Edge plasma emissivity profile reconstruction by forward modelling of diode bolometer signals at ASDEX Upgrade

1 INTRODUCTION 1.1 the energy problem The present energy scenario and the forecast for the next future reveal an increasing energy demand [9]. Moreover, the actual global energy supply is based on fossil fuels for 81%, while just for 13% on different forms of renewable energy (biomass, hydroelectric, combustible waste, etc). The rest relies on nuclear fission [5]. Considering the decreasing availability of fossil resources, the development of alternative and renewable energy sources has become a crucial challenge. Through a continuous research, new ways have been explored, solutions have been suggested, and some possible answers have been found first in nuclear fission, then in investing more in "green en- ergy". It seems anyway more logical to imagine a future where the energy demand is sustained by different sources, in order to maintain a stable en- ergetic and economic system. Energy from sun, wind or similar renewable resources cannot sustain the whole energy demand, being bound to partic- ular environmental conditions. Anyway they can be considered a good and environmentally-friendly alternative to the dependence on main energy re- sources as, for instance, the current coal, gas or fission power plants. But now the main challenge is thus to find a new main energy source: hope- fully long lasting, eco-friendly and inherently safe. A promising candidate fulfilling these conditions is fusion. 1.2 a possible solution to the increasing energy demand: fusion Generally speaking, fusion is a nuclear process in which two light nuclei merge to form a heavier element. In order to reach a fusion reaction, two positive charged nuclei have to overcome the mutual Coulomb repulsion. They have hence to be closer than a distance in the order of 10 -15 m [27]. A vast knowledge about fusion comes from stars, which are the oldest and biggest fusion "plants" existing. Studying the sun, the proton-proton fusion chain has been discovered. In this reaction helium is formed out of hydro- gen, releasing an energy of26.7MeV for each reaction. In the sun, this fusion process is possible due to the high core density (~10 31particles m 3 ), sustained by the gravitational force. This is not attainable on earth, since densities in this range cannot be reached. In order to exploit fusion processes on earth, the most feasible reaction is employing two hydrogen isotopes, namely deu- terium and tritium (reaction1). They are used because of their cross section, which is larger compared to other possible reactions (reactions 2,3,4, see figure 1). 2 D+ 3 T! 4 He+ 1 n+17.6MeV (1) 2 D+ 2 D! 3 He+ 1 n+3.27MeV (2) 1