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Proceedings Paper

Anti-reflection treatments for jet millimetre wave diagnostic windows
Author(s): T. P. Hughes
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Paper Abstract

This paper discusses low-power windows for millimetre-wave diagnostics on the JET torus. When tritium is used as afusion fuel in JET repairs will be difficult on the radioactive machine and additional precautions must be taken to avoidvacuum leaks. Double, interpumped vacuum windows will be necessary. Window design is further restricted by therequirement that the bond between the window itself and its supporting ferrule must withstand repeated cycling to aworking temperature of about 250° C. The most satisfactory arrangement for low power millimetre waves uses z-cutcrystal quartz windows, gold diffusion bonded to stainless steel ferrules, as manufactured by the Special TechniquesGroup of A E A Technology. Where possible wedged windows are avoided for ease of alignment.Even with a single window multiple reflections cause the transmission to be significantly frequency dependent. Figure1(a) shows the calculated intensity transmission spectrum for a 6 mm quartz window, assuming n = 2.1 over thefrequency range. With double windows the additional reflections in the multiple etalons cause the transmission to bestrongly frequency dependent and create severe problems for the diagnostic systems. Temperature effects are alsoimportant. Figure 1(b) shows the intensity transmission spectrum for two 6 mm windows separated by 5 mm.

Paper Details

Date Published: 30 August 1993
PDF: 2 pages
Proc. SPIE 2104, 18th International Conference on Infrared and Millimeter Waves, 21042I (30 August 1993); doi: 10.1117/12.2298522
Show Author Affiliations
T. P. Hughes, JET Joint Undertaking (United Kingdom)

Published in SPIE Proceedings Vol. 2104:
18th International Conference on Infrared and Millimeter Waves
James R. Birch; Terence J. Parker, Editor(s)

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