Investigation of Helium Arcs at 10 atm Pressure

The measured $\mathrm{“EI‐ER”}$ characteristics of wall‐confined helium arcs at 10 atm pressure, when interpreted with the Elenbaas‐Heller equation, show that the arcs are close to local thermodynamic equilibrium. A spectroscopic measurement is also made to investigate possible deviations from local thermodynamic equilibrium. The results show that, despite over‐all indications of a closer approach to local thermodynamic equilibrium at 10 atm than at 1 atm, the 10 atm arcs are still not in local thermodynamic equilibrium in the region near the walls. Theoretical criteria of local thermodynamic equilibrium tend to support the above results that local thermodynamic equilibrium is approached when the arc pressure is raised, but the complete local thermodynamic equilibrium is not attained at 10 atm. It is believed that the deduced transport properties from the arc measurement with the aid of the Elenbaas‐Heller equation are the first approximations. The deduced electrical conductivity and thermal conductivity agree with the theoretical prediction of Lick and Emmons within a factor of 2.