The TOTEM collaboration has measured the proton-proton total cross section at √s=8 TeV using a luminosity-independent method. In LHC fills with dedicated beam optics, the Roman pots have been ...inserted very close to the beam allowing the detection of ~90% of the nuclear elastic scattering events. Simultaneously the inelastic scattering rate has been measured by the T1 and T2 telescopes. By applying the optical theorem, the total proton-proton cross section of (101.7±2.9) mb has been determined, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity-independent elastic and inelastic cross sections: σ(el)=(27.1±1.4) mb; σ(inel)=(74.7±1.7) mb.
•Addition of up to 25% of C2F6 into a C3F8 refrigerant effectively decreases the evaporation temperature.•The heat transfer coefficient somewhat decreased with the progressive addition of ...C2F6.•Various flow regimes in the horizontal evaporator are clearly visible from the obtained data.
We have measured the flow boiling heat transfer coefficient (HTC) of saturated fluorocarbon blends in a horizontal copper-nickel tube with a diameter of 4mm. Direct (Joule) heating of the tube wall was used to obtain heat fluxes from 5 to 13.7kWm−2. Two different injection capillaries were used, permitting measurements at mass fluxes varying between 94 and 164kgm−2s−1. The evaporation pressure was approximately 0.2MPa for the mass fluxes close to 164kgm−2s−1 and 0.15MPa for the lower mass fluxes. The same tube dimensions and material are used in the on-detector cooling channels of the silicon micro-strip charged particle tracker (“SCT”) of the ATLAS experiment at the CERN Large Hadron Collider. The range of heat flux and mass flow studied encompasses the operating conditions of the tracker. When operating in the high radiation environment near to the proton beam collisions radiation tolerant coolants are essential. Saturated fluorocarbons (CnF(2n+2)) are radiation resistant and allow thermodynamic “tailoring” by blending saturated molecules of different orders. Measurements were made with pure C3F8 (R218) and zeotropic blends containing 5, 10, 15, 20 and 25% (molar) C2F6 (R116). This work is a continuation of a previous study which showed that the operating temperature of the ATLAS SCT could be reduced by around 10°C with the admixture of 25% (molar) C2F6, with no changes needed to the existing on-detector and circulatory pipework. The data analysis revealed multiple flow boiling regimes of the two-phase flow that varied as a function of coolant flow rate, heat flux, vapour quality and mixture composition. As expected, the HTC in pure C3F8 was higher than in blends with increasing C2F6 content. Nevertheless, the study confirmed that the ATLAS SCT could be operated at full power dissipation with cooling tube temperatures up to 10°C colder than in pure C3F8 with C3F8/C2F6 blends having relatively modest values of HTCs in the range 1500–4000Wm−2K−1.
The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of sqrts=7 TeV. By utilizing ...the very forward TOTEM tracking detectors T1 and T2, which extend up to |η|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section σDD=(116±25) μb for events where both diffractive systems have 4.7<|η|min<6.5.
The proton–proton elastic differential cross section
d
σ
/
d
t
has been measured by the TOTEM experiment at
s
=
2.76
TeV
energy with
β
∗
=
11
m
beam optics. The Roman Pots were inserted to 13 times ...the transverse beam size from the beam, which allowed to measure the differential cross-section of elastic scattering in a range of the squared four-momentum transfer (|
t
|) from 0.36 to
0.74
GeV
2
. The differential cross-section can be described with an exponential in the |
t
|-range between 0.36 and
0.54
GeV
2
, followed by a diffractive minimum (dip) at
|
t
dip
|
=
(
0.61
±
0.03
)
GeV
2
and a subsequent maximum (bump). The ratio of the
d
σ
/
d
t
at the bump and at the dip is
1.7
±
0.2
. When compared to the proton–antiproton measurement of the D0 experiment at
s
=
1.96
TeV
, a significant difference can be observed. Under the condition that the effects due to the energy difference between TOTEM and D0 can be neglected, the result provides evidence for the exchange of a colourless C-odd three-gluon compound state in the
t
-channel of the proton–proton and proton–antiproton elastic scattering.
Abstract The TOTEM collaboration has measured the elastic proton-proton differential cross section $$\mathrm{d}\sigma /\mathrm{d}t$$ d σ / d t at $$\sqrt{s}=13$$ s = 13 TeV LHC energy using ...dedicated $$\beta ^{*}=90$$ β ∗ = 90 m beam optics. The Roman Pot detectors were inserted to 10 $$\sigma $$ σ distance from the LHC beam, which allowed the measurement of the range 0.04 GeV $$^{2}$$ 2 ; 4 GeV $$^{2}$$ 2 $$$$ in four-momentum transfer squared | t |. The efficient data acquisition allowed to collect about 10 $$^{9}$$ 9 elastic events to precisely measure the differential cross-section including the diffractive minimum (dip), the subsequent maximum (bump) and the large-| t | tail. The average nuclear slope has been found to be $$B=(20.40 \pm 0.002^{\mathrm{stat}} \pm 0.01^{\mathrm{syst}})~$$ B = ( 20.40 ± 0 . 002 stat ± 0 . 01 syst ) GeV $$^{-2}$$ - 2 in the | t |-range 0.04–0.2 GeV $$^{2}$$ 2 . The dip position is $$|t_{\mathrm{dip}}|=(0.47 \pm 0.004^{\mathrm{stat}} \pm 0.01^{\mathrm{syst}})~$$ | t dip | = ( 0.47 ± 0 . 004 stat ± 0 . 01 syst ) GeV $$^{2}$$ 2 . The differential cross section ratio at the bump vs. at the dip $$R=1.77\pm 0.01^{\mathrm{stat}}$$ R = 1.77 ± 0 . 01 stat has been measured with high precision. The series of TOTEM elastic pp measurements show that the dip is a permanent feature of the pp differential cross-section at the TeV scale.
