G. Bronner

TPX power systems design overview

The power systems for the Tokamak Physics Experiment (TPX) supply the toroidal field (TF), poloidal field (PF), field error correction (FEC), and fast vertical position control (FVPC) coil systems, the neutral beam (NB), ion cyclotron (IC), lower hybrid (LH) and electron cyclotron (EC) heating and current drive systems, and all balance of plant loads. Existing equipment from the Tokamak Fusion Test Reactor (TFTR), including the motor-generator (MG) sets and the rectifiers, can be adapted for the supply of the TPX PF systems. A new TF power supply is required. A new substation is required for the heating and current drive systems (NB, IC, LH, and EC). The baseline TPX load can be taken directly from the grid without special provision, whereas if all upgrade options are undertaken, a modest amount of reactive compensation will be required. This paper describes the conceptual design of the power systems, with emphasis on the AC, TF, and PF systems, and the quench protection of the superconducting coils.

Quench protection circuits for superconducting magnets

In developing a scheme for the quench protection of the toroidal field (TF) and poloidal field (PF) superconducting magnets of the Tokamak Physics Experiment (TPX), an extensive review was performed of the design options and their performance characteristics. The general results and conclusions of these studies are reported herein. For tokamak magnets which have low enthalpy compared to their stored energy, quench protection requires the discharge of the stored energy at location(s) external to the magnets, typically in discharge resistors. Such discharge requires the interruption of large DC currents and the insertion of resistors using suitable DC circuit breaking methods. Since protection of the magnets is a crucial function, the system must be ultra-reliable, and new techniques are necessary.

TPX poloidal field (PF) power systems simulation

This paper describes the modeling and simulation of the PF power system for the Tokamak Physics Experiment (TPX), which is required to supply pulsed DC current to the poloidal field (PF) superconducting coil system. An analytical model was developed to simulate the dynamics of the PF power system for any PF current scenario and thereby provide the basis for selection of PF circuit topology, in support of the major design goal of optimizing the use of the existing Tokamak Fusion Test Reactor (TFTR) facilities at the Princeton Plasma Physics Lab (PPPL).

Model for TFTR motor-generator (MG)

This study is aimed at predicting steady-state and dynamic responses after a sudden load shed for the TFTR motor-generator (MG) system. In the paper, a discussion on the methods, assumptions, and validation of the MG computer model is presented. The model includes the salient pole features (using two-axis theory) and effects of saturation. The steady-state model describing MG performance under normal conditions ignores the changes in flux linkage of windings other than the field winding. This simplification reduces the complexity of the model, yet it still describes the regular pulses of the TFTR generator satisfactorily. Only the field relation is described by the differential equation, and the rest are algebraic. The dynamic response of load shed-a special case in dynamic study-can be of importance in predicting the behavior of the MG system associated with the severe overvoltage problem. More elaborate synchronous generator models are required in this case. Not only the field winding voltage relation, but also the damper winding voltage relation must be described by differential equations. The complete solution can be obtained by means of the Laplace transform. Validation of the MG computer model has been performed by comparison with actual MG load scenarios recorded on electronic digitizers for TFTR shots. The simulation results are comparable to the recorded MG performance data.

The BPX electrical power system

The design of the BPX (Burning Plasma Experiment) power system has evolved over a period of several years and has included studies of several alternative approaches. The reapplication of the existing TFTR (Tokamak Fusion Test Reactor) power and energy facilities has been basic to all approaches. The dynamics of the power requirements for the BPX poloidal coil system suggest that the TFTR facilities would be most suitably applied to that requirement. The chief concern related to that match has been the adequacy of the 4.5-GJ energy rating of the TFTR flywheel units. The toroidal field power requirements are the greatest of the BPX subsystems and, fortunately, are sufficiently free of dynamics to allow the consideration of different approaches to providing pulse power and energy. Additional design challenges were presented by the multiplicity of plasma control scenarios incorporated in the BPX physics planning and the power response demanded of the plasma position control system. The plasma control scenarios include upper, lower, and symmetrical poloidal diverter operation as well as limiter operation. The plasma position control coils (internal to the TF bore) have a collective peak power demand of 640 MVA, require four quadrant drive, and require 1 ms voltage response.<<ETX>>

