Vacuum pumping by freezing out or otherwise immobilizing the pumped gas is an old concept. In several plasma physics experiments for controlled fusion research, cryopumping has been used to provide clean, ultrahigh vacua. Present day fusion research devices, which rely almost universally upon neutral beams for heating, are high gas throughput systems, the pumping of which is best accomplished by cryopumping in the high mass-flow, moderate-to-high vacuum regime. Cryopumping systems have been developed for neutral beam injection systems on several fusion experiments (HVTS, TFTR) and are being developed for the overall pumping of a large, high-throughput mirror containment experiment (MFTF). In operation, these large cryopumps will require periodic defrosting, some schemes for which are discussed, along with other operational considerations. The development of cryopumps for fusion reactors is begun with the TFTR and MFTF systems. Likely paths for necessary further development for power-producing reactors are also discussed.

''Obfuscatory measurement'' is the practice, deliberate or not, of obscuring the true performance of a system through the use of misleading measures. Many of the traditional and widely used measures of computer system performance are obfuscatory: they measure the wrong things, the right things wrongly, or nothing at all. Several obfuscatory measures are considered; those aspects of the system they are thought to measure are contrasted with those that they actually measure; and alternative measures, which are more meaningful to the user community, are suggested. 3 figures, 1 table.

The effectiveness of course-grained igneous rocks as shelters for burying radioactive waste can be assessed by determining the rock permeabilities at their in situ pressures and stresses. Analytical and numerical methods were used to solve differential equations of one-dimensional fluid flow through rocks with permeabilities from 10/sup 4/ to 1 nD. In these calculations, upstream and downstream reservoir volumes of 5, 50, and 500 cm/sup 3/ were used. The optimal size combinations of the two reservoirs were determined for measurements of permeability, stress, strain, acoustic velocity, and electrical conductivity on low-porosity, coarse-grained igneous rocks.