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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Nonlinear integrable optics beam dynamics experiment and diagnostics

All present circular particle accelerators are built around linear focusing optics. Un-avoidable nonlinear elements appear in accelerators, such as magnetic aberrations and space-charge effects, which are typically corrected using nonlinear magnets. However, these added nonlinearities degrade particle beam stability, and in most cases, the system becomes non-integrable. The Integrable Optics Test Accelerator (IOTA), at Fermi National Accelerator Laboratory (Fermilab), is a test bed to study beam dynamics in integrable lattices for both electron and proton beams, independently. This work presents experimental results of the nonlinear electron beam dynamics behavior in IOTA using an elliptical nonlinear magnet. The elliptical nonlinear magnet allows for a large betatron tune spread, allowing for a stable high-intensity beam. In a future experimental run, minimally invasive beam instrumentation is needed to study time-dependent collective instabilities, and halo formation in space-chargedominated proton beams. Traditional profile monitors are too destructive to the beam or just measure one dimension of the beam. A gas sheet can be injected perpendicular to theproton beam at an angle. By doing so, a two-dimensional, turn-by-turn, transverse profile measurement can be made, which will preserve the integrity of the beam. The developmentand progress of a gas sheet beam profile monitor will also be presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures

We show that temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefield diagnostics and pulse profile reconstruction techniques.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Low Energy Muon Beam Diagnostics - Scintillating Fiber Profile Monitor (SFPM)

The MeV Test Area (MTA) houses the 400 MeV H^− Beam at the end of the Linac and a secondary beamline of muons and pions created from hitting a Tungsten target. The MTA is in the Irradiation Test Area (ITA), where experiments involve studying the effects of radiation on materials in the MTA beam. There is a need for a retractable detector to monitor the secondary beam s intensity and coarse profile. The SFPM was chosen when considering factors like ability to measure low rates and handle high intensities. The plan was to test different scintillating fibers & Silicon Photomultiplier (SiPM) models to figure out which combination gives the best signals, and gain familiarity with the detector assembly, operation, and data acquisition software before using with final detectors in beamline. The SiPM circuit has been tested with a LED pulser successfully. The immediate steps that follow will be to set the SiPM up on the monitor with three different types of optical fibers, use the Caen software to configure the best mode of data acquisition, and proceed with an offline source test using Strontium-90. Once the most efficient measurement method is clear, they will be ready for use in the beamline.

Leith, Justin↗
DOE OSTI2016

Pulsed inductive HF laser

We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H{sub 2} – F{sub 2}(NF{sub 3} or SF6{sub 6}) and He(Ne) – H{sub 2} – F{sub 2}(NF{sub 3} or SF{sub 6}) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%. (lasers)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Evaluation of low-frequency operational limit of proposed ITER low-field-side reflectometer waveguide run including miter bends

The present design concept for the ITER low-field-side reflectometer transmission line (TL) consists of an ~40 m long, 6.35 cm diameter helically corrugated waveguide (WG) together with ten 90° miter bends. This paper presents an evaluation of the TL performance at low frequencies (33-50 GHz) where the predicted HE11 mode ohmic and mode conversion losses start to increase significantly. Quasi-optical techniques were used to form a near Gaussian beam to efficiently couple radiation in this frequency range into the WG. We observed that the output beams from the guide remained linearly polarized with cross-polarization power levels of ~1.5%-3%. The polarization rotation due to the helical corrugations was in the range ~1°-3°. The radiated beam power profiles typically show excellent Gaussian propagation characteristics at distances >20 cm from the final exit aperture. The round trip propagation loss was found to be ~2.5 dB at 50 GHz and ~6.5 dB at 35 GHz, showing an inverse increase with frequency. This was consistent with updated calculations of miter bend and ohmic losses. At low frequencies (33-50 GHz), the mode purity remained very good at the exit of the waveguide, and the losses are perfectly acceptable for operation in ITER. Finally, the primary challenge may come from the future addition of a Gaussian telescope and other filter components within the corrugated guide, which will likely introduce additional perturbations to the beam profile and an increase in mode-conversion loss.

