Z = 50 core stability in 110Sn from magnetic-moment and lifetime measurements

Background: The structure of the semimagic 50Sn isotopes were previously studied via measurements of\u3cbr/\u3eB(E2; 21\u3cbr/\u3e+ → 01\u3cbr/\u3e+) and g factors of 21\u3cbr/\u3e+ states. The values of the B(E2; 21\u3cbr/\u3e+) in the isotopes below midshell at\u3cbr/\u3eN = 66 show an enhancement in collectivity, contrary to predictions from shell-model calculations.\u3cbr/\u3ePurpose: This work presents the first measurement of the 21\u3cbr/\u3e+ and 41\u3cbr/\u3e+ states’ magnetic moments in the unstable\u3cbr/\u3eneutron-deficient 110Sn. The g factors provide complementary structure information to the interpretation of the\u3cbr/\u3eobserved B(E2) values.\u3cbr/\u3eMethods: The 110Sn nuclei have been produced in inverse kinematics in an α-particle transfer reaction from\u3cbr/\u3e12C to 106Cd projectiles at 390, 400, and 410 MeV. The g factors have been measured with the transient field\u3cbr/\u3etechnique. Lifetimes have been determined from line shapes using the Doppler-shift attenuation method.\u3cbr/\u3eResults: The g factors of the 21\u3cbr/\u3e+ and 41\u3cbr/\u3e+ states in 110Sn are g(21\u3cbr/\u3e+) = +0.29(11) and g(41\u3cbr/\u3e+) = +0.05(14),\u3cbr/\u3erespectively. In addition, the g(41\u3cbr/\u3e+) = +0.27(6) in 106Cd has been measured for the first time. A line-shape\u3cbr/\u3eanalysis yielded τ (110Sn;21\u3cbr/\u3e+) = 0.81(10) ps and a lifetime of τ (110Sn;31\u3cbr/\u3e−) = 0.25(5) ps was calculated from the\u3cbr/\u3efully Doppler-shifted γ line.\u3cbr/\u3eConclusions: No evidence has been found in 110Sn that would require excitation of protons from the closed\u3cbr/\u3eZ = 50 core

Magnetic moment and lifetime measurements of Coulomb-excited states in 106Cd

Background: The Cd isotopes are well studied, but experimental data for the rare isotopes are sparse. At energies above the Coulomb barrier, higher states become accessible.\u3cbr/\u3e\u3cbr/\u3ePurpose: Remeasure and supplement existing lifetimes and magnetic moments of low-lying states in Cd 106 .\u3cbr/\u3e\u3cbr/\u3eMethods: In an inverse kinematics reaction, a Cd 106 beam impinging on a C 12 target was used to Coulomb excite the projectiles. The high recoil velocities provide a unique opportunity to measure g factors with the transient-field technique and to determine lifetimes from lineshapes by using the Doppler-shift-attenuation method. Large-scale shell-model calculations were carried out for Cd 106 .\u3cbr/\u3e\u3cbr/\u3eResults: The g factors of the 2 + 1 and 4 + 1 states in Cd 106 were measured to be g(2 + 1 )=+0.398(22) and g(4 + 1 )=+0.23(5) . A lineshape analysis yielded lifetimes in disagreement with published values. The new results are τ(Cd 106 ;2 + 1 )=7.0(3)ps and τ(Cd 106 ;4 + 1 )=2.5(2)ps . The mean life τ(Cd 106 ;2 + 2 )=0.28(2)ps was determined from the fully-Doppler-shifted γ line. Mean lives of τ(Cd 106 ;4 + 3 )=1.1(1)ps and τ(Cd 106 ;3 − 1 )=0.16(1)ps were determined for the first time.\u3cbr/\u3e\u3cbr/\u3eConclusions: The newly measured g(4 + 1 ) of Cd 106 is found to be only 59% of the g(2 + 1 ) . This difference cannot be explained by either shell-model or collective-model calculations.\u3cbr/\u3

Collective Thomson scattering model for arbitrarily drifting bi-Maxwellian velocity distributions

