Towards An H−H^{-} RF Source for Future CERN Accelerator Projectss

An increase of beam intensity and brightness is essential for future upgrades of existing CERN proton accelerator facilities. A first step can be an injection of H- ions from a new higher energy H- linear accelerator called Linac4 into the Proton Synchrotron Booster (PSB. A second step could be the complete replacement of the PSB by a highpower linear accelerator, called SPL, injecting directly into the Proton Synchrotron (PS. Both injection scenarios require a high performance, high reliability negative hydrogen ion source. This paper will present the challenging source requirements and the two approaches to fulfil them

Development of Thick-foil and Fine-pitch GEMs with a Laser Etching Technique

We have produced thick-foil and fine-pitch gas electron multipliers (GEMs) using a laser etching technique. To improve production yield we have employed a new material, Liquid Crystal Polymer, instead of polyimide as an insulator layer. The effective gain of the thick-foil GEM with a hole pitch of 140 um, a hole diameter of 70 um, and a thickness of 100 um reached a value of 10^4 at an applied voltage of 720 V. The measured effective gain of the thick-foil and fine-pitch GEM (80 um pitch, 40 um diameter, and 100 um thick) was similar to that of the thick-foil GEM. The gain stability was measured for the thick-foil and fine-pitch GEM, showing no significant increase or decrease as a function of elapsed time from applying the high voltage. The gain stability over 3 h of operation was about 0.5%. Gain mapping across the GEM showed a good uniformity with a standard deviation of about 4%. The distribution of hole diameters across the GEM was homogeneous with a standard deviation of about 3%. There was no clear correlation between the gain and hole diameter maps.Comment: 21 pages, 9 figure

Ion-induced effects in GEM & GEM/MHSP gaseous photomultipliers for the UV and the visible spectral range

We report on the progress in the study of cascaded GEM and GEM/MHSP gas avalanche photomultipliers operating at atmospheric pressure, with CsI and bialkali photocathodes. They have single-photon sensitivity, ns time resolution and good localization properties. We summarize operational aspects and results, with the highlight of a high-gain stable gated operation of a visible-light device. Of particular importance are the results of a recent ion-backflow reduction study in different cascaded multipliers, affecting the detector's stability and the photocathode's liftime. We report on the significant progress in ion-blocking and provide first results on bialkali-photocathode aging under gas multiplication.Comment: 6 pages, 8 figure

The SPL (II) at CERN, a Superconducting 3.5 GeV H- Linac

A revision of the physics needs and recent progress in the technology of superconducting (SC) RF cavities have triggered major changes in the design of a SC H-linac at CERN. With up to 5MW beam power, the SPL can be the proton driver for a next generation ISOL-type radioactive beam facility (âEURISOLâ) and/or supply protons to a neutrino () facility (conventional superbeam + beta-beam or -factory). Furthermore the SPL can replace Linac2 and the PS booster (PSB), improving significantly the beam performance in terms of brightness, intensity, and reliability for the benefit of all proton users at CERN, including LHC and its luminosity upgrade. Compared with the first conceptual design, the beam energy is almost doubled (3.5GeV instead of 2.2 GeV) while the length is reduced by 40%. At a repetition rate of 50 Hz, the linac reuses decommissioned 352.2MHz RF equipment from LEP in the low-energy part. Beyond 90MeV the RF frequency is doubled, and from 180MeV onwards high-gradient SC bulkniobium cavities accelerate the beam to its final energy of 3.5GeV. This paper presents the overall design approach, together with the technical progress since the first conceptual design in 2000

Conceptual design of the SPL II: A high-power superconducting H−H^- linac at CERN

An analysis of the revised physics needs and recent progress in the technology of superconducting RF cavities have led to major changes in the speci cation and in the design for a Superconducting Proton Linac (SPL) at CERN. Compared with the rst conceptual design report (CERN 2000012) the beam energy is almost doubled (3.5 GeV instead of 2.2 GeV), while the length of the linac is reduced by 40% and the repetition rate is reduced to 50 Hz. The basic beam power is at a level of 45MW and the approach chosen offers enough margins for upgrades. With this high beam power, the SPL can be the proton driver for an ISOL-type radioactive ion beam facility of the next generation (`EURISOL'), and for a neutrino facility based on superbeam C beta-beam or on muon decay in a storage ring (`neutrino factory'). The SPL can also replace the Linac2 and PS Booster in the low-energy part of the CERN proton accelerator complex, improving signi cantly the beam performance in terms of brightness and intensity for the bene t of all users including the LHC and its luminosity upgrade. Decommissioned LEP klystrons and RF equipment are used to provide RF power at a frequency of 352.2 MHz in the lowenergy part of the accelerator. Beyond 90 MeV, the RF frequency is doubled to take advantage of more compact normal-conducting accelerating structures up to an energy of 180 MeV. From there, state-ofthe- art, high-gradient, bulk-niobium superconducting cavities accelerate the beam up to its nal energy of 3.5 GeV. The overall design approach is presented, together with the progress that has been achieved since the publication of the rst conceptual design report

