1. magnetic confinement - ENEA - Fusione

1. MAGNETIC CONFINEMENT
35
[1.43] M. Talvard, G.
Giruzzi and W. D. Liu,
Proc. 19th EPS Conf. on
Contr. Fusion and Plasma
Physics (Innsbruck 1992)
Vol. 16C, 1103 (1992)
[1.44] S. Preische, P. C.
Efthimion and S. M. Kaye,
Rev. Sci. Instrum. 68,
409 (1997)
1.2 FTU Facilities
Oblique ECE measurements were performed for the first time at FTU. At present, this
is the only oblique ECE diagnostic installed in a fusion device, and the potential of
such a diagnostic appears to be still largely untapped [1.43-1.44]. High-field
operations on FTU and access to enhanced confinement regimes [1.42] allow this
diagnostic to have an excellent resolution in configuration and velocity space. This
capability can be exploited to determine the bulk form of the electron distribution
and the transition from the bulk to the tail of the distribution. This would allow a
detailed study of the kinetic processes involved in heating and current drive, in a
variety of transport mechanisms for which at present direct experimental evidence is
lacking.
New data acquisition system for the plasma-density laser interferometer
The two-colour interferometer was developed to get reliable density measurements
during pellet injection experiments. To calculate the density, the signal from the CO 2
detectors, the HgCdTe room-temperature photo resistor and HeNe photodiode has
to be acquired, amplified with the automatic gain control and then compared with
the signal taken from the Bragg cell driver.
A new acquisition system based on a PC with a 5-MHz ADC was installed to increase
the sampling rate of the old system. The system also processes, stores and sends the
signal data and density to the main pulse file (based on the UNIX system) so that
they are available to users through the usual display program (SHOX) (fig. 1.29).
Fig. 1.29 - Schematic of
the new PC-based
acquisition system.
The ADC VME module of
the old system was used
to acquire the phase
DAS
comparator outputs. It did
not have enough memory
to acquire the whole
discharge at the correct
sampling rate so, during
pellet injection or fast
machine vibrations, some
fringe jumps were
observed. The problem
was solved by acquiring
CH2
data with a National
Lab View CH1
Instruments NI6110E data
acquisition card that has
high performance, reliable
data acquisition capabilities and high speed. The new program is written in LabView
graphic language.
It is possible to acquire four analog inputs at 5 MS/s, with a 12-bit resolution. Data
are stored on the local hard disk and automatically processed to separate the density
and vibration contributions to the interferometer phase. The data are then
transferred via Ethernet to the main archive under “AFS” using a set of routines
(FTUWIN DLL) for the standard formatting of FTU archive files, via the LabView
program.
Turbulence measurements with correlation reflectometry
Turbulence physics is essential for understanding transport in tokamaks. It is
important to scale turbulence characteristics with the main discharge parameters; the
extension of turbulence measurements to high toroidal magnetic fields and densities
can be done in FTU by means of the recently installed correlation reflectometer. The