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Calculation of Eddy Currents In the CTH Vacuum Vessel and Coil Frame

Description: Knowledge of eddy currents in the vacuum vessel walls and nearby conducting support structures can significantly contribute to the accuracy of Magnetohydrodynamics (MHD) equilibrium reconstruction in toroidal plasmas. Moreover, the magnetic fields produced by the eddy currents could generate error fields that may give rise to islands at rational surfaces or cause field lines to become chaotic. In the Compact Toroidal Hybrid (CTH) device (R0 = 0.75 m, a = 0.29 m, B ≤ 0.7 T), the primary driver of the eddy currents during the plasma discharge is the changing flux of the ohmic heating transformer. Electromagnetic simulations are used to calculate eddy current paths and profile in the vacuum vessel and in the coil frame pieces with known time dependent currents in the ohmic heating coils. MAXWELL and SPARK codes were used for the Electromagnetic modeling and simulation. MAXWELL code was used for detailed 3D finite-element analysis of the eddy currents in the structures. SPARK code was used to calculate the eddy currents in the structures as modeled with shell/surface elements, with each element representing a current loop. In both cases current filaments representing the eddy currents were prepared for input into VMEC code for MHD equilibrium reconstruction of the plasma discharge. __________________________________________________
Date: September 25, 2012
Creator: Zolfaghari, A.; Brooks, A; Michaels, A.; Hanson, J. & Hartwell, G.
Partner: UNT Libraries Government Documents Department

Field errors introduced by eddy currents in Fermilab main injector magnets

Description: The Fermilab Main Injector ramps from 8 GeV to 120 GeV in about half a second. The rapidly changing magnetic field induces eddy currents in the stainless steel vacuum tubes, which in turn produce error fields that can affect the beam. Field calculations and measurements are presented for the dipole and quadrupole magnets.
Date: October 1, 1997
Creator: Walbridge, D.G.C.; Brown, B.C.; Dinanco, J.B.; Sharoran, S.A. & Sim, J.W.
Partner: UNT Libraries Government Documents Department

On the modeling, design and validation of two dimensional quasi-static eddy current forces in a mechanical oscillator.

Description: Damping vibrations is important in the design of some types of inertial sensing devices. One method for adding damping to a device is to use magnetic forces generated by a static magnetic field interacting with eddy currents. In this report, we develop a 2-dimensional finite element model for the analysis of quasistatic eddy currents in a thin sheet of conducting material. The model was used for design and sensitivity analyses of a novel mechanical oscillator that consists of a shuttle mass (thin sheet of conducting material) and a set of folded spring elements. The oscillator is damped through the interaction of a static magnetic field and eddy currents in the shuttle mass. Using a prototype device and Laser Dopler Velocimetry (LDV), measurements were compared to the model in a validation study using simulation based uncertainty analyses. Measurements were found to follow the trends predicted by the model.
Date: October 1, 2005
Creator: Mitchell, John Anthony; Epp, David S. & Wittwer, Jonathan W.
Partner: UNT Libraries Government Documents Department

AC Losses in the MICE Channel Magnets -- Is This a Curse or aBlessing?

Description: This report discusses the AC losses in the MICE channelmagnets during magnet charging and discharging. This report talks aboutthe three types of AC losses in the MICE magnets; the hysteretic AC lossin the superconductor, the coupling AC loss in the superconductor and theeddy current AC loss in the magnet mandrel and support structure. AClosses increase the heat load at 4 K. The added heat load increases thetemperature of the second stage of the cooler. In addition, AC losscontributes to the temperature rise between the second stage cold headand the high field point of the magnet, which is usually close to themagnet hot spot. These are the curses of AC loss in the MICE magnet thatcan limit the rate at which the magnet can be charge or discharged. Ifone is willing to allow some of the helium that is around the magnet toboil away during a magnet charge or discharge, AC losses can become ablessing. The boil off helium from the AC losses can be used to cool theupper end of the HTS leads and the surrounding shield. The AC losses arepresented for all three types of MICE magnets. The AC loss temperaturedrops within the coupling magnet are presented as an example of how boththe curse and blessing of the AC losses can be combined.
Date: January 31, 2008
Creator: Green, M.A.; Wu, H.; Wang, L.; Kai, L.L.; Jia, L.X. & Yang, S.Q.
Partner: UNT Libraries Government Documents Department

