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 [1–5]. 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 [1–4]. The short pulse length (<50？μsec.) enables us to disregard interaction with the walls of the vacuum system or residual gas. In fact only interactions within a radius of 20？mm 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 [7–9], Piezo driver [10, 11], or electromagnetic [12–17]). 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, 22–24] as originally developed for the earlier low-intensity continuous beams cannot be copied for high
References
[1]
R. C. Campargue, Atomic and Molecular Beams: The State of the Art 2000, Springer, Berlin, Germany, 2001.
[2]
G. Scoles, Atomic and Molecular Beam Methods, Oxford University Press, Oxford, UK, 1989-1992.
[3]
H. Pauly, Atom, Molecule, and Cluster Beams I, Springer, Berlin, Germany, 2000.
[4]
H. Haberland, Clusters of Atoms and Molecules, Springer, Berlin, Germany, 1994.
[5]
R. Campargue, A. Lebehot, and J. C. Lemonnier, in Rarefied Gas Dynamics, pp. 1033–1045, 1977.
[6]
A. Amirav, U. Even, and J. Jortner, “Absorption spectroscopy of ultracold large molecules in planar supersonic expansions,” Chemical Physics Letters, vol. 83, no. 1, pp. 1–4, 1981.
[7]
W. R. Gentry and C. F. Giese, “Ten‐microsecond pulsed molecular beam source and a fast ionization detector,” Review of Scientific Instruments, vol. 49, p. 595, 1978.
[8]
B. Yan, P. F. H. Claus, B. G. M. van Oorschot et al., “A new high intensity and short-pulse molecular beam valve,” Review of Scientific Instruments, vol. 84, no. 2, Article ID 023102, 2013.
[9]
M. D. Barry, N. P. Johnson, and P. A. Gorry, “A fast (30μs) pulsed supersonic nozzle beam source: application to the photodissociation of CS2 at 193？nm,” Journal of Physics E: Scientific Instruments, vol. 19, no. 10, pp. 815–819, 1986.
[10]
D. Irimia, D. Dobrikov, R. Kortekaas et al., “A short pulse (7？μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams,” Review of Scientific Instruments, vol. 80, no. 11, Article ID 113303, 2009.
[11]
D. L. Proctor, D. R. Albert, and H. F. Davis, “Improved piezoelectric actuators for use in high-speed pulsed valves,” Review of Scientific Instruments, vol. 81, Article ID 023106, 2010.
[12]
M. R. Adriaens, W. Allison, and B. Feuerbacher, “A pulsed molecular beam source,” Journal of Physics E: Scientific Instruments, vol. 14, no. 12, article no. 006, pp. 1375–1377, 1981.
[13]
D. Bahat, O. Cheshnovsky, U. Even, N. Lavie, and Y. Magen, “Generation and detection of intense cluster beams,” Journal of Physical Chemistry, vol. 91, no. 10, pp. 2460–2462, 1987.
[14]
D. Pentlehner, R. Riechers, B. Dick et al., “Rapidly pulsed helium droplet source,” Review of Scientific Instruments, vol. 80, no. 4, Article ID 043302, 2009.
[15]
E. Hendell and U. Even, “Cluster-surface interaction at high kinetic energy. I. Electron emission,” The Journal of Chemical Physics, vol. 103, no. 20, pp. 9045–9052, 1995.
[16]
O. F. Hagena, “Pulsed valve for supersonic nozzle experiments at cryogenic temperatures,” Review of Scientific Instruments, vol. 62, pp. 2038–2039, 1991.
[17]
C. E. Otis and P. M. Johnson, “A simple pulsed valve for use in supersonic nozzle experiments,” Review of Scientific Instruments, vol. 51, p. 1128, 1980.
[18]
M. Hillenkamp, S. Keinan, and U. Even, “Condensation limited cooling in supersonic expansions,” Journal of Chemical Physics, vol. 118, no. 19, pp. 8699–8705, 2003.
[19]
U. Even, J. Jortner, D. Noy, N. Lavie, and C. Cossart-Magos, “Cooling of large molecules below 1 K and He clusters formation,” Journal of Chemical Physics, vol. 112, no. 18, pp. 8068–8071, 2000.
[20]
W. Christen, “Stationary flow conditions in pulsed supersonic beams,” The Journal of Chemical Physics, vol. 139, Article ID 154202, 2013.
[21]
G. A. Bird, Molecular Gas Dynamics and the Direct Simulation of Gas Flows, Oxford University Press, Oxford, UK, 1994.
[22]
W. R. Gentry and C. F. Giese, “High-precision skimmers for supersonic molecular beams,” Review of Scientific Instruments, vol. 46, no. 1, p. 104, 1975.
[23]
G. A. Bird, “Transition regime behavior of supersonic beam skimmers,” Physics of Fluids, vol. 19, no. 10, pp. 1486–1491, 1976.
[24]
J. Braun, P. K. Day, J. P. Toennies, G. Witte, and E. Neher, “Micrometer-sized nozzles and skimmers for the production of supersonic He atom beams,” Review of Scientific Instruments, vol. 68, no. 8, pp. 3001–3009, 1997.
