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Measurement of the current and symmetry of the impact liner on the NTLX experiments

Description: A series of four liner implosion experiments, denoted the Near Tern Liner Experiments (NTLX) was recently conducted on the Shiva Star capacitor bank at the Air Force Research Laboratory (AFRL). Measurement of the driving currents in these experiments is required for postshot analysis of the liner implosion and experiments conducted in the target cylinder. A Faraday rotation measurement was fielded on Shiva Star to measure the current and compare with the current measured by a Rogowski coil technique. The Faraday rotation technique measured the 16 MA currents in these experiments with better than 1% precision. In addition, six B-dot probes were fielded at equal angles around a circle in the powerflow channel outside the liner to measure the symmetry of the liner impact on the target cylinder. The B-dot probes measure the local Idot, which has a jump when the liner impacts the target cylinder. A high-pass filter allows one to measure this jump more accurately. From the relative timing of the jump signals, the offset of the liner axis and the circularity of liner are inferred.
Date: January 1, 2001
Creator: Stokes, J. L. (John L.); Tabaka, L. J. (Leonard J.); Parker, J. V. (Jerald V.); Anderson, D. N.; Corrow, R.; Pritchett, R. et al.
Partner: UNT Libraries Government Documents Department

Hybrid permanent quadrupoles for the 8 GeV transfer line at Fermilab

Description: Hybrid Permanent Magnet Quadrupoles for specialized portions of the 8 GeV transfer line from the Fermilab Booster to the new Main Injector have been built, tested and installed. These magnets use a 0.635 m long iron shell and provide an integrated gradient of 1.48 T-m/m with an iron pole tip radius of 0.0416 m. and pole length of 0.508 m. Bricks of 0.0254 m thick strontium ferrite supply the flux to the back of the pole to produce the desired 2.91 T/m gradient. For temperature compensation, Ni-Fe alloy strips are interspersed between ferrite bricks to subtract flux in a temperature dependent fashion. Adjustments of the permeance of each pole using iron from between the pole and the flux return shell permits the matching of pole potentials. Magnetic potentials of the poles are measured with a Rogowski coil and adjusted to the desired value to achieve the prescribed strength and field uniformity. After these adjustments, the magnets are measured using a rotating coil to determine the integral gradient and the harmonics. These measurements are used to calibrate the production Rogowski coil measurements. Similar quadrupoles are included in the design of the Fermilab Recycler.
Date: June 1, 1997
Creator: Pruss, S. M.; Foster, G. W.; Glass, H. D.; Harding, D. J.; Jackson, G. P.; May, M. P. et al.
Partner: UNT Libraries Government Documents Department

A Superconducting transformer system for high current cable testing

Description: This article describes the development of a direct-current (dc) superconducting transformer system for the high current test of superconducting cables. The transformer consists of a core-free 10 464 turn primary solenoid which is enclosed by a 6.5 turn secondary. The transformer is designed to deliver a 50 kA dc secondary current at a dc primary current of about 50 A. The secondary current is measured inductively using two toroidal-wound Rogowski coils. The Rogowski coil signal is digitally integrated, resulting in a voltage signal that is proportional to the secondary current. This voltage signal is used to control the secondary current using a feedback loop which automatically compensates for resistive losses in the splices to the superconducting cable samples that are connected to the secondary. The system has been commissioned up to 28 kA secondary current. The reproducibility in the secondary current measurement is better than 0.05% for the relevant current range up to 25 kA. The drift in the secondary current, which results from drift in the digital integrator, is estimated to be below 0.5 A/min. The system's performance is further demonstrated through a voltage-current measurement on a superconducting cable sample at 11 T background magnetic field. The superconducting transformer system enables fast, high resolution, economic, and safe tests of the critical current of superconducting cable samples.
Date: February 15, 2010
Creator: Godeke, A.; Dietderich, D. R.; Joseph, J. M.; Lizarazo, J.; Prestemon, S. O.; Miller, G. et al.
Partner: UNT Libraries Government Documents Department

MEASUREMENT OF THE CURRENT AND SYMMETRY OF THE IMPACT LINER ON THE NTLX EXPERIMENTS

Description: A series of four liner implosion experiments, denoted the Near Term Liner Experiments (NTLX) was recently conducted on the Shiva Star capacitor bank at the Air Force Research Laboratory (AFRL). Measurement of the driving currents in these experiments is required for post-shot analysis of the liner implosion and experiments conducted in the target cylinder. A Faraday rotation measurement was fielded on Shiva Star to measure the current and compare with the current measured by a Rogowski coil technique. The Faraday rotation technique measured the 16 MA currents in these experiments with better than 1% precision. In addition, six B-dot probes were fielded at equal angles around a circle in the powerflow channel outside the liner to measure the symmetry of the liner impact on the target cylinder. The B-dot probes measure the local I-dot, which has a jump when the liner impacts the target cylinder. A high-pass filter allows one to measure this jump more accurately. From the relative timing of the jump signals, the offset of the liner axis and the circularity of liner are inferred.
Date: June 1, 2001
Creator: STOKES, J.; PARKER, J. & AL, ET
Partner: UNT Libraries Government Documents Department

