Diether Blechschmidt

Monte Carlo study of light transmission through a cylindrical tube

The transmission of light in vacuum through a cylindrical tube with specular walls has been evaluated using the Monte Carlo method. Uniform as well as cosine angular distributions have been assumed as the initial conditions at the entrance aperture; both cases were treated separately for a light cource of uniform density. From the results, which are given as a function of the tubes length-to-diameter ratio L / D and the reflectivity of the inner wall R (0 ≤ R ≤ 0.99), a simple expression has been derived that holds for long tubes L ≥ 4D/ln(1/R) and R ≤ 0.6. The relation T(L,D,R) also yields the molecular transmissivity if specular reflection applies with a sticking coefficient S = 1 − R.

An Ionization Gauge Using a Channel Electron Multiplier for Pressures Below 10−12 Torr

A new ionization gauge of an estimated low pressure limit below 10−15 Torr and of a sensitivity of 2×109  Torr−1 is presented. The ions, which are produced in an ionizer of conventional design, are extracted through a shield aperture and collected by the funnel-type cathode of a channel electron multiplier. Since the high gain of this multiplier allows the gauge to be operated with an emission current of only several nanoamperes, practically no heat is produced in the gauge. The gauge is mounted on a 412-in. flange and has approximately the size of a normal Bayard-Alpert gauge. A general expression for the low pressure limit of hot filament ionization gauges is given. The results as obtained from this expression for gauges of similar geometry are discussed together with the low pressure limit as found for the new gauge.

In situ conditioning for proton storage ring vacuum systems

Average pressure and vacuum‐stability limit as expected in the presence of a proton beam were measured after in situ treatments such as bakeout under various conditions, argon glow‐discharge cleaning and sputter deposition of titanium. Measurements were carried out for test pipes made of stainless steel (untreated, electropolished, or cooled to 77 K), pure titanium and aluminum alloy. The measurement method used to obtain the vacuum‐stability limit in the laboratory and in a prototype system is described. The results can be applied also to other systems of different geometry by use of scaling laws. In situ conditioning generally has a stronger influence on vacuum performance than a particular choice of material. Bakeout gives low average pressures and rather good vacuum stability. Glow discharges also increase the vacuum stability but have only a small effect on the static pressure. Coating the beam‐pipe wall with titanium by in situ sputtering provides large linear pumping, thus a lower pressure and an e...

Studies of 400 GeV superconducting proton storage rings

A study has been made of the feasibility of building Large Storage Rings (LSR) at CERN using superconducting dipoles and quadrupoles with the 400 GeV proton synchrotron, SPS, serving as injector. Proton-proton collisions at centre-of-mass energies of up to 800 GeV can be obtained in six interaction regions. Two of these provide luminosities exceeding 1033 cm−2 s−1 and would be dedicated to large-transverse-momentum physics. The other four p-p intersections offer much experimental flexibility at somewhat lower luminosity. Provision is made to add an electron storage ring of 20–25 GeV to obtain e-p collisions at up to 200 GeV centre-of-mass energy with a luminosity of 1032 cm−2 s−1 in each of two special e-p interaction regions. Antiproton-proton collisions could be obtained by a minor rearrangement of some elements in two of the interaction regions.