33 research outputs found
X-ray emission for 424 MeV/u C ions impacting on selected targets
In inertial Confinement Fusion (ICF), X-ray
radiation drives the implosion requiring not only
sufficient conversion efficiency of the drive
energy to the X-ray but also the highly spatial
symmetry..
Transport of intense ion beams in plasmas: collimation and energy-loss reduction
We compare the transport properties of a well-characterized hydrogen plasma
for low and high current ion beams. The energy-loss of low current beams can be
well understood, within the framework of current stopping power models.
However, for high current proton beams, significant energy-loss reduction and
collimation is observed in the experiment. We have developed a new
particle-in-cell code, which includes both collective electromagnetic effects
and collisional interactions. Our simulations indicate that resistive magnetic
fields, induced by the transport of an intense proton beam, act to collimate
the proton beam and simultaneously deplete the local plasma density along the
beam path. This in turn causes the energy-loss reduction detected in the
experiment
Anomalous stopping of laser-accelerated intense proton beam in dense ionized matter
Ultrahigh-intensity lasers (10-10W/cm) have opened up new
perspectives in many fields of research and application [1-5]. By irradiating a
thin foil, an ultrahigh accelerating field (10 V/m) can be formed and
multi-MeV ions with unprecedentedly high intensity (10A/cm) in short
time scale (ps) are produced [6-14]. Such beams provide new options in
radiography [15], high-yield neutron sources [16], high-energy-density-matter
generation [17], and ion fast ignition [18,19]. An accurate understanding of
the nonlinear behavior of beam transport in matter is crucial for all these
applications. We report here the first experimental evidence of anomalous
stopping of a laser-generated high-current proton beam in well-characterized
dense ionized matter. The observed stopping power is one order of magnitude
higher than single-particle slowing-down theory predictions. We attribute this
phenomenon to collective effects where the intense beam drives an decelerating
electric field approaching 1GV/m in the dense ionized matter. This finding will
have considerable impact on the future path to inertial fusion energy.Comment: 8 pages, 4 figure
Energy loss enhancement of very intense proton beams in dense matter due to the beam-density effect
Thoroughly understanding the transport and energy loss of intense ion beams
in dense matter is essential for high-energy-density physics and inertial
confinement fusion. Here, we report a stopping power experiment with a
high-intensity laser-driven proton beam in cold, dense matter. The measured
energy loss is one order of magnitude higher than the expectation of individual
particle stopping models. We attribute this finding to the proximity of beam
ions to each other, which is usually insignificant for relatively-low-current
beams from classical accelerators. The ionization of the cold target by the
intense ion beam is important for the stopping power calculation and has been
considered using proper ionization cross section data. Final theoretical values
agree well with the experimental results. Additionally, we extend the stopping
power calculation for intense ion beams to plasma scenario based on Ohm's law.
Both the proximity- and the Ohmic effect can enhance the energy loss of intense
beams in dense matter, which are also summarized as the beam-density effect.
This finding is useful for the stopping power estimation of intense beams and
significant to fast ignition fusion driven by intense ion beams
Target density effects on charge tansfer of laser-accelerated carbon ions in dense plasma
We report on charge state measurements of laser-accelerated carbon ions in
the energy range of several MeV penetrating a dense partially ionized plasma.
The plasma was generated by irradiation of a foam target with laser-induced
hohlraum radiation in the soft X-ray regime. We used the tri-cellulose acetate
(CHO) foam of 2 mg/cm density, and -mm interaction
length as target material. This kind of plasma is advantageous for
high-precision measurements, due to good uniformity and long lifetime compared
to the ion pulse length and the interaction duration. The plasma parameters
were diagnosed to be T=17 eV and n=4 10 cm.