Rapid host adaptation by extensive recombination

Experimental investigations into virus recombination can provide valuable insights into the biochemical mechanisms and the evolutionary value of this fundamental biological process. Here, we describe an experimental scheme for studying recombination that should be applicable to any recombinogenic viruses amenable to the production of synthetic infectious genomes. Our approach is based on differences in fitness that generally exist between synthetic chimaeric genomes and the wild-type viruses from which they are constructed. In mixed infections of defective reciprocal chimaeras, selection strongly favours recombinant progeny genomes that recover a portion of wild-type fitness. Characterizing these evolved progeny viruses can highlight both important genetic fitness determinants and the contribution that recombination makes to the evolution of their natural relatives. Moreover, these experiments supply precise information about the frequency and distribution of recombination breakpoints, which can shed light on the mechanistic processes underlying recombination. We demonstrate the value of this approach using the small single-stranded DNA geminivirus, maize streak virus (MSV). Our results show that adaptive recombination in this virus is extremely efficient and can yield complex progeny genomes comprising up to 18 recombination breakpoints. The patterns of recombination that we observe strongly imply that the mechanistic processes underlying rolling circle replication are the prime determinants of recombination breakpoint distributions found in MSV genomes sampled from nature

GEM - a novel gaseous particle detector

The work carried out within the framework of this PHD deals with the construction of gaseous prototype detectors using Gas Electron Multiplier electrodes for the amplification of charges released by ionizing particles.The Gas Electron Multiplier (GEM) is a thin metal-clad polymer foil, etched with a high density of narrow holes, typically 50-100mm-2. On the application of a potential difference between the conductive top and bottom sides each hole acts as independent proportional counter. This new fast device permits to reach large amplification factors at high rates with a strong photon and ion-mediated feedback suppression due to the avalanche confinement in the GEM-holes. Here, in particular studies have been performed, which should prove, that the GEM-technology is applicable for an efficient measurement of single Cherenkov photons. These UV-photons can be detected in different ways. An elegant solution to develop large area RICH-detectors is to evaporate a pad-segmented readout-cathode of a multi-wire proportional chamber with a thin layer of CsI (typically 300nm). This approach has advantages compared to other possibilities of detecting Cherenkov photons (e.g.: photosensitive gases, arrays of PMTs or HPDs).The subject of this thesis was the investigation of GEM-detectors with respect to RICH applications. The work contained the construction process of photon detectors based on the novel GEM-technology by using CsI as a photon converter. These detectors permit to efficiently record and localize single photoelectrons. The first Au-plated GEM, in a cascade of three or four, was coated with a photosensitive layer, to provide efficient and fast single photon detection, with excellent position resolution. General performances of a CsI-coated multi-GEM detector are described as well as the novel readout method, which is achieved by the so called HEXABOARD. This board consists of a matrix of interconnected hexagonal pads that permit an ambiguity-free reconstruction of multi-photon events, which is an essential requirement for RICH applications. Each single channel is connected to charge sensitive preamplifier (HARP-type) and afterwards to the ALTRO FEE, which is based on the ALTRO chip developed for the ALICE experiment. The recorded analog signals are digitized by 10 bit ADC with a 25MHz sampling rate.Die vorliegende Arbeit beschäftigt sich mit der Konstruktion von Gasdetektor-Prototypen, die sogenannte GEM-Elektroden (Gas Elektron Vervielfacher) verwenden, um die von ionisierenden Teilchen im Gas produzierte Ladung zu verstärken und detektierbar