BPX PF coil power system configuration studies

The Burning Plasma Experiment (BPX) poloidal field (PF) system is required to support a maximum plasma current of 10.6 MA while providing plasma position and shape control. The plasma shaping control scenarios of double null, asymmetrical single null, and limiter operations must be accommodated. The coil power is to be supplied by existing power supplies which are currently in use on the Tokamak Fusion Test Reactor (TFTR). The power supplies derive their power from two existing variable frequency TFTR motor generator sets. An additional requirement of the system is the ability to accommodate an upgrade of the maximum plasma current pulse from 10.6 MA to 11.8 MA with minimum impact on tokamak operation. The authors describe and analyze the various PF coil power system requirements, the switching circuits used to accomplish the required coil scenarios, and the optimal allocation of the TFTR power supplies to meet the base requirements and anticipated upgrade requirements. The results from the simulation studies which verify the operation of the PF power system design are also presented.<<ETX>>

TFTR-MG uprate, analysis and performance

The energy requirement for TFTR operation at 5.2 Tesla is 4.5 GJ, 950 MVA provided by two 13.8 kV flywheel generators. To achieve tokamak fields beyond 5.2 Tesla (up to 6.0 Tesla), the MG system must be uprated to 1300 MVA, 15.0 kV and store 4.8 GJ of energy. The uprate is attainable by exploiting existing excess capacity and accepting reduced life. Considerations for the MG uprate include the number, level, duration, repetition rate of uprated pulses, and the expected life reduction. The mechanical degradation of the equipment due to speed overcurrent and over voltage was analyzed, as well as the deterioration of insulation due to thermal and mechanical stresses. This paper describes the requirements, and analysis and includes data of MG performance above rating.

TPX power supply design and performance

TPX will utilize a combination of new and existing AC/DC converter equipment, the latter consisting of the inventory of equipment available at the PPPL site when TPX succeeds TFTR. To make best use of existing facilities, the TFTR (a.k.a. Transrex) converters are applied to the TPX duty when appropriate, but in general the pulse rated, high voltage converters do not match the long pulse, low voltage demand of the load during the plasma burn phase. In the Poloidal Field system the Transrex converters are suitable for the dynamic operation associated with plasma ramp up and ramp down, but are not well suited to the quasi-steady conditions during plasma burn. In this case a parallel combination of the Transrex converters with new high current, low voltage power supplies is proposed. In the Toroidal Field system a new dual voltage converter using AC bus transfer is proposed. In the Fast Plasma Position Control system an anti-parallel 12-pulse arrangement of Transrex converters is proposed. This paper presents a description of the design of the converter systems along with preliminary results of simulation studies of the AC/DC converter performance in terms of short circuit, voltage drop, and control.

PBX-M ohmic heating power supply upgrade

The ohmic heating (OH) power supply performs two functions in the PBX-M experiment. The OH system provides the voltage necessary for the initial discharge breakdown, and is the primary method of plasma current drive. In 1987 the PBX (Princeton Beta Experiment) device was upgraded to PBX-M (Princeton Beta Experiment-Modified). At that time, the OH power supply was reconfigured and portions of the control system were replaced. The upgrade provides control over the amount and duration of the voltage applied for initial discharge breakdown, more precise control of the overall current waveshape, and increases the total volt-seconds available for plasma current drive to 3 V-s. Details of the upgrade and operating experience from the previous run periods are presented along with discussions of the three leading candidate schemes for a proposed 1989-90 upgrade.<<ETX>>

Preliminary power supply design for the TF coil system of CIT

The initial operation plan of the Compact Ignition Tokamak (CIT) is described. The plan provides for a toroidal field (TF) of 8 T and a flat-top duration of 5 s. Ultimately, operation will be extended beyond 8 T. The power supply to be used for the initial phase of operation has been modeled using the parameters of the thyristor rectifier power supplies which are now in service in the Tokamak Fusion Test Reactor (TFTR). The preliminary design for the 8-T power supply and results of simulation studies are presented. Issues concerning transient behavior and fault modes are discussed.<<ETX>>