SE339253B - - Google Patents

Abstract

1,199,184. Electrical isolator tubes. HUGHES AIRCRAFT CO. 20 Oct., 1967 [19 Dec., 1966], No. 47884/67. Heading F2P. An electrical isolator 2 for a gas feed pipe 8 comprises a series of spaced-apart sections of electrical insulating material 10, made e.g. of glass, which are connected together by conductive pipe sections 8 and, at each end, to the pipe and uniform electrical resistances, e.g. resistors 6 which are connected across each section 10 to distribute evenly a potential, developed across the pipe from one end to the other, e.g. by the flow of ionized gas therein. The isolator 2 is particularly for use in a pipe 8 leading from a propellent reservoir, containing e.g. mercury, to an electron bombardment ion thrustor the propellent being passed through the pipe 8 as a vapour, or gas. With short sections the probability of voltage breakdown is reduced since the minimum breakdown voltage according to the Paschen curve, Fig. 1 (not shown), is not reached for all required lowpressure flow levels. In a modification, Fig. 3 (not shown), in which the isolator sections are each slightly conductive to provide their own voltage division, a glass envelope (32), located within a heater enclosure (20) to prevent vapour condensation is connected in a feed pipe (22), and accommodates a number of isolator sections (30) which are formed of a glass having slight conductivity, e.g. lead glass, and are separated by perforated stainless steel envelopes containing steel wool (34). The envelopes are adapted to intercept all charged particles so that they cannot spread from one isolator section to another. Continuity strips (36) connect the end envelopes to the respective adjacent portions of the pipe (22). In an alternative arrangement all of the sections 10 are coated with a high-resistance film, the resistors 6 being omitted.