Search

A heavy ion beam probe (HIBP) using a 3-MV tandem accelerator has been installed on large helical device (LHD). Electrostatic potential in core plasma can be measured under the toroidal magnetic field strength of up to 3 T. By using the HIBP, the transition of potential profiles from electron-root to ion-root is observed in core plasmas during ramp-up of the electron density. Potential fluctuations are also measured electron cyclotron current drive (ECCD). Two kind of characteristic fluctuations are observed. One is a reversed-shear-induced Alfven eigenmode (RSAE), whose frequency varies during the evolution of the rotational transform profile, and the other is with a constant geodeisc acoustic mode (GAM) frequency.

A method to measure magnetic field fluctuation using a heavy ion beam probe for a toroidal magnetically confined plasma is proposed by providing a mathematical formula to connect the probing beam movement with the change in the magnetic field. The first challenge of the method has been faced in an electron-cyclotron resonance heated plasma in the compact helical system (CHS). The results reveal the existence of three characteristic frequency regimes of the magnetic field fluctuations: a low frequency regime showing a long-distance correlation, an intermediate frequency regime obeying a power law and the turbulence regime. Discussion is held on the degree of the contaminations in the local magnetic field fluctuation that are caused by the magnetic field fluctuations integrated along the beam orbit and the local electric field fluctuations.

Effects of 'inset feeding' on microstrip antenna properties have been investigated by analysing the designed and experimental results. Dimensions of a single-patch antenna with this feed architecture have been optimized with an operating frequency of 11.74 GHz with the aim of using it to fabricate a superconducting microstrip array antenna for a direct broadcast satellite (DBS) communication system. In our observation, the antenna gain, resonant frequency and input impedance of the antenna are found to change with change of the feed architecture. A single-patch YBa2Cu3O7−δ (YBCO) superconducting antenna and a gold antenna with this optimized structure have been fabricated for the comparison of properties between these two types of antennas. The comparison of the gain between the YBCO superconducting and gold antennas measured at 77 K shows that the YBCO antenna has 1.8 dB higher gain than the gold antenna with an identical configuration.

Edge transport barrier (ETB) formation was observed in a compact helical system. A sharp decrease in Hα emission indicates the quick transition of edge particle transport. The increase in the density gradient at the edge was measured by using various profile diagnostics. The transition process has a slowly developing pre-phase, and a quick transition for which the fastest case is less than 0.2 ms. There exists a heating power threshold which is roughly proportional to the density and the magnetic field. The transition and back transition is controlled by the heating power. The magnetic configuration effect on ETB formation was also studied. The local density measurement by beam emission spectroscopy shows intermittent bursts of low frequency fluctuations during the ETB formation phase. When the initial density profile is very hollow, ETB formation together with the electron temperature increase (electron internal transport barrier) in the core region, was observed for the NBI discharges without ECH.

Epitaxial thin films of a Tl(Ba,Sr)2Ca2Cu3Oy (Tl-1223) superconductor with a thickness of 5000???were grown on a moderate dielectric constant (? = 23.8) substrate (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) in order to study the miniaturization of a superconducting thin film microwave filter. For the annealing conditions followed in this work, we observed two kinds of surface morphology: both of them have a large plate-like morphology with pits but they differ from each other by the presence of needle shaped (a-axis-oriented) grains on top of the plate-like surface. The superconducting transition temperature (Tc) and critical current density (Jc) for both kinds of films (with and without needles) are about 108?K and at 90?K, respectively. However, the values of the temperature dependence of the microwave surface resistance (Rs) of the films with needles are about one order higher than those for the films without needles, due to the absorption of microwaves by a-axis-oriented needles. The value of Rs for the films without needles at 90?K and 10?GHz is 507???, which satisfies the requirement for microwave device applications with high performance.

