Teruhiko Tazima

High-Frequency, High-Power Microwave Generation by a Virtual Cathode Oscillator

High-frequency, high-power microwave radiations by a virtual cathode oscillator have been observed using the “point pinch diode” which can produce a high electron beam density. The peak power of microwave pulses is typically 350 MW in the frequency region of 20-22 GHz. The radiation frequency increases almost linearly from 20 to 35 GHz with decreasing anode-cathode gap spacing. The mechanism for microwave emission is ascribed to the oscillation of the virtual cathode.

Effects of Plasma Motions on Transport of High-Voltage Pulse Power through a Slender Self-Magnetically Insulated Transmission Line

Direct electric power input to a pellet may prove to be the simplest method of compression in inertial confinement fusion. One of the crucial questions about this method, however, is how much power can be transported to the pellet through a slender self-magnetically insulated transmission line (MITL) without a large loss. Experimental results show that the transport efficiency of pulse power is determined by the gap closure time caused by plasma expansion from the anode and the cathode surface of the slender MITL. This implies that a shorter voltage pulse width (10~20 ns) is required for a gap length of a few millimeters to attain a high transport efficiency.

Direct Energy Input to Compressor for Inertial Confinement Fusion

An effective method for driving ICF pellet compression is proposed where neither laser beam nor charged particle beam is necessary but rather high electric pulse power is directly input into a vacant space between a shell tamper and its enclosed pellet. Electrons emitted from the pellet surface produce a dense, hot plasma on the inner side of the tamper. Photons and particles of the plasma irradiate the pellet surface and give rise to an effective ablation-driven compression. This direct energy input to compressor (DEIC) can be done efficiently and makes it easier to picture an ICF reactor.

A Pellet Model of DT Ignitor and DD Fuel for an ICF Reactor without Tritium Breeding Blanket

A pellet concept of a DT ignitor and DD fuel for an ICF reactor without a tritium breeding blanket is analytically examined under the condition that T is bred through the DD reactions. There is the additional restriction that the tritium breeding ratio in a pellet is unity, including the in situ DT burn in the DD region. Model calculations show that sufficiently high pellet gain can be obtained in a DT-DD pellet, when fuel ρR increases to ~40 g/cm2 and the fraction of energy released in the DD region becomes dominant. One-dimensional neutronics calculations carried out for a reference pellet model with ρR~40 g/cm2 show that the neutron heating in the compressed pellet model is evident and the total energy of the neutrons escaping from the pellet is reduced from ~2000 MJ to 330 MJ for a microexplosion of ~3000 MJ.

Light ion-beam fusion

The Technological University of Nagaoka and the Institute of Plasma Physics at Nagoya University report on experimental and theoretical studies in inertial confinement fusion by using an intense pulsed light-ion beam (LIB). The main efforts are made in the production, focusing, and transport of the LIB and the development of several diagnostic techniques, while fewer efforts are made to study a LIB-target interaction. New approaches are also tried for research and development of a medium-mass ion beam and a direct power input into pellets. A table summarized the activities and specifications of the pulse-power machines installed in universities in this particular field and a brief review is given.