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Experiments on the Self-Organized Critical State of ⁴He


Chatto, Andrew Rosenberg (2006) Experiments on the Self-Organized Critical State of ⁴He. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/NN9C-1A08.


When a heat flux is applied downwards through a sample of ⁴He near the superfluid transition temperature Tλ, the gradient in the temperature self-organizes to the gradient in Tλ caused by gravity. This creates the Self-Organized Critical (SOC) state. Previous experiments have observed the state, measured the self-organization temperature TSOC vs. heat flux, and investigated a remarkable wave that only travels upwards against the flow of the heat flux.

We report the first results of the heat capacity of the SOC state, C∇T, for heat fluxes 60 nW/cm² < Q < 13 uW/cm² and corresponding temperatures 9 nK > TSOC-Tλ > -1.1 uK. We find that C∇T tracks the static (i.e., zero heat flux) unrounded (i.e., in zero gravity) heat capacity C_0 with two exceptions. The first is that within 250 nK of Tλ, C_gradT is depressed relative to C₀ and the maximum in C∇T is shifted to 50 nK below Tλ. The second difference is that at high heat flux, C∇T is again depressed relative to C₀ with the departure starting at about 650 nK below Tλ.

We present the most extensive measurements of the speed and attenuation of the SOC wave to date. We report wave speed measurements taken over our full experimental range 30 nW/cm² < Q < 13 uW/cm² and attenuation results over the limited range that produced enough attenuation to measure. We also report the first accurate calculation of the speed of the SOC wave.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:helium; phase transition
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Goodstein, David L.
Thesis Committee:
  • Goodstein, David L. (chair)
  • Refael, Gil
  • Eisenstein, James P.
  • Yeh, Nai-Chang
Defense Date:12 April 2006
Record Number:CaltechETD:etd-06062006-094705
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2479
Deposited By: Imported from ETD-db
Deposited On:06 Jun 2006
Last Modified:31 Mar 2020 21:35

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