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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Misalignment of magnetic field in DIII-D assessed by post-mortem analysis of divertor targets

Abstract We assess the toroidal magnetic field B t asymmetry in DIII-D due to a misalignment of the toroidal field coils with respect to the poloidal magnetic field coils and vacuum vessel. The peak-to-peak variation of the divertor strike point (SP) radius is measured to be 1 cm, with an n = 1 toroidal pattern. We use the centre of a narrow carbon deposition band on tungsten-coated divertor tiles just inside the outer strike point (OSP) as a proxy for the divertor SP location. The band occurred in a series of reverse B t discharges with the OSP positioned on the divertor inserts due to strong E × B drift transport of C from the inner to the outer SP through the private flux region. The variation in band radius (and hence the magnetic SP) is a (4.89 ± 0.31) mm shift toward (310 ± 4)° toroidal direction. These measurements agree well with previous measurements of the 3D magnetic field distribution (Luxon 2003 Nucl. Fusion 43 1813), simulations performed by the mafot field line integration code, and recent Langmuir probe measurements in the small-angle-slot (SAS) divertor (Watkins et al 2019 Nucl. Mater. Energy 18 46). Comparison of these measurements in the SAS divertor also indicates that there is the possibility of a tilt (in conjunction with the shift) of the B t coil field of (0.04 ± 0.07)° towards the toroidal angle of (215 ± 25)°. Previous measurements suggested a field misalignment of (4.6 ± 0.3) mm in the 270° toroidal direction, and a tilt of (0.06 ± 0.02)° toward the 114° toroidal direction, which is similar to the results reported here. These studies will be important for better understanding the radial variation of the toroidal strike line in DIII-D, for designing the new generation of SAS divertor, and for developing an understanding of the impact of error fields on tokamaks with tightly baffled slot divertors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Adult head-sized coil-based low-field MRI

An ultra-low field pre-pulse Magnetic Resonance Imaging (PMRI) system for a head includes RF coils defining a bore for head access, a pre-pulse coil outside the RF coils, and a coil assembly including a main magnetic field coil and gradient coils outside the pre-pulse coil. The PMRI system includes a first cylindrical shield concentric with the RF coils and made from conductive materials. The first cylindrical shield partially encloses the RF coils and inside the pre-pulse coil for shielding the RF coils from environmental electromagnetic disturbances.

Schiff, Steven J.↗
DOE OSTI2020

Stellarators with Permanent Magnets

It is shown that the magnetic-field coils of a stellarator can, at least in principle, be substantially simplified by the use of permanent magnets. Such magnets cannot create toroidal magnetic flux but they can be used to shape the plasma and thus to create poloidal flux and rotational transform, thereby easing the requirements on the magnetic-field coils. As an example, a quasiaxisymmetric stellarator configuration is constructed with only 8 circular coils (all identical) and permanent magnets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

SU-G-JeP2-15: Proton Beam Behavior in the Presence of Realistic Magnet Fields

Purpose: To investigate the effects of magnetic fields on proton therapy beams for integration with MRI. Methods: 3D magnetic fields from an open-bore superconducting MRI model (previously developed by our group) and 3D magnetic fields from an in-house gradient coil design were applied to various mono energetic proton pencil beam (80MeV to 250MeV) simulations. In all simulations, the z-axis of the simulation geometry coincided with the direction of the B0 field and magnet isocentre. In each simulation, the initial beam trajectory was varied. The first set of simulations performed was based on analytic magnetic force equations (analytic simulations), which could be rapidly calculated yet were limited to propagating proton beams in vacuum. The second set is full Monte Carlo (MC) simulations, which used GEANT4 MC toolkit. Metrics such as the beam position and dose profiles were extracted. Comparisons between the cases with and without magnetic fields present were made. Results: The analytic simulations served as verification checks for the MC simulations when the same simulation geometries were used. The results of the analytic simulations agreed with the MC simulations performed in vacuum. The presence of the MRI’s static magnetic field causes proton pencil beams to follow a slight helical trajectory when there were some initial off-axis components. The 80MeV, 150MeV, and 250MeV proton beams rotated by 4.9o, 3.6o, and 2.8o, respectively, when they reached z=0cm. The deflections caused by gradient coils’ magnetic fields show spatially invariant patterns with a maximum range of 0.5mm at z=0cm. Conclusion: This investigation reveals that both the MRI’s B0 and gradient magnetic fields can cause small but observable deflections of proton beams at energies studied. The MRI’s static field caused a rotation of the beam while the gradient coils’ fields effects were spatially invariant. Dr. B Gino Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi-planar linac MR for commercialization)