Eddy current scanning at Fermilab

Description: In the framework of SRF cavity development, Fermilab is creating the infrastructure needed for the characterization of the material used in the cavity fabrication. An important step in the characterization of ''as received'' niobium sheets is the eddy current scanning. Eddy current scanning is a non-destructive technique first adopted and further developed by DESY with the purpose of checking the cavity material for sub-surface defects and inclusions. Fermilab has received and further upgraded a commercial eddy current scanner previously used for the SNS project. The upgrading process included developing new filtering software. This scanner is now used daily to scan the niobium sheets for the Fermilab third harmonic and transverse deflecting cavities. This paper gives a status report on the scanning results obtained so far, including a discussion of the typology of signals being detected. We also report on the efforts to calibrate this scanner, a work conducted in collaboration with DESY.
Date: July 1, 2005
Creator: Boffo, C.; Bauer, P.; Foley, M.; /Fermilab; Brinkmann, A.; /DESY et al.
Partner: UNT Libraries Government Documents Department

Non-Destructive Evaluation of Thermal Spray Coating Interface Quality By Eddy Current Method

Description: Thermal spray coating is usually applied through directing molten or softened particles at very high velocities onto a substrate. An eddy current non-destructive inspection technique is presented here for thermal spray coating interface quality characterization. Several high-velocity-oxy-fuel (HVOF) coated steel plates were produced with various surface preparation conditions or spray process parameters. A quad-frequency eddy current probe was used to manually scan over the coating surface to evaluate the bonding quality. Experimental results show that different surface preparation conditions and varied process parameters can be successfully differentiated by the impedance value observed from the eddy current probe. The measurement is fairly robust and consistent. This non-contact, nondestructive, easy-to-use technique has the potential for evaluating the coating quality immediately after its application so that any defects can be corrected immediately.
Date: August 10, 2006
Creator: Mi, B.; Zhao, G. & Bayles, R.
Partner: UNT Libraries Government Documents Department

Eddy sensors for small diameter stainless steel tubes.

Description: The goal of this project was to develop non-destructive, minimally disruptive eddy sensors to inspect small diameter stainless steel metal tubes. Modifications to Sandia's Emphasis/EIGER code allowed for the modeling of eddy current bobbin sensors near or around 1/8-inch outer diameter stainless steel tubing. Modeling results indicated that an eddy sensor based on a single axial coil could effectively detect changes in the inner diameter of a stainless steel tubing. Based on the modeling results, sensor coils capable of detecting small changes in the inner diameter of a stainless steel tube were designed, built and tested. The observed sensor response agreed with the results of the modeling and with eddy sensor theory. A separate limited distribution SAND report is being issued demonstrating the application of this sensor.
Date: August 1, 2011
Creator: Skinner, Jack L.; Morales, Alfredo Martin; Grant, J. Brian; Korellis, Henry James; LaFord, Marianne Elizabeth; Van Blarigan, Benjamin et al.
Partner: UNT Libraries Government Documents Department

Robotic Welding and Inspection System

Description: This paper presents a robotic system for GTA welding of lids on cylindrical vessels. The system consists of an articulated robot arm, a rotating positioner, end effectors for welding, grinding, ultrasonic and eddy current inspection. Features include weld viewing cameras, modular software, and text-based procedural files for process and motion trajectories.
Date: June 1, 2008
Creator: Smartt, H. B.; Pace, D. P.; Larsen, E. D.; McJunkin, T. R.; Nichol, C. I.; Clark, D. E. et al.
Partner: UNT Libraries Government Documents Department

A QR accelerated volume-to-surface boundary condition for finite element solution of eddy current problems

Description: We are concerned with the solution of time-dependent electromagnetic eddy current problems using a finite element formulation on three-dimensional unstructured meshes. We allow for multiple conducting regions, and our goal is to develop an efficient computational method that does not require a computational mesh of the air/vacuum regions. This requires a sophisticated global boundary condition specifying the total fields on the conductor boundaries. We propose a Biot-Savart law based volume-to-surface boundary condition to meet this requirement. This Biot-Savart approach is demonstrated to be very accurate. In addition, this approach can be accelerated via a low-rank QR approximation of the discretized Biot-Savart law.
Date: September 8, 2006
Creator: White, D; Fasenfest, B; Rieben, R & Stowell, M
Partner: UNT Libraries Government Documents Department

The Role of Eddy-Tansport in the Thermohaline Circulation

Description: Several research themes were developed during the course of this project. (1) Low-frequency oceanic varibility; (2) The role of eddies in the Antarctic Circumpolar Current (ACC) region; (3) Deep stratification and the overturning circulation. The key findings were as follows: (1) The stratification below the main thermocline (at about 500m) is determined in the circumpolar region and then communicated to the enclosed portions of the oceans through the overturning circulation. (2) An Atlantic pole-to-pole overturning circulation can be maintained with very small interior mixing as long as surface buoyancy values are shared between the northern North Atlantic and the ACC region.
Date: November 17, 2011
Creator: Cessi, Dr. Paola
Partner: UNT Libraries Government Documents Department