Rogowski Loop design for NSTX

Description: The Rogowski Loop is one of the most basic diagnostics for tokamak operations. On the National Spherical Torus Experiment (NSTX), the plasma current Rogowski Loop had the constraints of the very limited space available on the center stack, 5,000 volt isolation, flexibility requirements as it remained a part of the Center Stack assembly after the first phase of operation, and a +120 C temperature requirement. For the second phase of operation, four Halo Current Rogowski Loops under the Center Stack tiles will be installed having +600 C and limited space requirements. Also as part of the second operational phase, up to ten Rogowski Loops will installed to measure eddy currents in the Passive Plate support structures with +350 C, restricted space, and flexibility requirements. This presentation will provide the details of the material selection, fabrication techniques, testing, and installation results of the Rogowski Loops that were fabricated for the high temperature operational and bakeout requirements, high voltage isolation requirements, and the space and flexibility requirements imposed upon the Rogowski Loops. In the future operational phases of NSTX, additional Rogowski Loops could be anticipated that will measure toroidal plasma currents in the vacuum vessel and in the Passive Plate assemblies.
Date: January 6, 2000
Creator: McCormack, B.; Kaita, R.; Kugel, H. & Hatcher, R.
Partner: UNT Libraries Government Documents Department

Megagauss Magnetic Field Sensors Based on Ag2Te

Description: Pulsed power machines capable of producing tremendous energy face various diagnostic and characterizing challenges. Such devices, which may produce 10 - 100MAs, have traditionally relied on Faraday rotation and Rogowski coil technology for time-varying current measurements. Faraday rotation requires a host of costly optical components, including fibers, polarizers, retarders, lasers, and detectors, as well as setup, alignment, and time-consuming post-processing to unwrap the time-dependent current signal. Rogowski coils face potential problems such as physical distortion to the sensor itself due to the tremendous strain caused by magnetically induced pressures, which is proportional to the magnetic field squared (B2). Electrical breakdown in the intense field region is also a major concern. Other related challenges include, but are not limited to, bandwidth and inductance limitations and susceptibility issues related to electrical magnetic interference (EMI).
Date: November 30, 2006
Creator: Mitchen, Stephen; Johnson, Allen L. & Farley, John W.
Partner: UNT Libraries Government Documents Department

A modified Rogowski coil for measurements of hybrid permanent magnets

Description: For large permanent magnets, as proposed for the Fermilab Recycler Ring, it may be important to quickly verify that the magnet`s strength is correct. This may be important, for example, if a magnet is suspected of having changed due to some sort of accident. The field strength of a pure dipole can be readily measured with a Hall probe, but for indexed dipoles and for quadrupoles a Hall probe will not give very accurate results without precise positioning. We have investigated a different approach, the use of a modified Rogowski coil to measure the magnetic potential of each pole. As long as magnet geometry is fixed and known, measurement of the magnetic potential at each pole gives a good measurement of field strength even for magnets with large quadrupole components. The construction and use of such a coil and the precision of measurements made with it will be discussed. 4 refs., 5 figs.
Date: August 1, 1996
Creator: Bertsche, K.
Partner: UNT Libraries Government Documents Department

NSTX High Temperature Sensor Systems

Description: The design of the more than 300 in-vessel sensor systems for the National Spherical Torus Experiment (NSTX) has encountered several challenging fusion reactor diagnostic issues involving high temperatures and space constraints. This has resulted in unique miniature, high temperature in-vessel sensor systems mounted in small spaces behind plasma facing armor tiles, and they are prototypical of possible high power reactor first-wall applications. In the Center Stack, Divertor, Passive Plate, and vessel wall regions, the small magnetic sensors, large magnetic sensors, flux loops, Rogowski Coils, thermocouples, and Langmuir Probes are qualified for 600 degrees C operation. This rating will accommodate both peak rear-face graphite tile temperatures during operations and the 350 degrees C bake-out conditions. Similar sensor systems including flux loops, on other vacuum vessel regions are qualified for 350 degrees C operation. Cabling from the sensors embedded in the graphite tiles follows narrow routes to exit the vessel. The detailed sensor design and installation methods of these diagnostic systems developed for high-powered ST operation are discussed.
Date: November 1, 1999
Creator: B.McCormack; Kugel, H.W.; Goranson, P.; Kaita, R. & al, et
Partner: UNT Libraries Government Documents Department

Transient response of single-domain Y-Ba-Cu-O rings to pulsed magnetic fields.

