Effect of Synchrotron Radiation in the Proposed 4-GeV Argonne Microtron
Synchrotron radiation in the sector magnets of the 4 GeV microtron designed at the Argonne National Laboratory produces a small but noticeable distortion of the closed orbits of the system and a very significant growth of the horizontal and longitudinal phase space emittances. Because of the small apertures in the three 25 meter linacs, it is important that the expected growth of the beam be calculated as accurately as possible. The dynamical problem has been solved using a computer program which follows the motions of individual electrons in the four dimensional horizontal and longitudinal phase space as they are accelerated in the system. In this paper the authors call attention to the fact that there are 3 long 28 m linac sections separated by sector magnets from 3 dispersion sections where the orbits for different energies are separated. The interaction of the linac rf systems with the synchrotron energy loss in the sector magnets produces different orbit effects in the downstream and upstream linac sector magnets. The average synchrotron radiation energy loss per sector magnet is given.
Transverse Beam Containment in the ANL 4-GeV Microtron
Optical systems have been designed to contain the electrons during the acceleration from 0.185-4.0 GeV. These systems are located in the dispersive straight sectionX and maintain a matched dispersion free beam with ß* = 15.0 m in the linac centers, and transverse beam waists in the centers of the dispersive straight sections. A thin-lens code has been developed to design the multi-energy system. Three versions of the focussing systems have been evolved: (i) Two quadrupole triplets for E ¿ 1.62 GeV; (ii) A single triplet for 1.655 ¿ E 2.215 GeV, and (iii) A pentaquad system for E ¿ 2.250 GeV. For case (i) we step the exit edges for the 60° bending magnets so as to simulate a zero degree edge - this reduces vertical defocussing effects to an acceptable value. At the higher energies the exit edge angles are -60°. The entrance angles are 15° on the linac sides of the dipoles. Energy behavior of the Twiss parameters and quadrupole strengths are presented.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)