47 OTHER INSTRUMENTATION↗
NASA NTRS2006

Ion Beam Characterization of a NEXT Multi-Thruster Array Plume

Three operational, engineering model, 7-kW ion thrusters and one instrumented, dormant thruster were installed in a cluster array in a large vacuum facility at NASA Glenn Research Center. A series of engineering demonstration tests were performed to evaluate the system performance impacts of operating various multiple-thruster configurations in an array. A suite of diagnostics was installed to investigate multiple-thruster operation impact on thruster performance and life, thermal interactions, and alternative system modes and architectures. The ion beam characterization included measuring ion current density profiles and ion energy distribution with Faraday probes and retarding potential analyzers, respectively. This report focuses on the ion beam characterization during single thruster operation, multiple thruster operation, various neutralizer configurations, and thruster gimbal articulation. Comparison of beam profiles collected during single and multiple thruster operation demonstrated the utility of superimposing single engine beam profiles to predict multi-thruster beam profiles. High energy ions were detected in the region 45 off the thruster axis, independent of thruster power, number of operating thrusters, and facility background pressure, which indicated that the most probable ion energy was not effected by multiple-thruster operation. There were no significant changes to the beam profiles collected during alternate thruster-neutralizer configurations, therefore supporting the viability of alternative system configuration options. Articulation of one thruster shifted its beam profile, whereas the beam profile of a stationary thruster nearby did not change, indicating there were no beam interactions which was consistent with the behavior of a collisionless beam expansion.

Pencil, Eric J.↗
NASA NTRS1976

Cusped magnetic field mercury ion thruster

A residence time approach is used to explain the nonuniform beam current density profile of the SERT II thruster and to propose a magnetic field modification which should produce a highly uniform beam profile. Expressions are derived which relate the thruster performance parameters to the geometry and plasma properties of the discharge chamber. These relationships are applied to a cylindrical discharge chamber model of the SERT II thruster and suggest that, in addition to the magnetic field modification, the discharge chamber length of this thruster should be reduced. These modifications should result in a thruster which has a highly uniform beam profile, good performance, and a low double ion population. Experimental results indicate that at about the same thrust and performance levels the beam flatness parameter of the modified thruster is 40% higher than the SERT II thruster value.

Beattie, J. R.↗
DOE OSTI2015

Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma

A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω{sub 1}, ω{sub 2}) and wave numbers (k{sup →}{sub 1}, k{sup →}{sub 2}) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations (n{sup ′}=n{sub α0}e{sup iαz}) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ω{sub h} (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ω=ω{sub 1}−ω{sub 2} and k{sup →}=k{sup →}{sub 1}−k{sup →}{sub 2}+α{sup →}. The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters (a{sub 0}) of super Gaussian lasers. In the present scheme, efficiency ∼10{sup −2} is achieved with the optimization of all these parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Ponderomotive and weakly relativistic self-focusing of Gaussian laser beam in plasma: Effect of light absorption

This paper presents an influence of light absorption on self-focusing of laser beam propagation in plasma. The differential equation for beam-width parameter is obtained using the Wentzel-Kramers-Brillouin and paraxial approximations through parabolic equation approach. The nonlinearity in dielectric function is assumed to be aroused due to the combined effect of weakly relativistic and ponderomotive regime. To highlight the nature of propagation, behavior of beam-width parameter with dimensionless distance of propagation is presented graphically and discussed. The present work is helpful to understand issues related to the beam propagation in laser plasma interaction experiments where light absorption plays a vital role.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

SU-G-TeP1-10: Predicting Photon Percentage Depth Dose From Profile Due to Changes in Beam Quality

