Experimental studies on energy transport in a reversed-field theta pinch

The transport of energy and particles from a field-reversed configuration (FRC) produced by a theta pinch has been studied experimentally under the following typical plasma parameters in the quasi-static phase: Ti ∼ 300 eV, Te∼100eV, n̄e ∼ 5 × 1015 cm−3, ⟨β⟩ ∼ 1, ⟨Zeff⟩ ∼ 3 and separatrix radius rs ∼ 1.8 cm. Energy transport through various processes has been evaluated, consistent with the observed volume-averaged quantities which are changing in time in a quasi-static manner. As a result, it has been found that the dominant energy loss mechanism is particle loss, which accounts for more than 50% of the power flow out of the FRC. The second important process is the electron thermal conduction loss, which is estimated to be roughly 30% of the total loss if impurity radiation losses other than by carbon and oxygen are not important. In contrast, the ion thermal conduction loss is observed to be so small as to be hidden by the experimental errors. Radiation loss has been estimated to play a minor role if the observed ⟨Zeff⟩ can be ascribed to contaminations of only carbon and oxygen. The inferred energy confinement time τE is 7 is μs, which compares with the observed particle confinement time τp of 17 μs. The data indicate that τp is consistent with classical diffusion theory.