Characterization of a Josephson array for pulse-driven voltage standard in a cryocooler

partially_open6sìPulse-driven Josephson junctions allow the synthesis of very precise both spectrally pure and arbitrary wave forms with frequencies up to the megahertz range. We investigated the properties relevant for metrological applications of series arrays with 4000 Josephson junctions fabricated at PTB in cryocooler and liquid helium. DC electrical parameters were evaluated and Shapiro steps dependence on operating conditions was studied. Both cooling techniques provided similar results for all relevant parameters. In particular, we were able to observe Shapiro step widths of more than 1 mA in cryocooler. Yet, we found that some specific effects related to the different thermal conditions must be taken into account for proper operation in cryocooler.openSosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J.Sosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J

Closed-cycle gas flow system for cooling of high Tc d.c. SQUID magnetometers

A high Tc.d.c SQUID based magnetometer for magnetocardiography is currently under development at the University of Twente. Since such a magnetometer should be simple to use, the cooling of the system can be realized most practically by means of a cryocooler. A closed-cycle gas flow cooling system incorporating such a cooler has been designed, constructed and tested. The aimed resolution of the magnetometer is 0.1 pT Hz−1/2. The required operating temperature for the SQUIDs is 30 to about 77 K with a stability of 2 × 10−4 K Hz−1/2. After a cool-down time of 1–2 h, a stationary cooling power of at least 0.2 W is required. In the design, helium gas is cooled by a Leybold Heraeus RG 210 cryocooler, transported through a gas line, and subsequently passed through a heat exchanger on which SQUIDs can be installed. The lowest obtainable SQUID heat exchanger temperature is 31 ± 2 K. This can be reached in roughly 2–3 h with an optimal mass flow with respect to the cooling power of 6 × 10−6 kg s−1. At this mass flow the cooling power at the SQUID heat exchanger is 0.2 W at 42 K and roughly 1.2 W at 77 K. A temperature stability of 0.05 K was measured at a SQUID heat exchanger temperature of 54 K and a mass flow of 3 × 10kg s−5. The experience gained with this large cooling system will be used in the design of a smaller configuration cooling system, incorporating miniature Stirling cryocoolers. In this paper the design and the construction of the present closed-cycle system are described and test results are presented.\ud \u

Design of a Large Bandwidth Scanning SQUID Microscope using a Cryocooled Hysteretic dc SQUID

I present the design and analysis of a large bandwidth scanning Superconducting Quantum Interference Device (SQUID) microscope. Currently available SQUID microscopes are limited to detecting magnetic fields with frequencies less than 1 MHz. However, for observing nanosecond time scale phenomena such as logic operations in today's computer chips, SQUID microscopes with 1 GHz bandwidth and larger are required. The major limitation in SQUID microscope bandwidth is not the SQUID itself but the electronics and readout technique. To increase bandwidth, the fast transition of a hysteretic dc SQUID from the zero voltage state to the resistive state can be used as the detection element in a new SQUID readout technique, referred to as pulsed SQUID sampling. The technique involves pulsing the bias current to the dc SQUID while monitoring the voltage across it. As the pulse length shortens, the SQUID measures the applied external magnetic flux with shorter sampling time, which increases the bandwidth. Experimental tests of the technique have demonstrated the possibility of following signals with frequencies up to 1 GHz using a dc SQUID with Nb-AlOx-Nb Josephson junctions at around 4 K. Ringing in the pulse profile permitted the effective bandwidth of the sampling technique to be much greater than the nominal value suggested by the pulse length setting on the generator. I identify additional means of increasing bandwidth: redesigning the dc SQUID, implementing transmission line wiring, adding high speed superconducting circuits, etc. which should allow bandwidths to reach 40 GHz and higher. Towards creating a large bandwidth SQUID microscope, I also assembled and tested with collaborators a fully functional 4 K scanning SQUID microscope. With the microscope, which used a nonhysteretic niobium dc SQUID with conventional flux-locked-loop SQUID electronics, I was able to obtain the magnetic field image of a current carrying circuit

Multi-Technique Characterization of Superconducting Materials for Particle Accelerator Applications

We investigated the performance limitations of superconducting radio-frequency (SRF) cavities and materials using multiple experimental techniques. In particular, this study focuses on understanding the surface properties of nitrogen-doped Nb cavities and superconducting thin films with higher Tc such as Nb3Sn. The main goal of this work is to use different techniques to better understand each aspect of the complex loss mechanism in superconductors to further improve the already highly efficient SRF cavities. Nitrogen doping applied to a Nb SRF cavity significantly improves the quality factor Q0 compared to a conventional Nb cavity, at an expense of reduced maximum accelerating gradient. The early quench mechanism was analyzed by using temperature maps before and during the quenching. The temperature maps revealed insignificant heating before the quench, and we concluded that nitrogen doping reduces critical magnetic fields in local regions, leading to premature quenching. To understand the origin of the increasing Q0 with the rf field, the density of states (DOS) of cold spots from nitrogen-doped and standard cavities were measured and analyzed using scanning tunneling microscopy. The results suggested that nitrogen doping reduces the spatial inhomogeneity of superconducting properties and shrinks the metallic suboxide layers, which tunes the DOS in such a way as to produce the field-induced reduction in the surface resistance. To characterize SRF thin films, an experimental setup for measuring a coplanar waveguide (CPW) resonator was developed and tested. A surface impedance measurement of the Nb film showed good agreement with the BCS calculation. The preliminary results from measurements of Nb3Sn and NbTiN films are also presented here. The nonlinear Meissner effect was investigated in Nb3Sn film CPW resonators by measuring the resonant frequency as a function of a parallel magnetic field. Contrary to a conventional quadratic dependence of the penetration depth λ(B) on the applied magnetic field B, as expected in s-wave superconductors, nearly a linear increase of λ(B) with B was observed. It was concluded that this behavior of λ(B) is due to weakly linked grain boundaries on the polycrystalline Nb3Sn films, which can mimic the NLME expected in a clean d-wave superconductor

Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors

In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications. A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement

Study of a Bulk Superconducting Synchronous Machine（バルク超電導同期機に関する研究）

東京海洋大学博士学位論文 2019年度(2020年3月) 応用環境システム学 課程博士 甲第550号指導教員:和泉充全文公表年月日:2020-06-22東京海洋大学201

Experimental Study of Novel Materials and Module for Cryogenic (4K) Superconducting Multi-Chip Modules

The objectives of this proposal are to understand the science and technology of interfaces in the packaging of superconducting electronic (SCE) multichip modules (MCMs) at 4 K. The thermal management issue of the current SCE-MCMs was examined and the package assembly was optimized. A novel thermally conducting and electrically insulating nano-engineered polymer was developed for the thermal management of SCE-MCMs for 4 K cryogenic packaging. Finally, the nano-engineered polymer was integrated as underfill in a SCE-MCM and the thermal and electrical performance of SCE-MCM was demonstrated at 4 K. Niobium based superconducting electronics (SCE) are the fastest known digital logic which operate at 100GHz and greater. Nevertheless, the performance of the SCE device depends on the temperature of the SCE integrated circuits being maintained between 4.2 - 4.25 K. Additionally, as semiconductors are slowly approaching their performance limitations the SCE devices are viewed as a viable alternative for high end computing and commercial wireless applications. However, the successful implementation of SCE\u27s requires the demonstration of these devices in multichip module (MCM) architecture. Thus the stringent thermal constraint and the complex MCM architecture require an innovative method for thermal management which is addressed by the current research