L. Johnson

Neutron monitor using microfission chambers for the International Thermonuclear Experimental Reactor

We are designing microfission chambers, which are pencil size gas counters with fissile material inside, to be installed in the vacuum vessel as neutron flux monitors for the International Thermonuclear Experimental Reactor (ITER). We computed the neutron and gamma flux around the shielding blanket by a two-dimensional neutron calculation, in order to find suitable locations for microfission chambers. We found that the 238U microfission chambers are not suitable because the detection efficiency will increase up to 50% during the ITER lifetime by breeding 239U. We propose to install 235U microfission chambers on the front side of the back plate in the gap between adjacent blanket modules and behind the blankets at ten poloidal locations. One chamber will be installed in the divertor cassette, just under the dome. Employing both the pulse counting mode and Campbelling mode in the electronics, we can accomplish the ITER requirement of 107 dynamic range, with 1 ms temporal resolution, and eliminate the effect...

Irradiation Tests on ITER Diagnostic Components

Radiation effects on key components of diagnostic systems expected to be subjected to high neutron and gamma fluxes and fluences are being examined in irradiation tests to evaluate and establish an ITER-relevant database to support the design. A comprehensive irradiation database has been accumulated and permits conclusions to be drawn on the application of these components in ITER. The design studies on prototypical assemblies of diagnostic components are continuing based on the irradiation data bases, neutronics calculations for evaluating irradiation environment of diagnostic components and required specification of diagnostic systems. These studies will aid the recognition of detailed requirements of diagnostic systems leading to more specific irradiation tests on diagnostic components.

ITER physics program and implications for plasma measurements

Key objectives of the first ten years of ITER operation are the investigation of the physics of burning plasmas and the demonstration of long-pulse ignited plasma technologies. These include studies of plasma confinement and stability, divertor operation, disruption mitigation and control, noninductive current drive, and steady state operation under conditions when the plasma is heated predominantly by alpha particles. The ITER operational plan envisages two and a half years for commissioning and initial operation with hydrogen plasmas at up to 100 MW of auxiliary heating power when initial tests of divertor operation and evaluation of disruption effects will be made. In order to meet the operational and programmatic goals, it will be necessary to make a wide range of plasma measurements. In this article the preliminary operational plan and physics program are presented and the implications for plasma measurements are outlined.

Operation and control of ITER plasmas

Features incorporated in the design of the International Thermonuclear Experimental Reactor (ITER) tokamak and its ancillary and plasma diagnostic systems that facilitate operation and control of ignited and/or high?Q DT plasmas are presented. Control methods based upon straightforward extrapolation of techniques employed in the present generation of tokamaks are found to be adequate and effective for ITER plasma control with fusion powers of up to 1.5?GW and burn durations of ? 1000?s. Examples of simulations of key plasma control functions, including plasma magnetic configuration control and fusion burn (power) control, are given. The prospects for the creation and control of steady state plasmas sustained by non-inductive current drive and bootstrap current are also discussed.

ITER physics program and implications for plasma measurements (abstract)

Key objectives of the first ten years of ITER operation are the investigation of the physics of burning plasmas and the demonstration of long-pulse ignited plasma technologies. These include studies of plasma confinement and stability, divertor operation, disruption mitigation and control, noninductive current drive, and steady state operation under conditions when the plasma is heated predominantly by alpha particles. The ITER operational plan envisages two and a half years for commissioning and initial operation with hydrogen plasmas at up to 100 MW of auxiliary heating power when initial tests of divertor operation and evaluation of disruption effects will be made. In order to meet the operational and programmatic goals, it will be necessary to make a wide range of plasma measurements. In this article the preliminary operational plan and physics program are presented and the implications for plasma measurements are outlined.

A neutron camera for ITER (invited)

Based upon JET experience, the measurement of multichannel collimated neutron fluxes and of the neutron spectrum gives time-dependent information on spatial profiles of neutron emission and alpha–particle birth, the total neutron emission (fuel burn-up rate), plasma position, effects of plasma instabilities, triton burn-up, ion temperature, and fuel densities. The design for a horizontally viewing neutron camera for ITER is based upon the prototype and upgrade versions of the JET neutron emission profile monitor and the JET spectrometers. It is proposed that vertically stacked modules are installed in the ITER biological shield in a fan shaped viewing geometry, aimed at a focal point located at the slit opening of a preshield designed to reduce the streaming neutron flux. Each module contains a pair of sight lines with adjustable collimation, allowing for multiple detector neutron flux monitoring and neutron spectroscopy over a wide operating range. The modular system allows flexibility in detector choice...

A Neutron Camera for ITER: Conceptual Design

This paper presents the outline design of an ITER neutron camera, to provide control and plasma diagnostic information based on the deduced neutron emission profile. Information can be obtained on total neutron emission (fuel burn-up rate), alpha-particle birth profile, plasma position and the time dependent effects of plasma instabilities such as sawteeth. The design presented here concerns only a horizontally, radially, viewing (Horizontal) camera. A vertically viewing (Vertical) camera is also necessary for most requirements, and is assumed to have similar design principles and capabilities. This is primarily an engineering design paper, because the physics of neutron production and detection are well known.