Instrumentation for hydrogen slush storage containers

Hydrogen liquid and slush tank continuous inventory during ground storag

The PANDA GEM-based TPC Prototype

We report on the development of a GEM-based TPC prototype for the PANDA experiment. The design and requirements of this device will be illustrated, with particular emphasis on the properties of the recently tested GEM-detector, the characterization of the read-out electronics and the development of the tracking software that allows to evaluate the GEM-TPC data.Comment: submitted to NIMA 4 pages, 6 picture

Specific heat amplitude ratios for anisotropic Lifshitz critical behaviors

We determine the specific heat amplitude ratio near a $m$-axial Lifshitz point and show its universal character. Using a recent renormalization group picture along with new field-theoretical $\epsilon_{L}$-expansion techniques, we established this amplitude ratio at one-loop order. We estimate the numerical value of this amplitude ratio for $m=1$ and $d=3$. The result is in very good agreement with its experimental measurement on the magnetic material $MnP$. It is shown that in the limit $m \to 0$ it trivially reduces to the Ising-like amplitude ratio.Comment: 8 pages, RevTex, accepted as a Brief Report in Physical Review

A Halomethane thermochemical network from iPEPICO experiments and quantum chemical calculations

Internal energy selected halomethane cations CH3Cl+, CH2Cl2+, CHCl3+, CH3F+, CH2F2+, CHClF2+ and CBrClF2+ were prepared by vacuum ultraviolet photoionization, and their lowest energy dissociation channel studied using imaging photoelectron photoion coincidence spectroscopy (iPEPICO). This channel involves hydrogen atom loss for CH3F+, CH2F2+ and CH3Cl+, chlorine atom loss for CH2Cl2+, CHCl3+ and CHClF2+, and bromine atom loss for CBrClF2+. Accurate 0 K appearance energies, in conjunction with ab initio isodesmic and halogen exchange reaction energies, establish a thermochemical network, which is optimized to update and confirm the enthalpies of formation of the sample molecules and their dissociative photoionization products. The ground electronic states of CHCl3+, CHClF2+ and CBrClF2+ do not confirm to the deep well assumption, and the experimental breakdown curve deviates from the deep well model at low energies. Breakdown curve analysis of such shallow well systems supplies a satisfactorily succinct route to the adiabatic ionization energy of the parent molecule, particularly if the threshold photoelectron spectrum is not resolved and a purely computational route is unfeasible. The ionization energies have been found to be 11.47 ± 0.01 eV, 12.30 ± 0.02 eV and 11.23 ± 0.03 eV for CHCl3, CHClF2 and CBrClF2, respectively. The updated 0 K enthalpies of formation, ∆fHo0K(g) for the ions CH2F+, CHF2+, CHCl2+, CCl3+, CCl2F+ and CClF2+ have been derived to be 844.4 ± 2.1, 601.6 ± 2.7, 890.3 ± 2.2, 849.8 ± 3.2, 701.2 ± 3.3 and 552.2 ± 3.4 kJ mol–1, respectively. The ∆fHo0K(g) values for the neutrals CCl4, CBrClF2, CClF3, CCl2F2 and CCl3F and have been determined to be –94.0 ± 3.2, –446.6 ± 2.7, –702.1 ± 3.5, –487.8 ± 3.4 and –285.2 ± 3.2 kJ mol–1, respectively

FlashCam: a fully-digital camera for the medium-sized telescopes of the Cherenkov Telescope Array

The FlashCam group is currently preparing photomultiplier-tube based cameras proposed for the medium-sized telescopes (MST) of the Cherenkov Telescope Array (CTA). The cameras are designed around the FlashCam readout concept which is the first fully-digital readout system for Cherenkov cameras, based on commercial FADCs and FPGAs as key components for the front-end electronics modules and a high performance camera server as back-end. This contribution describes the progress of the full-scale FlashCam camera prototype currently under construction, as well as performance results also obtained with earlier demonstrator setups. Plans towards the production and implementation of FlashCams on site are also briefly presented.Comment: 8 pages, 6 figures. In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

