Internal Coil Research Articles

An Unusual Shearing of the Internal Coil of a Stimulating Peripheral Nerve Block Catheter

An Unusual Shearing of the Internal Coil of a Stimulating Peripheral Nerve Block Catheter

Avoidance of tearing mode locking with electro-magnetic torque introduced by feedback-based mode rotation control in DIII-D and RFX-mod

Disruptions caused by tearing modes (TMs) are considered to be one of the most critical roadblocks to achieving reliable, steady-state operation of tokamak fusion reactors. Here we have demonstrated a promising scheme to avoid mode locking by utilizing the electro-magnetic (EM) torque produced with 3D coils that are available in many tokamaks. In this scheme, the EM torque is delivered to the modes by a toroidal phase shift between the externally applied field and the excited TM fields, compensating for the mode momentum loss through the interaction with the resistive wall and uncorrected error fields. Fine control of torque balance is provided by a feedback scheme. We have explored this approach in two widely different devices and plasma conditions: DIII-D and RFX-mod operated in tokamak mode. In DIII-D, the plasma target was high βN in a non-circular divertor tokamak. Here βN is defined as βN = β/(Ip/aBt) (%Tm/MA), where β, Ip, a, Bt are the total stored plasma pressure normalized by the magnetic pressure, plasma current, plasma minor radius and toroidal magnetic field at the plasma center, respectively. The RFX-mod plasma was ohmically-heated with ultra-low safety factor in a circular limiter discharge with active feedback coils outside the thick resistive shell. The DIII-D and RFX-mod experiments showed remarkable consistency with theoretical predictions of torque balance. The application to ignition-oriented devices such as the International Thermonuclear Experimental Reactor (ITER) would expand the horizon of its operational regime. The internal 3D coil set currently under consideration for edge localized mode suppression in ITER would be well suited for this purpose.

Wideband vibrational electromagnetic energy harvesters with nonlinear polyimide springs based on rigid-flex printed circuit boards technology

A wideband vibrational electromagnetic energy harvester employing nonlinear spring effects is proposed and demonstrated. The harvesters were designed and fabricated by commercial rigid-flex printed circuit boards technology. Rigid FR-4 boards were used for mechanical support and coil winding, whereas flexible polyimide films were patterned for mechanical springs and mass platforms. Two sets of coils were patterned and fabricated in the harvester with an internal coil resistance of about 16 Ω each. Two rare-earth magnets were attached to the central platform as shuttle mass. The total dimension of the harvester was 20 × 20 × 4 mm3. In vibration tests, nonlinearity could be observed even at 0.1 grms vibration level due to the spring hardening effect. The frequency for peak induced voltage increased from 187 Hz at low vibration to 382 Hz at 5 grms vibration. The effective half-power bandwidth increased from 8 Hz at 0.1 grms to 32 Hz at 1 grms and 52 Hz at 5 grms due to the hysteresis in frequency response. For a matched load and 1 grms vibration at 250 Hz, the maximum output power was 160 nW, corresponding to a power density of 100 nW cm−3.

DTT: a divertor tokamak test facility for the study of the power exhaust issues in view of DEMO

In parallel with the programme to optimize the operation with a conventional divertor based on detached conditions to be tested on the ITER device, a project has been launched to investigate alternative power exhaust solutions for DEMO, aimed at the definition and the design of a divertor tokamak test facility (DTT). The DTT project proposal refers to a set of parameters selected so as to have edge conditions as close as possible to DEMO, while remaining compatible with DEMO bulk plasma performance in terms of dimensionless parameters and given constraints. The paper illustrates the DTT project proposal, referring to a 6 MA plasma with a major radius of 2.15 m, an aspect ratio of about 3, an elongation of 1.6–1.8, and a toroidal field of 6 T. This selection will guarantee sufficient flexibility to test a wide set of divertor concepts and techniques to cope with large heat loads, including conventional tungsten divertors; liquid metal divertors; both conventional and advanced magnetic configurations (including single null, snow flake, quasi snow flake, X divertor, double null); internal coils for strike point sweeping and control of the width of the scrape-off layer in the divertor region; and radiation control. The Poloidal Field system is planned to provide a total flux swing of more than 35 Vs, compatible with a pulse length of more than 100 s. This is compatible with the mission of studying the power exhaust problem and is obtained using superconducting coils. Particular attention is dedicated to diagnostics and control issues, especially those relevant for plasma control in the divertor region, designed to be as compatible as possible with a DEMO-like environment. The construction is expected to last about seven years, and the selection of an Italian site would be compatible with a budget of 500 M€.

