Overlap of intense charged particle beams for intertial confinement fusion
One approach to controlled thermonuclear fusion for power production requires the irradiation of centimetre-size targets containing heavy hydrogen (D–T) fuel by intense charged particle beams (CPB). Beam energy and pulse length requirements are ∼1 MJ and 10ns. In certain studies1 the CPBs are beams of light ions, such as helium, with kinetic energies per nucleon in the range 1–5 MeV. These beams can be transported by preformed, current-carrying, plasma discharge channels. The fields from the channel currents (supplied by capacitor banks) confine the CPBs. These channels can be laser-initiated in a background gas that has a pressure between 10 and 100 torr. This gas blanket enables first wall loading, by X rays, shocks and thermal radiation to be mitigated. Although intense relativistic electron beams (REBs), which were developed before intense light ion beams, have achieved higher intensities2, ion beams have more favourable deposition characteristics in targets3. Proton beams have driven exploding pusher targets4 to implosion velocities of 20 cm µs−1 and have attained power of ∼1 TW cm−2, which is a factor of 40 below that estimated (G. Allshouse, personal communication) to be necessary for target ignition and for net system energy gain. To close the gap between present capabilities and future requirements, beam bunching and beam overlap are being studied. The current density gain G is important to the CPB overlap process and is the ratio of beam current density at the target surface to that of the individual beams in the transport channels; it depends on particle species, transverse energy, geometry of the channel-target interface, and so on. Detailed calculations5–7 indicate that for electron beams, G<3, while for practical cases of light ions, G can exceed 10. This is due to the difference in masses and effective temperatures of the two types of beams. Sources providing multiple ion beams are not available to test this overlap theory experimentally, hence it has been tested using a multiple electron beam system. Here we outline the experiment and describe the apparatus, and then summarize the theoretical treatment of beam overlap, describe diagnostic procedures, and compare the experimental results with calculations.
Production of 0. 5-TW proton pulses with a spherical focusing, magnetically insulated diode
The production, focusing, and numerical simulation of a 0.5-TW proton beam is reported. This beam is produced with a spherical, magnetically insulated, ion diode fed symmetrically by the dual--pulse-line Proto I generator. The ions are accelerated with electric fields due to a virtual cathode supported by magnetic field surfaces. Approximately 75% of the diode electrical power is delivered to ions and 25% of the ion beam is focused upon thin, 1-cm-diam, 1-cm-long conical targets to produce the first experimental ion-driven implosions.
Tethering the Administrative State: The Case Against Chevron Deference for FCC Jurisdictional Claims
Like many other agencies, the Federal Communications Commission has seen significant regulatory growth under President Obama. But unlike health care, financial reform, and other areas, this growth has come without statutory guidance from Congress. The FCC’s assertion of jurisdiction over broadband service is reminiscent of its earlier attempts to regulate cable and to deregulate telephone service, efforts that courts have viewed skeptically in the absence of specific statutory authorization. But this skepticism is in tension with Chevron, which grants agencies substantial deference to interpret ambiguities in the statutes that they administer. This article argues that Chevron deference should not extend to agency jurisdictional claims, such as the FCC’s claim to authority over broadband. For both constitutional and policy reasons, courts should distinguish between agency action that fills a gap in a statutory scheme and action that defines the outer boundary of that scheme. As the Commission’s net neutrality project winds its way through the judicial system, courts should not allow the agency to define the limits of its own authority, and should instead search closely for a grant of authority from Congress.