The average charge states passing through the plasma were observed to be higher
than those predicted by the commonly-used semiempirical formula. Through
solving the rate equations, we attribute the enhancement to the target density
effects which will increase the ionization rates on one hand and reduce the
electron capture rates on the other hand. In previsous measurement with
partially ionized plasma from gas discharge and z-pinch to laser direct
irradiation, no target density effects were ever demonstrated. For the first
time, we were able to experimentally prove that target density effects start to
play a significant role in plasma near the critical density of Nd-Glass laser
radiation. The finding is important for heavy ion beam driven high energy
density physics and fast ignitions.Comment: 7 pages, 4 figures, 35 conference
Association between social support and recovery from post-traumatic stress disorder after flood: a 13–14 year follow-up study in Hunan, China
Distinct Impacts of Two Types of Developing El Niño–Southern Oscillations on Tibetan Plateau Summer Precipitation
El Niño–Southern Oscillation (ENSO) has remarkable impacts on Tibetan Plateau (TP) summer precipitation. However, recently identified ENSO spatial diversity brings complexity to these impacts. This study investigates the distinct impacts of the Eastern Pacific (EP) and Central Pacific (CP) ENSOs on TP summer precipitation based on numerous precipitation data and satellite-observed and reanalyzed circulation data. The results show that the EP El Niño and the CP La Niña have opposite effects on summer precipitation in the southwestern TP, with significant decreases and increases, respectively, indicating a trans-type inversion. In contrast, the CP El Niño causes significant decreases in summer precipitation in the central-eastern TP. No significant anomaly occurs during the EP La Niña. Moisture budget and circulation analyses suggest that these distinct precipitation characteristics can be attributed to different atmospheric teleconnections, which provide varying vertical motion and moisture conditions. The EP El Niño triggers an atmospheric response similar to the Indian Summer Monsoon–East Asian Summer Monsoon teleconnection, and the CP La Niña generates a teleconnection in the opposite phase. In contrast, the CP El Niño mainly causes a teleconnection resembling the East Asian–Pacific pattern. This study may deepen our understanding of ENSO impacts on TP summer precipitation and have implications for regional climate predictions
Intense heavy ion beam-induced material evaporation and the resulting dynamic vacuum deterioration of the beam line
Charge state effect on K-shell ionization of silicon induced by iodine
In near Bohr velocity ion-atom collisions, a dependence of target K-shell ionization cross sections upon the ionic charge states has been observed. Experiments were performed in silicon solid target with 2–5 MeV iodineq+ ions incident in charge states +20 to +25. K-shell ionization cross section of silicon for q = 20 and 22 iodine ions impact with the same incident energy are almost equal, and are well described by the theory of binding-energy-modified BEA. However, for q = 25 iodine ions collisions, 3d vacancies of projectile transfer to the 1s orbit of target atom via rotational coupling of 3dπ, δ-3dσ molecular orbits in the framework of quasi-molecular model, which results in an increase of the K-shell ionization cross section of silicon
Collision-induced atomic alignment of silver after L3 ionization by 10–50 keV electron impact: Influence of Coster–Kronig transition effect
This work reports atomic alignment of silver after L3-subshell ionization in collisions with electrons in energy range 10–50 keV, i.e., (3∼15)EL3, where EL3(=3.351 keV) is the binding energy of electrons in the L3-subshell. The characteristic spectra are measured at different emission angles from -40∘ to 40∘ intervals of 10∘. The angular dependence of X-ray emission is studied for Lα(L3→M4,5) and Lβ2(L3→N5) lines respectively, using a thin target. The anisotropy parameter β is determined from two angular distribution measurements of differential X-ray intensity ratios dI(Lα,θ)/dI(Lβ1,θ) and dI(Lβ2,θ)/dI(Lβ1,θ). This served to reduce the experimental uncertainties. For the derivation of the alignment factor A20 we took into account the Coster–Kronig (CK) correction factor κ, which allows for, CK transition probabilities fij among L-subshells. We found that the sign of A20 is mostly negative, and the influence of CK transition is significant for large alignment parameters. In addition, the experimental results are compared to theoretical predictions within the framework of Plane Wave Born Approximation (PWBA) and reasonable agreement is found in the energy range studied in the present work. Simultaneously, good scaling property of atomic alignment is demonstrated when we consider also previous experimental results. Our measurement extends the scaled velocity V (=vp/vt) to a range of 1∼4 for medium-Zt targets, and the results of atomic alignment can provide a fundamental testing ground for ionization models