Crystallization of liquids confined in disordered low-density nanoporous scaffolds is poorly understood. Here, we use relaxation calorimetry to study the liquid-solid phase transition of H2 in a series of silica and carbon (nanotube- and graphene-based) aerogels with porosities ≳94%. Results show that freezing temperatures of H2 inside all the aerogels studied are depressed but do not follow predictions of the Gibbs-Thomson theory based on average pore diameters measured by conventional gas sorption techniques. Instead, we find that, for each material family investigated, the depression of average freezing temperatures scales linearly with the ratio of the internal surface area (measured by gas sorption) and the total pore volume derived from the density of aerogel monoliths. The slope of such linear dependences is, however, different for silica and carbon aerogels, which we attribute to microporosity of carbons and the presence of macropores in silica aerogels. Our results have important implications for the analysis of pore size distributions of low-density nanoporous materials and for controlling crystallization of fuel layers in targets for thermonuclear fusion energy applications.

Behavior of hydrogen isotopes confined in disordered low-density nanoporous solids remains essentially unknown. Here, we use relaxation calorimetry to study freezing and melting of H2 and D2 in an ∼85%-porous base-catalyzed silica aerogel. We find that liquid–solid transition temperatures of both isotopes inside the aerogel are depressed. The phase transition takes place over a wide temperature range of ∼4 K and non-trivially depends on the liquid filling fraction, reflecting the broad pore size distribution in the aerogel. Undercooling is observed for both H2 and D2 confined inside the aerogel monolith. Results for H2 and D2 are extrapolated to tritium-containing hydrogens with the quantum law of corresponding states.

The LIFE target design incorporates many considerations to generate the desired fusion gain including the physics design, the cost of manufacturing of the target, the injectability of the target, the aerodynamic flight characteristics of the target, the ability to track and engage the target and to maintain the structural and thermal integrity of the target. This document describes the effort that was made in support of issues of survivability of the target during injection which included issues massmanufactural materials and processes which could be used in the target.

Thermodynamic properties of condensed hydrogen in geometric confinement remain poorly understood. Here, we use relaxation calorimetry to study solidification and melting of H2 in a series of Vycor-type nanoporous silica glasses with interconnected pores with average diameters in a wide range of ∼100–3000 Å. We find that the depression of freezing and melting temperatures for this quantum system follows the classical Gibbs–Thomson-like behavior, scaling inversely with the pore size when correlated to pore diameters measured directly by electron microscopy, rather than conventional gas sorption techniques. The shapes of pore size distributions derived from hydrogen thermoporometry are, however, more complex than those measured by gas sorption. The ratio between temperatures of the depression of freezing and melting suggests that the actual pore geometry in Vycor-type nanoporous glasses deviates from cylindrical.

We report measurements of the mechanical \(Q\) of a 32.7 kHz quartz tuning fork as a function of pressure for helium and argon at T \(=\) 300 K and for helium in the temperature range 7.0–0.7 K. In the low pressure ballistic regime, the damping due to the surrounding gas is inversely proportional to \(P\), while for higher pressures, a hydrodynamic treatment accounts for most of the variation of \(Q\) with \(P\). We have combined the ballistic and hydrodynamic models together with calculations of the thermal transpiration correction to correlate the tuning fork \(Q\) at low temperature with the pressure measured with a room temperature pressure gauge. The fork was found to be useful as an in situ pressure gauge for pressures above \(\sim \)0.1 mTorr. A dissipation peak and frequency drop associated with the superfluid transition in the adsorbed helium film is also observed for \(T<1.4\) K.

A relaxation calorimeter for measuring the heat capacity of hydrogen isotopes in nanoporous solids is described. Apparatus' features include (i) cooling by a pulse tube refrigerator, (ii) a modular design, allowing for rapid reconfiguration and sample turn around, (iii) a thermal stability of ≲1 mK, and (iv) a bottom temperature of ~5 K. The calorimeter is tested on effective heat capacity measurements of H2 in Vycor (silica) nanoporous glass, yielding a very detailed pore size distribution analysis with an effectively sub-Angstrom resolution.

Due to a large fraction of undercoordinated surface atoms in nanoporous solids, the surface composition could have a profound effect on their properties. Here, we use mass spectrometry to study ion-beam-induced desorption from silica aerogels. Results show that the dominant ion-beam-induced desorption species is the hydrogen molecule. Bombardment with ions of different masses causes dehydroxylation of silica nanoligaments, with the desorption efficiency scaling linearly with the electronic stopping power of ions. These results demonstrate that ion bombardment can be used for controlling surface hydroxylation of nanoporous silica.

We have designed and constructed a continuously operating 3 He cryostat with windows for laser ablation and spectroscopy. A two-stage pulse-tube refrigerator cools two platforms to base temperatures of approximately 40 K and 4 K respectively. The platforms are equipped with heat exchangers that cool separate streams of 4 He and 3 He. The 4 He stream is used to run a thermally isolated evaporative refrigerator with a base temperature of approximately 1.5 K and a cooling power of 20 mW. The 4 He refrigerator is used to condense 3 He, which is used to run a 3 He evaporative refrigerator on the experimental cell. The cryostat runs continuously at temperatures from 10 K to 0.4 K with a cooling power of 1.5 mW at 0.5 K.

We have developed a cryogenic pulsed laser deposition (PLD) system to deposit lithium films onto a quartz crystal microbalance (QCM) at 4 K. Adsorption isotherms of 4He on lithium were measured in the temperature range between 1.42 K and 2.5 K. The isotherms are qualitatively different from isotherms on strong substrates such as gold and weak substrates such as cesium. There is no evidence of the formation of solid-like layers of helium, and the helium coverage is approximately linear in the pressure over a wide range. By measuring the low coverage slope of the isotherms, the binding energy of helium to lithium was found to be approximately −13.6 K. For lithium substrates less than approximately 100 layers thick, the chemical potential at which the superfluid transition was observed was surprisingly sensitive to the details of lithium deposition.

The results in the EDM proposal, chapter 5H, for the sensitivity of the EDM experiment have been checked using pseudo data and least squares fitting techniques. The applicability of the formula in Chibane et al. has been tested for the case of small backgrounds. The role of the phase factor in the fitting is clarified. In the case of EDM pseudo-data, the sensitivity is mapped as a function of the efficiency for identifying and vetoing the UCN beta decays, with a factor-of-two improvement found if all beta decays are removed. Finally, the sensitivity of the experiment is determined to be twice the limit given by the Heisenberg UncertaintyPrinciple when beta decays are not identified and equal to the limit when they are removed from the data stream. The Uncertainty-Principle limit is found to be optimally small at a different measuring time than in the EDM proposal, i.e. 2000 s.