zu machen. Eine GEM-Elektrode besteht aus einer zweifach mit Kupfer beschichteten Kaptonfolie, in die kleine Löcher (typischerweise 50-100mm-2 mit einem Durchmesser von 50m) geätzt werden. Diese Löcher wirken bei Anlegen einer Potentialdifferenz (~400V) als voneinander unabhänige Proportionalzähler. Mit Hilfe dieser neuen Verstärkereinheit können Gasverstärkungsfaktoren in der Grössenordung von 106 erreicht werden, wenn man mehrere GEM-Folien in einer Kaskade zusammenfasst.Im speziellen wird in dieser Arbeit erforscht, ob die GEM-Technologie auf RICH (Ring Imaging Cherenkov) Detektoren angewandt werden kann. In derartigen Teilchendetektoren werden Photokathoden verwendet um die von geladenen hochenergetischen Teilchen erzeugten Cherenkov Lichtringe abzubilden. Damit können die Teilchen identifiziert und unterschieden werden.Um die einzelnen UV-Photonen effizient nachweisen zu können gibt es mehrere Möglichkeiten. Die kostenintensivste ist die Photonen mit einer Matrix aus einzelnen Photokathoden (PMTs oder HPDs) zu messen.Photosensitive Gase (TAE, TMAE) mit hoher Quanteneffizienz sind billiger aber umständlich in der Verwendung. Derartige Gase beschränken ausserdem aufgrund der geringeren Driftgeschwindigkeit die Hochratenkapazität der dementsprechenden Photodetektoren.Aufgrunddessen wurde ein photosensitives Material entwickelt, das es erlaubt grossflächige Photokathoden zu bauen - Cäsiumiodid (CsI).Bedampft man die segmentierte Kathode einer Vieldrahtkammer mit CsI, dann hat man eine grossflächige Photokathode zur Verfügung mit der Cherenkov Photonen nachgewiesen und eindeutig unterscheiden werden können (multi-hit capability).In den hier präsentierten Detektor-Prototypen wurde CsI auf den ersten Gold überzogenen GEM einer Kaskade von drei oder vier, aufgedampft. Auf diese Weise erreicht man eine effiziente und schnelle Photon-Detektierung mit einer ausgezeichneten Ortsauflösung. Koppelt man die Verstärkungskaskade an ein neuartiges Ausleseboard, das unter dem Name HEXABOARD bekannt ist, dann ist eine eindeutige Rekonstruktion der Photonentreffer möglich, Das Ausleseboard besteht aus einer Matrix aus hexagonalen Feldern, die abwechselnd mit den Auslesekanälen dreier Projektionen verbunden sind. Dieser Umstand ermöglicht eine eindeutige Rekonstruktion der Photonentreffer.Die hohen erreichbaren Gasverstärkungsfaktoren zusammen mit einer starken Unterdrückung des Photon- und Ionen-Feedbacks machen die GEM-Technologie interessant für RICH-Anwendungen. Ausserdem werden die Probleme der Vieldrahtkammern beseitigt (begrenzte Ortsauflösung, beschränkte Hochratenkapazität).11

„Roll-out“ Systeme und deren Einsatzmöglichkeiten im produktiven Schulumfeld

Das Ziel dieser Diplomarbeit ist es, anhand der Betrachtung von verschiedenen, technisch möglichen Systemen der Bereitstellung und Verteilung auf Arbeitsstationen für Endbenützer, die möglichen Einsparungspotentiale aufzuzeigen. Es wird im speziellen der Vergleich dreier Hersteller untereinander analysiert und die Erkenntnisse diskutiert. Die Entscheidungstheorien geben Auskunft und Begründungen über die bevorzugte Technologie. Diese wird im produktiven Umfeld, unter laufenden Bedingungen, Schritt für Schritt umgesetz

GEM-based photon detector for rich applications

We describe the performance of a photon detector based on the Gas Electron Multiplier (GEM). With a CsI photocathode deposited on the first GEM in a cascade, the device permits to efficiently detect and localize single photoelectrons produced by UV photons between the CsI threshold (~6.2eV) and the quartz window cutoff (~7.5eV). The single-photon position accuracy achieved, ~55m rms, and the excellent multi-photon resolution makes it well suited for Cherenkov Ring Imaging applications

A Radio Frequency Driven H- Source for Linac4.

Future requirements on higher beam intensity and brightness will need an upgrade of the present CERN accelerator chain. Linac4 will be an essential part of the upgrade of the proton accelerator facility. The source for this H(-) linac will be based on a copy of the DESY rf driven H(-) source. New possible radio frequency quadrupole alternatives (with different injection energies) and a pressing linac schedule made it necessary to develop a flexible two-source design