Biomedical subjects

T C Sangster

Publications and source records attributed to T C Sangster.

10 recordsLinked to original sources

PubMed2006

Measuring E and B fields in laser-produced plasmas with monoenergetic proton radiography.

Electromagnetic (E/B) fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to inertial confinement fusion have been measured for the first time using novel monoenergetic proton radiography methods. High-resolution, time-gated radiography images of a plastic foil driven by a 10(14) W/cm(2) laser implied B fields of approximately 0.5 MG and E fields of approximately 1.5 x 10(8) V/m. Simulations of these experiments with LASNEX+LSP have been performed and are in overall (though not exact) agreement with the data both for field strengths and for spatial distributions; this is the first direct experimental test of the laser-generated B-field package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.

Journal Article↗

PubMed2005

Observation of self-similar behavior of the 3D, nonlinear Rayleigh-Taylor instability.

The Rayleigh-Taylor unstable growth of laser-seeded, 3D broadband perturbations was experimentally measured in the laser-accelerated, planar plastic foils. The first experimental observation showing the self-similar behavior of the bubble size and amplitude distributions under ablative conditions is presented. In the nonlinear regime, the modulation sigma(rms) grows as alpha(sigma)gt(2), where g is the foil acceleration, t is the time, and alpha(sigma) is constant. The number of bubbles evolves as N(t) alpha(omegat sq.rt(9) + C)(-4) and the average size evolves as (t) alpha omega(2)gt(2), where C is a constant and omega = 0.83 +/- 0.1 is the measured scaled bubble-merging rate.

Journal Article↗

PubMed2005

Fourier-space nonlinear Rayleigh-Taylor growth measurements of 3D laser-imprinted modulations in planar targets.

Nonlinear growth of 3D broadband nonuniformities was measured near saturation levels using x-ray radiography in planar foils accelerated by laser light. The initial target modulations were seeded by laser nonuniformities and later amplified during acceleration by Rayleigh-Taylor instability. The nonlinear saturation velocities are measured for the first time and are found to be in excellent agreement with Haan predictions. The measured growth of long-wavelength modes is consistent with enhanced, nonlinear, long-wavelength generation in ablatively driven targets.

Journal Article↗

PubMed2004

Effects of nonuniform illumination on implosion asymmetry in direct-drive inertial confinement fusion.

Target areal density (rhoR) asymmetries in OMEGA direct-drive spherical implosions are studied. The rms variation / for low-mode-number structure is approximately proportional to the rms variation of on-target laser intensity / with an amplification factor of approximately 1/2(C(r)-1), where C(r) is the capsule convergence ratio. This result has critical implications for future work on the National Ignition Facility as well as OMEGA.

Journal Article↗

PubMed2004

Dependence of shell mix on feedthrough in direct drive inertial confinement fusion.

The mixing of cold, high-density shell plasma with the low-density, hot spot plasma by the Rayleigh-Taylor instability in inertial confinement fusion is experimentally shown to correlate with the calculated perturbation feedthrough from the ablation surface to the inner shell surface. A fourfold decrease in the density of shell material in the mix region of direct drive implosions of gas filled spherical plastic shells having predicted convergence ratios approximately 15 was observed when laser imprint levels were reduced and the initial shell was thicker, corresponding to a reduction in the feedthrough rms level by a factor of 6. Shell mix is also shown to limit the spherical compression of the implosion.

Journal Article↗

PubMed2003

Time-resolved areal-density measurements with proton spectroscopy in spherical implosions.

The temporal history of the target areal-density near peak compression of direct-drive spherical target implosions has been inferred with 14.7-MeV deuterium-helium-3 D3He proton spectroscopy of the 60-beam, 30-kJ UV OMEGA laser system. The target areal-density grows by a factor of approximately 8 during the time of neutron-production ( approximately 400 ps) before reaching 123+/-16 mg/cm(2) at peak compression in the implosion of a 950-micrometer-diam, 20-micrometer-thick plastic CH capsule filled with 4 atm of D3He fuel.

Journal Article↗

PubMed2003

Measuring implosion dynamics through rhoR evolution in inertial-confinement fusion experiments.

The areal density (rhoR) of D3He filled plastic capsules imploded at OMEGA has been measured at shock coalescence (1.7 ns) and, 400 ps later, during compressive burn, through the energy downshift of 14.7-MeV D3He protons. In this time interval, the azimuthally averaged rhoR changes from 13+/-2.5 to 70+/-8 mg/cm(2). The experiments demonstrate that fuel-shell mix is absent in the central regions at shock coalescence, and that the shell has no holes during compressive burn. We conjecture that rhoR asymmetries measured during compressive burn may be seeded by the time of shock coalescence.

Journal Article↗

PubMed2002

Effects of fuel-shell mix upon direct-drive, spherical implosions on OMEGA.

Fuel-shell mix and implosion performance are studied for many capsule types in direct-drive experiments at OMEGA. The amount of mixing and the size of the mix region are inferred from charged-particle spectrometry data and confirmed with an experimentally constrained model. Measured yields and convergence ratios CR fall short of one-dimensional predictions, especially for low capsule fill pressures. CR is approximately 11 for pressures from 3 to 15 atm, in contrast to predictions of approximately 25 for 3 atm and approximately 12 for 15 atm. The performance shortfalls are likely to be caused by fuel-shell mix.

Journal Article↗

PubMed2002

Shell mix in the compressed core of spherical implosions.

The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be 3.4(+/-1.2) g/cm(3) from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, 3.6(+/-1) g/cm(3), accounts for only approximately 50% of the neutron-burn-averaged electron density, n(e)=2.2(+/-0.4)x10(24) cm(-3).

Journal Article↗

PubMed2000

Intense high-energy proton beams from Petawatt-laser irradiation of solids.

An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.

Journal Article↗