The use of high-temperature superconducting films for the fabrication of antennas allows us to realize radiating structures that are small in size and have a very high efficiency. In this paper, we investigate the properties of a novel compact antenna obtained by crossing a square patch with diagonal and transverse slots. Single patch antennas, with both linear and circular polarization operating in the X-band, with a size reduction of about 40% as compared to conventional square patches, have been designed and tested at prototype level. They have been realized by using double-sided YBa2Cu3O7−x(YBCO) and Tl2Ba2Ca1Cu2O8(Tl-2212) superconducting films grown on MgO substrates and have been measured using a portable cryocooler. At T = 77 K, the experimental scattering parameter, S11, agrees well with simulations, showing a power handling of 23 dBm for YBCO devices. The miniaturized patch antenna investigated has allowed us to realize a 4 × 4 array of linear polarization antennas at 11.5 GHz, using a YBCO film grown on a MgO substrate with a 2'' diameter, by considering a reduced interspace (more than 20%) between the elements. The far-field pattern and the 16-array gain are in good agreement with the simulated results.

Single-feed circularly polarized microstrip patch and patch array antennas for `direct-to-home' receiving system at around 12?GHz are studied by theoretical analysis and experiments. A full-wave microwave circuit simulator (Em), based on the method of moments and capable of handling the microwave surface impedance, has been used in the theoretical analysis of the antennas. Antennas have been fabricated from both normal conductor (gold) and YBa2Cu3O7-x (YBCO) superconductor for comparison. Measured results on resonant frequency (fr), return loss, gain, bandwidth, and axial ratio are presented. The antennas are found to show a very low axial ratio and a moderate bandwidth. In the comparison of gain, the superconducting antennas showed a remarkable improvement over their gold counterparts. The receiving power of a four-element array fabricated from a single-side YBCO thin film on (100) MgO single crystal substrate is found to be 1.8?dB higher than that of a gold array with identical configuration and both measured at 77?K.

High-temperature superconducting (HTS) passive microwave devices, such as filters and antennas, are promising devices. In particular, HTS filters may be successfully marketed in the near future. Cross-coupled filters, ring filters, and coplanar waveguide filters are good options to reduce filter size. On the other hand, HTS patch antennas which can be cooled by a cryo-cooler are also promising devices as well, since they show higher efficiency than normal antennas. This paper examines the design process and filter properties of HTS filters as well as the gains, directivity, and cooling system of HTS patch antennas.

International audience; We describe a 1 GHz reference signal with 10-15 level fractional frequency stability for averaging times longer than 1 s, synthesized from a 10.8 GHz oscillation frequency of a cryogenic-sapphire-resonator-based ultra-stable oscillator and phase locked to a hydrogen maser with a time constant of about 1000 s. The degradation of the short term stability of the reference signal by phase locking to the hydrogen maser was evaluated. We also report on the implementation of the 1 GHz signal down converted to 5 MHz as a reference oscillator for a cesium atomic fountain frequency standard.

Alkali zeolite is often used as an ion source material owing to its easy extraction of alkali ions. In our laboratory, we fabricated zeolite containing a particular alkali species through a replacement reaction with sodium zeolite. In this paper, we present a simple mathematical model for describing this replacement reaction for making zeolite containing a particular alkali species. In this model, the fraction of alkali ions trapped in the zeolite lattice is expressed as a function of the numbers of substitution reactions in a concise recursion formula. This formula gives a simple estimation of efficiency for fabricating alkali zeolite in terms of the consumptions of time and chemicals.

We have developed microwave kinetic inductance detectors (MKIDs) consisting of dual-purpose rewound spirals (spiral-MKIDs) made of a metal nitride superconductor for terahertz imaging applications. An NbN-based spiral-MKID array with 25 pixels was fabricated, and the fundamental performance of the terahertz receptivity was evaluated at the equilibrium temperature of a conventional 4He refrigerator (3 K). The microwave transmission property of the array showed the 25 resonance lines, equally separated by frequency, in the microwave range from 2.70 to 2.95 GHz. To evaluate its optical performance as a terahertz detector, we measured the spiral-MKID's spectral response, response time, and noise equivalent power (NEP), and confirmed that it revealed a broad spectral response from 1 to 9 THz and an effective response time of approximately 80 μs. The noise-equivalent power was estimated to be .

