Plasma formation in the intense pulsed neutron source (IPNS) rapid cycling synchrotron (RCS)

Abstract

Summary form only given. The intense pulsed neutron source (IPNS) rapid cycling synchrotron (RCS) accelerates a single bunch of 3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> protons from 50 to 450 MeV, 30 times per second. The acceleration period from injection to extraction is approximately 14 ms. Peak beam current near extraction is 10 Amps. Typically, the average background gas density in the synchrotron vacuum vessel is two orders of magnitude greater than the average beam density. The cross section for ionization in the background gas (mainly nitrogen and water vapor), especially near injection energy, is large enough such that the DC beam neutralization time, tau <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> =(n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> langsigmavrang) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is approximately 0.5 ms. Some positive ions are ejected from the beam path by the positive space charge of the bunched beam; however, simulation shows that ionization of the background gas leads to a buildup of ions in the beam path. Many electrons are present to neutralize the positive background space charge leading to plasma formation. Confinement time is enhanced in the combined-function dipole magnets in the synchrotron. The magnet region occupies just over one-half of the beam path within the RCS. The consequence of plasma formation on beam properties such as focusing and damping is explored