Description: Shielding current limits and magnetic diffusion characteristics have been measured at 77 K for a set of YBCO single-domain rings. These were fabricated from melt-textured cylindrical YBCO monoliths that were densified to nearly 100%, and then oriented from a single seed. The rings were surrounded by a drive coil that can, under pulse conditions, achieve applied magnetic fields in excess of 1 T and induce currents in excess of 50 kA. Simultaneous magnetic characterization with a Rogowski coil and Hall probe was used to determine the induced current in the sample and the magnetic field in the center of the sample. Magnetic fields trapped in the samples were mapped with a scanning Hall probe. When compared with similar measurements on multidomain c-axis-oriented YBCO rings, the flux penetration is faster and more uniform around the circumference of the ring. The observed critical current density, 15,000 A/cm{sup 2} at 77 K, is suitable for application in penetration-type fault current limiters. Separate measurements of the trapped magnetic field and critical current density in the rings are compared with results obtained by analysis of magnetic diffusion characteristics.
Date: July 30, 2002
Creator: Askew, T. R.; Weber, J. M.; Cha, Y. S.; Claus, H. & Veal, B. W.
Partner: UNT Libraries Government Documents Department

Design and Fabrication of the Lithium Beam Ion Injector for NDCX-II

Description: A 130 keV injector is developed for the NDCX-II facility. It consists of a 10.9 cm diameter lithium doped alumina-silicate ion source heated to {approx}1300 C and 3 electrodes. Other components include a segmented Rogowski coil for current and beam position monitoring, a gate valve, pumping ports, a focusing solenoid, a steering coil and space for inspection and maintenance access. Significant design challenges including managing the 3-4 kW of power dissipation from the source heater, temperature uniformity across the emitter surface, quick access for frequent ion source replacement, mechanical alignment with tight tolerance, and structural stabilization of the cantilevered 27-inch OD graded HV ceramic column. The injector fabrication is scheduled to complete by May 2011, and assembly and installation is scheduled to complete by the beginning of July. The Neutralized Drift Compression eXperiment (NDCX-II) is for the study of high energy density physics and inertial fusion energy research utilizing a lithium ion (Li+) beam with a current of 93 mA and a pulse length of 500 ns (compressed to 1 ns at the target). The injector is one of the most complicated sections of the NDCX-II accelerator demanding significant design and fabrication resources. It needs to accommodate a relatively large ion source (10.9 cm), a high heat load (3-4 kW) and specific beam optics developed from the physics model. Some specific design challenges are noted in this paper.
Date: March 1, 2011
Creator: Takakuwa, J.
Partner: UNT Libraries Government Documents Department

Measurement techniques

Description: The discussion will be restricted to measurements of voltage and current. Also, although the measurements themselves should be as quantitative as possible, the discussion is rather nonquantitative. Emphasis is on types of instruments, how they may be used, and the inherent advantages and limitations of a given technique. A great deal of information can be obtained from good, clean voltage and current data. Power and impedance are obviously inherent if the proper time relationships are preserved. Often an associated, difficult-to-determine, physical event can be evaluated from the V-I data, such as a time-varying load characteristic, or the time of light emission, etc. The lack of active high voltage devices, such as 50-kV operational amplifiers, restricts measurement devices to passive elements, primarily R and C. There are a few more exotic techniques that are still passive in nature. There are several well-developed techniques for voltage measurements. These include: spark gaps; electrostatic meters; capacitive dividers; mixed RC dividers; and the electro-optic effect. Current is measured by either direct measurement of charge flow or by measuring the resulting magnetic field.
Date: October 1, 1980
Creator: Willis, W.L.
Partner: UNT Libraries Government Documents Department

Electrical measurement techniques for pulsed high current electron beams

Description: The advent of high current (1 to 100 kA), moderate energy (>10 MeV), short pulse (1 to 100 ns) electron accelerators used for charged particle beam research has motivated a need to complement standard diagnostics with development of new diagnostic techniques to measure electron beam parameters. A brief survey is given of the diagnostics for measuring beam current, position, size, energy, and emittance. While a broad scope of diagnostics will be discussed, this survey will emphasize diagnostics used on the Experimental Test Accelerator (ETA) and Advanced Test Accelerator (ATA). Focus is placed on diagnostics measuring beam current, position and size. Among the diagnostics discussed are resistive wall current monitors, B/sub theta/ loops, Rogowski coils, Faraday cups, and x-ray wire diagnostics. Operation at higher current levels also increases radiation and electromagnetic pulse interference. These difficulties and methods for circumventing them are also discussed.
Date: April 1, 1986
Creator: Struve, K.W.
Partner: UNT Libraries Government Documents Department