60 APPLIED LIFE SCIENCES↗
NASA NTRS1965

Experimental Investigation of a Constant-Velocity Traveling Magnetic Wave Plasma Engine

The previously reported traveling magnetic wave plasma engine has been redesigned to reduce the high heat loss to the tube walls downstream of the last magnetic-field coil. The present configuration uses a 3-inch-diameter pyrex tube flared out to a 6-inch diameter immediately downstream of the last magnetic-field coil. This configuration has been studied to determine the effects of flared-tube geometry, molecular weight of the propellant, engine length, and use of a ferrite core on the engine performance. Argon and xenon gases were used as propellants. Two engine lengths were tested. One engine was nominally 1-magnetic-wavelength long (4 coils) and the other nominally 2 1/2-magnetic wavelengths long (10 coils). The magnetic wave speed for both of these lengths corresponds to a specific impulse of 4750 seconds. The maximum kinetic efficiency of the 4-coil engine was 10 percent at a specific impulse of 3200 seconds using argon gas and 22.5 percent at 4200 seconds using xenon gas as the propellant.

TRAVELING WAVE↗
NASA NTRS2019

Design of Magnetic Shielding and Field Coils for a TES X-Ray Microcalorimeter Test Platform

The performance of transition-edge sensors (TES) and their SQUID multiplexed readouts is very sensitive to ambient magnetic field and its fluctuations. In order to run ground experiments on thousands of X-ray TES microcalorimeters with a small uniform ambient magnetic field (< 1 μT, with a uniformity < 0.1 μT), we need a very low ambient field to be trapped into the superconducting magnetic shields. We have designed a sub-Kelvin test platform to reach these specifications. For this purpose, we modeled a new design for the shielding consisting of a series of different mu-metal and superconducting shields, including a niobium shield at 50 mK, a cryoperm (A4K) shield at 3 K, and a mu-metal shield at 300 K. A magnetic field coil is used to vary the local perpendicular magnetic field over the TES array. To optimize this field, we have studied a number of different field-coil designs and the impact of the different shield geometries, in order to reach the required field uniformity.

Miniussi, Antoine R.↗
DOE OSTI2021

Pulse width dependence of magnetic field generation using laser-powered capacitor coils

Megagauss magnetic fields were generated by a current flowing through a U-shaped coil connecting two parallel copper foils. Two kJ-class lasers at various pulse widths from 2 ns to 9.9 ns passed through holes in the front foil and were focused on the back foil with an intensity of ~1.7×10 16 W/cm 2 . The coil current and resulting magnetic fields were characterized using ultrafast proton radiography, timed at the end of the laser pulses. Additionally, the measurements show that magnetic field strength decays with increasing laser pulse width. A lumped-circuit model was developed and showed consistency with the experimental measurements, demonstrating an ion shorting effect: as the ion current neutralizes the electron current contribution to interplate voltage, the coil current peaks on a timescale close to the ion transit time t i = d/v ion . FLASH simulations of the coil current are performed, and the calculated resistance values are used to constrain ion speed as a function of hot electron temperature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2004

Magnetic-Nozzle Studies for Fusion Propulsion Applications: Gigawatt Plasma Source Operation and Magnetic Nozzle Analysis