Simulation of EAST vertical displacement events by tokamak simulation code

Vertical instability is a potentially serious hazard for elongated plasma. In this paper, the tokamak simulation code (TSC) is used to simulate vertical displacement events (VDE) on the experimental advanced superconducting tokamak (EAST). Key parameters from simulations, including plasma current, plasma shape and position, flux contours and magnetic measurements match experimental data well. The growth rates simulated by TSC are in good agreement with TokSys results. In addition to modeling the free drift, an EAST fast vertical control model enables TSC to simulate the course of VDE recovery. The trajectories of the plasma current center and control currents on internal coils (IC) fit experimental data well.

Endovascular Treatment of Ruptured Vertebral Artery Dissecting Aneurysms

Background: Various endovascular treatment methods have been used to treat ruptured vertebral artery dissecting aneurysms (VADAs). However, the efficacy and long-term durability of the various endovascular techniques have remained unestablished. Objectives: The purpose of the present study is to report the therapeutic efficacy and long-term clinical and angiographic results of various endovascular treatment methods, and to evaluate the predictive factors of favorable outcomes. Patients and Methods: Between January 2010 and August 2014, 30 patients with ruptured VADAs were classified according to the dominancy of the affected vertebral artery (VA) and the involved major perforating vessels. Allotted endovascular therapy was performed for each of the ruptured VADA subtypes. Immediate angiographic and follow-up imaging results were retrospectively reviewed, and long-term clinical results were evaluated. Various clinical, angiographic, and procedural factors were evaluated to determine their associations with clinical outcomes. Results: Dissecting aneurysms involving the dominant VA were found in five patients. Of 25 aneurysms involving the non-dominant VA, 12 lesions showed involvement of the posterior inferior cerebellar artery (PICA), and one lesion’s origin was the anterior spinal artery. Stent-assisted coiling (SAC) was performed in seven patients, stent-only therapy (SOT) was conducted for six patients, and the remaining 17 patients were treated with internal coil trapping (ICT). Of the seven patients treated with SAC, five showed partial obliteration and four experienced recurrence. Two of the four patients with recurrence died. One patient with incomplete trapping for patency of the involved PICA experienced rebleeding. No recurrence was observed in six patients treated with SOT, or among 16 patients with ICT. The preoperative neurologic status (represented by the world federation of neurosurgical societies grading) and immediate post-treatment angiographic results were confirmed as significant predictive factors of clinical outcomes (P =0.018 for both variables). Conclusion: Incomplete obliteration of a ruptured VADA using SAC was associated with a higher recurrence rate and fatal clinical outcomes. ICT is a useful technique that completely eliminates the risk of rebleeding. However, under a limited set of conditions, SOT can be an effective alternative.

Large animal canine endovascular ischemic stroke models: A review.

Stroke is one of the leading causes of death and long-term disability worldwide. Recent exciting developments in the field with endovascular treatments have shown excellent outcomes in acute ischemic stroke. Prior to translating these treatments to human populations, a large-animal ischemic stroke model is needed. With the advent of new technologies in digital subtraction angiography, less invasive endovascular stroke models have been developed. Canines have gyrencephalic brain similar to human brain and accessible neurovascular anatomy for stroke model creation. Canine stroke model can be widely utilized to understand the disease process of stroke and to develop novel treatment. Less invasive endovascular internal carotid emboli injection and coil embolization methods can be used to simulate transient or permanent middle cerebral artery occlusion. Major restriction includes the extensive collateral circulation of canine cerebral arteries that can limit the stroke size. Transient internal carotid artery occlusion can decrease collateral circulation and increase stroke size to some degree. Additional method of manipulating the extent of collateral circulation needs to be studied. Other types of canine stroke models, including vertebral artery occlusion and basilar artery occlusion, can also be accomplished by endovascular thrombi injection. We extensively review the literature on endovascular technique of creating canine ischemic stroke models and their application in finding new therapies for ischemic stroke.

