Wall conditioning techniques based on radio frequency (RF) discharges in fusion devices with permanent magnetic field were developed a few years ago. The first experiments of RF plasma discharges in the ion cyclotron frequency range called ion cyclotron conditioning were performed in Tore Supra and Textor and later also in HT-7 and W7-AS. A high conditioning efficiency in terms of hydrogen removal and surface cleaning has been demonstrated. The other alternative, RF conditioning discharges in the electron cyclotron range of frequencies and called electron cyclotron conditioning, has also been studied in the recent past. Besides surface hydrogen removal and surface cleaning, RF discharges have also been applied to thin film deposition. We report in this paper the main results obtained with several fusion devices on RF conditioning discharges and present conclusions for future devices such as ITER.

https://iopscience.iop.org/article/10.1088/0741-3335/47/2/001/pdf

Review of radio frequency conditioning discharges with magnetic fields in superconducting fusion reactors

Using the Tore Supra infrared thermography diagnostics, a new real time feedback control has been successfully implemented to maximize additional RF power while preventing plasma facing components (PFCs) from overheating and damage. As a first step, a thermography feedback control has been used to detect and extinguish electric arcs on lower hybrid current drive (LHCD) launchers. Secondly, heating sources on PFCs have been identified highlighting the role of the power from each ion cyclotron resonance heating (ICRH) antenna and LHCD launcher and the interactions between them. A new feedback control algorithm was developed to control the additional power. The real time feedback control of PFC temperatures which makes part of an integrated feedback controller, is a reliable tool routinely used as a basic protection system. Furthermore, it has proven its capability to operate in parallel with other control schemes such as the current profile control.

RF heating optimization on Tore Supra using feedback control of infrared measurements

An overview of the preliminary design of the ITER plasma control system (PCS) is described here, which focusses on the needs for 1st plasma and early plasma operation in hydrogen/helium (H/He) up to a plasma current of 15 MA with moderate auxiliary heating power in low confinement mode (L-mode). Candidate control schemes for basic magnetic control, including divertor operation and kinetic control of the electron density with gas puffing and pellet injection, were developed. Commissioning of the auxiliary heating systems is included as well as support functions for stray field topology and real-time plasma boundary reconstruction. Initial exception handling schemes for faults of essential plant systems and for disruption protection were developed. The PCS architecture was also developed to be capable of handling basic control for early commissioning and the advanced control functions that will be needed for future high performance operation. A plasma control simulator is also being developed to test and validate control schemes. To handle the complexity of the ITER PCS, a systems engineering approach has been adopted with the development of a plasma control database to keep track of all control requirements.

https://iopscience.iop.org/article/10.1088/1741-4326/aa8177/pdf

Overview of the preliminary design of the ITER plasma control system

The preliminary design of the ITER plasma control system

Progress in real-time feedback control systems in RFX

The real time plasma control system of Tore Supra

From the conceptual design to the first simulation of the new WEST plasma control system

The conditioning procedures in Tore Supra after CIEL implementation

The timing system is an essential part of the tokamak Tore Supra. It provides the synchronisation of all of the triggers necessary for a plasma discharge. Operational since 1988, it has been used for 26000 pulses of Tore Supra without significant change or upgrade. However in 1999 it has been undergoing a staged modernisation. Hence this new timing system with a designed flexible and open-ended architecture, together with a more user-friendly man-machine interface, is ready to accept new concepts which will be necessary for the control of long discharges (up to 1000 s).

Upgrade of the timing system for Tore Supra long pulses

The new WEST configuration of Tore Supra facility leads to control challenges and the need to handle events of a modern diverted and metallic machine (vertical stabilization, impurity control, …). To address them, a new Plasma Control System (PCS) has been built based on the ASDEX upgrade (AUG) real-time framework called DCS (Discharge Control System). This contribution summarizes the work done during the 5 years of the project from the definition of the PCS concepts to its operation during the WEST campaigns. The integration into the Tore Supra control infrastructure is detailed as well as the different real-time control processes. The efficiency and the versatility of the PCS are illustrated by several examples of plasma operation.

F. Saint Laurent

Papers

The real time plasma control system of Tore Supra

From the conceptual design to the first simulation of the new WEST plasma control system

The conditioning procedures in Tore Supra after CIEL implementation

Upgrade of the timing system for Tore Supra long pulses

The WEST plasma control system: Integration, commissioning and operation on first experimental campaigns