\u3cp\u3eIn this paper we derive the equations of collective Thomson scattering (CTS) for an arbitrarily drifting magnetized plasma described by a bi-Maxwellian distribution. The model allows the treatment of anisotropic plasma with different parallel and perpendicular temperatures (with respect to the magnetic field) as well as parallel and perpendicular plasma drift. As could be expected, parallel observation directions are most sensitive to the parallel temperature and drift, whereas perpendicular observation directions are most sensitive to the perpendicular temperature and the perpendicular drift along the observation direction. The perpendicular drift can be related to the radial electric field. Measurements with a spectral resolution better than 0.5 MHz are necessary for the inference of the radial electric field. This spectral resolution and the required scattering geometry are attainable with the current setup of the CTS diagnostic on Wendelstein 7-X.\u3c/p\u3

Fast analysis of collective Thomson scattering spectra on Wendelstein 7-X

\u3cp\u3eTwo methods for fast analysis of Collective Thomson Scattering (CTS) spectra are presented: Function Parametrization (FP) and feedforward Artificial Neural Networks (ANNs). At this time, a CTS diagnostic is being commissioned at the Wendelstein 7-X (W7-X) stellarator, with ion temperature measurements in the plasma core as its primary goal. A mapping was made from a database of simulated CTS spectra to the corresponding ion and electron temperatures (T\u3csub\u3ei\u3c/sub\u3e and T\u3csub\u3ee\u3c/sub\u3e). The mean absolute mapping errors are 4.2% and 9.9% relative to the corresponding T\u3csub\u3ei\u3c/sub\u3e, for the ANN and FP, respectively, for spectra with Gaussian noise equivalent to 10% of the average of the spectral maxima in the database at 650 sampling points per GHz and within a limited parameter space. Although FP provides some insight into the information contents of the CTS spectra, ANNs provide a higher accuracy and noise robustness, are easier to implement, and are more adaptable to a larger parameter space. These properties make ANN mappings a promising all-round method for fast CTS data analysis. Addition of impurity concentrations to the current parameter space will enable fast bulk ion temperature measurements in the plasma core region of W7-X.\u3c/p\u3

154 GHz collective Thomson scattering in LHD

\u3cp\u3eCollective Thomson scattering (CTS) was developed by using a 154 GHz gyrotron, and the first data has been obtained. Already, 77 GHz CTS has worked successfully. However, in order to access higher density region, 154 GHz option enhances the usability that reduces the refraction effect, which deteriorates in the local measurements. The system in the down converted frequency was almost identical to the system for 77 GHz. Probing beam, a notch filter, a mixer, and a local oscillator in the receiver system for 77 GHz option were replaced to those for the 154 GHz option. 154 GHz gyrotron was originally prepared for the second harmonic electron cyclotron heating (ECRH) at 2.75 T. However, scattering signal was masked by the second harmonic electron cyclotron emission (ECE) at 2.75 T. Therefore, 154 GHz CTS was operated at 1.375 T with fourth harmonic ECE, and an acceptable signal to noise ratio was obtained. There is a signature of fast ion components with neutral beam (NB) injection. In addition, the CTS spectrum became broader in hydrogen discharge than in deuterium discharge, as the theoretical CTS spectrum expects. This observation indicates a possibility to identify ion species ratio by the 154 GHz CTS diagnostic.\u3c/p\u3

Deuterium temperature, drift velocity, and density measurements in non-Maxwellian plasmas at ASDEX Upgrade

