{sup 4}He very near T{sub {lambda}} heated from above
- Univ. of California, Santa Barbara, CA (United States)
- California Institute of Technology, Pasadena, CA (United States)
The authors discuss the feasibility and likely results of measurements of the thermal conductivity {lambda}(Q,t) of {sup 4}He very near T{sub {lambda}} {equivalent_to} T{sub {lambda}}(Q=0) as a function of the heat current Q and the reduced temperature t {equivalent_to} [T - T{sub {lambda}}]/T{sub {lambda}} by heating of a sample from above and cooling it from below. Although the expansion coefficient is negative, the experiment should be possible without inducing convection in the He I layer provided the sample length does not significantly exceed one cm. For t {approx_lt} 10{sup {minus}7} (Q {approx_gt} 0.2 erg/s cm{sup 2}), a state of self-organized criticality can be attained. For these conditions, the thermal gradient cancels the gradient in T{sub {lambda}} induced by gravity, thus permitting measurements extremely close to the transition even in an Earthbound laboratory. However, the data will be only for a unique path in the Q - t plane. For 0.2 {approx_lt} Q {approx_lt} 0.5 erg/s cm{sup 2} (10{sup {minus}7} {approx_lt} t {approx_lt} 10{sup {minus}8}) they will be in the range of linear response and give {lambda}(0,t); for Q between about 0.5 and 10 erg/s cm{sup 2} and over a temperature range of about 20 nK, the experimental path samples the regime where the conductivity is expected to be influenced by nonlinear finite-current effects. The small currents and narrow temperature range of the experiment imply that ultra-high resolution thermometry as well as very careful control of stray heat currents will be required. For Q {approx_lt} 10 ergs/s cm{sup 2} and up to very large Q, the method can be used to determine the onset temperature T{sub c}(Q) of thermal resistance.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 482495
- Journal Information:
- Journal of Low Temperature Physics, Vol. 105, Issue 1-2; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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