume. The dpa—He gas production ratio and nuclear heating were also estimated inside the standard samples.

Ionization-induced blue shift of KrF laser pulses in an underdense plasma.

The ionization-induced blue-shifted spectra for helium, neon, and nitrogen have been measured at various gas densities up to 5\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at a vacuum intensity of 8\ifmmode\times\else\texttimes\fi{}${10}^{16}$ W/${\mathrm{cm}}^{2}$ for picosecond KrF laser pulses at 248 nm. A 1-mm diameter gas jet target was used in the experiment to minimize the refraction of the laser beam and thus higher laser intensities were obtained in the gas than in previously reported experiments. For helium, a distinct shifted peak was observed at intermediate densities which was not seen before. For helium and nitrogen, spectra were also measured of the light scattered outside of the original focal cone angle. In this region there was little signal for electron densities below 2\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ consistent with limited refraction at lower densities and at higher densities the spectra were predominantly blue shifted. These results indicate the importance of refraction in the correct interpretation of ionization blue-shifted spectra. \textcopyright{} 1996 The American Physical Society.

Quasi-elastic and inelastic inclusive electron scattering from an oxygen jet target

The results of an experiment on inclusive electron scattering from an oxygen jet target, performed in a wide range of energy and momentum transfer covering both quasi-elastic and $\Delta$(1232) resonance regions, are reported. In the former region the theoretical predictions, obtained including effects of nucleon-nucleon correlations in both initial and final states, give a good description of the experimental data. In the inelastic region a broadening as well as a damping of the resonant part of the cross section with respect to the free nucleon case is observed. The need of more detailed calculations including nuclear structure effects on the electroproduction cross section of nucleon resonances is highlighted.

A 4π recoil-ion electron momentum analyzer: a high-resolution “microscope” for the investigation of the dynamics of atomic, molecular and nuclear reactions

A high-resolution recoil-ion momentum spectrometer based on a precooled localized supersonic jet target (COLTRIMS) has been combined with a novel low-energy electron analyzer with 4π solid angle for electrons with energies E e ≤ 30 eV including E e = 0 eV. Thus, three recoil-ion momentum components, the recoil-ion charge state and three momentum components of one electron emitted in any collision-induced ionization reaction are measured simultaneously with a coincidence efficiency of 28%. In order to accept large recoil-ion longitudinal momenta (along the beam) of p R‖ ≤ 160 a.u. and simultaneously guarantee a superior resolution in this direction (Δ P R‖ ≤ ± 0.08 a.u.), recoil ions are extracted in the longitudinal direction different from all former concepts. Test measurements, details on the present design and results of a kinematically complete experiment for single ionization are presented and possible further improvements are discussed. The future potential of such spectrometers for the investigation of collision-induced atomic many-particle reactions, the “Coulomb-explosion” of molecules and the spectroscopy of electronic states in heavy few-electron systems is illustrated. Similar techniques might be used to measure angular correlations and even the neutrino mass in β-decay experiments.

The pp → ppη reaction near the kinematical threshold

The pp → ppη reaction has been measured at six energies close to threshold, from 1258 MeV to 1352 MeV, using an internal cluster gas jet target in the CELSIUS storage ring. The η is detected through its decay photons, in an array of CsI detectors, and the forward-going protons are detected in a plastic scintillator spectrometer. A complete event reconstruction is obtained at the higher energies in the measured interval. The new data, together with earlier data, give an accurate determination of the energy dependence close to threshold. The influence of the η-proton FSI is seen in the total cross section data as well as in a Dalitz plot of the η-p invariant mass distributions.

Development of internal jet targets for high-luminosity experiments

We report on recent developments of the internal supersonic gas jet target at IUCF. The emphasis has been on hydrogen jets that can be used as targets of ∼ 10 16 atoms/cm 2 thickness in high-luminosity experiments. A method of scanning jets with an ionizing 1 keV electron beam has been employed in order to study jet formation as a function of nozzle geometry and temperature. We summarize our results, obtained by scanning H 2 jets from 23 different nozzles, most of them made from glass capillaries. The present setup of the jet target in the Cooler storage ring is described.

Single capture and transfer ionization in collisions of Cl q+ projectile ions incident on helium

The Kansas State University linac has been used to measure the ratio of the cross sections for the processes of transfer ionization (TI) and single capture (SC) for 2 MeV/amu Cl q+ where q = 7, 9, 13, 14, and 15 projectile ions incident on a helium target. The ratio was determined using a helium gas jet target by measuring coincidences between projectile-ion and recoil-ion final charge states. The σ TI σ SC for Cl q+ were compared to measurements of bare F 9+ and hydrogenlike F 8+ and O 7+ taken at the same velocity. The ratios deviate from a q 2 scaling which is predicted in the perturbative regime. This deviation is attributed to screening by the projectile electrons for low q = 7 and 9, and to the collision being non-perturbative for high q. A possible saturation effect in the ratio was observed for q ∼ 14.

State selective scattering angle dependent capture cross sections measured by cold target recoil ion momentum spectroscopy.

We have developed a new kind of recoil ion momentum spectroscopy technique, using a precooled supersonic gas jet target, to determine state selective, scattering angle dependent cross sections for swift ion-atom collisions ( $0.25,\dots{},1\mathrm{MeV}{\mathrm{He}}^{2+}$ on He), by measuring the transverse and longitudinal momentum of the recoil ion. A longitudinal momentum resolution of $\ifmmode\pm\else\textpm\fi{}0.13\mathrm{a}.\mathrm{u}.$ was achieved, about a factor of 30 better than ever obtained before, which enables a clear separation of K and L shell capture. In the transverse direction a resolution corresponding to a projectile scattering angle uncertainty of $\ensuremath{\Delta}{\ensuremath{\vartheta}}_{P}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}1\ensuremath{\mu}\mathrm{rad}$ was obtained.