Frequency of Mammary Artery Coiling in Single-Ventricle Patients and Future Coronary Artery Grafting.

Pre-Fontan coil closure of aorto-pulmonary collaterals decreases single-ventricle volume load and improves outcome. Coiling of right and left internal mammary arteries may present a challenge to cardiothoracic surgery teams caring for these patients when future coronary artery bypass grafting is needed for SV patients. The goal of this study was to determine the frequency of internal mammary artery coil closure in SV patients in a single tertiary care center. A retrospective review of all pediatric single-ventricle patients who underwent cardiac catheterization between March 2009 and October 2015 at Rush Center for Congenital Heart Disease was performed. Fifty-one patients' charts were reviewed. Twenty-five patients received coil closure of one or more internal mammary artery (coil group) and 26 received no coil closure (no-coil group). In the coil group, 21 (84%) had their collateral vessels coiled in the pre-Fontan period and 4 (16%) had their vessels coiled in the post-Fontan period. In the coil group, 18 (72%) had their right internal mammary artery coiled and 7 (28%) had both right and left internal mammary arteries coiled. None of the coil group had isolated coil closure of the left internal mammary artery. This study is the first to verify the frequency of right and/or left internal mammary artery coil closure in SV patients and the potential impact on future coronary artery bypass grafting. Extensive peri-Fontan coiling of the internal mammary arteries presents a significant potential challenge for subsequent management of SV patients as older adults.

Bangbang controller design and implementation for EAST vertical instability control

In the EAST 2014 campaign, a new internal coil (IC) power supply was used in order to enhance the control over the plasma’s vertical instabilities. The IC power supply now allows for current and voltage working modes with much higher peak voltages and currents and faster response time. In comparison the previous power supply only allowed for the current mode. A Bangbang and PID composite controller has been designed for the voltage mode based on optimal control theory and the RZIP rigid plasma response model. This paper will demonstrate that faster and enhanced controllability are realized with the combination of Bangbang and PID controller. For the large z position drift, the Bangbang controller will export the maximum voltage to achieve much faster power supply response and slow the vertical displacement events (VDEs). The PID controller is used for the small z drifts which will finally stabilize the VDEs with minimum z position oscillation. Furthermore, to evaluate the time latency of this control system and power supply, the stability and performance of the closed loop were simulated and analysed. This controller was finally implementation and test on EAST using the Quasi-snowflake shape which achieved growth rates of 500s−1. This paper shows that the new power supply using the bangbang+PID controller can significantly enhance the control over vertical instabilities.

Simulations on shifting medium and its application in wireless power transfer system to enhance magnetic coupling

Shifting medium is a kind of an anisotropic but homogeneous metamaterial designed by transformation optics. An object or free space enclosed by the shifting medium could be moved to a certain distance away from the original position. In this paper, we propose a cone-shaped shifting medium shell to move an internal coil to the given position. In this way, the two coils in a wireless power transfer system could be equivalently moved closer; thus, their magnetic coupling is enhanced. The theoretical models and numerical simulations are presented and analyzed to validate the effects of the shifting medium shell. Both ohmic loss and magnetic loss are also considered for practical concerns. Finally, we discuss the simplification of such a shifting medium to facilitate its fabrication.

SNR in MI Catheter Receivers for MRI

Internal coils have a signal-to-noise ratio (SNR) advantage during magnetic resonance imaging. However, coils with continuous cables are generally unsafe, due to the risk of RF heating. Segmented cables, such as magneto-inductive waveguides, should introduce inherent safety at the price of increased noise, from both the cable and the body. Here, we derive analytical SNR expressions for both types of noise, develop a model to compare the SNR of different types of receiver, and validate the model with data from imaging experiments at 3T. Experiments and theory confirm that body noise does not prevent an SNR gain compared with an eight-element external coil, even when a long section of waveguide is loaded with tissue.

