Diagnostic study of steady state advanced fuel (deuterium-deuterium and deuterium-tritium) fusion in an IEC device.

摘要

The ionized fusion fuels (D-D & D-3He) have been accelerated to fusion velocities using two concentric grids maintained at a high potential difference in an Inertial Electrostatic Confinement (IEC) device. Though the gridded IEC device currently has a low efficiency (Q ≡ fusion power/input power ∼10-5), the energetic protons and neutrons generated within this device can be used for many near-term applications, such as medical isotope production, landmine detection, neutron activation analysis, etc. The present work is centered upon understanding the operation of the device and finding new ways to increase the overall efficiency.; The steady state fusion of D-3He fuel in an IEC device was successfully studied. At a pressure of ∼2 mtorr the source of such reactions was identified to be principally beam-target reactions and was theoretically explained using the Monte Carlo - Stopping and Range of Ions in Matter (SRIM) code. The first simultaneous measurement of DD and D-3He protons was accomplished during the present thesis work that confirmed that D- 3He fusion reactions indeed occur in an IEC device. A new pressure independent diagnostic was invented to measure the average ion energy. That diagnostic uses the D-D proton energy spectra from a single loop cathode grid and the SRIM code predictions. A second diagnostic called the eclipse disc was co-invented to characterize the various fusion regimes in an IEC device. This diagnostic verified that a converged core fusion source exists for the DD reactions but the D-3He reactions that are principally embedded source reactions. A third diagnostic called the chordwire was invented to study the effects of various sources of electrons---thermionic, photo and field emission electrons, that decrease the efficiency of the device. This diagnostic also helped map the ion flux into the cathode in 2D, besides helping identify the high performance grid materials (W-25%Re and pure Re). Understanding the electron current contributions helped correct previous recirculation ion current equation in the literature. Sequential grid construction experiments where a new loop was added in a sequence (in various orientations) while monitoring the performance of the grid showed fusion rate saturation of the fusion rate with just a 3 loop grid. Hence, further increases in symmetry of the grid are deemed unnecessary. It was also found that the fusion occurred mostly in the microchannels that form in the regions where the cathode field is a minimum (i.e., in the open areas between the wires). This is an important conclusion because all earlier work had assumed a uniform spherical volume source of incoming ions and this work suggests otherwise. A new method of calibration was derived using the non-uniform volume source that takes into account the surface area of the detector visible to the protons that are born anywhere within the IEC chamber.; As a consequence of the above research and valuable input from others in the IEC group, at UW Madison, there has been an increase in D-3 He rate by 5 orders of magnitude, in a span of 4 yrs, while those of the D-D reaction rate increased by 3 orders of magnitude.