Background Reduction Methods and Vacuum Technology at the KATRIN Spectrometers

The goal of KATRIN is to measure the absolute mass of the electron-antineutrino with a sensitivity of 200 meV by analyzing the shape of the tritium-beta-decay energy spectrum. To minimize the background due to residual gas ionization, a pressure in the lower 10E-11 mbar region is required. This work focuses on the applied vacuum technology. In addition a system of LN2 cooled baffles was designed that eliminates radon-induced background, which is essential for a neutrino mass measurement

The KATRIN Pre-Spectrometer at reduced Filter Energy

The KArlsruhe TRItium Neutrino experiment, KATRIN, will determine the mass of the electron neutrino with a sensitivity of 0.2 eV (90% C.L.) via a measurement of the beta-spectrum of gaseous tritium near its endpoint of E_0 =18.57 keV. An ultra-low background of about b = 10 mHz is among the requirements to reach this sensitivity. In the KATRIN main beam-line two spectrometers of MAC-E filter type are used in a tandem configuration. This setup, however, produces a Penning trap which could lead to increased background. We have performed test measurements showing that the filter energy of the pre-spectrometer can be reduced by several keV in order to diminish this trap. These measurements were analyzed with the help of a complex computer simulation, modeling multiple electron reflections both from the detector and the photoelectric electron source used in our test setup.Comment: 22 pages, 12 figure

Improved Upper Limit on the Neutrino Mass from a Direct Kinematic Method by KATRIN.

We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic end point at 18.57 keV gives an effective neutrino mass square value of (-1.0_{-1.1}^{+0.9})  eV^{2}. From this, we derive an upper limit of 1.1 eV (90% confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of 2 and provides model-independent input to cosmological studies of structure formation

Stochastic Heating by ECR as a Novel Means of Background Reduction in the KATRIN Spectrometers

The primary objective of the KATRIN experiment is to probe the absolute neutrino mass scale with a sensitivity of 200 meV (90% C.L.) by precision spectroscopy of tritium beta-decay. To achieve this, a low background of the order of 10^(-2) cps in the region of the tritium beta-decay endpoint is required. Measurements with an electrostatic retarding spectrometer have revealed that electrons, arising from nuclear decays in the volume of the spectrometer, are stored over long time periods and thereby act as a major source of background exceeding this limit. In this paper we present a novel active background reduction method based on stochastic heating of stored electrons by the well-known process of electron cyclotron resonance (ECR). A successful proof-of-principle of the ECR technique was demonstrated in test measurements at the KATRIN pre-spectrometer, yielding a large reduction of the background rate. In addition, we have carried out extensive Monte Carlo simulations to reveal the potential of the ECR technique to remove all trapped electrons within negligible loss of measurement time in the main spectrometer. This would allow the KATRIN experiment attaining its full physics potential

Commissioning of the vacuum system of the KATRIN Main Spectrometer

The KATRIN experiment will probe the neutrino mass by measuring the beta-electron energy spectrum near the endpoint of tritium beta-decay. An integral energy analysis will be performed by an electro-static spectrometer (Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m^3, and a complex inner electrode system with about 120000 individual parts. The strong magnetic field that guides the beta-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. A system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300{\deg}C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016

The design, construction, and commissioning of the KATRIN experiment

The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns

Improved Upper Limit on the Neutrino Mass from a Direct Kinematic Method by KATRIN

We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic end point at 18.57 keV gives an effective neutrino mass square value of $(−1.0^{+0.9}_{−1.1}) eV^2$. From this, we derive an upper limit of 1.1 eV (90% confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of 2 and provides model-independent input to cosmological studies of structure formation

Biosynthesis of Taxol: Cloning and expression of taxa-4(5),11(12)-diene synthase gene from Taxus baccata