We have developed a laser system for use in the velocity selection of cesium atoms through stimulated Raman transition. The laser system consisted of two phase-locked extended-cavity diode lasers with a frequency offset of 9.2 GHz, whose intensity was also stabilized using an acoustooptic modulator. The power concentration and the intensity stability were 93% and 0.1%, respectively.

45° grain boundaries, which drastically increase surface resistance (RS) in superconducting YBa2Cu3O7- films for microwave devices on MgO substrates, are eliminated using a new buffer layer of BaSnO3.BaSnO3 buffer layers and YBa2Cu3O7- films are grown by ArF pulsed laser deposition. Epitaxial relationships among BaSnO3, YBa2Cu3O7- and MgO are confirmed by x-ray -scanning. The RS values of the YBa2Cu3O7- films are measured using a dielectric resonator with 22 GHz TE011 mode. The epitaxial YBa2Cu3O7- films grown on BaSnO3 buffered MgO substrates show lower RS than YBa2Cu3O7- films directly grown on MgO substrates. The BaSnO3 buffer layer which enables YBa2Cu3O7- films to grow without 45° grain boundaries at a optimum film growth condition is attractive for microwave applications.

We investigated the effect of introducing artificial pinning centers (APCs) into YBa2Cu3O7-δ (YBCO) thin films to improve the critical current density (Jc) and reduce the microwave surface resistance (Rs) in a high dc magnetic field. Introduction of the APC was realized by dispersing BaHfO3(BHO) particulates in the YBCO thin films. Four types of sintered YBCO ceramics with x wt % (x = 0.5, 1.0, 2.0) BHO were used as laser targets in order to fabricate YBCO thin films with various amounts of BHO and investigate the influence of the BHO doping concentration. Jc was measured by a four probe method. We measured Jc in a magnetic field which was applied parallel to the c-axis (Jc(p)), and Jc in a magnetic field which was applied perpendicular to the c-axis (Jc(n)). The Rs was calculated using a correlating equation of Jc and Rs. The Jc(p) at 5 T and 20 K of 1.5 wt% BHO doped YBCO thin film was the largest at 3.4 MA/cm 2 . The Jc(n) of 1.5 wt% BHO doped YBCO thin film was 2.5 MA/cm 2 , which is comparable to non-doped. The Rs(n) and Rs(p) of all YBCO thin films was less than 25 μΩ at 500 MHz. Therefore, we clarified the possibility that the most effective way to fabricate thin film for NMR coil application is by doping YBCO with BHO 1.5 wt%.

The effect of magnetic field configurations on plasma flow velocity was investigated by measuring the parallel flow velocity (v∥) using a charge-exchange recombination spectroscopy during neutral beam injection in three different toroidal mirror configurations of Heliotron J: high, standard and reversed mirror configurations. The magnetic ripple strengths, γ, for these mirror configurations were γ = 0.073 m−1, 0.031 m−1 and 0.027 m−1, respectively, at the normalized averaged minor radius ρ = 0.07. The magnetic ripple strength is defined as γ = {〈(∂B/∂l)2/B2〉}1/2, where 〈...〉 is the flux surface averaged value and l is the length along the magnetic field line. At ρ = 0.07, the parallel flow velocity in the high mirror configuration (v∥ ~ 4 km s−1) was 2–3 times smaller than those in the standard and reversed mirror configurations (v∥ ~ 10–12 km s−1). An anticipated interpretation is that the difference in the neoclassical damping force contributes to the difference in v∥ among the three mirror configurations.

