Observation of a Mg xi forbidden satellite line in an optically thickX-pinch plasma

An observation of a forbidden transition in Mg xi at 8.50 {} is reported. A Mg wire X pinch generated a {}1-keV, {~}10²³-cm^-3 Mg plasma in which the intensity of an allowed transition was reduced by a factor of about 100 by self-absorption, permitting the forbidden transition to be observed.