Efficient Fusion Neutron Generation Using a 10-TW High-Repetition Rate Diode-Pumped Laser

Abstract

The first use of a high-repetition-rate laser-diode (LD)-pumped laser in a fusion target experiment is demonstrated. An LD-pumped Nd-solid state laser's output is coupled to a Ti:sapphire laser, enabling the resulting HAMA laser to generate 2-J, 815-nm-wavelength output with a pulse width of 150 fs and a repetition rate of 10 Hz. A photon-to-photon efficiency of 1.25% (electric-to-photonic 0.7%) is achieved, which is an order of magnitude higher than that of current flash-lamp lasers. Irradiation of a 500-µm-thick deuterated polystyrene film by a 0.6 -J pulse yielded 10 5 DD fusion neutrons. The efficiency from the electric input to the neutron yield is 10 times higher than the flash-lamp-pumped table-top lasers. The National Ignition Facility (NIF) [1] is expected to begin fuel burning soon. However, the flash-lamp-pumped lasers typically used are unsuitable for power plants, because the electric-to-photonic conversion efficiency of the flash lamp is less than 0.5%. A power plant requires a laser with an efficiency of more than 10%. The solution is the use of high-repetition-rate laser-diode (LD)-pumped lasers [2][3][4][5][6]. Here we demonstrate the first use of an LD-pumped laser, HAMA, in fusion target experiments. HAMA generated 2 J with a pulse width of 150 fs at 10 Hz and its efficiency was 1.25%. Irradiation of a 500-µm-thick deuterated polystyrene film by a 0.6-J HAMA pulse yielded 10 5 DD fusion neutrons [7]. The efficiency from the electric input to the yield is 8×10 5 neutrons/kW, 10 times higher than those using flash-lamp-pumped tabletop lasers [8][9][10]. The results will also assist in developing industrial and commercial neutron sources. The present result is still far from a true working accelerator sources (a neutron generator). Typically a deuteron beam of 1 mA generates 10 9 n/s, whereas, our results show 10 5 n/s from 15 nC, corresponding to 7×10 9 n/mA. However, since current neutron sources using accelerators are too big to meet industrial demands, a compact neutron source using a laser must have an advantage over the rf sources.author's e-mail: kitagawa@gpi.ac.jp Figure 1 shows the key issues together with the roadmap for achieving an inertial confinement fusion (ICF) power plant [11]. Soon the National Ignition Facility (NIF) Other regions indicate the main path using repetitive-shot mode toward a fusion power plant. This main path is divided into three phases: engineering test and neutron production(zeroth or pre-phase), break-even machine (first phase), and demonstration (second phase). Yellow boxes indicate problems that need to be resolved. We focuse here on the first step toward achieving the main path, by a star.

Fusion Using Fast Heating of a Compactly Imploded CD Core

“…We used an LD-pumped high-repetition-rate HAMA laser [11,12], which consists of a seed beam supplier laser "BEAT", a Ti:sapphire optical parametric chirped pulse amplification system (OPCPA) [13], and a pump laser "KURE-I", an LD-pumped Nd:glass laser system (Hamamatsu Photonics) [14]. The latter pumps a Ti:sapphire crystal ( 50-mm diameter and 20-mm length) to amplify the seed beam from "BEAT".…”

Progress toward a unified kJ-machine CANDY

“…Deuterated polystyrene (C 8 D 8 or CD) bead pellets, after free-falling for a distance of 18 cm at 1 Hz, are successfully engaged in flight by two counter laser beams from a diode-pumped, ultra-intense laser HAMA [1]. The snapshot of a flying pellet at the instance of engagement by using a 2ω harmonic laser probe is in Fig.…”

“…The zeroth goal is to construct an unified experimental machine CANDY. We have developed a laser-diode-(LD-)pumped laser system HAMA with a repetition rate of 10 Hz [1,2]. We have done the fast ignition experiment at OSAKA to test this scheme.…”

Hi-rep. Counter-Illumination Fast Ignition Scheme Fusion

“…"BEAT" is a Ti:sapphire optical paramet- ric chirped pulse amplification system [4,5]. KURE-I is an LD-pumped Nd:glass laser system (Hamamatsu Photonics Product), which pumps a Ti:sapphire crystal to amplify the seed beam from "BEAT".…”

“…The vertical error bar is the shot-to-shot deviation (standard error) for every 10 shots. A neutron detector ND3 is a 6-inch plastic scintillator (NE102, 15 cm in diameter and 6 cm in length) coupled to a 2-inch photomultiplier (H7195) located 1.43 m from the target normal to the laser axis [4]. After accumulating each 10 shots, we have filtered the low frequency noises less than 150 MHz out through a Fast Fourier Transform filter, which shows a small peak around 1.4 ns as in Fig.…”