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- Abel, I, et al.
(author)
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Overview of the JET results with the ITER-like wall
- 2013
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Journal article (peer-reviewed)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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- Romanelli, F, et al.
(author)
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Overview of the JET results
- 2011
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Journal article (peer-reviewed)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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4. |
- Romagnoni, A, et al.
(author)
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Comparative performances of machine learning methods for classifying Crohn Disease patients using genome-wide genotyping data
- 2019
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In: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1, s. 10351-
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Journal article (peer-reviewed)abstract
- Crohn Disease (CD) is a complex genetic disorder for which more than 140 genes have been identified using genome wide association studies (GWAS). However, the genetic architecture of the trait remains largely unknown. The recent development of machine learning (ML) approaches incited us to apply them to classify healthy and diseased people according to their genomic information. The Immunochip dataset containing 18,227 CD patients and 34,050 healthy controls enrolled and genotyped by the international Inflammatory Bowel Disease genetic consortium (IIBDGC) has been re-analyzed using a set of ML methods: penalized logistic regression (LR), gradient boosted trees (GBT) and artificial neural networks (NN). The main score used to compare the methods was the Area Under the ROC Curve (AUC) statistics. The impact of quality control (QC), imputing and coding methods on LR results showed that QC methods and imputation of missing genotypes may artificially increase the scores. At the opposite, neither the patient/control ratio nor marker preselection or coding strategies significantly affected the results. LR methods, including Lasso, Ridge and ElasticNet provided similar results with a maximum AUC of 0.80. GBT methods like XGBoost, LightGBM and CatBoost, together with dense NN with one or more hidden layers, provided similar AUC values, suggesting limited epistatic effects in the genetic architecture of the trait. ML methods detected near all the genetic variants previously identified by GWAS among the best predictors plus additional predictors with lower effects. The robustness and complementarity of the different methods are also studied. Compared to LR, non-linear models such as GBT or NN may provide robust complementary approaches to identify and classify genetic markers.
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5. |
- Aktas, A, et al.
(author)
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First measurement of charged current cross sections at HERA with longitudinally polarised positrons
- 2006
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 634:2-3, s. 173-179
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Journal article (peer-reviewed)abstract
- Data taken with positrons of different longitudinal polarisation states in collision with unpolarised protons at HERA are used to measure the total cross sections of the charged current process, e(+) p -> nu X, for negative four-momentum transfer squared Q(2) > 400 GeV2 and inelasticity gamma < 0.9. Together with the corresponding cross section obtained from the previously published unpolarised data, the polarisation dependence of the charged current cross section is measured for the first time at high Q(2) and found to be in agreement with the Standard Model prediction. (c) 2006 Elsevier B.V. All rights reserved.
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17. |
- Niemi, MEK, et al.
(author)
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- 2021
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swepub:Mat__t
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18. |
- Kanai, M, et al.
(author)
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- 2023
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swepub:Mat__t
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19. |
- Aaron, F. D., et al.
(author)
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A search for excited neutrinos in e(-) p collisions at HERA
- 2008
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 663:5, s. 382-389
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Journal article (peer-reviewed)abstract
- A search for first generation excited neutrinos is performed using the full e(-) p data sample collected by the HI experiment at HERA at a centre-of-mass energy of 319 GeV, corresponding to a total luminosity of 184 pb(-1). The electroweak decays of excited neutrinos nu* -> nu gamma, v* -> nu Z and nu* -> eW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited neutrino production is found. Mass dependent exclusion limits on nu* production cross sections and on the ratio of the coupling to the compositeness scale f/boolean AND are derived within gauge mediated models. A limit on f/boolean AND A, independent of the relative couplings to the SU(2) and U(1) gauge bosons, is also determined. These limits extend the excluded region to higher masses than has been possible in previous excited neutrino searches. (c) 2008 Elsevier B.V. All rights reserved.
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20. |
- Adloff, C, et al.
(author)
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A measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA
- 2002
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 539:1-2, s. 25-39
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Journal article (peer-reviewed)abstract
- The helicity structure of the diffractive electroproduction of rho mesons, e + p --> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV2, where t' = - min. The data used are collected with the HI detector at HERA in the kinematic domain 2.5 < Q(2) < 60 GeV2, 40 < W < 120 GeV No t dependence of the r(00)(04) spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r(00)(5) + 2r(11)(5) and r(00)(1) + 2r(11)(1). These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.
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21. |
- Adloff, C, et al.
