55678390
TESTS AND DEVELOPMENT OF DUOPLASMATRON AND MULTI-APERTURE HEAVY ION SOURCES FOR AN RF LINAC
The goal of the program of ion source development for an rf linac has been to produce currents of up to 100 mA of the heavier gaseous ions such as argon and xenon, of good emittance (.02 ..pi.. cm mr, normalized) and charge state 1/sup +/. Existing facilities and hardware utilized included the 470 kV Bevatron injector, the 750 kV injector for the 50 MeV ESCAR linac, the 80 kV Bevatron test stand, a 20 kV LLL test stand and existing duoplasmatron and CTR sources. A summary of test results is shown.
122734759
Measurement and Optimization of the Emittance of a 300-ns 250-A 3.4-MeV Electron Beam
Author(s): Allison, R.W.; Beal, J.W.; Everett, W.L.; Guggemos, J.R.; Lamb, W.A.S.; Richter, R.M.; Sherwood, W.A.; Spoerlein, R.L.; Tanabe, J.; Wright, R.E.; Zajec, E.
121259350
Pulsed Heavy Ion Source for the Bevatron
A Phillips ion gauge source (Fig. 1) of the type used by the heavy ion accelerator in Berkeley has been adapted for use at the Bevatron. The objective was to achieve high charge state ions (4+, 5+) of carbon and nitrogen. All source parameters are pulsed. The ion source performance regarding linac acceleration is discussed. The light ion (deuteron, alpha) performance of the PIG source and duoplasmatron is compared.
40263937
Heavy Ion Source Development at the Bevatron
The Bevatron 20 MeV duoplasmatron source is currently being modified with the goal of producing 1 mA of 20Ne3+. Initital tests at 420 KeV show a total beam of 20 mA of which 400 ¿A is 20Ne3+. The quantity of beam in various charge states is determined with a pulse field magnetic spectrometer. Titanium sublimation and cryogenic pumping of the PIG source in the High Voltage Terminal and its resultant effects on the acceleration of carbon and nitrogen will be discussed.
16346923
(Non-)BPS bound states and D-brane instantons
We study non-perturbative effects in four-dimensional = 1 supersymmetric orientifold compactifications due to D-brane instantons which are not invariant under the orientifold projection. We show that they can yield superpotential contributions via a multi-instanton process at threshold. Some constituents of this configuration form bound states away from the wall of marginal stability which can decay in other regions of moduli space. A microscopic analysis reveals how contributions to the superpotential are possible when new BPS states compensate for their decay. We study this concretely for D2-brane instantons along decaying special Lagrangians in Type IIA and for D5-branes instantons carrying holomorphic bundles in Type I theory.
19809846
Development of Fast High-Resolution Muon Drift-Tube Detectors for High Counting Rates
Abstract Pressurized drift-tube chambers are efficient detectors for high-precision tracking over large areas. The Monitored Drift-Tube (MDT) chambers of the muon spectrometer of the ATLAS detector at the Large Hadron Collider (LHC) reach a spatial resolution of 35 μ m and almost 100% tracking efficiency with 6 layers of 30 mm diameter drift tubes operated with an Ar:CO 2 (93:7) gas mixture at 3 bar and a gas gain of 20 000. The ATLAS MDT chambers are designed to cope with background counting rates due to neutrons and γ rays of up to about 300 kHz per tube which will be exceeded for LHC luminosities larger than the design value of 10 34  cm −1  s −1 . Decreasing the drift-tube diameter to 15 mm while keeping the other parameters, including the gas gain, unchanged reduces the maximum drift time from about 700 to 200 ns and the drift-tube occupancy by a factor of 7. New drift-tube chambers for the endcap regions of the ATLAS muon spectrometer have been designed. A prototype chamber consisting of 12 times 8 layers of 15 mm diameter drift tubes of 1 m length has been constructed with a sense wire positioning accuracy of 20 μ m . The 15 mm diameter drift-tubes have been tested with cosmic rays in the Gamma Irradiation Facility at CERN at γ counting rates of up to 1.85 MHz.
118634238
Development of muon drift-tube detectors for high-luminosity upgrades of the Large Hadron Collider
Abstract The muon detectors of the experiments at the Large Hadron Collider (LHC) have to cope with unprecedentedly high neutron and gamma ray background rates. In the forward regions of the muon spectrometer of the ATLAS detector, for instance, counting rates of 1.7 kHz / cm 2 are reached at the LHC design luminosity. For high-luminosity upgrades of the LHC, up to 10 times higher background rates are expected which require replacement of the muon chambers in the critical detector regions. Tests at the CERN Gamma Irradiation Facility showed that drift-tube detectors with 15 mm diameter aluminum tubes operated with Ar : CO 2 ( 93 : 7 ) gas at 3 bar and a maximum drift time of about 200 ns provide efficient and high-resolution muon tracking up to the highest expected rates. For 15 mm tube diameter, space charge effects deteriorating the spatial resolution at high rates are strongly suppressed. The sense wires have to be positioned in the chamber with an accuracy of better than 50 μ m in order to achieve the desired spatial resolution of a chamber of 50 μ m up to the highest rates. We report about the design, construction and test of prototype detectors which fulfill these requirements.
120584442
Modelling of the space-to-drift-time relationship of the ATLAS monitored drift-tube chambers in the presence of magnetic fields
Abstract The ATLAS muon spectrometer uses tracking chambers consisting of up to 5 m long drift tubes filled with Ar : CO 2 ( 93 : 7 ) at 3 bar. The chambers are run in a average toroidal magnetic field of 0.4 T created by 8 air core coils. They provide a track-point accuracy of 40 μ m if the space-to-drift-time relationship r ( t ) is known with 20 μ m accuracy. The magnetic field B influences the electron drift inside the tubes: the maximum drift time t max = 700 ns increases by ≈ 70 ns / T 2 B 2 . B varies by up to ± 0.4 T along the tubes of the chambers mounted near the magnet coils which translates into a variation of t max of up to 45 ns. The dependence of r ( t ) on B must be taken into account. Test-beam measurements show that the electron drift in case of B ≠ 0 can be modelled with the required accuracy by a Langevin equation with a friction term which is slightly non-linear in the drift velocity.
110855495
Performance of novel silicon n-in-p planar pixel sensors
Abstract The performance of novel n-in-p planar pixel detectors designed for future upgrades of the ATLAS Pixel system is presented. The n-in-p silicon sensors technology is a promising candidate for the pixel upgrade thanks to its radiation hardness and cost effectiveness that allow for enlarging the area instrumented with pixel detectors. The n-in-p modules presented here are composed of pixel sensors produced by CiS connected by bump-bonding to the ATLAS read-out chip FE-I3. The characterization of these devices has been performed before and after irradiation up to a fluence of 5×10 15 1 MeV n eq cm −2 . Charge collection measurements carried out with radioactive sources have proven the functioning of this technology up to these particle fluences. First results from beam test data with a 120 GeV/ c pion beam at the CERN-SPS are also discussed, demonstrating a high tracking efficiency of (98.6±0.3)% and a high collected charge of about 10 ke for a device irradiated at the maximum fluence and biased at 1 kV.