ICF Laser Research Articles

Corrigendum to: “Spectrum-tailored random fiber laser towards ICF laser facility” [Matter and Radiation at Extremes 8, 025902 (2023)

First Page

Spectrum-tailored random fiber laser towards ICF laser facility

Broadband low-coherence light is considered to be an effective way to suppress laser plasma instability. Recent studies have demonstrated the ability of low-coherence laser facilities to reduce back-scattering during beam–target coupling. However, to ensure simultaneous low coherence and high energy, complex spectral modulation methods and amplification routes have to be adopted. In this work, we propose the use of a random fiber laser (RFL) as the seed source. The spectral features of this RFL can be carefully tailored to provide a good match with the gain characteristics of the laser amplification medium, thus enabling efficient amplification while maintaining low coherence. First, a theoretical model is constructed to give a comprehensive description of the output characteristics of the spectrum-tailored RFL, after which the designed RFL is experimentally realized as a seed source. Through precise pulse shaping and efficient regenerative amplification, a shaped random laser pulse output of 28 mJ is obtained, which is the first random laser system with megawatt-class peak power that is able to achieve low coherence and efficient spectrum-conformal regenerative amplification.

Wavefront control technology for ICF facility in China

In the high-power laser system for inertial confinement fusion, wavefront control is one of the key technologies for the laser system to ensure it operates safely and reaches the beam quality criteria. In this article, the development of the wavefront control technology from its first being putting forward for the ICF laser system to its application in the latest ICF laser system in China was introduced. During the development of the ICF facilities, the wavefront control methods are varying to satisfy the varied demands promoted by these facilities. Based on different facilities, the methods and the application results are illustrated, including the climbing wavefront method for far-field spot optimization, the full-facility wavefront control method based on the data fusion acquired from two wavefront sensors, and the full-system wavefront control method with bi-deformed mirrors in the rotation chamber laser structure.

X-ray phase contrast imaging of spherical capsules.

We demonstrate that a laser-based synchrotron X-ray source can be used to image and characterize in a single laser shot spherical capsules similar to ICF targets. Thus, we establish this source potential for real-time ultrafast imaging of the ICF laser driver interaction with the target. To produce the X-ray beam we used a 160 TW high power laser system with 3.2 J and 20 fs incident on a supersonic gas jet target at 2.5 Hz repetition rate. We produced 2.7 × 109 photons/0.1% BW/sr/shot at 10 keV with a critical energy Ec = 15.1 keV. In our experimental conditions the spatial resolution was 4.3 μm in the object plane. We show that it is feasible to image the capsule structure and experimentally retrieve the phase information.

SRRS Effects on ICF Laser Drive Beam with the Variation of Pump Light Distribution on Space

SRRS Effects on ICF Laser Drive Beam with the Variation of Pump Light Distribution on Space

惯性约束聚变激光驱动装置用光学元器件的研究进展

惯性约束聚变激光驱动装置用光学元器件的研究进展

ICF激光装置靶场光束引导路径的优化研究

ICF激光装置靶场光束引导路径的优化研究

A novel solution to the gated x-ray detector gain droop problem.

Microchannel plate (MCP), microstrip transmission line based, gated x-ray detectors used at the premier ICF laser facilities have a drop in gain as a function of mircostrip length that can be greater than 50% over 40 mm. These losses are due to ohmic losses in a microstrip coating that is less than the optimum electrical skin depth. The electrical skin depth for a copper transmission line at 3 GHz is 1.2 μm while the standard microstrip coating thickness is roughly half a single skin depth. Simply increasing the copper coating thickness would begin filling the MCP pores and limit the number of secondary electrons created in the MCP. The current coating thickness represents a compromise between gain and ohmic loss. We suggest a novel solution to the loss problem by overcoating the copper transmission line with five electrical skin depths (∼6 μm) of Beryllium. Beryllium is reasonably transparent to x-rays above 800 eV and would improve the carrier current on the transmission line. The net result should be an optically flat photocathode response with almost no measurable loss in voltage along the transmission line.

ICF激光装置的任务可用性模型和分析方法

ICF激光装置的任务可用性模型和分析方法

Develop Course of Chinese Laser Fusion

Inertial confinement fusion has been concerned in the year 1963. It was from the 1970s that China began to study inertial confinement fusion devices, and got lots of achievements in recent decades. The development of Inertial Confinement Fusion has an important and special meaning, whether to the national economy, military applications or for basic research. This paper comprehensively discussed the process of several large-scale ICF laser devices, the major technical indicators and the main experiment related to the devices.