Energy deposition by hot electrons in ultra-short, high intensity laser produced dense plasma was investigated by X-ray spectroscopy. Kα lines from partially ionized chlorine embedded in a triple layered, reduced mass target was observed to derive electron temperatures. Fast electrons generated by intense laser were confined in the smaller mass target, showing efficient increase of temperature. Heating efficiency by electron refluxing was one percent of laser energy and surface heating is significant at the laser intensity of ~ 1×1018 W/cm2.

An edge transport barrier (ETB) formation and an improved L-mode (IL mode) have been simultaneously realized in the high density region ( ) on the Compact Helical System (CHS). When the ETB is formed during the IL mode, the density reduction in the edge region is suppressed by the barrier formation. As a result of the continuous increase in the temperature by the IL mode, the stored energy during the combined mode increased up to the maximum stored energy (W p ∼ 9.4 kJ) recorded in the CHS experiments. The plasma pressure in the peripheral region increases up to three times compared with the L-mode, and the large edge plasma pressure gradient is formed accompanying the pedestal structure. This is caused by the anomalous transport reduction that is confirmed by the sharp drop in the density fluctuation in the edge region. The neutral particle density reduction in the peripheral region and the metallic impurity accumulation in the core plasma are simultaneously observed during the high density ETB formation.

Edge transport barrier (ETB) formation and a reheat mode have been simultaneously realized on the Compact Helical System (CHS). The new mode is induced by neutral particle reduction in the edge region, which is caused by shutting off fueling after a strong gas-puffing. When both the reheat mode and the ETB are simultaneously realized, the density reduction is suppressed by the ETB in the peripheral region, and the temperature continues to increase by the reheat mode. This mode provides an enhanced confinement in the high density region (e ~ 1.2 × 1020mr-3) compared to the ETB formation without the reheat mode, because of a large suppression of an anomalous transport, which is confirmed with fluctuation measurements in the edge region.

We designed transmit bandpass filters (BPFs) by using superconducting bulk ring resonators and dielectric trimming rods at a 5.0 GHz center frequency with a 100 MHz bandwidth. The filter with ring resonators was smaller than the filter with disk resonators, where the size was defined as the distance between the input/output ports. We found that the size contributes significantly to the miniaturization of multi-pole filters. A trimming mechanism was also evaluated. The frequency shift region of a single ring resonator reached more than 500 MHz after we moved a dielectric rod whose dielectric constant was 39 into the ring resonator. A 3-pole strip-line BPF was also designed using a Chebyshev function by using three pairs of ring resonators and dielectric trimming rods with the same dimensions and by adjusting the positions of the trimming rods. We obtained the optimal frequency response with a low loss and passband ripple for this BPF.

A synthesized microwave local oscillator for a cesium atomic frequency standard has been implemented using an ultra-stable oscillator. The oscillator was based on a high Q-factor cryogenic-sapphire-resonator cooled with liquid helium which operates on a Whispering Gallery mode. The cesium hyperfine transition frequency of 9.192 GHz was synthesized from the 10.812 GHz oscillation frequency, chosen because the corresponding mode had the best frequency stability. When compared with a hydrogen maser reference the local oscillator exhibited a fractional frequency stability of 6×10-15 for integration times of 600 to 1200 s at 9.192 GHz, limited only by the cryogenic sapphire oscillator.

A continuous-wave optical parametric oscillator (OPO) of RbTiOAsO4 (RTA) is used as a light source for an optical frequency interval divider. Pumped by 1.5 W of the 532-nm second harmonic of the high power YAG laser, the OPO generates a power-stable signal-idler mode pair at 912 nm and 1292 nm with an output of 40 mW and spectral bandwidth of less than 5 KHz. The tuning characteristics are examined in detail. The result of the optical frequency interval division is presented.

We developed a magnetic shield and generated a uniform magnetic field for an atomic fountain time and frequency standard at the National Research Laboratory of Metrology in Japan. The shielding factor was 8000 and the uniformity of the generated magnetic field was 0.2%, both of which are sufficient for the magnetic field to realize a required accuracy of 1 ×10-16.