Speaker
Mr
Rafael Henriques
(IPFN-IST)
Description
ISTTOK is an iron core tokamak (R = 46 cm, a = 8.5 cm, BT = 0.5 T) which operates regularly in
alternate current (AC) mode, extending the plasma duration up to 1 second by inverting the plasma
current sequentially. However, during the current reversal process, the signal integrity of the
magnetic diagnostics (Mirnov coils) is degraded due to low plasma current leading to wrong plasma
position measurements. One alternative solution is the use of Langmuir Probes (LP) to measure the
floating potential and inferring indirectly the plasma position. Nevertheless, in some cases, the LP
diagnostics have limitations when measuring the plasma position leading to wrong measurements
that eventually lead to a plasma disruption. Also, during edge biasing experiments, the floating
potential is strongly affected and the LPs are not reliable to measure the plasma position.
The Heavy Ion Beam Diagnostic (HIBD) has been upgraded to measure fast neσ(Te) profiles to
improve the signal to noise ratio in 12 sample volumes vertically distributed along the plasma minor
radius (-0.7a < r < 0.7a). The neσ(Te) quantity (product of the density times the effective ionization
cross-section for the Xe+ to Xe2+ ionization) can be regarded as a proxy for the plasma pressure which
is a good indicator of the plasma position. Off-line HIBD data processing for the determination of the
plasma vertical position has demonstrated promising results. The fast neσ(Te) profiles can be
acquired up to 150 kHz which is more than 10 times faster than the ISTTOK real-time control cycle
(100 μs). These characteristics bring up the HIBD as a promising diagnostic for the plasma vertical
position measurements and feedback control using magnetic actuators.
This work presents the integration of the HIBD data for real-time plasma position
measurement and control in a closed loop using a combined fast digital processing implemented in a
FPGA (Field Programmable Gate Array) and MARTe (Multi-threaded Application Real-Time executor)
software framework. The overall implementation and integration will be described and the first
experimental results presented together with a comparison with the existing control schemes.
Author
Mr
Rafael Henriques
(IPFN-IST)
Co-authors
Mr
André Duarte
(IPFN-IST)
Dr
António Batista
(IPFN-IST)
Prof.
Artur Malaquias
(IPFN-IST)
Prof.
Bernardo Carvalho
(IPFN-IST)
Dr
Carlos Silva
(IPFN-IST)
Prof.
Horácio Fernandes
(IPFN-IST)
Dr
Ivo Carvalho
(IPFN-IST)
