The Woodruff School

SUMMARY

An increasing number of facilities around the world continue to install and upgrade high-powered multi-terawatt and petawatt lasers. Experimenters can focus these laser beams in vacuum to high intensities in excess of 10$^{17}$ W cm$^{-2}$ onto target material to study matter under extreme conditions. The interaction of a high-intensity laser beam with matter creates a plasma, and additional interaction of the laser pulse with the plasma can generate an ionizing radiation hazard for personnel working on or near these facilities, especially in the absence of sufficient shielding and other radiological controls. The relation between the laser-plasma interaction and the generated ionizing radiation yields are crucial in developing radiological controls. The particle-in-cell (PIC) method plasma code EPOCH can simulate the laser-plasma interaction and characterize key parameters of the electron source term: energy distribution, angular distribution, and laser-to-electron energy conversion efficiency. The Monte Carlo radiation transport code FLUKA can utilize EPOCH’s electron source term to calculate both the photon dose generated at various angles and the transmission factors of common shielding materials. A systematic study was performed to develop a bremsstrahlung photon source term as a function of laser intensity by coupling EPOCH and FLUKA. Comparison with measurement data are also made to confirm the bremsstrahlung source term. This bremsstrahlung source term will be used for performing hazard analysis and developing radiological controls for high-intensity laser facilities around the world.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Taiee Liang

TIME:	Tuesday, March 7, 2017, 1:00 p.m.

PLACE:	Boggs, 3-28

TITLE:	Characterization of Ionizing Radiation Generated from High-Intensity Laser Interactions with Matter

COMMITTEE:	Dr. Nolan Hertel, Chair (NRE) Dr. Chaitanya S. Deo (NRE) Dr. Anna Erickson (NRE) Dr. C. K. Chris Wang (NRE) Dr. Sayed H. Rokni (SLAC National Accelerator Laboratory)

SUMMARY An increasing number of facilities around the world continue to install and upgrade high-powered multi-terawatt and petawatt lasers. Experimenters can focus these laser beams in vacuum to high intensities in excess of 10$^{17}$ W cm$^{-2}$ onto target material to study matter under extreme conditions. The interaction of a high-intensity laser beam with matter creates a plasma, and additional interaction of the laser pulse with the plasma can generate an ionizing radiation hazard for personnel working on or near these facilities, especially in the absence of sufficient shielding and other radiological controls. The relation between the laser-plasma interaction and the generated ionizing radiation yields are crucial in developing radiological controls. The particle-in-cell (PIC) method plasma code EPOCH can simulate the laser-plasma interaction and characterize key parameters of the electron source term: energy distribution, angular distribution, and laser-to-electron energy conversion efficiency. The Monte Carlo radiation transport code FLUKA can utilize EPOCH’s electron source term to calculate both the photon dose generated at various angles and the transmission factors of common shielding materials. A systematic study was performed to develop a bremsstrahlung photon source term as a function of laser intensity by coupling EPOCH and FLUKA. Comparison with measurement data are also made to confirm the bremsstrahlung source term. This bremsstrahlung source term will be used for performing hazard analysis and developing radiological controls for high-intensity laser facilities around the world.