Suppression of type-I ELMs with reduced RMP coil set on DIII-D

Recent experiments on DIII-D have demonstrated that having a toroidally-monochromatic spectral content of edge-resonant magnetic perturbations (RMPs) is not a necessary condition for suppression of edge localized modes (ELMs). Robust ELM suppression has been reproducibly obtained on DIII-D during experiments in which various non-axisymmetric coil loops were turned off pseudo-randomly producing a variety of , , and spectral contributions. It was shown that RMP ELM suppression could be achieved with as few as 5 out of 12 internal coil loops (I-coils) on DIII-D at similar coil currents and with good plasma confinement. Linear MHD plasma response (m3dc1, ipec, mars) and vacuum (surfmn, trip3d) modelling have been performed in order to understand the effects of the perturbation spectrum on the plasma response and ELM suppression. The results suggest that reduction of the dominant perturbation field is compensated by increased field in the plasma that may lead to RMP ELM suppression at lower levels of perturbative magnetic flux from the I-coils. These results provide additional confidence that ITER may be capable of RMP ELM suppression in the event of multiple internal coil failures.

Therapeutic Progress in Treating Vertebral Dissecting Aneurysms Involving the Posterior Inferior Cerebellar Artery.

Among the variations of vertebral artery dissecting aneurysms (VDAs), VDAs involving the posterior inferior cerebellar artery (PICA), especially ruptured and high-risk unruptured aneurysms, are the most difficult to treat. Because the PICA is an important structure, serious symptoms may occur after its occlusion. Retained PICAs are prone to re-bleeding because VDAs are difficult to completely occlude. There is therefore confusion regarding the appropriate treatment for VDAs involving the PICA. Here, we used the PubMed database to review recent research concerning VDAs that involve the PICA, and we found that treatments for VDAs involving the PICA include (i) endovascular treatment involving the reconstruction of blood vessels and blood flow, (ii) occluding the aneurysm using an internal coil trapping or an assisted bypass, (iii) inducing reversed blood flow by occluding the proximal VDA or forming an assisted bypass, or (iv) the reconstruction of blood flow via a craniotomy. Although the above methods effectively treat VDAs involving the PICA, each method is associated with both a high degree of risk and specific advantages and disadvantages. The core problem when treating VDAs involving the PICA is to retain the PICA while occluding the aneurysm. Therefore, the method is generally selected on a case-by-case basis according to the characteristics of the aneurysm. In this study, we summarize the various current methods that are used to treat VDAs involving the PICA and provide schematic diagrams as our conclusion. Because there is no special field of research concerning VDAs involving the PICA, these cases are hidden within many multiple-cases studies. Therefore, this study does not review all relevant documents and may have some limitations. Thus, we have focused on the mainstream treatments for VDAs that involve the PICA.

Nonlinear electromagnetic energy harvesters fabricated by rigid-flex printed circuit board technology

In this paper, a wideband electromagnetic energy harvester designed and fabricated by commercial rigid-flex PCB technology is demonstrated. The rigid FR-4 boards are used for mechanical frames and coil winding whereas the flexible polyimide film is used for mechanical springs and mass platforms. The total dimension of the device is 20 × 20 × 2 mm3. The internal coil resistance is 15 Ω. In vibration tests, nonlinearity can be observed even at 0.1 g vibration level due to the spring hardening effect. The peak frequency was increased as the vibration level increased. The effective bandwidth was increased from 6 Hz at 0.1 g to 21 Hz at 0.5 g and 27 Hz at 1 g, respectivel, due to the hysteresis effect. For a matched load and 1 g vibration at 240 Hz, the maximum output power is 24.5 nW, corresponding to a power density of 31 nW/cm3.

Field Mapping and Automated Shimming of an HTS Magnet by “Internal” Active Shim Coils Located in the Bore of the Magnet

In order to obtain the target field homogeneity of a nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) magnet, commonly used are active shim coils, i.e., axial and radial, that typically locate radially outside of the magnet. In a high-temperature superconducting (HTS) magnet, however, we reported a “strong” hysteresis in the field-to-current ratio of an external (placed radially outside the HTS magnet) active shim coil by the screening-current-induced fields (SCFs). This nonlinear behavior of an external active shim due to the SCF is one of the major technical challenges to achieve the target field homogeneity of an HTS NMR or MRI magnet. In this paper, we constructed and operated active shim coils, i.e., two axial ( Z1 and Z2) and two radial (X and Y) , that were installed inside of an HTS magnet to investigate effectiveness of internal shim coils. The HTS magnet, wound with GdBCO coated conductors, consists of ten double pancakes. With the active shim coils, a customized field mapping and shimming system was constructed, which consists of a 3-D field mapper, a field analysis software package, and a set of power supplies to control the shim coils. A pre-shim field error of 953 ppm at a 10-mm-diameter cylinder was improved to 464 ppm after iterative automated shimming using the internal shim coils. The results demonstrate that the internal shim coils are effective to eliminate the SCF-oriented field errors, both radial and axial, which was practically impossible for the external shim coils.

