Pure copper has a high electrical and thermal conductivity, which substantially depends on the oxygen content of the material. Since copper has a high affinity to oxygen, thermal joining processes are therefore to be regarded as critical. Even under shielding gas, oxygen-uptake cannot be prevented. Hence, arc welding of high-purity copper in an XHV-adequate oxygen-free process atmosphere will be developed in the subproject. A comprehensive model starting from the temperature development in the plasma and the corresponding dissolution of the process gases, to the final component purity will be developed.