ECR heating on the WEGA stellarator

The plasma in the WEGA stellarator is generated and heated by Electron Cyclotron Resonance Heating (ECRH). The microwave is emitted from the low field side mid-plane with power of up to 6+20 kW and with a frequency of 2.45GHz (λ=12.45 cm). The low cut-off density of ncutoff=7.5×10¹⁶m⁻³ makes ECRH on the WEGA stellarator inefficient in both O-mode and X-mode regime. This was confirmed in the first experimental campaign by perpendicular launch of the microwave with a TE11 antenna. In these experiments only edge heating was observed. Density and temperature profiles were hollow [1]. For the over dense plasma heating, mode conversion into the electrostatic electron Bernstein waves (EBW) is required. Two schemes have been tested: the direct X-B (X-mode to Bernstein mode) conversion, where an X-wave must be launched perpendicular to the magnetic field into an over dense plasma with a steep density gradient. In these experiments the strong reflection of the microwave power at the cut-off layer prohibited efficient plasma heating. Another possibility is the O-X-B conversion scheme [2]. The methods of its achievement with different antennas are the subject of this paper.Плазма у стеллараторі WEGA утворюється та нагрівається за допомогою НВЧ-нагріву на електронно- циклотронній частоті (ЕЦР). Ввід НВЧ-енергії здійснюється із зовнішнього боку тору у його екваторіальній площині, на частоті 2.45 ГГц (λ=12.45 см) та з максимальною потужністю до 26 кВт. Низька критична щільність плазми для цієї частоти (ncutoff=7.5×10¹⁶м⁻³ ) робить традиційний ЕЦР-нагрів неефективним, як у режимі «Звичайної» (З-хвиля), так і у режимі «Незвичайної» хвилі (Н-хвиля), що було підтверджено у ході першої експериментальної кампанії, коли НІЧ-енергія вводилась перпендикулярно силовим лініям магнітного поля за допомогою циліндричного ТЕ11 хвилеводу. У цих експериментах спостерігався нагрів периферичної плазми, профілі щільності та температури мали порожній характер [1]. Для нагріву плазми з щільністю вище щільності відсічки необхідна трансформація в електростатичну Бернштейн хвилю (ЕБХ). Два сценарії нагріву було випробувано на установці: перший з трансформацією Н-хвилі у ЕБХ, в цьому випадку Н-хвиля повинна бути введена перпендикулярно магнітному полю в плазму з щільністю, яка перевищує критичну. У цих експериментах сильне відбиття НВЧ-енергії у шарі відсічки перешкоджало ефективному нагріву плазми. У другому випадку використовується сценарій з подвійною конверсією спочатку З-хвилі у Н-хвилю з наступною трансформацією Н-хвилі в ЕБХ [2]. Методи реалізації такого сценарію і є темою цієї роботи.Плазма в стеллараторе WEGA создается и нагревается при помощи СВЧ-нагрева на электронно- циклотронной частоте (ЭЦР). Ввод СВЧ-энергии производится с внешней стороны тора в его экваториальной плоскости на частоте 2.45 ГГц (λ=12.45 см) и с максимальной мощностью до 26 кВт. Низкая критическая плотность плазмы для данной частоты (ncutoff=7.5×10¹⁶м⁻³ ) делает традиционный ЭЦР-нагрев неэффективным, как в режиме «обыкновенной» (О-волна), так и в режиме «необыкновенной» волны (Н-волна), что было подтверждено в ходе первой экспериментальной кампании, когда СВЧ-энергия вводилась перпендикулярно силовым линиям магнитного поля при помощи цилиндрического ТЕ11 волновода. В этих экспериментах наблюдался нагрев периферийной плазмы, профили плотности и температуры имели полый характер [1]. Для нагрева плазмы с плотностью, выше плотности отсечки, необходима трансформация в электростатическую Бернштейн волну (ЭБВ). Два сценария нагрева были протестированы на установке: первый с непосредственной трансформацией Н-волны в ЭБВ, в этом случае Н-волна должна быть запущена перпендикулярно магнитному полю в плазму с плотностью, превышающей критическую. В этих экспериментах сильное отражение СВЧ- энергии в слое отсечки препятствовало эффективному нагреву плазмы. Во втором случае используется сценарий с двойной конверсией сначала О-волны в Н-волну с последующим превращением Н-волны в ЭБВ[2]. Методы реализации такого сценария и есть тема настоящей работы

A consistent analysis of (e,e'p) and (d,3He) experiments

The apparent discrepancy between spectroscopic factors obtained in (e,e'p) and (d,3He) experiments is investigated. This is performed first for 48Ca(e,e'p) and 48Ca(d,3He) experiments and then for other nuclei. It is shown that the discrepancy disappears if the (d,3He) experiments are re-analyzed with a non-local finite range DWBA analysis with a bound-state wave function that is obtained from (e,e'p) experiments.Comment: 23 pages, 7 figure

Semigroup Closures of Finite Rank Symmetric Inverse Semigroups

We introduce the notion of semigroup with a tight ideal series and investigate their closures in semitopological semigroups, particularly inverse semigroups with continuous inversion. As a corollary we show that the symmetric inverse semigroup of finite transformations $\mathscr{I}_\lambda^n$ of the rank $\leqslant n$ is algebraically closed in the class of (semi)topological inverse semigroups with continuous inversion. We also derive related results about the nonexistence of (partial) compactifications of classes of semigroups that we consider.Comment: With the participation of the new coauthor - Jimmie Lawson - the manuscript has been substantially revised and expanded. Accordingly, we have also changed the manuscript titl