Plasma conditions during single bubble sonoluminescence.

There is a remarkable lack of experimental data on the conditions created during cavitation bubble collapse. Indeed, only recently has strong evidence of plasma formation been obtained during single bubble cavitation. Here we have determined for the first time the plasma electron density and the ion broadening parameter during single-bubble sonoluminescence and examined them as a function of acoustic driving pressure. We find that the electron density spans four orders of magnitude and can exceed 10×1021/cc (which is comparable to the densities produced by intense laser-induced inertial confinement fusion experiments, e.g., the NOVA ICF laser at Livermore) with effective plasma temperatures ranging from 7000 to more than 16 000 K. At the highest acoustic driving force, neutral Ar lines can no longer be used as spectroscopic reporters due to the extent of ionization and to leveling of the population of states. Accounting for the temporal profile of the sonoluminescence pulse suggests that the ultimate conditions generated inside the collapsing bubble may far exceed those determined from emission from the outer transparent region of the plasma core.

Laser damage phenomena relevant to the design and operation of an ICF laser driver

Laser damage performance of optical components is a defect related material characteristic. Recent advances were made to realize repeatable and accurate measurements of surface density of damage initiation due to pulses of nanosecond duration. This new measurement technique was used to guide the improvement of surface damage resistance. Fractures must be eliminated from surfaces, in order not to suffer a damage growth phenomenon, whose exponential character will endanger the optical component. A dedicated set-up was mounted on ALISě laser. With it, laser damage growth was measured accurately, as well as its dependence on parameters like pulse length and pulse shape. Using data from LIL, a prototype of Laser Megajoule (LMJ), and from a specific set-up, we can estimate the effect of multi wavelength illumination on damage growth. High intensity hot spots due to beam modulations can also cause surface damage. New measurements of self-focusing were obtained. The predictions derived from this laboratory work were cross checked with LIL data. They are also useful to predict damage events during the operation of a large laser facility.

High Pressure Tritium Fill System for the Omega Upgrade ICF Laser

We describe a high pressure cryogenic fill station and a novel method to retrieve and transport filled inertial confinement fusion targets at cryogenic temperatures. The fill station (currently under construction) will be capable of filling millimeter-size plastic spheres with DT or D2 to pressures exceeding 150 MPa. After filling, the thin-walled targets are cooled and kept below 20 K to prevent them from bursting. After cooling the targets, a cryogenic wrench is used to open the pressurization cell. The fill station cryostat is designed to allow a second cryostat to retrieve the filled targets. This second cold transfer cryostat features removable shrouds with seals that can be repeatably made and broken at cryogenic temperatures.

ICF laser beam focal uniformity and diagnostics (abstract)

Laser fusion requirements for ignition of thermonuclear fuel include high levels of irradiation uniformity on target. The quality of each beam’s focal spot is a major source of the dominant modes of nonuniformity. The problem is proportionately more difficult at the shorter wavelengths required for high energy-to-target coupling efficiency. Phase conversion is a focusing strategy that incorporates several wave-front modulation techniques which, when operating together, cause a reduction in the spatial coherence of the laser and thus an increase in focal uniformity. Phase masks are central to phase conversion by providing a reproducible source of multibeamlet superposition. A second type of wave-front modulation involves the addition of time-dependent phase to the laser beam, thus producing a time-dependent spectrum. Further manipulation of the beam with a diffraction grating creates color cycling over the elements of the phase mask. Another technique of interest utilizes a static, spatially distributed differential phase. This effectively doubles the number of incoherent beams that are available to overlap and better averages the various intensity nonuniformities. These three techniques have been implemented on the OMEGA laser system producing the highest quality short wavelength ICF laser. Various diagnostics are required to ensure that spatial coherence is rapidly reduced. Focal plane measurements of the spatially integrated spectrum, the spatially resolved irradiation pattern and of the one-dimensional, spatially resolved pulse shape are successfully used to understand the time resolved and time integrated uniformity levels for the OMEGA laser. This work was supported by the U.S. Department of Energy Office of Inertial Fusion under agreement No. DE-FC03-85DP40200 and by the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.

Key materials issues for near term fusion reactors

Materials problems in near term fusion devices tend not to be dominated by structural alloys, but more by specialized components. Prevention of radiation damage to superconducting magnet materials (insulators, stabilizers and superconductors) tends to have a large impact on the size, and hence the cost of fusion devices. Other problems such as impurity control components, breeder materials, and coatings for ICF laser optics will also be the focus of near term materials research and sometimes may require solutions which are not relevant for commercial reactors.