R. Hatcher

National spherical torus experiment (NSTX) Center Stack Upgrade

The purpose of the NSTX Center Stack Upgrade project is to expand the NSTX operational space and thereby the physics basis for next-step ST facilities. The plasma aspect ratio (ratio of plasma major to minor radius) of the upgrade is increased to 1.5 from the original value of 1.26, which increases the cross sectional area of the center stack by a factor of ∼ 3 and makes possible higher levels of performance and pulse duration.

Computing hardware for the PBX-M Plasma Control System

This paper describes architectural and performance aspects of the digital computer control system used for the PBX-M Plasma Control System (PPCS). The goal of the PPCS is to achieve integrated and improved plasma control. Integration consists of replacing control functions presently served by several analog systems with a realtime digital control system. The inherently dynamic control capabilities of a high performance digital system foster exploration of advanced plasma control concepts to serve future tokamaks. The PPCS runs concurrent multiple feedback control loops, with input, processing, and output times ranging from 100 /spl mu/S to 10 milliseconds. The initial control loop for plasma shaping was expected to complete in approximately 300 /spl mu/S. The VME-based realtime computing hardware is described. In addition, measurements of the systems performance such as data i/o rates and computing performance are shown. The information presented herein covers the results of the computer systems design, configuration, and laboratory testing. Actual plasma control has not been accomplished to date.

Performance of the plasma shaping control system on the PBX-M tokamak

The plasma-shaping control system for the PBX-M (Princeton Beta Experiment-Modified) tokamak generates highly indented plasmas inside a closely fitting conducting shell. The feedback system has been linearized about a predetermined plasma shape. Three modes of a singular value decomposition (determined from the design shape) are used to control the plasma position and shape. Plasma shape is determined using flux-difference measurements around the circumference of the plasma. An analog computer reduces the magnetic measurements to current corrections in seven sets of symmetric external shaping coils. Though limited to a single design shape, this system offers sufficient flexibility to control the plasma shape throughout the discharge.<<ETX>>

NSTX-U Digital Coil Protection System Software Detailed Design

The national spherical torus experiment (NSTX) currently uses a collection of analog signal processing solutions for coil protection. Part of the NSTX upgrade (NSTX-U) entails replacing these analog systems with a software solution running on a conventional computing platform. The new digital coil protection system (DCPS) will replace the old systems entirely, while also providing an extensible framework that allows adding new functionality as desired. The development of the DCPS was a multidiscipline engineering effort. The fact that long-trusted yet presently inadequate protection mechanisms were being replaced with a first-of-a-kind system at NSTX-U has led to a carefully crafted, full-featured software design. Real-time concurrent RedHawk Linux provides the deterministic environment in which the software runs, and the software architecture follows a unified modeling language design with industry standard patterns.

Power Supply for NSTX Resistive Wall Mode Coils

The National Spherical Torus Experiment (NSTX) has been designed and installed in the existing facilities at Princeton Plasma Physics Laboratory (PPPL). Most of the hardware, plant facilities, auxiliary sub-systems, and power systems originally used for the Tokamak Fusion Test Reactor (TFTR) have been used with suitable modifications to reflect NSTX needs. Until 2004, the NSTX power system was feeding twelve (12) circuits in the machine. In 2004, resistive wall mode (RWM) coils were installed in the machine to suppress resistive wall modes and to correct error fields. There are six of these coils installed around the machine on the mid-plane. Since these coils need fast and accurate controls, a switching power amplifier (SPA) has been procured, installed and commissioned along with other circuit components. One of the existing thyristor rectifiers is used as the DC source to the SPA. The controls for the RWM have been integrated into the overall computer control of the DC power systems for NSTX. This paper describes the RWM power supply for NSTX

Overview of the PBX-M plasma control system upgrade

The PBX-M group is developing a control system to integrate multiple independently-operating and mutually-interacting systems used for plasma control. Central to this effort has been the procurement of a SKYbolt 1 Shamrock AP computing platform as the Central Control Unit (CCU). The engineering and experimental effort for this program will occur in two phases. In Phase I of the program a minimum hardware configuration will be used to duplicate the functionality of the existing PBX-M plasma shape, current, and radial and vertical position control systems on the CCU. Phase II will expand the hardware configuration increasing the number of slow (10 kHz) A/D data acquisition channels and adding 32 fast (250 kHz) A/D channels. The expandable hardware system will facilitate integration of and improvements to the individual Phase I control systems and allow us to pursue topics in advanced discharge control (e.g., MHD control, disruption avoidance, and profile control and modification). In this paper we present an overview of the PBX-M plasma control system program. We discuss the properties of the Phase I and II processes and how they influenced our choices for the systems hardware and impact the software design. Also important are the increased general computing capabilities afforded by our choice of hardware and the impact it have on our between shot analysis capabilities. We also describe the Phase I control processes and present some details of their implementation.

Vertical position feedback system for PBX-M

The PBX-M (Princeton Beta Experiment-Modified) tokamak produces highly shaped discharges that can be vertically unstable. The PBX-M vertical position control-system hardware is described, results from plasma operation are shown, and results of analyses of the PBX-M device with respect to vertical displacements of the plasma are presented. A rigid displacement model indicates that terms proportional to plasma position and velocity are required in the control function to effectively damp oscillatory motion of the discharge. Simulations from the Princeton Tokamak Simulation Code (TSC) have confirmed the severity of these instabilities. Sawtooth analysis of soft X-ray data is used to independently assess the effectiveness of the system in operation.<<ETX>>

Hardwired control system changes for NSTX DC power feeds

The National Spherical Torus Experiment (NSTX) has been designed and installed in the existing facilities at Princeton Plasma Physics Laboratory (PPPL). Most of the hardware, plant facilities, auxiliary sub-systems, and power systems originally used for the Tokamak Fusion Test Reactor (TFTR) have been used with suitable modifications to reflect NSTX needs. The original TFTR Hardwired Control System (HCS) with electromechanical relays was used for NSTX DC Power loop control and protection during NSTX operations. As part of the NSTX Upgrade, the HCS is being changed to a PLC-based system with the same control logic. This paper gives a description of the changeover to the new PLC-based system.

NSTX-U Digital Coil Protection System software design

The National Spherical Torus Experiment (NSTX) currently uses a collection of analog signal processing solutions for coil protection. Part of the NSTX Upgrade (NSTX-U) entails replacing these analog systems with a software solution running on a conventional computing platform. The new Digital Coil Protection System (DCPS) will replace the old systems entirely, while also providing an extensible framework that allows adding new functionality as desired. The development of the DCPS was a multi-discipline engineering effort. The fact that long-trusted yet presently-inadequate protection mechanisms were being replaced with a first-of-a-kind system at NSTX-U has led to a carefully crafted, full-featured software design. Real-time Concurrent RedHawk Linux provides the deterministic environment in which the software runs, and the software architecture follows a UML design with industry standard patterns.

Digital coil protection system I/O and data subsystem for NSTX-U

The Digital Coil Protection System (DCPS) for NSTX-U is a system that evaluates operational parameters in real time and prevents physical damage to the reactor and its coils. The system is built upon commercial products: a realtime Linux operating system and analog and digital I/O boards. Signals from various digital and analog sources are captured, conditioned, validated and stored before being passed to a system of parallel algorithms for processing. Incremental data must be recorded during processing for postshot analysis. Additionally, algorithm parameter data must be stored in a fashion that prevents both inadvertent and malicious tampering which could result in exposing the machine to the risk of severe damage. This paper will discuss the object oriented design and implementation used to address these challenges. Details of how real time Linux tools were used to ensure predictable and stable operation will also be discussed.