Jack Pouchet has been promoted to director of corporate communications for Racal Instruments group, working with companies located in the UK, France, Germany, Italy, India, Korea, Hong Kong and the US. He remains marketing director for Racal Instruments Inc.    . . .    MKS Instruments announced that its president and COO, Peter Younger, will resign to pursue other opportunities. MKS chairman and CEO John Bertucci will also assume the position of president. MKS said it's moving to a flatter management structure to increase flexibility and responsiveness to customer needs.