Transcript Slide 1
Measuring E and B fields in Laser-produced Plasmas with Monoenergetic Proton Radiography FSC C. K. Li MIT 9th International Fast Ignition Workshop Cambridge, MA 3-5 Nov. 2006 Collaborators FSC F. H. Séguin J. A. Frenje J. R. Rygg R. D. Petrasso MIT R. P. J. Town P. A. Amendt S. P. Hatchett O. L. Landen A. J. Mackinnon P. K. Patel M. Tabak LLNL J. P. Knauer T. C. Sangster V. A. Smalyuk LLEMIT Summary E and B fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to ICF are measured with novel monoenergetic proton radiography A monoenergetic backlighter proton spectrum simplifies experiment design and interpretation. High-resolution, time gated radiography images of a plastic foil driven by a 1014 W/cm2 laser implied B fields of ~ 0.5 MG and E fieldsMIT of ~ 1.5108 V/m. Simulations of these experiments with LASNEX+LSP are in overall agreement with the data both for field strengths and for spatial distributions while the laser is on; this is the first direct experimental test of the B-field generation package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure. The generation of E and B fields by laser-plasma interactions is a process of fundamental interest in high-energy density (HED) physics 5 mm CH Laser 1 ns square spot diameter 800 mm I ~ 1014 W/cm2 Te ne B E B 1 v B ne Te t ene Proton radiographs already made of B fields generated by laser-plasma interactions demonstrate feasibility for Fast Ignition studies D3Heimplosion backlighter Mesh and foil Grid Laser beam Before laser real images Mesh Implosion cartoon image ~ 0.6 ns after laser The same concept can be applied to investigate B field generated by short-pulse laser-plasma interaction Laser protons B e Laser B E Fast ignition (Short pulse) protons Monoenergetic protons can be generated in nuclear fusion reactions through ICF implosions 10 Yield / MeV (x 108) DD proton 2 mm SiO2 5 D3He proton 0 0 5 10 Energy (MeV) 15 D + 3He + p (14.7 MeV) D + D T + p (3.0 MeV) RSI 2006 20 Several nuclear and x-ray diagnostics are used to characterize the proton backlighter Proton emission image Proton production history Laser x-ray emission image Protons 0 500 1000 Time (ps) 1500 Proton spectrum Yield 0 5 10 15 Energy (MeV) 20 E and B fields can be simultaneously measured using a single proton backlighter side-on Interaction beam mesh CR-39 “Backlighter” Backlighter drive beams face-on CH foil Face-on radiography is sensitive to the B field, while side-on radiography is sensitive to the E field Experimental data and LASNEX+LSP simulations agree both for field strengths and for spatial distributions 0 ns 0.33 ns 0.64 ns Data 2.3 mm 0 ns Simulation By R. Town PRL 2006 0.30 ns 0.63 ns LASNEX simulations indicate that the toroidal B fields are concentrated on a hemispherical shell surrounding the ablative plasma bubble 0.30 ns 0.63 ns 0.05 0.35 0.3 ns 0.65 0.95 MG 0.06 0.6 ns 0.03 Laser 0 -0.03 -0.06 0.08 0.04 0 0.08 Z (cm) 0.04 0 R (cm) Experimental data and LASNEX+LSP simulation show that the largest B field occurs near the surface of the plasma bubble protons Simulation Data The smaller diameter of the SG2 beam resulted in an intensity 2.6 times higher than SG4, causing greatly increased image distortion. 0 ns 0.41 ns 0.77ns SG4 2.3 mm 0 ns SG2 0.41 ns 0.71ns Experiments demonstrate that laser phase plates substantially reduce medium-scale chaotic field structure 2.3 mm With phase plates Without phase plates A CH foil driven by a 1014 W/cm2 laser beam results in E field of ~ 1.5108 V/m E Ep Te/Te Lineout Simulation lineout Data 2.3 mm Summary E and B fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to ICF are measured with novel monoenergetic proton radiography A monoenergetic backlighter proton spectrum simplifies experiment design and interpretation. High-resolution, time gated radiography images of a plastic foil driven by a 1014 W/cm2 laser implied B fields of ~ 0.5 MG and E fieldsMIT of ~ 1.5108 V/m. Simulations of these experiments with LASNEX+LSP are in overall agreement with the data both for field strengths and for spatial distributions while the laser is on; this is the first direct experimental test of the B-field generation package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.