Proton radiography of laser-driven imploding target in cylindrical geometry

Abstract

An experiment was done at the Rutherford Appleton Laboratory ͑Vulcan laser petawatt laser͒ to study fast electron propagation in cylindrically compressed targets, a subject of interest for fast ignition. This was performed in the framework of the experimental road map of HiPER ͑the European high power laser energy research facility project͒. In the experiment, protons accelerated by a picosecond-laser pulse were used to radiograph a 220 m diameter cylinder ͑20 m wall, filled with low density foam͒, imploded with ϳ200 J of green laser light in four symmetrically incident beams of pulse length 1 ns. Point projection proton backlighting was used to get the compression history and the stagnation time. Results are also compared to those from hard x-ray radiography. Detailed comparison with two-dimensional numerical hydrosimulations has been done using a Monte Carlo code adapted to describe multiple scattering and plasma effects. Finally we develop a simple analytical model to estimate the performance of proton radiography for given implosion conditions.

Shock Induced Symmetric Compression in a Spherical Target

“…It is to be noted that the time dependence of temperature thus exhibited also agrees qualitatively with experimental and simulation results in cylindrical geometry [15]. …”

“…It has been shown in Figure 3(b). It is to be noted that in our uniform compression model predicts a good qualitative agreement with the corresponding experimental and simulation results for both cylindrical [13]- [15] and spherical geo-metries [18] [19]. However, there may be more complicated physics behind the compression during stagnation time.…”

“…Hwang et al considered potential flow model for incompressible fluid of a hydromagnetic situation to study the linear behavior of the dynamic effects of plasma in the cylindrical geometry [12]. The problem of implosion in cylindrical geometry under a variety of physical conditions has recently been investigated both experimentally and numerically [13]- [15]. The results of these studies show that during a laser induced implosion (deceleration phase), the interface of cylinder/spherical target is compressed and the radius of the cylinder/sphere decreases and consequently, the density of the internal plasma increases [16] [17] and reaches a maximum value for a critical value of the two fluid interface radius.…”

Diagnostics of laser-produced plasmas

“…Laser--based proton beams can be generated by irradiating a thin metal layer (usually gold or titanium) with an ultra-short (from picoseconds to femtosecond), ultra--high intensity (I ~ 10 19-21 W/cm 2 ) laser beam. They are characterized by a small source, high degree of collimation, and a short duration [38][39][40][41][42].…”

Large-scale proton radiography with micrometer spatial resolution using femtosecond petawatt laser system

“…For the case of θ 0 ∼ 80 o for 0.5-MeV protons, as calculated above, ∆ ∼ 9.5 cm for L = 10 cm, leading to blurring on the detector. 40 The greater the value of L, the more blurred the image. Thus, the blurring of the proton image may be reduced by attaching the dragonfly to the RCFs in experiment, corresponding to ∆ → 0 for L → 0.…”