Patent Number: 
Section: description

This application is a divisional application of U.S. patent application Ser. No. 11/754,928, filed May 29, 2007, for Method and System for Controlled Fusion Reactions, claiming priority to U.S. Provisional Patent Application No. 60/809,453 entitled “Method & Apparatus for Controlled Fusion Reactions” filed May 30, 2006. The foregoing applications are hereby incorporated herein by reference in their entireties. The present invention relates to a system for producing electromagnetic radiation incorporating a drift tube modified to enable output of higher frequencies from a high power RF source incorporating the drift tube. Prior art Magnetically Insulated Linear Oscillators (MILOs) are high power RF sources, which have typical outputs between 300 MHz and 3.5 GHz. For various applications, it would be desirable to provide a high power RF source that can achieve even higher frequencies. The present invention relates to a system for producing electromagnetic radiation incorporating a drift tube which includes a hollow cylindrical conductive element having a grating surface formed on its inner surface, with the ends of the cylindrical conductive element being radiused to minimize electrical stress buildup. The interaction between a relativistic electron beam from an electron source passing through the inner space of the hollow element and the internal grating produces RF radiation by the Smith-Purcell Effect. The spacing, face angle and shape of the grating, and the energy of the electron beam, are determinants of the frequency of the RF radiation. The foregoing drift tube, having a grating on the inner surface of a cylindrical drift tube, can be used advantageously to increase the frequency output of such devices as a Magnetically Insulated Linear Oscillator (MILO) beyond the aforementioned range of 300 MHz to 3.5 GHz mentioned for a MILO. A list of drawing reference numbers, their associated parts and preferred materials for the parts can be found near the end of this description of the preferred embodiments. FIG. 1 shows a cross-section of a Stimulated X-ray Emitter (SXE) combined with a Magnetically Insulated Linear Oscillator (MILO) at the output (right-shown) end of the SXE. The Stimulated X-ray Emitters were first described by the inventor of this current invention in U.S. Pat. No. 4,723,263. The MILO is another well known, high power RF source, similar to the Vircator. The significant difference is that it can produce much higher frequencies than the Vircator. Structurally, the major difference is the incorporation of a drift tube 122 of FIG. 3A and use of a Traveling Wave Electron Gun (TWEG) instead of the planar cathode 90 and grid 92 of the Vircatron. There is a resonant cavity 98 and its dimensions in conjunction with the dimensions of the drift tube 122 (FIG. 3A) determine the output range. Conventional MILO devices have outputs between 300 MHz and 3.5 GHz. The inventor of the present invention has experimentally verified that by placing a grating surface on the inner face of the drift tube 122 (FIG. 3A), as shown in FIG. 3B, it is possible to generate RF at much higher frequencies than those available from a smooth bore drift tube 122. The source of this RF is due to the Smith-Purcell effect which describes the interaction of a relativistic electron beam with a grating surface 123. Outputs in the THz range are possible. The grating surface can be formed by many methods. The spacing, face angle and grating geometry all are determinants in the frequency achieved (FIG. 3B). It has been determined that the preferred embodiment of the drift tube grating is an internal thread as shown in FIGS. 3A and 3B. By altering the thread parameters, the output frequency is changed. The ends of the Drift Tube 125 are radiused to minimize formation of undesirable electric field perturbations inside the Resonant Cavity 98. The balance of the SXE-MILO driver is the same as the SXE-Vircator. In fact, the RF heads—Vircator and MILO—can be interchanged. As in the case of the SXE-Vircator, the TWEG of the MILO has a hollow center through which the x-rays pass. The electron output from the TWEG is compressed by the drift tube 122 and oscillates in the resonant cavity 98. The following list of drawing reference numbers has three columns. The first column includes drawing reference numbers; the second column specifies the parts associated with the reference numbers; and the third column mentions a preferred material (if applicable) for the parts. REFERENCE NUMBER LISTPREFERRED MATERIAL64AnodeRefractory Metal; Hi-Z66GridRefractory Metal68CathodeGraphite (PreferredEmbodiment)70Coaxial CapacitorDielectric/Metal Layers72Cathode FeedthroughCeramic & Metal74Grid FeedthroughCeramic & Metal78Radiation ShieldLead94Anode MeshRefractory Metal96Output WindowRF Transparent Low-ZCeramic98Resonant Circular CavityStainless Steel or Copper100Mounting FlangeStainless Steel102Cathode FeedthroughCeramic & Metal106Grid FeedthroughCeramic & Metal110Getter Pumpn/a112Getter Pump FeedthroughCeramic & Metal114MILO CathodeGraphite116MILO Cathode SupportRefractory Metal118MILO GridRefractory Metal120MILO Grid supportrefractory Metal122Drift TubeRefractory Metal123Grating SurfaceRefractory Metal124Drift Tube SupportCeramic125Radiused end of Drift TubeRefractory Material126Internal Anode InsulatorCeramic142Grid Output TerminalRefractory Metal The foregoing describes a drift tube where the inclusion of a grating surface on the inner surface of the tube generates higher frequencies of RF radiation. While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention.