Collisional heating and adiabatic expansion of warm dense matter with intense relativistic electrons

Abstract

Adiabatic expansion of a warm dense Ti plasma has been observed after isochoric heating of a 100-μm-thick Ti foil with an ∼100-ns-long intense relativistic electron bunch at an energy of 19.8 MeV and a current of 1.7 kA. The expansion fits well with the analytical point-source solution. After 10 J is deposited and the plasma rapidly expands out of the warm dense phase, a stable degenerate plasma (T∼1.2eV) with n_{e}>10^{17}cm^{-3} is measured for >100 ns. This is the first temporal measurement of the generation and adiabatic expansion of a large volume (3×10^{-4}cm^{3}) of warm dense plasma isochorically heated by intense monochromatic electrons. The suite of diagnostics is presented, which includes time-resolved plasma plume expansion measurements on a single shot, visible spectroscopy measurements of the emission and absorption spectrum, measurements of the beam distribution, and plans for the future.

Hydrodynamic disassembly and expansion of electron-beam-heated warm dense copper

“…In previous reviews the heating and expansion process for electron beam driven Ti & Cu was explained [20,25]. Briefly, we are performing an identical two-stage heating technique.…”

“…As mentioned in a previous review [20], WDM has been produced and characterized by several approaches, the largest contribution is from the laser community. Several authors, only a small subset is referenced here, have produced isochoric heating with sub-ps pulses at peak amplitudes in 0.1-100 µm thick targets [21][22][23][24].…”

“…[24] indicate the prepulse causes premature energy deposition by lower energy electrons and expansion before the peak of the pulse. WDM produced directly by particle beam impact has been investigated with ions through several approaches, but only recently with monochromatic relativistic electrons [20,25]. GSI has used GeV-class Uranium ions to heat W, Au, and Pb [26,27].…”

“…In addition the Pb target pressure and displacement were indirectly measured ∼1 µs after heating by measuring the displacement history on volume constraining sapphire plates [37]. These particle beam driven approaches [20,25,26,35] have measured the expansion of the subsequent plasma with optical imaging techniques, but not the target itself. To date there has been no direct measurement of the target dynamics for particle beam driven, collisional, isochoric heating of a solid target: hydrodynamic disassembly time, pressure, and target velocity.…”

“…Recently we have begun investigating two-stage heating with a monochromatic 20 MeV, 1.7 kA bunch of electrons [20,25]. The physics of experiments producing relativistic electron plasmas are much different than direct heating with monochromatic relativistic electrons for several reasons: how the energy is initially deposited, the number of particles providing the heating, heating time scales, and the energy distribution of the particles.…”