Purpose: To predict photon percentage depth dose (PDD) from profile due to a change in flattened (FF) and flattening-filter-free (FFF) beam quality. Methods: 6MV photon beam PDDs and profiles in a 3D water tank (3DW) and profiles in an ionization chamber array (ICP) were collected for different field sizes and depths with FF and FFF beams in a Versa HD (Elekta Ltd.). The energy was adjusted by changing the bending magnet current (BMC) ±15% from the clinical beam (6MV) in 5% increments. For baseline establishment, PDDs(depth≥3cm) were parameterized with bi-exponential functions and the PDD 20 to 10cm ratios (PDD{sub 20,10}) were calculated. Then, the FF profile at 10cm from the central axis (Pr{sub 10}) and the slope of the FFF central linear region (SFFF) were calculated. Calibration curves were established: (1) change in Pr{sub 10} and SFFF as functions of the change in PDD{sub 20,10} and (2) change in PDD(depth=3, 15 and 30cm) as function of the change in PDD{sub 20,10}. The differences between Pr{sub 10} and SFFF from baseline were calculated and, from calibration curves, changes in PDD{sub 20,10} and PDD(depth=3, 15 and 30cm) were obtained. Then, absolute PDD(depth=3, 15 and 30cm) values were input into a least-square-optimization algorithm to calculate the bi-exponential function’s optimal coefficients and generate the PDD(depths≥3cm). Results: The change in PDD{sub 20,10} relative to baseline increased (<±4%) with BMC. Pr{sub 10} increased (±6%) and SFFF decreased (±11%) with BMC. Relative differences between measured and calculated (i.e. PDD calculation from Pr{sub 10} and SFFF) PDDs were less than 1%. Results apply to FF and FFF beams measured in 3DW and ICP. Conclusion: Pr{sub 10} and SFFF are more sensitive than PDD to changes in beam energy and PDD information can be accurately generated from them. With known 3DW and ICP profile relationship, ICP can be used to obtain PDD for current photon beam.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Depth profile characterization with noncollinear beam mixing

Noncollinear beam mixing is an ultrasonic approach to quantify elastic nonlinearity within a subsurface volume of material. The technique requires interaction between two beams of specific frequency, angle, and vibration mode to generate a third beam propagating from the intersection volume. The subsurface depth to interaction zone is controlled by changing the separation distance between the two input transducers, and the amplitude of the third generated beam is proportional to the elastic nonlinearity within the interaction zone. Therefore, depth profiling is possible if a suitable parameter is established to normalize the detected signal independent of propagation distances and input amplitudes. This foundational effort has been conducted toward developing such a parameter for depth profile measurements in homogeneous aluminum that includes corrective terms for attenuation, beam overlap noise, beam spread, and input amplitudes. Experimental and analytical results are provided, and suggested applications and improvements are discussed toward characterizing subsurface material property profiles.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

RHIC electron lenses upgrades

In the Relativistic Heavy Ion Collider (RHIC) 100 GeV polarized proton run in 2015, two electron lenses were used to partially compensate for the head-on beam-beam effect for the first time. Here, we describe the design of the current electron lens, detailing the hardware modifications made after the 2014 commissioning run with heavy ions. A new electron gun with 15-mm diameter cathode is characterized. The electron beam transverse profile was measured using a YAG screen and fitted with a Gaussian distribution. During operation, the overlap of the electron and proton beams was achieved using the electron backscattering detector in conjunction with an automated orbit control program.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Advanced ion beam calorimetry for the test facility ELISE

