Experiments relevant to understanding the interaction of stellar radiation with molecular clouds R. VanDervort 1 , J. Davis 1 , M. Trantham 1 , S. Klein 1 , P. A. Keiter 1 , R. P. Drake 1 1 University of Michigan, USA Stellar radiation compresses or explodes local gas clouds (Cloud Explosion) [1] P. A. Keiter et al.: “Design of laboratory experiments to study radiation-driven implosions,” High Energy Density Physics, Volume 22, p. 37-40 (2017) [2] F. Bertoldi: “The Photoevaporation of Interstellar Clouds. I. Radiation-Driven Implosion,” Astrophysical Journal, vol. 346, p. 735-755 (1989) Interaction dependent on incident photon energy, cloud thickness, and cloud density ▶ Optically thick: Photons absorbed at one cloud edge ▶ Drives asymmetric shock into cloud ▶ Optically thin: Photons permeate and heat cloud ▶ Cloud explodes The platform is driven by laser-irradiated thin-gold foil and a variable-density foam sphere [3] J. Davis et al.: ”Soft X-ray emission from laser-irradiated gold foils,” Physics of Plasmas 25, 073304 (2018) Foil temperature, foam diameter, and foam density determine the optical depth (τ ) ▶ τ ∼ Diameter/λ mfp = D/λ mfp ▶ Mean free path: λ mfp = 1/(ρσ ) ▶ τ ∼ Dρσ ▶ Carbon foam ▶ Peak photon energy ∼ 230 eV ▶ σ ∼ 3600 cm 2 /g [4] [4] Estimated from http://henke.lbl.gov/optical_constants/filter2.html 2D CRASH radiation hydrodynamic simulations show both compression and explosion limits ▶ Sphere diameter initially 500-μm ▶ Foil edge to sphere center distance initially 1-mm 10 mg/cc 2.5 ns Photons 100 mg/cc 2.5 ns Photons [5] B. van der Holst et al; “CRASH: A Block-adaptive-mesh Code for Radiative Shock Hydrodynamics-Implementation and Verification” Optically thick limit provides a well-understood starting point to test the platform Target Stalk Foam Sphere Gold Foil Plane Foam Sphere Gold Foil Plane Soft x-ray radiography from the first experiment indicates compression Backlit-pinhole radiography from the second experiment shows asymmetric compression Foam sphere Density increase Gold source photons We are developing an experimental platform to explore the range of conditions found when stars irradiate gas clouds ▶ Local hot, massive stars cause gas clumps to explode or compress ▶ Gas cloud fate dependent on initial optical depth ▶ Simulations show the platform can reach optically thin and thick limits by changing foam density ▶ Initial experiments started in the optically thick regime for physics and diagnostic simplicity ▶ First optical depths ∼ 11 and 22 ▶ Asymmetric compression of spheres radiographed ▶ Data sets are under analysis Funding acknowledgments This work is funded by the U.S. DOE, through the NNSA-DS and SC-OFES Joint Program in HEDPLP, grant No. DE-NA0002956, and the NLUF Program, grant No. DE-NA0002719, and through LLE, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944. This work is funded by the Lawrence Livermore National Laboratory under subcontract B614207. 11

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Page 1: Experiments relevant to understanding the interaction of …mipse.umich.edu/files/MIPSE_GS2018_VanDervort.pdfExperiments relevant to understanding the interaction of stellar radiation

Experiments relevant to understanding the interaction of stellar radiation with molecular cloudsR. VanDervort1, J. Davis1, M. Trantham1, S. Klein1, P. A. Keiter1, R. P. Drake1

1 University of Michigan, USA

Stellar radiation compresses orexplodes local gas clouds

(Cloud Explosion)

[1] P. A. Keiter et al.: “Design of laboratory experiments to study radiation-drivenimplosions,” High Energy Density Physics, Volume 22, p. 37-40 (2017)[2] F. Bertoldi: “The Photoevaporation of Interstellar Clouds. I. Radiation-DrivenImplosion,” Astrophysical Journal, vol. 346, p. 735-755 (1989)

Interaction dependent on incident photon energy,cloud thickness, and cloud density

▶ Optically thick: Photons absorbed at one cloud edge▶ Drives asymmetric shock into cloud

▶ Optically thin: Photons permeate and heat cloud▶ Cloud explodes

The platform is driven by laser-irradiated thin-goldfoil and a variable-density foam sphere

[3] J. Davis et al.: ”Soft X-ray emission from laser-irradiated gold foils,”Physics of Plasmas 25, 073304 (2018)

Foil temperature, foam diameter, and foam densitydetermine the optical depth (τ )

▶ τ ∼ Diameter/λmfp = D/λmfp

▶ Mean free path: λmfp = 1/(ρσ)

▶ τ ∼ Dρσ

▶ Carbon foam

▶ Peak photon energy ∼ 230 eV

▶ σ ∼ 3600 cm2/g [4]

[4] Estimated from http://henke.lbl.gov/optical_constants/filter2.html

2D CRASH radiation hydrodynamic simulations showboth compression and explosion limits

▶ Sphere diameter initially 500-µm▶ Foil edge to sphere center distance initially 1-mm

10 mg/cc 2.5 ns

Photons

100 mg/cc 2.5 ns

Photons

[5] B. van der Holst et al; “CRASH: A Block-adaptive-mesh Code for Radiative ShockHydrodynamics-Implementation and Verification”

Optically thick limit provides a well-understoodstarting point to test the platform

Target Stalk

Foam SphereGold Foil Plane

Foam Sphere

Gold Foil Plane

Soft x-ray radiography from the first experimentindicates compression

Backlit-pinhole radiography from the secondexperiment shows asymmetric compression

Foam sphere

Density increase

Gold sourcephotons

We are developing an experimental platform toexplore the range of conditions found when stars

irradiate gas clouds▶ Local hot, massive stars cause gas clumps to explode or compress

▶ Gas cloud fate dependent on initial optical depth

▶ Simulations show the platform can reach optically thin and thick limitsby changing foam density

▶ Initial experiments started in the optically thick regime for physics anddiagnostic simplicity▶ First optical depths ∼ 11 and 22▶ Asymmetric compression of spheres radiographed

▶ Data sets are under analysis

Funding acknowledgmentsThis work is funded by the U.S. DOE, through the NNSA-DS and SC-OFES JointProgram in HEDPLP, grant No. DE-NA0002956, and the NLUF Program, grant No.DE-NA0002719, and through LLE, University of Rochester by the NNSA/OICF underCooperative Agreement No. DE-NA0001944. This work is funded by the LawrenceLivermore National Laboratory under subcontract B614207.

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