This project has been a multiyear effort to assess the feasibility of a key process inherent to virtually all fusion propulsion concepts: the expansion of a fusion-grade plasma through a diverging magnetic field. Current fusion energy research touches on this process only indirectly through studies of plasma divertors designed to remove the fusion products from a reactor. This project was aimed at directly addressing propulsion system issues, without the expense of constructing a fusion reactor. Instead, the program designed, constructed, and operated a facility suitable for simulating fusion reactor grade edge plasmas, and to examine their expansion in an expanding magnetic nozzle. The approach was to create and accelerate a dense (up to l0(exp 20)/m) plasma, stagnate it in a converging magnetic field to convert kinetic energy to thermal energy, and examine the subsequent expansion of the hot (100's eV) plasma in a subsequent magnetic nozzle. Throughout the project, there has been a parallel effort between theoretical and numerical design and modelling of the experiment and the experiment itself. In particular, the MACH2 code was used to design and predict the performance of the magnetoplasmadynamic (MPD) plasma accelerator, and to design and predict the design and expected behavior for the magnetic field coils that could be added later. Progress to date includes the theoretical accelerator design and construction, development of the power and vacuum systems to accommodate the powers and mass flow rates of interest to out research, operation of the accelerator and comparison to theoretical predictions, and computational analysis of future magnetic field coils and the expected performance of an integrated source-nozzle experiment.

Gilland, James H.↗
DOE OSTI2026

Minimizing the Electromechanical Stresses in Poloidal Field Coils by Optimizing their Numbers and Locations using FREDA Framework

Poloidal field (PF) and central solenoid (CS) coils play a crucial role in sustaining the equilibrium and preserving the shape of highly confined tokamak plasmas. Ensuring that PF coil current and mechanical stress stay within superconducting and structural limitations is an important check in the design assessment. Minimizing the PF coil currents and mechanical stresses influences reliability, cost, and performance. A free-boundary MHD equilibrium code—FreeGS is employed within the fusion reactor design and assessment (FREDA) whole facility modeling (WFM) framework to construct the plasma equilibrium based on the configuration and currents in the PF coils. Here, we present the capability of the FreeGS code to minimize the currents, forces, and electromagnetic stresses on the PF coils by optimizing their number, sizes, structures, and locations while maintaining an MHD stable plasma configuration with a large confinement factor. The workflow is initialized with a configuration of plasma parameters and coils’ locations from the 0-D tokamak build systems code in the FREDA framework. Then, FreeGS is called to calculate the initial equilibrium at the minimum total current in PF coils. Thereafter, FreeGS’s internal optimizer minimizes the currents and hoop and central forces on the PF coils while maintaining the reference equilibrium. Finally, the input configuration is updated with the optimized parameters for equilibria over the ramp-up phase of a burning-plasma operation. FREDA’s whole facility optimization capability, which includes all magnetic field coil systems, blanket, vacuum vessel (VV), first wall, divertor, etc., is under development and out of the scope for this study.

Hassan, Ehab [ORNL] (ORCID:0000000181060301)↗
DOE OSTI2016

Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ∼1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ∼3 × 10{sup 16 }W/cm{sup 2}. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ∼40–50 T magnetic fields at the center of the coil ∼3–4 ns after laser irradiation. The experiments provide significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1966

Solenoid magnetic fields calculated from superposed semi-infinite solenoids

Calculation of a thick solenoid coils magnetic field components is made by a superposition of the fields produced by four solenoids of infinite length and zero inner radius. The field produced by this semi-infinite solenoid is dependent on only two variables, the radial and axial field point coordinates.

