Ordinary-mode fundamental electron cyclotron resonance absorption and emission in the Princeton Large Torus Page: 8 of 15
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7
magnetic field BfR^). An absolute calibration of the receiver
was achieved with the aid of a noise tube. For the data used in
this figure, n (0) = 4 * 1013 cm'3 and Te(0) = 1.4 keV. Thus,
according to Eg. (1), r C0) - 3.2. Hence:, only in the neighborhood
of the plasma center is the emitting cyclotron layer optically
thick since ne anc Tg are decreasing with r. This indicates that
reflections from the vacuum vessel leading to multiple transits
of the emitted radiation are enhancing the emission to near the
blackbody level for r > 2C cm. If b is the wall reflection
coefficient, then the effective collected power becomes
Pe^ - (1-e T)/(l-be T). Even though the measured ng and Tg
at r = 30 cm give t = 0.42, the measured power will be -90% of the
blackbody level for b f 0.95. Thus, a reflectivity of this level is
indicated for the stainless steel vessel of PLT.
Taking advantage of this large reflectivity, we measure
f (r,t) profiles from ordinary cyclotron emission detection
over the outer half of the plasma column by repetitively sweeping
the local oscillator frequency from 60 to 90 GHz every 10 msec.
In Fig. 3 a three-dimensional computer plot of the time evolution
of the electron temperature profile, T (r,t), measured for a
typically ohmically heated PLT discharge is given.8 Such mea-
surements significantly facilitate monitoring T (r,t) during a
single discharge and are particularly valuable in evaluating
effects of auxiliary heating of plasmas.
In conclusions, we have presented the first experimental
verification of the predictions of relativistic hot plasma
theory (of Refs. 5 and 6) for the propagation of the ordinary
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Efthimion, P. C.; Arunasalam, V. & Hosea, J. C. Ordinary-mode fundamental electron cyclotron resonance absorption and emission in the Princeton Large Torus, report, November 1, 1979; New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc1097251/m1/8/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.