(author)
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Diffractive photoproduction of psi(2S) mesons at HERA
- 2002
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 541:3-4, s. 251-264
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Journal article (peer-reviewed)abstract
- Results on diffractive photoproduction of psi(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb(-1). The energy dependence of the diffractive psi(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/psi mesons. The dependences of the elastic and proton dissociative psi(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as e(bt), yields b(el)(psi(2S)) = (4.31 +/- 0.57 +/- 0.46) GeV-2, compatible with that of the J/psi. For the proton dissociative channel the result b(pd)(psi(2S)) = (0.59 +/- 0.13 +/- 0.12) GeV-2 is 2.3 standard deviations smaller than that measured for the J/psi. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well. (C) 2002 Elsevier Science B.V. All rights reserved.
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22. |
- Adloff, C, et al.
(author)
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Energy flow and rapidity gaps between jets in photoproduction at HERA
- 2002
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 24:4, s. 517-527
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Journal article (peer-reviewed)abstract
- Dijet events in photon-proton collisions in which there is a large pseudorapidity separation, Deltaeta > 2.5 between the two highest E-T jets are studied with the H1 detector at HERA. The inclusive dijet cross sections are measured as functions of the longitudinal momentum fractions of the proton and photon which participate in the production of the jets, x(p)(jets) and x(gamma)(jets) respectively, Deltaeta, the pseudorapidity P separation between the two highest E-T jets, and E-T(gap), the total summed transverse energy between the jets. Rapidity gap events are defined as events in which E-T(gap) is less than E-T(cut), for E-T(cut) varied between jets 0.5 and 2.0 GeV. The fraction of dijet events with a rapidity gap is measured differentially in Deltaeta, x(p)(jets) and x(gamma)(jets). An excess of events with rapidity gaps at low values of E-T(cut) is observed above the expectation from standard photoproduction processes. This excess can be explained by the exchange of a strongly interacting colour singlet object between the jets.
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23. |
- Adloff, C, et al.
(author)
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Inelastic leptoproduction of J/psi mesons at HERA
- 2002
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 25:1, s. 41-53
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Journal article (peer-reviewed)abstract
- The leptoproduction of J/psi mesons is studied in inelastic reactions for four momentorri transfers 2 < Q(2) < 100GeV(2). The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of 77 pb(-1). Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the non-relativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the J/psi fractional energy. z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced J/psi meson is analysed.
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24. |
- Adloff, C, et al.
(author)
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Inelastic photoproduction of J/psi mesons at HERA
- 2002
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 25:1, s. 25-39
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Journal article (peer-reviewed)abstract
- An analysis of inelastic photoproduction of J/psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80 pb(-1), Differential and double I < P-t/psi(2) < differential cross sections are measured in a wide kinematic region: 60 < W-gammap < 260 GeV, 1 p(t,psi)(2) < 60 GeV2 and 0.05 < z < 0.9. where z is the fraction of the energy of the exchanged photon transferred to the J/psi meson in the rest frame of the target proton. Cross sections at z less than or similar to 0.3 are presented for the first time. Theoretical calculations within the Colour Singlet Model at NLO for direct photon processes are shown to give a good description of the data in the medium z region (0.3 < z < 0.9) up to the highest p(t,psi)(2) values. A calculation using a k(t) factorisation approach in LO in the Colour Singlet Model is also able to describe these data. The data in the full z range are also compared to LO calculations within a non-relativistic QCD framework including colour octet and colour singlet contributions for direct and resolved photons. It seems possible to reconcile data and theory with modest contributions from colour octet processes. The polarisation of the J/psi meson is measured as a function of z and p(t,psi) and is reasonably described by the theoretical predictions.
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25. |
- Adloff, C, et al.
(author)
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Measurement and QCD analysis of neutral and charged current cross sections at HERA
- 2003
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 30:1, s. 1-32
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Journal article (peer-reviewed)abstract
- The inclusive e(+)p single and double differential cross sections for neutral and charged current processes axe measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of roots = 319 GeV and correspond to an integrated luminosity of 65.2 pb(-1). The cross sections are measured in the range of four-momentum transfer squared Q(2) between 100 and 30 000 GeV2 and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e(+)p data and the earlier e-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F-L at high Q(2) (110 - 700 GeV2). A new measurement of the structure function x (F) over tilde (3) is obtained using the new e(+)p and previously published e p neutral current cross section data at high Q(2). These data together with H1 low Q(2) precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.
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