[25]
G. Bird, http://www.gab.com.au/.
[26]
K. J. Daun, G. J. Smallwood, and F. Liu, “Molecular dynamics simulations of translational thermal accommodation coefficients for time-resolved LII,” Applied Physics B, vol. 94, no. 1, pp. 39–49, 2009.
[27]
W. F. N. Santos, “Gas-surface interaction effect on round leading edge aerothermodynamics,” Brazilian Journal of Physics, vol. 37, no. 2, pp. 337–348, 2007.
[28]
J. F. Padilla and I. D. Boyd, “Assessment of gas-surface interaction models for computation of rarefied hypersonic flow,” Journal of Thermophysics and Heat Transfer, vol. 23, no. 1, pp. 96–105, 2009.
[29]
D. J. Rader, W. M. Trott, J. R. Torczynski, J. N. Casta？eda, and T. W. Grasser, Sandia National Laboratories SAND2005-6084, 2005, http://prod.sandia.gov/techlib/access-control.cgi/2005/056084.pdf.
[30]
H. Ashkenas and S. F. Sherman, Proceedings of the 4th International Symposium on Rarefied Gas Dynamics: Experimental Methods in Rarefied Gas Dynamics, Academic Press, New York, NY, USA, 1966.
[31]
R. Campargue, “Characteristics of supersonic beams applicable in collision or semi-collision experiments,” Journal de Chimie Physique et de Physico-Chimie Biologique, vol. 77, no. 3, p. R15, 1980.
[32]
R. Campargue, “Progress in overexpanded supersonic jets and skimmed molecular beams in free-jet zones of silence,” The Journal of Physical Chemistry, vol. 88, no. 20, pp. 4466–4414, 1984.
[33]
S. Semushin and V. Malka, “High density gas jet nozzle design for laser target production,” Review of Scientific Instruments, vol. 72, no. 7, pp. 2961–2965, 2001.
[34]
H. V. Tafreshi, G. Benedek, P. Piseri, S. Vinati, E. Barborini, and P. Milani, “A simple nozzle configuration for the production of low divergence supersonic cluster beam by aerodynamic focusing,” Aerosol Science and Technology, vol. 36, no. 5, pp. 593–606, 2002.
[35]
J. P. Toennies and K. Winkelman, “Theoretical studies of highly expanded free jets: Influence of quantum effects and a realistic intermolecular potential,” The Journal of Chemical Physics, vol. 66, no. 9, p. 3965, 1977.
[36]
J. T. McDaniels, R. E. Continetti, and D. R. Miller, “The effect of nozzle geometry on cluster formation in molecular beam sources,” in Proceedings of the 23rd international Symposium on Rarefied Gas Dynamics, A. D. Ketsdever, Ed., American Institute of Physics, 2003.
[37]
K. Luria, N. Lavie, and U. Even, “Dielectric barrier discharge source for supersonic beams,” Review of Scientific Instruments, vol. 80, Article ID 104102, 2009.
[38]
E. Narevicius, C. G. Parthey, A. Libson et al., “An atomic coilgun: Using pulsed magnetic fields to slow a supersonic beam,” New Journal of Physics, vol. 9, article 358, 2007.
[39]
E. Narevicius, A. Libson, M. F. Riedel et al., “Coherent slowing of a supersonic beam with an atomic paddle,” Physical Review Letters, vol. 98, no. 10, Article ID 103201, 2007.
[40]
K. Luria, W. Christen, and U. Even, “Generation and propagation of intense supersonic beams,” Journal of Physical Chemistry A, vol. 115, no. 25, pp. 7362–7367, 2011.
[41]
W. Christen, “Stationary flow conditions in pulsed supersonic beams,” The Journal of Chemical Physics, vol. 139, no. 15, Article ID 154202, 2013.
[42]
U. Even, I. Al-Hroub, and J. Jortner, “Small he clusters with aromatic molecules,” Journal of Chemical Physics, vol. 115, no. 5, pp. 2069–2073, 2001.
[43]
H. Stapelfeldt, “Laser aligned molecules: applications in physics and chemistry,” Physica Scripta, vol. T110, p. 132, 2004.
[44]
H. Stapelfeldt and T. Seideman, “Colloquium: Aligning molecules with strong laser pulses,” Reviews of Modern Physics, vol. 75, no. 2, pp. 543–557, 2003.
[45]
I. Nevo, L. Holmegaard, J. H. Nielsen et al., “Laser-induced 3D alignment and orientation of quantum state-selected molecules,” Physical Chemistry Chemical Physics, vol. 11, no. 42, pp. 9912–9918, 2009.
[46]
N. F. Ramsey, Molecular Beams, Oxford University Press, Oxford, UK, 1956.
[47]
A. B. Bailey, R. Dawbarn, and M. R. Busby, “Effects of skimmer and endwall temperature of condensed molecular beams,” AIAA Journal, vol. 14, no. 1, pp. 91–92, 1976.
[48]
D. C. Jordan, R. Barling, and R. B. Doak, “Refractory graphite skimmers for supersonic free-jet, supersonic arc-jet, and plasma discharge applications,” Review of Scientific Instruments, vol. 70, no. 3, pp. 1640–1648, 1999.
