Abstracts

P/1460. Studies of High Current Gas Discharges at High Rates of Build-up. S. C. CURRAN, K. W. ALLEN, H. A. B. B~DIN, R. A. FITCH, N. J. PEACOCK and J. A. REYNOLDS (United Kingdom).

1. Phenomena associated with high current gas discharges in straight tubes will be reported. Condenser banks up to 150 PF and voltages in the range 10 to 30 kV have been used in circuits specially devised to give the maximum rate of rise of current. 2. The condensers, which are connected in parallel, are each provided with spark gaps, all of which may be discharged within ~10-8 set by means of a special triggering circuit. This parallel connexion of condensers and spark gaps results in very low inductance, and rates of rise of current in excess of lOI2 amp/set. 3. Neutron emission from discharges in deu- terium have been observed for currents in the range 105 to 106 amperes. Data showing the dependence of neutron production on the circuit inductance, voltage, current and gas pressure will be presented. 4. The quenching effect of impurities has been investieated. and it has been found that neutrons are stic observed when as much as 5 per cent of nitrogen is added to the deuterium. In this respect, the results appear to differ from those of other observers who have studied similar discharges. 5. The effect of axial magnetic fields on the discharge characteristics will also be reported.

P/1519. The Design and Performance of Zeta. P. C. THONEMANN, J. BLEARS, R. CARRUTHERS, E. R. HARTILL, J. T. D. MITCHELL and R. S. PEASE (United Kingdom).

1. Zeta is a zero energy thermonuclear assembly in which a toroidal electrodeless d.c. pulsed discharge is used to produce a high temperature plasma isolated from any material walls by the self-magnetic constriction of the current channel. The prime requirement of Zeta was that it should produce a detectable thermonuclear reaction rate in deuterium, using a method capable of extension to a power-producing system. Zeta was designed to achieve this by means of 5 milli- second current pulses of 100 k amp and more, which were estimated to yield temperatures exceeding 106 “K with densities of about 1014 particles per c.c.

The three main components of Zeta to be described are :

(a) A 1,600 b&F, 25 kV condenser bank, which discharges into the primary winding of a transformer through a mechanical switch;

(b) The transformer, which is iron-cored and capable of handling 7 volt-seconds per turn at each pulse;

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The aluminium torus, in which the low pressure gas acts as the transformer secondary. The torus has a bore of one metre and a mean circumference bf 12 metres, and is constructed with a liner system to avoid power arcing. Windings on the torus are used to generate a mag- netic field B, of up to 1,000 gauss parallel to the gas current.

The performance of Zeta has been studied as a function of condenser voltage, gas type, gas pressure, and of B,. Electrical characteristics have been measured and analysed; and the hot plasma has been studied with sweep pictures, ;nagnetic probes, spectrographic iec‘hniques, microwaves. Langmuir vrobes. and with the X-ray and ieutroi radia<on generated. Typical results obtained will be presented. 2. When the axial magnetic field B, is zero, the discharge is observed to be unstable and to have a predominantly resistive electrical impedance. 3. When B, exceeds about 100 gauss, the imped- ance is inductive, and direct observation with streak pictures and magnetic and Langmuir probes show that the discharge is stable and isolated from the torus wall for a large proportion -_ _ of the 5 millisecond current pulse. 4. The neutron vield is found to maximize at

J

about 160 gauss, and with one-eighth micron pressure the neutron yield, first detectable at about 90 k amp, increases with current up to several million neutrons per pulse at the maxi- mum current achieved, about 200 k amp. 5. There is considerable evidence on the nature of the reactions; in particular Doppler widths of spectral lines of impurities indicate temperatures of several million degrees centigrade. These temperatures together with estimated densities indicate that the reactions could well be of thermonuclear origin. Studies of the spatial, temporal and energy distribution of the neutrons will also be reported.

P/1520. Diagnostic Techniques in Controlled Thermonuclear Research. G. N. HARDING, A. N. DELLIS, A. GIBSON, B. JONES, D. J. LEES, R. W. P. MCWHIRTER, S. A. RAMSDEN and S. WARD (United Kingdom).

1. In experimental studies directed towards the production of controlled thermonuclear reac- tions by the gas discharge method, a variety of techniques must be developed for obtaining essential information on the physical conditions of the plasma during the discharge. This paper describes techniques at A.E.R.E., Harwell for determining the temperature, pressure, and other parameters of the large ring-discharge apparatus Zeta.

Spectroscopy 2. Photographic and photoelectric spectroscopy in the visible. ultra-violet and vacuum ultra-violet