This paper deals with thermal equilibrium between the particles in argon plasma arcs. The current limit for LTE is experimentally defined as a function of the pressure. Plasma parameters were spectroscopically determined. In particular, the electron temperature and heavy particle temperature were measured. The electron temperature was determined from an absolute continuum radiation strength. Two temperatures were obtained for the heavy particles, one of which was determined from the Doppler component of the H, line when argon gas seeded with hydrogen was used. The second was obtained through a kinetic formula using the measured density and temperature of the electron. The results show that the electrons did not equilibrate with the heavy particles at low currents and pressures. The limit value of the current for LTE increased with decreasing gas pressure. It is shown, furthermore, that the measured field strength of the arc was remarkably lower than those calculated at currents less than the above limits.

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IN A PREVIOUS paper (IMAZU, 1986), it was demonstrated that fusion reaction rates in high temperature plasma decrease when increasing the magnetic field. Referring to this report, the recent letter by Dr.Jarvis makes the following point: An error is found in equation ( 7), i.e. the limitation of V , for ut > 2n.

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The results of a theoretical study of the effect of a magne;ic field. B. on the coliision frequencies.F,. for fusion reactions at comparaiively low energies are presented. i n a usual magnetic field strength. both the cross-section for fusion reactions and the cross-section for the coulomb scattering betueen the ion-ion coilisions are unaffected by B. However. due to both the gyration of the particle and the coulomb scatterings occurring during a free path for fusion reactions. the relative \elocit> between colliding parriclcs making the fusion reaction is affected by B.If (!I is a g!rofrequenc> and I, the deflection time for a 90 deflection of multipie coulomb scattering. when ( U t c > Zz. it h a s determined that the velocit! component contribution to the collision for fusion reactions is only the belocity component along the field axis and that FJ decreases with increasing E.However. u hen cJfc < 2:. FJ is unaffected b! B because a number of collisions for the 90 defleciion occur during the path of a Larmor orbit.

A RECENT paper (IMAZU, 1986) purports to demonstrate that the fusion reaction rates in high temperature plasmas decrease as the strength of the applied magnetic field rises. The magnitudes of the claimed effect is significant, the B = 5T rate being only half the B = 0 rate.If we leave aside the question of the reacting particles being spin polarized, then it is well known (JANCEL and KAHAN, 1966) that a magnetic field has no effect whatever on the velocity distribution of particles in thermal equilibrium, hence it can have no effect on the fusion reaction rate.The error in the paper by Imazu can be found in equation 7 where a geometrical model of the particle orbits has been misinterpreted.