Handbook of Accelerator Physics and Engineering, 2nd edition, by Alexander Wu Chao, Karl Hubert Mes, Maury Tigner and Frank Zimmermann

ing R and the proton radius of the hydrogen atom, and the measurements of the fundamental constants alpha and c. After the publication of this Handbook, further progress was made in optical clock technology. Using of Al and Hg optical lattice clocks, an atomic clock with a 10 instability was demonstrated by Ludlow’s group at NIST front range, and published in Nature Vol. 341, No. 6151 pp. 1215–1218. The opportunities made available by this have been described in Nature Vol. 341, No. 6151 pp. 1185–1186 by Helen S. Margolis under the heading: ‘Opportunities Knock with a More Stable Optical Clock’.