Study of the p p -> p p pi+ pi- Reaction in the Low-Energy Tail of the Roper Resonance

Exclusive measurements of the p p -> p p pi+ pi- reaction have been carried out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes N* -> N sigma and N* -> Delta pi -> N sigma their energy-dependent relative branching ratio is determined

Relativistic versus Nonrelativistic Optical Potentials in A(e,e'p)B Reactions

We investigate the role of relativistic and nonrelativistic optical potentials used in the analysis of ($e,e'p$) data. We find that the relativistic calculations produce smaller ($e,e'p$) cross sections even in the case in which both relativistic and nonrelativistic optical potentials fit equally well the elastic proton--nucleus scattering data. Compared to the nonrelativistic impulse approximation, this effect is due to a depletion in the nuclear interior of the relativistic nucleon current, which should be taken into account in the nonrelativistic treatment by a proper redefinition of the effective current operator.Comment: Added one new figure, the formalism section has been enlarged and the list of references updated. Added one appendix. This version will appear in Phys. Rev. C. Revtex 3.0, 6 figures (not included). Full postscript version of the file and figures available at http://www.nikhefk.nikhef.nl/projects/Theory/preprints

Comparison of Isoscalar Vector Meson Production Cross Sections in Proton-Proton Collisions

The reaction $pp\to pp\bf \omega$ was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum J\"ulich, Germany). Total as well as differential cross sections were determined at an excess energy of $93 MeV$ ($p_{beam}=2950 MeV/c$). Using the total cross section of $(9.0\pm 0.7 \pm1.1) \mu b$ for the reaction $pp\to pp\omega$ determined here and existing data for the reaction $pp\to pp\bf \phi$, the ratio $\mathcal{R}_{\phi/\omega}=\sigma_\phi/\sigma_\omega$ turns out to be significantly larger than expected by the Okubo-Zweig-Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the $\omega$ production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for $\omega$ production to published distributions for $\phi$ production at $83 MeV$ shows that the data are consistent with an identical production mechanism for both vector mesons

Top-squark searches at the Tevatron in models of low-energy supersymmetry breaking

We study the production and decays of top squarks (stops) at the Tevatron collider in models of low-energy supersymmetry breaking. We consider the case where the lightest Standard Model (SM) superpartner is a light neutralino that predominantly decays into a photon and a light gravitino. Considering the lighter stop to be the next-to-lightest Standard Model superpartner, we analyze stop signatures associated with jets, photons and missing energy, which lead to signals naturally larger than the associated SM backgrounds. We consider both 2-body and 3-body decays of the top squarks and show that the reach of the Tevatron can be significantly larger than that expected within either the standard supergravity models or models of low-energy supersymmetry breaking in which the stop is the lightest SM superpartner. For a modest projection of the final Tevatron luminosity, L = 4 fb-1, stop masses of order 300 GeV are accessible at the Tevatron collider in both 2-body and 3-body decay modes. We also consider the production and decay of ten degenerate squarks that are the supersymmetric partners of the five light quarks. In this case we find that common squark masses up to 360 GeV are easily accessible at the Tevatron collider, and that the reach increases further if the gluino is light.Comment: 32 pages, 9 figures; references adde

Dark Matter, Light Stops and Electroweak Baryogenesis

We examine the neutralino relic density in the presence of a light top squark, such as the one required for the realization of the electroweak baryogenesis mechanism, within the minimal supersymmetric standard model. We show that there are three clearly distinguishable regions of parameter space, where the relic density is consistent with WMAP and other cosmological data. These regions are characterized by annihilation cross sections mediated by either light Higgs bosons, Z bosons, or by the co-annihilation with the lightest stop. Tevatron collider experiments can test the presence of the light stop in most of the parameter space. In the co-annihilation region, however, the mass difference between the light stop and the lightest neutralino varies between 15 and 30 GeV, presenting an interesting challenge for stop searches at hadron colliders. We present the prospects for direct detection of dark matter, which provides a complementary way of testing this scenario. We also derive the required structure of the high energy soft supersymmetry breaking mass parameters where the neutralino is a dark matter candidate and the stop spectrum is consistent with electroweak baryogenesis and the present bounds on the lightest Higgs mass.Comment: 24 pages, 8 figures; version published in Phys.Rev.

The Effects of Media and their Logic on Legitimacy Sources within Local Governance Networks: A Three-Case Comparative Study

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Binding Energy of Hydrogen-Like Impurities in Quantum Well Wires of InSb/GaAs in a Magnetic Field

The binding energy of a hydrogen-like impurity in a thin size-quantized wire of the InSb/GaAs semiconductors with Kane’s dispersion law in a magnetic fieldBparallel to the wire axis has been calculated as a function of the radius of the wire and magnitude ofB, using a variational approach. It is shown that when wire radius is less than the Bohr radius of the impurity, the nonparabolicity of dispersion law of charge carriers leads to a considerable increase of the binding energy in the magnetic field, as well as to a more rapid growth of binding energy with growth ofB