Hydrogen recycling during RF plasma heating in the U-3M torsatron

The hydrogen recycling behavior has been studied during the plasma experiments in torsatron U-3M. For this purpose, the time dependence of the molecular hydrogen pressure in the U-3M torsatron vacuum chamber in the modes of RF wall conditioning and RF plasma heating has been measured. The experimental results show that the hydrogen pumping from the vacuum chamber runs at constant rate during the RF discharge for each mode. After RF power switching-off the inverse desorption of hydrogen, accumulated during the RF discharge in the vacuum chamber walls and helical coil surfaces, is observed. When the antenna anode voltages and the RF pulse duration in both modes are increasing, the character of the time dependences of hydrogen pressure does not change significantly.Изучено поведение рециклинга водорода во время плазменных экспериментов на торсатроне У-3М. Для этой цели было проведено измерение временных зависимостей давления водорода в вакуумной камере торсатрона У-3М в режимах ВЧ-чистки стенок камеры и ВЧ-нагрева плазмы. Экспериментальные результаты показали, что в обоих режимах во время ВЧ-разряда скорость откачки водорода из вакуумной камеры остается постоянной для каждого из режимов. После выключения ВЧ-мощности наблюдается обратная десорбция водорода, накопленного во время ВЧ-разряда в стенках вакуумной камеры и винтовых катушек. Повышение анодных напряжений на ВЧ-антеннах и увеличение длительности ВЧ-импульса существенно не влияют на характер временных зависимостей давления водорода.Вивчено поведінку рециклінгу водню під час плазмових експериментів на торсатроні У-3М. Для цієї мети було проведено вимірювання часових залежностей тиску водню у вакуумній камері торсатрона У-3М в режимах ВЧ-чистки стінок камери і ВЧ-нагріву плазми. Експериментальні результати показали, що в обох режимах під час ВЧ-розряду швидкість відкачування водню з вакуумної камери залишається постійною для кожного з режимів. Після виключення ВЧ-потужності спостерігається зворотна десорбція водню, накопиченого під час ВЧ-розряду в стінках вакуумної камери і гвинтових котушок. Підвищення анодних напруг на ВЧ-антенах і збільшення тривалості ВЧ-імпульсу істотно не впливають на характер тимчасових залежностей тиску водню

Test of pure hydrogen inflow system during dischare cleaning and work regimes of the Uragan-3M torsatron

The tests of the pure hydrogen inflow system had been carried out during pulsed discharge cleaning and work regimes of the Uragan-3M torsatron. It had been shown that the inflow system provides required steady flows of hydrogen over the pressure range from 5x10⁻⁷ Torr to 10⁻⁴ Torr. The special cyclic procedures of membrane heating and pumping to provide the long life time of membranes, and required reliability and stable flow are described.Проведено іспити системи напуску чистого водню в робочому режимі й у режимі чищення високочастотними імпульсами торсатрону Ураган-3М. Показано, що система напуску забезпечує необхідні потоки в діапазоні тисків 5x10⁻⁷ – 10-⁻⁴ Торр. Для забезпечення необхідної надійності, тривалості терміну служби і стабільності потоку водню пропонується спеціальна процедура періодичного нагрівання і відкачки дифузійних мембран.Проведены испытания системы напуска чистого водорода в рабочем режиме и в режиме чистки высокочастотными импульсами торсатрона Ураган-3М. Показано, что система напуска обеспечивает требуемые потоки в диапазоне давлений 5x10⁻⁷ – 10⁻⁴ Торр. Для обеспечения требуемой надежности, продолжительности срока службы и стабильности потока водорода предлагается специальная процедура периодического нагрева и откачки диффузионных мембран

Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments

The experimental method was developed for evaluation of a hydrogen particle flux balance over a wide range of operating conditions in the Uragan-3M torsatron (U-3M) in the course of RF discharges. Standard pressure gauges were tested for measurement of non-stationary hydrogen pressure in the U-3M vacuum chamber. The average lifetime of hydrogen ions was determined for each operation mode of U-3M.Разработана экспериментальная методика оценки баланса потоков частиц водорода во время ВЧ-разрядов в торсатроне Ураган-3М (У-3М) в широком диапазоне рабочих параметров. Для измерения нестационарного давления водорода в вакуумной камере У-3М были апробированы стандартные датчики давления. Для каждого из рабочих режимов работы У-3М было определено среднее время жизни ионов водорода.Розроблено експериментальну методику оцінки балансу потоків частинок водню під час ВЧ-розрядів у торсатроні Ураган-3М (У-3М) в широкому діапазоні робочих параметрів. Для вимірювання нестаціонарного тиску водню у вакуумній камері У-3М були апробовані стандартні датчики тиску. Для кожного з робочих режимів У-3М було визначено середній час життя іонів водню

First tests of the biased movable B4C-limiter in the Uragan-2M torsatron under RF and UHF wall conditioning

The work describes the design of a multifunctional B4C-limiter, and reports preliminary results from experimental study of the limiter operated at steady-state and pulsed RF discharge cleaning regimes in the Uragan-2M torsatron.Представлены конструкция и предварительные результаты экспериментального исследования использования B4C-лимитера во время стационарных и импульсных режимов чистки ВЧ-разрядами в торсатроне Ураган-2М.Представлено конструкцію і попередні результати експериментального дослідження використання B4C-лимитера під час стаціонарних і імпульсних режимів чищення ВЧ-розрядами в торсатроні Ураган-2М

Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s=13 TeV using the ATLAS detector

The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb−1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements

A search for resonances decaying into a Higgs boson and a new particle X in the XH → qqbb final state with the ATLAS detector

A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb−1 of proton–proton collision data at collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle X is assumed to decay to a pair of light quarks, and the fully hadronic final state is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the resonance

Combination of searches for Higgs boson pairs in pp collisions at \sqrts = 13 TeV with the ATLAS detector

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 &lt; kappa(lambda) &lt; 12.0 (-5.8 &lt; kappa(lambda) &lt; 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model. For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135103</p

Searches for lepton-flavour-violating decays of the Higgs boson in s=13\sqrt{s}=13 TeV pp\mathit{pp} collisions with the ATLAS detector

This Letter presents direct searches for lepton flavour violation in Higgs boson decays, H → eτ and H → μτ , performed with the ATLAS detector at the LHC. The searches are based on a data sample of proton–proton collisions at a centre-of-mass energy √s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess is observed above the expected background from Standard Model processes. The observed (median expected) 95% confidence-level upper limits on the leptonflavour-violating branching ratios are 0.47% (0.34+0.13−0.10%) and 0.28% (0.37+0.14−0.10%) for H → eτ and H → μτ , respectively.publishedVersio

Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb⁻¹ of pp collisions at \sqrts = 13 TeV with the ATLAS experiment

A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb−1 of proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqγ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tuγ coupling of 36 fb (78 fb) and on the branching ratio for t→γu of 2.8×10−5 (6.1×10−5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tcγ coupling of 40 fb (33 fb) and on the branching ratio for t→γc of 22×10−5 (18×10−5). © 2019 The Author(s

Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at Ebeam =4 TeV

Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the \textscFluka Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared quantitatively with data. Through these comparisons the origins of the BIB leading to different observables in the ATLAS detectors are analysed. The level of agreement between simulation results and BIB measurements by ATLAS in 2012 demonstrates that a good understanding of the origin of BIB has been reached