An unfavorable effect of gas impurities on the throttling process inside a small-diameter tube, i.e. a capillary tube, has been studied in detail. A special testing capillary tube equipped with ...precise temperature and pressure sensors has been used for an experimental investigation of the capillary flow of a saturated fluorocarbon refrigerant, R218, contaminated by dissolved nitrogen. The gas impurities significantly affected the throttling process, since the two-phase flow started notably earlier than in the case of pure refrigerant flow. Moreover, the gas contamination resulted in a decreased mass flow rate of refrigerant delivered through the capillary tube. A comprehensive numerical model has been developed to simulate the capillary flow of gas-contaminated refrigerant. The model takes into account two coincident thermodynamic events: the throttling process of the refrigerant (solvent) and the gradual release of the dissolved gas impurities (solute) from the refrigerant liquid phase. The gas release is in principle described by using the temperature correlation of the Henry’s law constant. The model considers adiabatic, thermodynamically equilibrated capillary flow with homogeneous two-phase flow. The numerical simulation is in good agreement with our experimental data measured for R218 contaminated by nitrogen.
Custom ultrasonic instruments have been developed for simultaneous monitoring of binary gas mixture and flow in the ATLAS Inner Detector. Sound transit times are measured in opposite directions in ...flowing gas. Flow rate and sound velocity are respectively calculated from their difference and average. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database, based on the direct dependence of sound velocity on component concentrations in a mixture at known temperature and pressure. Five devices are integrated into the ATLAS Detector Control System. Three instruments monitor coolant leaks into N2 envelopes of the silicon microstrip and Pixel detectors. Resolutions better than ±2×10−5 and ±2×10−4 are seen for C3F8 and CO2 leak concentrations in N2 respectively. A fourth instrument detects sub-percent levels of air ingress into the C3F8 condenser of the new thermosiphon coolant recirculator. Following extensive studies a fifth instrument was built as an angled sound path flowmeter to measure the high returning C3F8 vapour flux (∼1.2kgs−1). A precision of <2.3% FS for flows up to 10ms−1 was demonstrated. These instruments have many potential applications where continuous binary gas composition measurement is required, including hydrocarbon and anaesthetic gas mixtures.
This paper describes an automated measuring apparatus with an ultrasonic gas analyzer and realtime analysis of the composition of the gas. The apparatus is designed for preparing binary gas mixtures ...and making measurements in a wide range of pressures (from 0.8 bar sub(a) to 15 bar sub(a)) and temperatures (between -15degreesC and 80degreesC). The apparatus was developed to determine the thermophysical properties of fluorocarbon mixtures for potential use in the cooling circuits of several Large Hadron Collider projects at CERN. The design of its control system took into account the safety and reliability o the gas analyzer, and the need to limit the presence of laboratory personnel. The control system was implemented in PVSS-II, the Supervisory, Control and Data Acquisition standard chosen for LHC and its experiments at CERN. The second part of the paper describes the implementation and verification of the algorithm for continuous real-time determination of the composition of the refrigerant mixture. The algorithm is based on minimizing the quadratic norm from the measured data and from the pre-generated look-up tables acquired from the NIST REFPROP software package.
•Ultrasonic instruments allow real time binary gas mixture monitoring.•High precision is demonstrated (>10–4 M) depending on molecular weight difference.•They can be used in binary gas analysis with ...known concentration of third-party gases.•Other applications of these instruments are foreseen.
We have developed ultrasonic instrumentation to simultaneously monitor flow and composition in a variety of gas mixtures. Flow and mixture composition are respectively derived from measurements of the difference and average of sound transit times in two opposite directions in a flowing process gas blend. Gas composition is then determined from an automated comparison of the measured sound velocities with a velocity/composition database.
Continuous, real-time precision measurements of binary gas mixtures are required in many applications. While the most natural application of this instrumentation is in the analysis of such mixtures, analysis of mixtures with additional components is also possible, as discussed in this paper.
In the ATLAS experiment at CERN, several instruments are presently used in the Detector Control System. Three instruments monitor octafluoropropane (C3F8, R218) and carbon dioxide (CO2, R744) coolant leaks into the nitrogen-purged envelopes surrounding elements of the inner silicon tracker. Precision in molar concentration of better than 2.10−5 is routinely seen in mixtures of C3F8 in nitrogen in the presence of known concentrations of the third party gas CO2.
Two further instruments are used to monitor the new 60 kW thermosiphon C3F8 evaporative coolant recirculator which exploits the 90 m depth of the ATLAS pit to circulate coolant without the need for pumps or compressors in the primary loop. These instruments are used to verify the absence of air leaks in the thermosiphon cooling circuit and to measure the vapour-phase coolant flow in real-time.
This instrumentation is also used to measure zeotropic fluorocarbon blends containing C3F8 and up to 25% hexafluoroethane (C2F6, R116), achieving a precision around 0.16% in the range 0–25% C2F6. We also report on measurements of heat transfer coefficient in these blends: our experimental data were compared to several empirical correlations, with typical differences less than 10%.
This analysis technique, targeting binary pairs of gases of dissimilar molecular weight, is particularly promising for mixtures of anesthetic gases, including in the developing area of anesthesia using xenon. The instrument and its various applications will be discussed.
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