\u3cp\u3eWe measure the deuterium density, the parallel drift velocity, and parallel and perpendicular temperatures (T\u3csub\u3e∥\u3c/sub\u3e, T\u3csub\u3e⊥\u3c/sub\u3e) in non-Maxwellian plasmas at ASDEX Upgrade. This is done by taking moments of the ion velocity distribution function measured by tomographic inversion of five simultaneously acquired spectra of D\u3csub\u3eα\u3c/sub\u3e-light. Alternatively, we fit the spectra using a bi-Maxwellian distribution function. The measured kinetic temperatures (T\u3csub\u3e∥\u3c/sub\u3e = 9 keV, T⊥ = 11 keV) reveal the anisotropy of the plasma and are substantially higher than the measured boron temperature (7 keV). The Maxwellian deuterium temperature computed with TRANSP (6 keV) is not uniquely measurable due to the fast ions. Nevertheless, simulated kinetic temperatures accounting for fast ions based on TRANSP (T∥= 8.3 keV, T\u3csub\u3e⊥\u3c/sub\u3e = 10.4 keV) are in excellent agreement with the measurements. Similarly, the Maxwellian deuterium drift velocity computed with TRANSP (300 km s\u3csup\u3e-1\u3c/sup\u3e) is not uniquely measurable, but the simulated kinetic drift velocity accounting for fast ions agrees with the measurements (400 km s\u3csup\u3e-1\u3c/sup\u3e) and is substantially larger than the measured boron drift velocity (270 km s\u3csup\u3e-1\u3c/sup\u3e). We further find that ion cyclotron resonance heating elevates T\u3csub\u3e∥\u3c/sub\u3e and T\u3csub\u3e⊥\u3c/sub\u3e each by 2 keV without evidence for preferential heating in the D\u3csub\u3eα\u3c/sub\u3e spectra. Lastly, we derive an expression for the 1D projection of an arbitrarily drifting bi-Maxwellian onto a diagnostic line-of-sight.\u3c/p\u3

High-resolution spectroscopy diagnostics for measuring impurity ion temperature and velocity on the COMPASS tokamak

High-resolution spectroscopy is a powerful tool for the measurement of plasma rotation as well as ion temperature using the Doppler shift of the emitted spectral lines and their Doppler broadening, respectively. Both passive and active diagnostic variants for the COMPASS tokamak are introduced. The passive diagnostic focused on the C III lines at about 465 nm is utilized for the observation of the poloidal plasma rotation. The current set-up of the measuring system is described, including the intended high-throughput optics upgrade. Different options to increase the fiber collection area are mentioned, including a flower-like fiber bundle, and the use of micro-lenses or tapered fibers. Recent measurements of poloidal plasma rotation of the order of 0–6 km/s are shown. The design of the new active diagnostic using a deuterium heating beam and based on charge exchange recombination spectroscopy (C VI line at 529 nm) is introduced. The tool will provide both space (0.5–5 cm) and time (10 ms) resolved toroidal plasma rotation and ion temperature profiles. The results of the Simulation of Spectra code used to examine the feasibility of charge exchange measurements on COMPASS are shown and connected with a selection of the spectrometer coupled with the CCD camera

Collective Thomson scattering diagnostic at Wendelstein 7-X

\u3cp\u3eA Collective Thomson Scattering (CTS) diagnostic is installed at Wendelstein 7-X for ion temperature measurements in the plasma core. The diagnostic utilizes 140 GHz gyrotrons usually used for electron cyclotron resonance heating (ECRH) as a source of probing radiation. The CTS diagnostic uses a quasi-optical transmission line covering a distance of over 40 m. The transmission line is shared between the ECRH system and the CTS diagnostic. Here we elaborate on the design, installation, and alignment of the CTS diagnostic and present the first measurements at Wendelstein 7-X.\u3c/p\u3

Alpha-particle velocity-space diagnostic in ITER

We discuss α-particle velocity-space diagnostic in ITER based on the planned collective Thomson scattering (CTS) and γ-ray spectrometry (GRS) systems as well as ASCOT simulations of the α-particle distribution function. GRS is sensitive to α-particles with energies MeV at all pitches p, and CTS for MeV and . The remaining velocity space is not observed. GRS and CTS view the plasma (almost) perpendicularly to the magnetic field. Hence we cannot determine the sign of the pitch of the α-particles and cannot distinguish co- and counter-going α-particles with the currently planned α-particle diagnostics. Therefore we can only infer the sign-insensitive 2D distribution function by velocity-space tomography for MeV. This is a serious limitation, since co- and counter-going α-particle populations are expected to have different birth rates and neoclassical transport as well as different anomalous transport due to interaction with modes such as Alfvén eigenmodes. We propose the installation of an oblique GRS system on ITER to allow us to diagnostically track such anisotropy effects and to infer the full, sign-sensitive for MeV. α-particles with MeV are diagnosed by CTS only, which does not allow velocity-space tomography on its own. Nevertheless, we show that measurements of the α-particle energy spectrum, which is an ITER measurement requirement, are now feasible for MeV using a velocity-space tomography formalism assuming isotropy in velocity space

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

\u3cp\u3eFusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy.\u3c/p\u3