The Atom: discovery

Many independent discoveries led to the discovery of the atom. Einstein’s explanation of Brownian motion provided proof that atoms exist. J.J. Thomson identified the cathode rays produced in Crookes‘ tube as electrons. Rutherford discovered that most atom mass is concentrated in a small central region. Bohr combined this with Planck’s quantized energy results from blackbody radiation studies to create the first physical model of the atom. Schrodinger, Heisenberg, and Born mathematically model the behavior of orbiting electrons, Heisenberg discovers uncertainty, Pauli defines exclusion, Dirac predicts spin, Chadwick discovers neutrons, and Fermi discovers weak interaction. Finally, Hahn, Meitner, and Strassmann discover nuclear fission, Yukawa discovers the strong interaction, the Stanford Linear Accelerator discovers the quark, and physicists capture the strong, weak, and electromagnetic fundamental interactions in the Standard Model.

Sidney David Drell (September 13, 1926–December 21, 2016): A Biographical Memoir

Sidney David Drell, professor emeritus at Stanford University and senior fellow at the Hoover Institution, died shortly after his 90th birthday in Palo Alto, California. In a career spanning nearly 70 years, Sid—as he was universally known—achieved prominence as a theoretical physicist, public servant, and humanitarian. Sid contributed incisively to our understanding of the electromagnetic properties of matter. He created the theory group at the Stanford Linear Accelerator Center (SLAC) and led it through the most creative period in elementary particle physics. The Drell-Yan mechanism is the process through which many particles of the Standard Model, including the famous Higgs boson, were discovered. Sid advised Presidents and Cabinet Members on matters ranging from nuclear weapons to intelligence, speaking truth to power but with keen insight for offering politically effective advice. His special friendships with Wolfgang (Pief) Panofsky, Andrei Sakharov, and George Shultz highlighted his work at the interface between science and human affairs. He advocated widely for the intellectual freedom of scientists and in his later years campaigned tirelessly to rid the world of nuclear weapons.

Mechanical requirement and influence on the design and manufacturing of beam position monitor of Taiwan photon source

The beam position monitors (BPMs) with submicron-level resolution act as the major eyes of storage ring in detecting the position of electron beams and are used for feedback system to guide the beam orbit to the desired track. Compared to major improvements on backend electronics, the physical devices generate and transmit signals had little improvement due to the lack of control on manufacturing processes including all mechanical tolerance requirements. The design started with ANSYS to simulate mechanical deformation. Due to the small size (submillimetre) and complicated assembly of feedthrough structure, it is difficult to achieve 1 % tolerance (submicron) in all aspects including machining and brazing. The smallest tolerance for machining is 5 µ and the overall tolerance will be 30 µm. The influence of the tolerance on mechanical will be shown on time-domain reflectometry measurement. The resulted heat-related issue will also be discussed and addressed since the problem happened at SLAC (private communication with Albert Sheng at Stanford Linear Accelerator Center) and DIAMOND (presented at the RF Button Heating Mini-Workshop at EPAC 2008). Manufacturing steps will be described. The consequence of mismatch on manufacturing will be discussed. All related measurement and simulation data are presented in this paper.