Fast ignition with laser-driven proton and ion beams

Abstract

Fusion fast ignition (FI) initiated by a laser-driven particle beam promises a path to high-yield and high-gain for inertial fusion energy. FI can readily leverage the proven capability of inertial confinement fusion (ICF) drivers, such as the National Ignition Facility, to assemble DT fusion fuel at the relevant high densities. FI provides a truly alternate route to ignition, independent of the difficulties with achieving the ignition hot spot in conventional ICF. FI by laser-driven ion beams provides attractive alternatives that sidestep the present difficulties with laser-driven electron-beam FI, while leveraging the extensive recent progress in generating ion beams with high-power density on existing laser facilities. Whichever the ion species, the ignition requirements are similar: delivering a power density ≈1022 W cm−3 (∼10 kJ in ≈20 ps within a volume of linear dimension ≈20 µm), to the DT fuel compressed to ∼400 g cm−3 with areal density ∼2 g cm−2. High-current, laser-driven beams of many ion species are promising candidates to deliver such high-power densities. The reason is that high energy, high-power laser drivers can deliver high-power fluxes that can efficiently make ion beams that are born neutralized in ∼fs–ps timescales, making them immune to the charge and current limits of conventional beams. In summary, we find that there are many possible paths to success with FI based on laser-driven ion beams. Although many ion species could be used for ignition, we concentrate here on either protons or C ions, which are technologically convenient species. We review the work to date on FI design studies with those species. We also review the tremendous recent progress in discovering, characterizing and developing many ion-acceleration mechanisms relevant to FI. We also summarize key recent technological advances and methods underwriting that progress. Based on the design studies and on the increased understanding of the physics of laser-driven ion acceleration, we provide laser and ion-generation laser-target design points based on several distinct ion-acceleration mechanisms.

Proton Acceleration by Ultrashort Intense Laser Interaction with Microstructured Snow Targets

“…Using this processing procedure, we have seen that at fluence higher than 1 J/cm 2 on target a definite damage has been occurred to the target, as can be seen in Figure 2 (a.1-3). At laser fluence on target less than 0.35 J/cm 2 we could not see any damage with our imaging system and processing procedure (Figure 2 (c.1-3)). At fluence of the laser on the target of 0.45 J/cm 2 we can hardly see any damage 7 nanosecond after the interaction (Figure 2 (b.2)); though long after the interaction due to thermal conductivity it is obvious that ablation occurred (Figure 2(b.3)).…”

“…Proton acceleration by the interaction of an ultra high intensity laser beam with matter is very important for basic science and has several wide prospective applications, including cancer treatment, OPEN ACCESS nuclear physics and astrophysics in lab, (see [1][2][3] for review). In recent years, several promising acceleration schemes were suggested and demonstrated, among them Target Normal Sheath Acceleration (TNSA) [4,5], Radiation Pressure Acceleration (RPA) [6,7] collisionless shock acceleration [8] and Break Out Afterburner (BOA) [9].…”

Ion beam requirements for fast ignition of inertial fusion targets

“…vi) If beam focusing were demonstrated for advanced schemes, such as the break-out afterburner scheme [6], quasi-monoenergetic ions instead of TNSA ions should be used due to their better coupling with the compressed fuel.…”

“…The beam temperatures are T p = 7 MeV and T C = 200 MeV, respectively. The pulse of quasi-monoenergetic carbon ions with a mean energy E = 650 MeV and an energy spread of δE/E = 0.125 [6] is also shown for comparison. All beams have an energy of 10 kJ and are generated at a distance to the simulation box d = 500 µm.…”

“…Ion fast ignition [4,5] offers several advantages over EFI, such as generation of collimated beams, well known interaction with the plasma and higher flexibility. Some examples of such a flexibility are the control of ion spectra [6,7], the possibility of choosing the optimal ion species [8,9], including deuterium ions [10], and the use of multiple beams for target irradiation [9,11,12]. IFI progress so far can be summarized by the experimental achievement of the required ion energies, high conversion efficiencies [13] and ion beam focusing [14].…”