|
 At
our March 2002
Newsletter we reported the shipment of unique
52-85GHz Heterodyne Sweeping ECE
Radiometer for Physics Lab of Instituto de Fisica da USP (San
Paulo, Brazil).
This equipment was shipped as the result of
our continued cooperation with this
Brazilian customer since
1998,
when ELVA's Multi-channel Interferometer was initially
installed at the Tokamak site.
Fig.1. ELVA representatives Dr. Leonid Bogdanov
and Mr. Alex Sergeev (in the centre) with their colleagues
from Physics Lab staff at
TCABR Tokamak site.
The plasma
temperature measurement theory is based on a fact that the
intensity of the ECE (Electron Cyclotron Emission) is
proportional to the electron plasma temperature in situations
when the plasma may be considered as the black body for its
own cyclotron radiation. So the magnetized plasma electrons
emit electromagnetic energy at electron cyclotron frequencies
with intensity proportional to the plasma temperature.
As there is
toroidal magnetic field gradient in the tokamak plasma,
electrons at different points along the major radius of the
torus radiate at different frequencies. So the radial electron
temperature distribution can be measured by scanning the
frequency, received by the radiometer.
 During
summer 2002 time, our engineers visited customer site, taking
part in radiometer tuning and a series of plasma experiments.
These were measurements at 52GHz to 75GHz on second harmonic
of electron-cyclotron frequency. ELVA’s ECE Radiometer was
used to register an evolution of frequency
content emission at a mode of plasma heating by Alfen waves.
The measured dependence of electron temperature vs time for
various frequencies is shown in Fig.2.
Fig.2.
Electron temperature vs time, 1– 52,2 GHz, 2– 58,2 GHz, 3–
63,6 GHz, 4 – 70,0 GHz, 5 – 80,0 GHz.
To get an
experimental data on electron temperature profile line
dynamics, the scientists use a dependence of
electron-cyclotron frequency from a radius to torus axis at
its equatorial plane. The measured dependence of electron
temperature Te vs torus radius R for various points
of time is shown in Fig.3.
Fig.3. Electron temperature vs torus radius. For t0=6ms, t1– t0+4ms,
2– t0+14ms, 3– t0+24ms, 4 – t0+34ms, 5 – t0+94ms. Where t0 –
time zero of discharge.
The
experimental diagrams confirm radiometer efficiency at real
experiment condition of TCABR Tokamak. The principal
distinctive features of 52-85GHz Radiometer are highly
sensitive receiver and wideband BWO sweep generator, plus low
cost of the equipment.
"Your visit to
our laboratory was important. We are operating the machine in various
regimes and everything seems to me working very well", - praised
Prof. Dr.Ruy Pepe da Silva from Plasma Physics Laboratory.
|