Brown, G. V.↗
DOE OSTI2019

DC to DC electrical transformer

An electrical transformer system using helical electrodes applied to a plasma. Systems and methods transform DC voltages and currents to different DC voltages and currents. Instead of using wires and iron cores similar to known transformers, the present DC to DC transformer system exploits plasma, helical electrodes, an axial magnetic field and radial magnetic field coils, with a control system to specify a radial magnetic field at the edge of a specified magnitude. A DC input voltage is applied, and an output is taken from electrodes at opposite the ends of the central apparatus. The system and apparatus contains a radial magnetic field embedded in the helical electrodes; the secondary current is taken from either solid or split (slotted) electrodes. Methods are disclosed for changing the output voltage and current relative to the input values. The system can function as either a stepup or a stepdown transformer.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2025

Record magnetic field generation by short-pulse laser-driven capacitor-coil targets

Magnetic fields generated by capacitor-coil targets driven by intense short-pulse lasers have been characterized using ultrafast proton radiography. A 1-kJ, 15-ps laser at a center wavelength of 1053 nm irradiated the back plate of the capacitor with an intensity of ∼8.3 × 10 18 W/cm 2 , creating ultra large currents in the connecting coils. High-quality proton data obtained in the axial probing geometry show definitive signatures of magnetic field generation, allowing precision measurement of the field distribution and strength. The data show a coil current of 120 ± 10 kA producing 200 ± 20 Tesla magnetic fields at the coil center at 1.127 ns after the laser drive. In conclusion, this sets a record for magnetic field generation by the short-pulse-powered capacitor-coil targets.

Gao, Lan [Princeton Plasma Physics Laboratory (PPP↗
DOE OSTI2014

Design of vacuum vessel for Aditya Upgrade Tokamak

Aditya tokamak is a limiter tokamak device with a torus vacuum vessel having square cross section. The existing Aditya Tokamak is being upgraded into a machine with divertor operation and good plasma control to support the future Indian Fusion program in a big way. The up-gradation of Aditya Tokamak to diverter tokamak needs additional magnetic field coils for diverter operation, close to the vessel. To accommodate the coils, the existing vessel of square cross section will be replaced with a circular cross section. This vacuum vessel will be made up of stainless steel 304L. It is bakeable up to 150° C. The ultimate vacuum is ∼ 10{sup -9} torr. Two numbers of identical semi torus will be assembled to torus shaped vessel. The end flanges of the semi torus are connected with sealing double Viton 'O' rings to form a torus. The major radius of torus vessel is 750 mm and inner radius is 305 mm. Its wall thickness is ∼8 mm. The vacuum vessel will have 110 various sizes of ports/openings including 4 tangential ports. The nonstandard ports like rectangular and triangular ports are blanked with wire seals. In this paper, the design of vacuum vessel for Aditya Upgrade tokamak is presented. (author)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Eddy Current Lift-Off Sensor Model

Eddy current sensors measure the lift-off or distance between the sensor head and a conducting surface. The sensor consists of a conducting coil carrying an alternating electrical current. By Faraday’s Law, a magnetic field is generated within the coil. This field induces electrical current loops within the conducting surface which in turn generate a magnetic field. This induced magnetic field opposes the coil magnetic field and thus, the current in the coil. This reduces the inductance of the coil while increasing its resistance. The strength of the induced magnetic field and consequently the coil inductance are proportional to the lift-off of the coil from the surface. Thus, a measurement of the coil inductance may yield a measure of the lift-off.

42 ENGINEERING↗
DOE OSTI2012

Stability of fusion target concepts on Z

The key scientific issue for magnetically driven fusion concepts is the stability of the cylindrical liner surrounding the fuel. The liner is susceptible to the magneto Rayleigh-Taylor instability, which can disrupt the liner implosion and prevent it from successfully compressing and confining the fuel. We summarize an LDRD project to investigate the stability of aluminum and beryllium liner implosions on the Sandia Z pulsed power facility. Much of the work was conducted in the specific context of a new magnetized liner inertial fusion (MagLIF) concept, and continued modeling of that concept was supported by this project. However, the liner stability data is fundamental to magnetically driven systems, and the idea of magnetizing and preheating fuel applies to any inertial confinement fusion platform. We also demonstrated prototype 10 T axial magnetic field coils, which are needed both to test the MagLIF concept and the idea of stabilizing liner implosions using magnetic fields.

Sinars, Daniel Brian↗