Weld quality evaluation using a high temperature SQUID array

Description: This paper presents preliminary data for evaluating weld quality using high temperature SQUIDS. The SQUIDS are integrated into an instrument known as the SQUID Array Microscope, or SAMi. The array consists of ll SQUIDs evenly distributed over an 8.25 mm baseline. Welds are detected using SAMi by using an on board coil to induce eddy currents in a conducting sample and measuring the resulting magnetic fields. The concept is that the induced magnetic fields will differ in parts of varying weld quality. The data presented here was collected from three stainless steel parts using SAMi. Each part was either solid, included a good weld, or included a bad weld. The induced magnetic field's magnitude and phase relative to the induction signal were measured. For each sample considered, both the magnitude and phase data were measurably different than the other two samples. These results indicate that it is possible to use SAMi to evaluate weld quality.
Date: January 1, 2002
Creator: Clark, D. D. (David D.); Espy, M. A. (Michelle A.); Kraus, Robert H., Jr.; Matlachov, A. N. (Andrei N.) & Lamb, J. S. (Jessica S.)
Partner: UNT Libraries Government Documents Department


Description: Recent beam experiments at BNL's AGS Booster have enabled us to study in more detail the effects of eddy currents on the lattice structure and our control over the betatron tune. The Booster is capable of operating at ramp rates as high as 9 T/sec. At these ramp rates eddy currents in the vacuum chambers significantly alter the fields and gradients seen by the beam as it is accelerated. The Booster was designed with these effects in mind and to help control the field uniformity and linearity in the Booster Dipoles special vacuum chambers were designed with current windings to negate the affect of the induced eddy currents. In this report results from betatron tune measurements and eddy current simulations will be presented. We will then present results from modeling the accelerator using the results of the magnetic field simulations and compare these to the measurements.
Date: June 23, 2006
Creator: BROWN, K.A.; AHRENS, L.; GARDNER, C.; GLENN, J.W.; HARVEY, M.; MENG, W. et al.
Partner: UNT Libraries Government Documents Department

Accurate Micrometer for Corrosion Samples

Description: A micrometer that utilizes eddy current techniques is described. The gage is capable of measuring nominal 0.5000-in. aluminum rods to an accuracy of plus or minus 0.00005 in., and is unaffected by residual nonconductive surface filins such as oxides or corrosion products. (auth)
Date: June 1, 1960
Creator: Woodward, W. J.
Partner: UNT Libraries Government Documents Department


Description: ing. Radiography was used to ore fter bending. The ultrainspect the alloys cores, ished fuel elements. as used to determine element core blanks. at ing fatigue tests were performed in the range 1300 to 1500 F, for frequencies of 6 and 60 cpm. Continuous traces of load and strain were made to determine relationships between stress, strain, and lifetime, for lifetimes vithin the range of 10/sup 3/ and 10/sup 5/ cycles. The data obtained indicate that fatigue strength, whether measured in stress, total strain, or plastic strain, is a function of both temperature and frequency. It was found that the relationship between stress and strain varies with cycles of stress reversal, never reaching an equilibrium condition. In addition, the strain behavior of a specimen during stress cycling is not continuous. Strain in the plastic region was found to occur in sudden, steplike increments which are predictable functions of temperature, stress, frequency, and cycles. (auth)
Date: June 1, 1959
Creator: Renken, C.J. & Myers, R.G.
Partner: UNT Libraries Government Documents Department

The conducting shell stellarator: A simple means for producing complicated fields

Description: One of the main characteristics of stellarators, both helical and modular, is that their coil sets must take difficult shapes in order to produce the complicated stellarator magnetic fields. The complex coil shapes make fabrication difficult and costly compared to say the toroidal field, TF, coil set of a tokamak. The conducting shell stellarator, CSS, configuration described in this report shows that complicated stellarator fields can be produced by inducing eddy currents in a conducting shell from a simple TF coil set (a field that varies like 1/R). This technique is applicable not only to a pulsed system at room or cryogenic temperatures, but can be implemented for a superconducting TF with a superconducting shell in a stellarator reactor. The CSS has the added benefit that within this device the metallic shell which can be made up of discrete plates can be changed out and replaced with new plates to create a different stellarator configuration within the same TF coil set. The work of creating the complicated magnetics is done by the passive conductor reshaping the simple TF field.
Date: January 1, 1997
Creator: Sheffield, G.V.
Partner: UNT Libraries Government Documents Department