Basic of and Advances in Gyrotrons

More than nine billion people will live on Earth by 2050, at least one billion people more than today. As the population grows, so does the world’s energy demand. At the same time, energy sources that base on gas, oil and coal are to be replaced by renewable carbon-free ones. An alternative approach is to generate energy by controlled nuclear fusion of light hydrogen nuclei in magnetically confined plasmas. Related public research is ongoing worldwide since long time already. The development of ITER, for which India is an important contributor, is the most prominent example eventually. Based on the advance in research and development, and fuelled by the urgent need for carbon-free energy sources, several exciting start-ups with billion-dollar budgets are emerging around the world. All of those require significant advances in all kind of nuclear fusion technologies. Considering the heating of magnetically confined plasmas, it requires powerful, flexible and efficient heating methods. Electron Cyclotron Resonance Heating (ECRH) has become one of the major plasma heating methods. It makes very localized plasma heating and stabilization possible. ... mehrGyrotron oscillators (Gyrotrons) are the only known vacuum electron sources that offer the required output power at megawatt-level with sufficient efficiencies and at the required millimeter wave (sub-THz) frequencies ranging from approximately 100 GHz to above 200 GHz. Even more, latest research in gyrotrons offer advanced operating modes for plasma heating and diagnostics. In this talk, the basics of gyrotrons will be introduced briefly. Advances in gyrotron research and development, focusing on the developments at Europe, will be provided. It includes the advances in hollow-cavity gyrotrons for European plasma experiments, coaxial-cavity development for future DEMO, the multi-stage depressed collector concept and advanced frequency control of megawatt-class gyrotrons.