Abstract
In this thesis the metrological performances of the R SQUID intended to
be used as a cryogenic thermometer is verified.The R SQUID consists of the
Josephson junction which converts voltage noise from the shunt resistor into
frequency fluctuations.Measuring the value of the shunt resistor and the
variance of the frequency fluctuations, the temperature of the bath can be
determined.Unfortunately, the absolute temperature determination is disturbed
by several effects: a rolloff introduced by a post detection filter,
additional noise caused by the rf amplifiers, a mixed noise effect caused by
the nonlinearity of the Josephson junction together with rf noise in the tank
circuit, and the limited number of the frequency counts.In addition, the
determination of the shunt resistor may cause a systematic error.In this work
the influence of the post detection filter and the additive noise on the
frequency variance is analyzed and the analytic models for the dc impedance
and the noise performances of the R SQUID are derived.All our theoretical
models are nowadays experimentally verified; some of the experiments are
reported in this work.The analytic models are used to estimate the total
inaccuracy of the noise thermometer and to find the optimal choice of the
device parameters.The work reveals that the ultimate accuracy of the
temperature determination is proportional to the total measurement time and
the pump frequency and inversely proportional to the noise temperature of the
preamplifier.This work shows that the R SQUID is complex gauge to maintain a
cryogenic temperature scale.However, the careful choice of the device
parameter and the point of operation, the use of the low noise cooled
preamplifier, and the operation at high pump frequencies, enable very accurate
determination of the temperature of the bath in which the R SQUID is
immersed.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Award date  2 Jun 1989 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513834352 
Publication status  Published  1989 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 thermometry
 Josephson junction
 cryogenics
 thermometers
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Cite this
Seppä, H. (1989). Analysis of an RSQUID noise thermometer: Dissertation. VTT Technical Research Centre of Finland.