Gyro-electron ghost images due to microchannel plate operation in transverse magnetic fields

A multi-anode microchannel plate (MCP) detector was operated in a transverse magnetic field. When a collimated ion beam of approx.4-mm diameter impinged on one area of the plate, ghost images were observed elsewhere on the plate at anodes up to several centimeters from the beam spot. This effect is due to secondary electrons which are emitted from the interstitial surfaces around the MCP pores and returned to the surface of the plate under the influence of E-tilde X B-tilde fields, where E-tilde is the electric field perpendicular to the plate due to the MCP bias potential and B-tilde is the externally applied transverse magnetic field. A regenerative process is observed in which the secondary electrons traverse the surface of the plate in the E-tilde X B-tilde direction by successive gyro-orbit steps. A method for suppressing the ghost images is discussed

Technique for measuring the fast /sub 3/He/sup + +/ distribution during /sub 3/He/sup + +/ minority ICRF heating

A technique for measuring the fast /sub 3/He/sup + +/ distribution during /sub 3/He/sup + +/ minority ICRF heating is discussed. The technique involves the use of 10 to 100 keV neutral helium beams to neutralize the fast /sub 3/He/sup + +/ ions by double charge exchange (/sub 3/He/sup + +/ + /sub 4/He/sup 0/ ..-->.. /sub 3/He/sup 0/ + /sub 4/He/sup + +/). The neutralized fast /sub 3/He atoms then escape from the plasma and are detected by conventional neutral particle analyzing apparatus. By the use of such a technique, the effectiveness of the coupling of the ion cyclotron waves to the /sub 3/He/sup + +/ minority could be measured

Performance study of the TFTR diagnostic neutral beam for active charge exchange measurements

A neutral beam source will be incorporated in the Tokamak Fusion Test Reactor (TFTR) charge exchange diagnostic to provide a time modulated, spatially localized enhancement of the charge exchange efflux. Two autonomous Charge Exchange Neutral Analyzer (CENA) systems are being designed for the TFTR. One system measures the plasma ion temperature along twelve vertical line-of-sight chords spaced approximately equidistantly across the torus minor diameter. The other system is dedicated primarily to measurement of ion phenomena associated with neutral beam injection heating and has a fan-like field of view along eight sight-lines in the equitorial plane. The neutral beam is steerable in order to access the viewing field of both CENA systems, though in general not simultaneously. The performance of the diagnostic neutral beam is evaluated to determine the optimal beam specifications for active charge exchange measurements. Using the optimal beam design parameters, the efficacy of the neutral doping is examined for both CENA systems over the envisioned range of the TFTR plasma density and temperature

Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments

An overview of the developments post-circa 1980's of the instrumentation and application of charge exchange neutral particle diagnostics on Magnetic Fusion Energy experiments is presented

Neutral beam interlock system on TFTR using infrared pyrometry

Although the region of the TFTR vacuum vessel wall which is susceptible to damage by neutral beam strike is armored with a mosaic of TiC-clad POCO graphite titles, at power deposition levels above 2.5 kW/cm/sup 2/ the armor surface temperature exceeds 1200/sup 0/C within 250 ms and itself becomes susceptible to damage. In order to protect the wall armor, a neutral beam interlock system based on infrared pyrometry measurement of the armor surface temperature was installed on TFTR. For each beamline, a three-fiber-optic telescope views three areas of approx.30 cm diameter centered on the armor hot spots for the three ion sources. Each signal is fiber-optic coupled to a remote 900 nm pyrometer which feeds analog signals to the neutral beam interrupt circuits. The pyrometer interlock system is designed to interrupt each of the twelve ion sources independently within 10 ms of the temperature exceeding a threshold settable in the range of 500 to 2300/sup 0/C. A description of the pyrometer interlock system and its performance will be presented