Double layer formation caused by contact between different temperature plasmas

The formation of an electrical potential difference between hot and cold plasmas is studied by means of a particle simulation. It is found that a double layer structure is formed on the hot-plasma side of the contact surface between the cold and hot plasmas. The potential difference is given approximately by φDL∼Teh/2e, where Teh and e are the hot-electron temperature and the electronic charge, respectively. The double layer is accompanied by a negative potential dip on the low potential side (cold plasma) of the double layer, the depth of which is φdip∼2Tec/e, where Tec is the cold-electron temperature. Interestingly, however, the positive potential difference and the negative potential dip are created independently.