Increase In Stored Energy Research Articles

Off-resonance effects on electrons in mirror-contained plasmas

Resonant heating by microwave power has been used to produce high β plasmas with electron temperatures near 1 MeV. Typically plasmas are produced with ωpe∼ωce. Further experimental heating studies described here have shown that a large increase in stored plasma energy is produced by microwave power with a frequency higher than the cold-electron resonance frequency. This increase, caused by off-resonance heating, is attributed both to stochastic heating and to the control of an instability through changes in the electron distribution function. Alternatively, a decrease in the stored plasma energy is produced by microwave power at a frequency below the cold-electron resonance frequency. This effect is attributed in part to enhanced diffusion into the loss cone. However, a small fraction of the plasma is heated to high energies.

Solvent‐induced crack growth in rubbery block polymers

AbstractThe rapid cracking of lightly stressed rubbery block polymers of styrene and isoprene in certain liquids and vapors has been examined experimentally, by using model test pieces containing a single crack. Solvents which preferentially dissolve the rigid molecular end blocks rather than the rubbery center blocks are efficient cracking agents. The stress required for crack growth to occur is shown to be in accord with a simple energy criterion: the stored elastic energy must be sufficient to provide a characteristic energy for the newly formed surface. This characteristic energy ranges from values close to the surface energy of simple liquids up to about 100 times this value for thicker test pieces or slowly diffusing vapors, when some tearing of an incompletely swollen core is inferred. “Induction times,” before the initial crack starts to grow, are shown to be due to a progressive increase in stored energy under a constant stress as the material absorbs solvent and softens until the critical energy criterion is met. Thus, a timedependent fracture process is shown to be in accord with a constant energy criterion. Above the critical condition the rate of crack growth depends strongly upon stress, like tearing of amorphous elastomers, and the crack then accelerates rapidly.