%0 Journal Article
%T Pulsed Supersonic Beams from High Pressure Source: Simulation Results and Experimental Measurements
%A U. Even
%J Advances in Chemistry
%D 2014
%R 10.1155/2014/636042
%X Pulsed beams, originating from a high pressure, fast acting valve equipped with a shaped nozzle, can now be generated at high repetition rates and with moderate vacuum pumping speeds. The high intensity beams are discussed, together with the skimmer requirements that must be met in order to propagate the skimmed beams in a high-vacuum environment without significant disruption of the beam or substantial increases in beam temperature. 1. Introduction Supersonic beams have proven to be an essential source of information on molecular properties and collision processes. The early stage of their development relied on the production of continuous beams and was limited by available pumping capacity. Beam propagation was limited by collisions with background gases, usually to a distance of only a few mm before the beam was dispersed and attenuated. Much effort was required to ensure that the jet was interrogated before it was degraded, and building such a supersonic beam instrument became an art [1每5]. The introduction of pulsed supersonic beams solved some of the problems of CW (continuous wave) machines and is widely spread today, covering too many research areas to enumerate concisely. Since its early years it was evident that using pulsed beams enables the generation of more intense and colder beams at reduced pumping capacity [1每4]. The short pulse length (<50ˋ米sec.) enables us to disregard interaction with the walls of the vacuum system or residual gas. In fact only interactions within a radius of 20ˋmm from the beam are relevant to these time scales, and the pumps have all the time between pulses to reduce the background pressure to negligible values. Many designs of pulsed beam sources are based on various actuating mechanisms (mechanical [6], Lorenz force [7每9], Piezo driver [10, 11], or electromagnetic [12每17]). Several years ago we introduced a shaped nozzle, which combined with a high pressure fast-acting pulsed valve enabled us to reach high beam intensities and lower jet temperatures than what was previously available [18, 19]. The development of this valve and its operating characteristics are described here, along with the changes in skimmer design that are required in order to make use of the higher on-axis beam intensities. A comprehensive review of our pulsed valve was recently published [20]. Simulations of gas flow [21] as well as measurements of actual beam parameters are presented. Previous designs of molecular beam skimmers [5, 20, 22每24] as originally developed for the earlier low-intensity continuous beams cannot be copied for high
%U http://www.hindawi.com/journals/ac/2014/636042/