Efficient multi-keV X-ray sources from laser-exploded metallic thin foils

Abstract

A set of materials—titanium, copper, and germanium—has been experimented with at the OMEGA laser facility [Boehly, Opt. Commun. 133, 495 (1997)] by irradiating thin foils with a prepulse prior to a main pulse with variable delay, in order to design efficient x-ray laser-sources for backlighting, material testing, and code validation. This concept led to increasing factors from 2 to 4 comparing to cases without prepulse, in the experimental conditions. As a result, high multi-keV x-ray conversion rates have been obtained: 9% for titanium around 4keV, 1% for copper around 8keV, and 2.5 to 3% for germanium around 10keV, which places these pre-exploded metallic targets close to the gas with respect to their performance, with wider energy range. A good agreement with hydroradiative code FCI2 [Schurtz, Phys. Plasmas 7, 4238 (2000)] calculations is found for titanium and copper on all diagnostics, with nonlocal-thermal-equilibrium atomic physics and, either nonlocal thermal conduction taking self-generated B-fields into account, or limited thermal conduction with intensity-dependent factor f. The results for germanium indicate that dielectronic processes could play a more significant role when higher irradiation intensity on higher Z material.

Multi-keV x-ray source development experiments on the National Ignition Facility

“…For certain applications, such as the study of x-ray driven electromagnetic phenomena, or radiography of high-density objects, high-energy, deeply penetrating x-ray photons are required. In addition to the K-shell Kr and Xe sources, x-ray sources at other energies need to be developed; for example, pre-exploded metal foils 22,23 , foil-lined cylinders 24 , metal nano-fiber low-density targets 21 , and metal-doped aerogel materials 20 are all candidates for highly efficient xray sources. In conclusion, an enormous expanse of x-ray source development activities exist, now that an unexplored regime of laser energy and power is available at the NIF.…”

“…The target design for the current experiments builds on experience at the Nova 29 and Omega 30 laser facilities using modeling and simulation tools that have been validated against experiments [12][13][14][15][16][17][18][19][20][21][22][23][24] . The desired x-ray source characteristics for the present experiments were: a) significant multi-keV x-ray output with energies >3 keV, b) x-ray pulse width of order 5 ns, and c) x-ray rise-time of order 1 ns or longer.…”

“…During the last decade, many research groups have been developing bright, multi-keV x-ray sources [12][13][14][15][16][17][18][19][20][21][22][23][24] . The goal has been to create millimeter-scale, homogeneous, keV-scale-temperature plasmas that are efficient laser-to-x-ray converters.…”

Multi-keV X-ray sources from metal-lined cylindrical hohlraums

“…Solid metallic targets [3] enable the creation of sources which span a wider photon energy range but have shown low CE's. To improve the CE's, new source principles have been considered as metal-doped aerogel targets [4,5], pre-pulsed thin metallic foils [6] and metal-lined hohlraums which are plastic cylinders coated with metallic materials. Two campaigns using titanium (Ti) and germanium (Ge) lined hohlraums were performed on Omega in 2005 and 2007 [7].…”

Multi-keV x-ray sources from HYBRID targets on GEKKO and OMEGA facilities

“…The feasibility of efficient X-ray sources for radiography on the LMJ (Laser MégaJoule) in the multi-kJ/ns range was demonstrated on the OMEGA laser facility (Univ. Rochester) from 2002 to 2004 [1,2]. We significantly enhanced the conversion efficiency of titanium (4-6 keV), copper (8-10 keV) and germanium (9-13 keV) foils by using an optimized pre-pulse/pulse combination.…”