170 In Vivocardiac magnetic resonance imaging of adult zebrafish

Introduction While the embryonic zebrafish has been widely used for basic cardiac research the adult zebrafish has been used less partly due to difficulties in evaluating the hearts structure and function in-vivo. Currently available cardiac imaging techniques are limited by the hearts small size and rapid rate. Successful development of cardiac MRI for the adult zebrafish could have significant scientific, ethical and economic benefits for cardiac research. Methods We have developed a novel magnetic resonance imaging (MRI) scanning system, designed to study cardiac structure and function in the live adult zebrafish. This has involved the development of an integrated zebrafish life support and monitoring system with an internal custom MRI solenoid microimaging coil – the ‘flow cell’ (Figure 1). Zebrafish are anesthetised (MS222) and held in position within a flow chamber that intersects the MRI coil for scanning (internal diameter 6.9 mm, SNR >130). Water flows through the system via a non-pulsatile pump from outside the scanner room (2.00 ml min –1 ). Water temperature and oxygenation of the flow cell is monitored using in line MRI compatible optical sensors (FirestingO 2 , PyroScience) to provide continuous monitoring of the fish while it is in the scanner. Scanning is performed on a 7T preclinical MRI scanner (Bruker BioSpec). FLASH and RARE based sequences are used for locator and structural information, while functional images are obtained using a retrospective cardiac gated gradient echo imaging sequence (IntragateFLASH). All scans are at Results We have created a working flow cell for obtaining cardiac MRI images from zebrafish (Figure 2). Zebrafish scanned under our current in vivo protocol have all successfully recovered from the experimental procedure (up to 40 mins) with no obvious signs of distress or injury allowing for longitudinal imaging studies. Conclusion Our aim is to deliver in vivo MRI images with spatial and temporal quality matching rodent MRI. While we have already met with significant success generating anatomical images further refinement is required, in terms of image contrast, quality and reproducibility, before deployment in full cardiac studies. Acknowledgement This work is funded by a BHF New Horizons grant.

The negative triangularity tokamak: stability limits and prospects as a fusion energy system

The paper discusses edge stability, beta limits and power handling issues for negative triangularity tokamaks. The edge magnetohydrodynamic stability is the most crucial item for power handling. For the case of negative triangularity the edge stability picture is quite different from that for conventional positive triangularity tokamaks: the second stability access is closed for localized Mercier/ballooning modes due to the absence of a magnetic well, and nearly internal kink modes set the pedestal height limit to be weakly sensitive to diamagnetic stabilization just above the margin of the localized mode Mercier criterion violation. While a negative triangularity tokamak is thought to have a low beta limit with its magnetic hill property, it is found that plasmas with reactor-relevant values of normalized beta βN > 3 can be stable to global kink modes without wall stabilization with appropriate core pressure profile optimization against localized mode stability, and also with increased magnetic shear in the outer half-radius. The beta limit is set by the n = 1 mode for the resulting flat pressure profile. The wall stabilization is very inefficient due to strong coupling between external and internal modes. The n > 1 modes are increasingly internal when approaching the localized mode limit, and set a lower beta in the case of the peaked pressure profile leading to a Mercier unstable core. With the theoretical predictions supported by experiments, a negative triangularity tokamak would become a prospective fusion energy system with other advantages including a larger separatrix wetted area, more flexible divertor configuration design, wider trapped particle-free scrape-off layer, lower background magnetic field for internal poloidal field coils, and larger pumping conductance from the divertor room.