FACT - Threshold prediction for higher duty cycle and improved scheduling

The First G-APD Cherenkov telescope (FACT) is the first telescope using silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise a higher photon detection efficiency, more robustness and higher precision than photo-multiplier tubes. Being operated during different light-conditions, the threshold settings of a Cherenkov telescope have to be adapted to feature the lowest possible threshold but also an efficient suppression of triggers from night-sky background photons. Usually this threshold is set either by experience or a mini-ratescan. Since the measured current through the sensors is directly correlated with the noise level, the current can be used to set the best threshold at any time. Due to the correlation between the physical threshold and the final energy threshold, the current can also be used as a measure for the energy threshold of any observation. This presentation introduces a method which uses the properties of the moon and the source position to predict the currents and the corresponding energy threshold for every upcoming observation allowing to adapt the observation schedule accordingly

FACT - Long-term Monitoring of Bright TeV-Blazars

Since October 2011, the First G-APD Cherenkov Telescope (FACT) is operated successfully on the Canary Island of La Palma. Apart from the proof of principle for the use of G-APDs in Cherenkov telescopes, the major goal of the project is the dedicated long-term monitoring of a small sample of bright TeV blazars. The unique properties of G-APDs permit stable observations also during strong moon light. Thus a superior sampling density is provided on time scales at which the blazar variability amplitudes are expected to be largest, as exemplified by the spectacular variations of Mrk 501 observed in June 2012. While still in commissioning, FACT monitored bright blazars like Mrk 421 and Mrk 501 during the past 1.5 years so far. Preliminary results including the Mrk 501 flare from June 2012 will be presented.Comment: 4 pages, 4 figures, presented at the 33rd ICRC (2013

FACT - How stable are the silicon photon detectors?

The First G-APD Cherenkov telescope (FACT) is the first telescope using silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise a higher photon detection efficiency, more robustness and higher precision than photo-multiplier tubes. Since the properties of G-APDs depend on auxiliary parameters like temperature, a feedback system adapting the applied voltage accordingly is mandatory. In this presentation, the feedback system, developed and in operation for FACT, is presented. Using the extraction of a single photon-equivalent (pe) spectrum as a reference, it can be proven that the sensors can be operated with very high precision. The extraction of the single-pe, its spectrum up to 10\,pe, its properties and their precision, as well as their long-term behavior during operation are discussed. As a by product a single pulse template is obtained. It is shown that with the presented method, an additional external calibration device can be omitted. The presented method is essential for the application of G-APDs in future projects in Cherenkov astronomy and is supposed to result in a more stable and precise operation than possible with photo-multiplier tubes

FACT - Long-term stability and observations during strong Moon light

The First G-APD Cherenkov Telescope (FACT) is the first Cherenkov telescope equipped with a camera made of silicon photon detectors (G-APD aka. SiPM). Since October 2011, it is regularly taking data on the Canary Island of La Palma. G-APDs are ideal detectors for Cherenkov telescopes as they are robust and stable. Furthermore, the insensitivity of G-APDs towards strong ambient light allows to conduct observations during bright Moon and twilight. This gain in observation time is essential for the long-term monitoring of bright TeV blazars. During the commissioning phase, hundreds of hours of data (including data from the the Crab Nebula) were taken in order to understand the performance and sensitivity of the instrument. The data cover a wide range of observation conditions including different weather conditions, different zenith angles and different light conditions (ranging from dark night to direct full Moon). We use a new parmetrisation of the Moon light background to enhance our scheduling and to monitor the atmosphere. With the data from 1.5 years, the long-term stability and the performance of the camera during Moon light is studied and compared to that achieved with photomultiplier tubes so far.Comment: 3 pages, 3 figures, FACT Contribution to the 33rd International Cosmic Ray Conference (ICRC), Rio de Janeir

Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope

The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of the performance of silicon photo detectors in Cherenkov Astronomy. For more than two years it is operated on La Palma, Canary Islands (Spain), for the purpose of long-term monitoring of astrophysical sources. For this, the performance of the photo detectors is crucial and therefore has been studied in great detail. Special care has been taken for their temperature and voltage dependence implementing a correction method to keep their properties stable. Several measurements have been carried out to monitor the performance. The measurements and their results are shown, demonstrating the stability of the gain below the percent level. The resulting stability of the whole system is discussed, nicely demonstrating that silicon photo detectors are perfectly suited for the usage in Cherenkov telescopes, especially for long-term monitoring purpose