Reply To: scaleablity of a reactor?
ohiovr wrote: Getting break even and beyond is of course the primary concern but is it possible to scale the power of these reactors? The polywell people think they can get a gigawatt out of a reactor 10 meters across. Lots of little reactors is fine of course but could something larger be made? I’m looking for electrical generators for space applications. Focus fusion is already a plus because it doesn’t use thermal effects for power generation and thermal management is not so great in space with no cold air or water to sync to. Any chance for gigawatt reactors?
Yes, I think so as follows:
Overview and Rationale
I propose a new type of inertial confinement fusion (ICF) based device to test materials in conditions of extreme temperature and pressure, to gather data to aid in computer modeling of nuclear weapons and to provide a backbone technology for a high efficiency, high gain, and high output fusion reactor.
Currently, the Z machine is the largest X-ray generator in the world and is designed to test materials in conditions of extreme temperature and pressure. Operated by Sandia National Laboratories, it gathers data to aid in computer modeling of nuclear weapons. The Z machine is located at Sandia’s main site in Albuquerque, New Mexico.
The primary weakness in the current Z machine approach is the inefficiency in the way it produces and applies x-rays to the target. Most of its energy is radiated way by various mechanisms including alpha particles, high energy electrons, light, heat, and x-ray dispersion. Only a modest faction of the input power reaches the target in the form of x-rays.
The LIFE laser fusion reactor is also inefficient in its delivery of power to its target. The efficiency of its lasers is less than one percent.
Xcon
One way to improve the design of these types of ICF device is to construct a high efficiency multi-stage fusion based focused X-ray source and concentrator (Xcon).
The principle behind Xcon is simple. Using a few hundred fusion based x-ray production modules, produce hard X-rays and gamma rays using aneutronic fusion and concentrate them into a small volume of space in the same way as the LIFE laser reactor concentrates laser light into a millimeter sized spherical volume.
General Design.
An x-ray production module is a small aneutronic fusion reactor shaped like the circular headlight of an automobile. It uses aneutronic boron based fusion to produce a point source of x-rays, fast electrons and alpha particles.
This reactor fires a very powerful electrical discharge into a hollow tube in tube cathode/anode pair where the anode is hollow. During the electrical discharge, this sparkplug like device forms a plasmoid near the anode tip at the focal point of a parabolic hard radiation lens system.
This parabolic lens can reflex x-rays and gamma rays form this plasmoid point source and focus them on a point in space about N meters away.
The cathode/anode pair is composed of boron doped diamond. This pair is highly conductive, transparent to x-rays and gamma rays, optimally resistive to erosive ware and can withstand an operating temperature up to 3000C.
The electrodes are enclosed and anchored in a paraboloid shaped polycrystalline diamond support structure formed with large 100 nanometer sized crystals. The diamond paraboloid is faced with a flat lens composed of graphite that provides an enclosed volume that can hold a vacuum. Puff injection of boron and hydrogen gas near the anode and is coordinated with the electrical discharge and provides the fusion fuel source.
The Lens System
In order to cover energies up to about100 KeV – and maybe beyond – High-Energy Photons lens geometries such as Kirkpatrick/Baez Optics, Bragg-Lenses, Laue-Lenses, and Fresnel lenses can be used together with multilayer coatings as a mirror surface.
These multilayer coatings consist of alternating layers of high and low index n of High-Energy Photons refraction materials: The reflection by a multilayer mirror is described by the constructive interference of the reflections at all low-high n interfaces This result in a sizable total reflectivity of the system. Similar to the Bragg-diffraction in crystals, the reflections have to be added with the correct phase relationship, leading to a boundary condition that relates incidence angle q, layer thickness d and wavelength l
2 d sin q = n l
Where n, the order of the reflection is an integer >= 1(multilayers are most commonly used in the first order, n = 1). Consequently, the response of so called Uniform Period Multilayers results in a narrow energy-bandpass. High reflectivity in a broad energy-bandpass can be achieved with graded multilayer coatings, here the film thickness d is varied over the stack. These Extremely Broad Band (EBB) Multilayers with reflectivities over bandpasses of > 20 keV are currently being intensely developed.
The materials for the reflector/spacer coatings are selected for their different indices of refraction of hard readiation and for minimum absorption – presently considered material combinations are W/Si, W/C, Ni/C, and Pt/C.
Recent development work for the hard X-ray telescopes has indicated potential up to around 200 keV for this technique.
See the following graphic representation of the parabolic shaped back reflector structure:
Rather than reflect the high energy photons along a parallel path as in the diagram, they will be bent to converge at a point N meters distant based on overall reactor design requirements. This provision is in place to optimize the performance of the front lens system.
Continued in next post.