열교환코일 내장형 태양열 축열조의 성능향상 (제1보 실증실험)

Abstract A thermal storage tank with internal heat exchange coils is commonly used in solar thermal systems with a collectorarea below 100 m 2 . The coils are installed in the lower part of the tank because the temperature of the upper part of thetank can drop if the outlet temperature of the collector becomes lower than the upper temperature of the tank, which is a kind of temperature reversal. As an alternative to the well-mixed storage tank with lower coil only, we have proposed a tank with lower and upper coils and have achieved superior thermal stratification in the tank, which results in increasedcollector efficiency and solar fraction. But, the phenomenon of temperature reversal was often observed in the tank when the load or solar radiation changed rapidly. In the present work, revised control was successfully applied, i.e., to heat only the lower coil using a three way valve if temperature reversal occurs and to operate the collector at a low flow rate whenthe quality of solar radiation is not good.

Long-pulse stability limits of the ITER baseline scenario

DIII-D has made significant progress in developing the techniques required to operate ITER, and in understanding their impact on performance when integrated into operational scenarios at ITER-relevant parameters. Long duration plasmas, stable to m/n = 2/1 tearing modes, with an ITER-similar shape and Ip/aBT, have been demonstrated in DIII-D, that evolve to stationary conditions. The operating region most likely to reach stable conditions has normalized pressure, βN ≈ 1.9–2.1 (compared to the ITER baseline design of 1.6–1.8), and a Greenwald normalized density fraction, fGW 0.42–0.70 (the ITER design is fGW ≈ 0.8). The evolution of the current profile, using internal inductance (li) as an indicator, is found to produce a smaller fraction of stable pulses when li is increased above ≈1.1 at the beginning of βN flattop. Stable discharges with co-neutral beam injection are generally accompanied with a benign n = 2 magnetohydrodynamic mode. However if this mode exceeds ≈10 G, the onset of a m/n = 2/1 tearing mode occurs with a loss of confinement. In addition, stable operation with low applied external torque, at or below the extrapolated value expected for ITER has also been demonstrated. With electron cyclotron injection, the operating region of stable discharges has been further extended at ITER equivalent levels of torque and to edge-localized mode (ELM) free discharges at higher torque but with the addition of an n = 3 magnetic perturbation from the DIII-D internal coil set. The characterization of the ITER baseline scenario evolution for long pulse duration, extension to more ITER-relevant values of torque and electron heating, and suppression of ELMs have significantly advanced the physics basis of this scenario, although significant effort remains in the simultaneous integration of all these requirements.

Endovascular Treatment of Vertebral Artery Dissecting Aneurysms That Cause Subarachnoid Hemorrhage : Consideration of Therapeutic Approaches Relevant to the Angioarchitecture.

ObjectiveIntracranial ruptured vertebral artery dissecting aneurysms (VADAns) are associated with high morbidity and mortality when left untreated due to the high likelihood of rebleeding. The present study aimed to establish an endovascular therapeutic strategy that focuses specifically on the angioarchitecture of ruptured VADAns.MethodsTwenty-three patients with ruptured VADAn received endovascular treatment (EVT) over 7 years. The patient group included 14 women (60.9%) and 9 men (39.1%) between the ages of 39 and 72 years (mean age 54.2 years). Clinical data and radiologic findings were retrospectively analyzed.ResultsFour patients had aneurysms on the dominant vertebral artery. Fourteen (61%) aneurysms were located distal to the posterior inferior cerebellar artery (PICA). Six (26%) patients had an extracranial origin of the PICA on the ruptured VA, and 2 patients (9%) had bilateral VADAns. Eighteen patients (78%) were treated with internal coil trapping. Two patients (9%) required an adjunctive bypass procedure. Seven patients (30%) required stent-supported endovascular procedures. Two patients experienced intra-procedural rupture during EVT, one of which was associated with a focal medullary infarction. Two patients (9%) exhibited recanalization of the VADAn during follow-up, which required additional coiling. No recurrent hemorrhage was observed during the follow-up period.ConclusionEVT of ruptured VADAns based on angioarchitecture is a feasible and effective armamentarium to prevent fatal hemorrhage recurrence with an acceptable low risk of procedural complications. Clinical outcomes depend mainly on the pre-procedural clinical state of the patient. Radiologic follow-up is necessary to prevent hemorrhage recurrence after EVT.