Taxol ist ein hochwirksames Antikrebsmittel gegen Brust- und Eierstockkrebs, das in geringen Mengen in der Rinde aller Taxus-Arten gefunden wird. Taxol stellt ein hoch funktionalisiertes cyclisches Diterpen dar, das durch chemische Synthese nur schwer zugänglich ist. Durch die begrenzte Verfügbarkeit von Taxol durch natürliche Ressourcen, ist es von großem biotechnologischem Interesse, die an der Biosynthese beteiligten Enzyme zu erforschen. Die vorliegende Arbeit beschäftigte sich mit der Klonierung und Expression des Taxa-4(5),11(12)-dien-Synthase-Gens aus der Europäischen Eibe Taxus baccata. Die Taxadien-Synthase stellt ein Schlüsselenzym in der Biosynthese des Taxols dar. Sie katalysiert die Cyclisierung des Diterpens Geranylgeranylpyrophosphat zu Taxa-4(5),11(12)-dien. Für die Charakterisierung des Taxadien-Synthase-Gens wurde dieses mittels PCR amplifiziert und in Escherichia coli kloniert. Die Sequenzanalyse des Gens ergab einen offenen Leserahmen von 3980 bp, bestehend aus 13 Exons und 12 Introns. Aus dem ORF lässt sich für die Taxadien-Synthase eine Größe von 98 kDa vorhersagen. Ein Sequenzvergleich mit verschiedenen pflanzlichen Isoprensynthasen zeigte eine hohe Übereinstimmung hinsichtlich der Intron/Exon-Struktur im C-terminalen Bereich, als auch das Vorhandensein eines, in allen verglichenen Isoprensynthasen vorhandenen, konservierten Motivs DDXXD. Interessanterweise weist die Isoprensynthase aus T. baccata höhere Ähnlichkeit im mittleren Bereich der Gen-Struktur zu der Linalool-Synthase, eine Hydroxylase, aus Clarkia concinna auf als zu den anderen Isoprencyclasen. Der N-terminale Bereich der Isoprensynthase-Gene zeichnet sich durch eine hohe Variabilität aus, da dieser Bereich für das Signalpeptid codiert, das für den Transport der Synthasen in die jeweiligen Plastide zuständig ist. Für die Expression der rekombinaten Synthase in E. coli wurde mittels RT-PCR die entsprechende cDNA isoliert, und anschließend das Protein durch Affinitäts-Chromatographie an Nickel-Agarose angereinigt. Die Ausbeute an Taxadien-Synthase betrug 20 mg/l Kulturmedium. Durch Western Blot-Analyse mit Antikörpern sowohl gegen His5-Tag als auch gegen ein Peptid aus der Taxadien-Synthase und durch GC-MS-Analyse konnte das funktionale Enzym nachgewiesen werden. Mittels SDS-PAGE unter denaturierenden Bedingungen konnte für die rekombinante Taxadien-Synthase ein Molekulargewicht von 97 kDa bestimmt werden. Im Gegensatz dazu ist für das native Protein aus T. brevifolia eine Größe von 80 kDa beschrieben worden. Diese Diskrepanz lässt den Schluss zu, dass das rekombinante Protein (Preprotein) aus einem Transitpeptid für das Plastid und der eigentlichen Isoprensynthase besteht. Ein Vergleich der Aminosäure-Sequenzen der Taxadien-Synthasen aus T. baccata, T. brevifolia und T. chinensis zeigt, dass der Verwandtschaftsgrad der Synthasen aus T. baccata und T. brevifolia untereinander höher ist als zu der Taxadien-Synthase aus T. chinensis.Taxol is a highly potent antitumor drug with activity against breast and ovarian cancer. It can be found in small amounts in the bark of Taxus species. Taxol represents a highly functionalized cyclic diterpene. The yields by total synthesis are too low to be commercially viable. Due to the limited supply of the drug from its natural ressources it is of highly biotechnological interest to study the enzymes involved in taxol biosynthesis. The present work deals with the cloning and expression of the taxa-4(5),11(12)-diene synthase gene from European yew (Taxus baccata). Taxadiene synthase is a key enzyme in taxol biosynthesis. It catalyzes the cyclization of geranylgeranyl diphosphate to form taxa-4(5),11(12)-diene. To characterize the taxadiene synthase gene it was amplified by PCR and cloned in Escherichia coli. Sequence analysis of the gene revealed an ORF of 3980 bp, consisting of 13 exons and 12 introns, predicting a molecular mass of 98 kDa for the enzyme. Sequence comparison with various plant terpene synthases showed high homology regarding the intron/exon structure at the C-terminal region as well as the presence of the conserved motif DDXXD which can be found in all cyclases compared. Interestingly, taxadiene synthase from T. baccata exhibits a higher degree of similarity (regarding the gene structure between exons 3-9) to linalool synthase from Clarkia concinna, than to terpene cyclases. The N-terminal parts of the terpene synthase genes are highly variable because this region encodes for the transit peptide necessary for localization of the enzymes to the corresponding plastids. For the expression of the recombinant synthase in E. coli the corresponding cDNA was isolated by RT-PCR. The protein was partially purified by affinity chromatography using NTA-Agarose. The yield of taxadiene synthase was 20 mg/l culture medium. The enzyme could be detected by Western Blot analysis using an anti His antibody and an antibody directed against an internal sequence of taxadiene synthase, respectively. In addition, taxadiene synthase activity was detected by GC-MS analysis. Using SDS Page a molecular mass of 97 kDa for the recombinant protein could be determined. In contrast a molecular mass of 80 kDa was found for the native taxadiene synthase from T. brevifolia. The difference of 17 kDa suggests the presence of a putative plastidial transit peptide at the N-terminus of the recombinant protein (preprotein). Amino acid sequence comparison between taxadiene synthases from T. baccata, T. brevifolia and T. chinensis shows that the synthases from T. baccata and T. brevifolia exhibit a higher degree of relationship to each other then to taxadiene synthase from T. chinensis