Barry McQuillan

The PAMS/GDP Process for Production of ICF Target Mandrels

AbstractAn improved process for production of ICF Target Mandrels has been developed. Shells made from PAMS (poly-α-methylstyrene) are coated with GDP (glow discharge polymer). The PAMS is then removed by depolymerization and volatilization at 300°C, leaving a GDP mandrel. Compared to past polymer mandrels, this process yields GDP mandrels with significant improvements in wall thickness control, sphericity and concentricity, and the complete absence of vacuoles. The process is capable of making GDP shells with a wide size range (from 300 < o.d. < 2700 µm), and an independently controlled wall thickness (from 1 to 30 µm). The GDP can be doped with a variety of elements.

PROGRESS IN 2 mm GLOW DISCHARGE POLYMER MANDREL DEVELOPMENT FOR NIF

Abstract All planned National Ignition Facility (NIF) capsule targets except machined beryllium require a glow discharge polymer (GDP) mandrel upon which the ablator is applied. This mandrel, ~2 mm in diameter, must at least meet if not exceed the symmetry and surface finish requirements of the final capsule. Such mandrels are currently produced by the three-step depolymerizable mandrel technique. The quality of the final mandrel depends upon precise optimization and execution of each of the three steps. We had shown previously that fabrication of a mandrel which met the symmetry and surface finish requirements was feasible using this technique. In this paper we will discuss recent progress towards converting this process into a high yield, production scale process.

Development of high quality poly(α-methylstyrene) mandrels for NIF

Abstract Recently, we developed a new method for making spherical poly(α-methylstyrene) (PαMS) mandrels. The process utilizes a small amount (<0.1wt%) of high-molecular-weight poly(acrylic acid) (PAA) in the suspending medium, which substantially increases the interfacial tension during curing relative to methods using poly(vinyl alcohol) (PVA) and yields extremely round capsules. The PAA is also beneficial for centering of the core water, leading to exceptionally concentric capsules. However, fully cured capsules made by this method displayed a significant level of high frequency surface debris that became especially problematic when the mandrels were subsequently overcoated. To solve this problem we examined the use of PAA in conjunction with PVA in order to reduce these surface features, and explored numerous variations of concentration and timing of the PVA addition. The optimum conditions were found to be initial use of PAA for centering and symmetry of the mandrels, followed by removal of the PAA medium, washing of the mandrels with water, and finally transfer to PVA solution for completion of the curing cycle. Glow discharge polymer shells made from these mandrels have power spectra that meet the ignition capsule design requirements.

Removal of mode 10 surface ripples in ICF PAMs shells

Abstract Plastic spherical shells made by microencapsulation show a surface roughness over modes within the range 7–20, generically termed “the mode 10 problem.” The roughness mode number corresponds with theoretical models of Marangoni convection cells formed during the curing of the initial wet shells. The roughness is removed, by appropriate changes in shell processing conditions, changes guided by the understanding of Marangoni convection.

Demonstrating a Target Supply for Inertial Fusion Energy

Abstract A central feature of an Inertial Fusion Energy (IFE) power plant is a target that has been compressed and heated to fusion conditions by the energy input of the driver. The technology to economically manufacture and then position cryogenic targets at chamber center is at the heart of future IFE power plants. For direct drive IFE (laser fusion), energy is applied directly to the surface of a spherical CH polymer capsule containing the deuterium-tritium (DT) fusion fuel at approximately 18K. For indirect drive (heavy ion fusion, HIF), the target consists of a similar fuel capsule within a cylindrical metal container or ’’hohlraum’’ which converts the incident driver energy into x-rays to implode the capsule. For either target, it must be accurately delivered to the target chamber center at a rate of about 5-10Hz, with a precisely predicted target location. Future successful fabrication and injection systems must operate at the low cost required for energy production (about

Developing a commercial production process for 500 000 targets per day : A key challenge for inertial fusion energy

0.25/target, about 104 less than current costs). Z-pinch driven IFE (ZFE) utilizes high current pulses to compress plasma to produce x-rays that indirectly heat a fusion capsule. ZFE target technologies utilize a repetition rate of about 0.1 Hz with a higher yield. This paper provides an overview of the proposed target methodologies for laser fusion, HIF, and ZFE, and summarizes advances in the unique materials science and technology development programs.

Investigation of Larger Poly(α-Methylstyrene) Mandrels for High Gain Designs Using Microencapsulation

As is true for current-day commercial power plants, a reliable and economic fuel supply is essential for the viability of future Inertial Fusion Energy (IFE) [Energy From Inertial Fusion, edited by W. J. Hogan (International Atomic Energy Agency, Vienna, 1995)] power plants. While IFE power plants will utilize deuterium-tritium (DT) bred in-house as the fusion fuel, the “target” is the vehicle by which the fuel is delivered to the reaction chamber. Thus the cost of the target becomes a critical issue in regard to fuel cost. Typically six targets per second, or about 500 000∕day are required for a nominal 1000MW(e) power plant. The electricity value within a typical target is about

Solutocapillary convection in spherical shells

3, allocating 10% for fuel cost gives only 30 cents per target as-delivered to the chamber center. Complicating this economic goal, the target supply has many significant technical challenges—fabricating the precision fuel-containing capsule, filling it with DT, cooling it to cryogenic temperatures, layering the DT into a unifo...

Recent progress in the development of capsule targets for the National Ignition Facility

Abstract In recent years we have demonstrated that 2-mm-diameter poly(α-methylstyrene) mandrels meeting indirect drive NIF surface symmetry specifications can be produced using microencapsulation methods. Recently higher gain target designs have been introduced that rely on frequency doubled (green) laser energy and require capsules up to 4 mm in diameter, nominally meeting the same surface finish and symmetry requirements as the existing 2-mm-diameter capsule designs. Direct drive on the NIF also requires larger capsules. In order to evaluate whether the current microencapsulation-based mandrel fabrication techniques will adequately scale to these larger capsules, we have explored extending the techniques to 4-mm-diameter capsules. We find that microencapsulated shells meeting NIF symmetry specifications can be produced, the processing changes necessary to accomplish this are presented here.

Mass Production Methods for IFE Targets

A linear stability study of solutocapillary driven Marangoni instabilities in small spherical shells is presented. The shells contain a binary fluid with an evaporating solvent. The viscosity is a strong function of the solvent concentration, the inner surface of the shell is assumed impermeable and stress free, while nonlinear boundary conditions are modeled and prescribed at the receding outer boundary. A time-dependent diffusive state is possible and may lose stability through the Marangoni mechanism due to surface tension dependence on solvent concentration (buoyant forces are negligible in this microscale problem). A frozen-time or quasisteady state linear stability analysis is performed to compute the critical Reynolds number and degree of surface harmonics, as well as the maximum growth rate of perturbations at specified parameters. The development of maximum growth rates in time was also computed by solving the initial value problem with random initial conditions. Results from both approaches are ...