Statement of Problem & DOE/Public Interest: Commercial fusion companies received billions of dollars in funding in recent years, bringing outside investment in fusion energy to over five billion dollars across 35 companies. Investors clearly expect commercially viable, fusion energy in the near future. In order to initiate and maintain controlled fusion reactions, the plasma must be heated to fusion temperatures. For economical, steady state tokamak reactors, efficient current drive is required. Ion Cyclotron Range of Frequencies (ICRF) have been demonstrated in reactor grade plasmas to be effective at plasma heating and central current drive. For high magnetic field fusion devices 60-240 MHz systems are envisioned, which are ideal for solid-state devices. Conventional megawatt-class Vacuum Electron Devices (VEDs) RF sources have very high life cycle costs, and become increasingly inefficient at frequencies above approximately 120 MHz; 240 MHz is beyond the operating frequency range of present-day fusion-class tetrodes. In addition, Due to limited market and few remaining manufacturers, there is serious concern about the long-term availability of fusion-class tetrodes. Traditional solid-state megawatt-class RF sources are very large, requiring a large physical plant, and extremely costly to produce. It is in the publics interest for DOE to investigate a fusion heating and current drive technology applicable across the fusion industry. All fusion machines can therefore benefit from an effective and timely resolution to a critical problem. DTI has patented and demonstrated DCC solid-state transmitters at L-band and UHF and, utilizing this proven approach, can produce low-cost solid-state megawatt VHF transmitters for fusion applications. How the Problem Will Be Addressed: DTI will design and build a high power (megawatt class) Direct Cavity Combiner (DCC) Transmitter in a single compact and efficient amplifier. The problem will be addressed by theoretical design, numerical analyses, and hardware construction. This will be based on previous successful DCC demonstrations at 650 MHz and 1300 MHz. The concept is being worked in collaboration with MIT for future installation on a prototype fusion device. Phase I Work: In Phase I, DTI will design and build a full-size test cavity and multiple 9 kW Tri-Quad RF modules to demonstrate the DCC technology at 120 MHz (approximately the center of the ICRF band). The cavity and modules will undergo test and evaluation to compare the amplifier performance to that predicted by the simulations and calculations performed as part of the design effort.