The negative ion source test facility ELISE (Extraction from a Large Ion Source Experiment) is in operation since beginning of 2013 at the Max-Planck-Institut für Plasmaphysik (IPP) in Garching bei München. The large radio frequency driven ion source of ELISE is about 1×1 m{sup 2} in size (1/2 the ITER source) and can produce a plasma for up to 1 h. Negative ions can be extracted and accelerated by an ITER-like extraction system made of 3 grids with an area of 0.1 m{sup 2}, for 10 s every 3 minutes. A total accelerating voltage of up to 60 kV is available, i.e. a maximum ion beam power of about 1.2 MW can be produced. ELISE is equipped with several beam diagnostic tools for the evaluation of the beam characteristics. In order to evaluate the beam properties with a high level of detail, a sophisticated diagnostic calorimeter has been installed in the test facility at the end of 2013, starting operation in January 2014. The diagnostic calorimeter is split into 4 copper plates with separate water calorimetry for each of the plates. Each calorimeter plate is made of 15×15 copper blocks, which act as many separate inertial calorimeters and are attached to a copper plate with an embedded cooling circuit. The block geometry and the connection with the cooling plate are optimized to accurately measure the time-averaged power of the 10 s ion beam. The surface of the blocks is covered with a black coating that allows infrared (IR) thermography which provides a 2D profile of the beam power density. In order to calibrate the IR thermography, 48 thermocouples are installed in as many blocks, arranged in two vertical and two horizontal rows. The paper describes the beam calorimetry in ELISE, including the methods used for the IR thermography, the water calorimetry and the analytical methods for beam profile evaluation. It is shown how the maximum beam inhomogeneity amounts to 13% in average. The beam divergence derived by IR thermography ranges between 1° and 4° and correlates relatively well with the values measured by beam emission spectroscopy with up to 30% difference. It has also been observed that the beam inhomogeneity decreases with lower beam divergence.

43 PARTICLE ACCELERATORS↗
NASA NTRS1973

Correlation of ion and beam current densities in Kaufman thrusters.

In the absence of direct impingement erosion, electrostatic thruster accelerator grid lifetime is defined by the charge exchange erosion that occurs at peak values of the ion beam current density. In order to maximize the thrust from an engine with a specified grid lifetime, the ion beam current density profile should therefore be as flat as possible. Knauer (1970) has suggested this can be achieved by establishing a radial plasma uniformity within the thruster discharge chamber; his tests with the radial field thruster provide an example of uniform plasma properties within the chamber and a flat ion beam profile occurring together. It is shown that, in particular, the ion density profile within the chamber determines the beam current density profile, and that a uniform ion density profile at the screen grid end of the discharge chamber should lead to a flat beam current density profile.

Wilbur, P. J.↗
NASA NTRS2006

Optical profile determining apparatus and associated methods including the use of a plurality of wavelengths in the reference beam and a plurality of wavelengths in a reflective transit beam

An optical profile determining apparatus includes an optical detector and an optical source. The optical source generates a transmit beam including a plurality of wavelengths, and generates a reference beam including the plurality of wavelengths. Optical elements direct the transmit beam to a target, direct a resulting reflected transmit beam back from the target to the optical detector, and combine the reference beam with the reflected transmit beam so that a profile of the target is based upon fringe contrast produced by the plurality of wavelengths in the reference beam and the plurality of wavelengths in the reflected transmit beam.

Montgomery, Robert M.↗
DOE OSTI2017

High frequency fishbone driven by passing energetic ions in tokamak plasmas

High frequency fishbone instability driven by passing energetic ions was first reported in the Princeton beta experiment with tangential neutral-beam-injection (Heidbrink et al 1986 Phys. Rev. Lett. 57 835–8). It could play an important role for ITER-like burning plasmas, where α particles are mostly passing particles. In this work, a generalized energetic ion distribution function and finite drift orbit width effect are considered to improve the theoretical model for passing particle driving fishbone instability. For purely passing energetic ions with zero drift orbit width, the kinetic energy $\delta {{W}_{k}}$ is derived analytically. The derived analytic expression is more accurate as compared to the result of previous work. For a generalized energetic ion distribution function, the fishbone dispersion relation is derived and is solved numerically. As a result, numerical results show that broad and off-axis beam density profiles can significantly increase the beam ion beta threshold ${{\beta}_{c}}$ for instability and decrease mode frequency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

SU-E-T-660: Quantitative Fault Testing for Commissioning of Proton Therapy Machines

Purpose: To ensure proper fault testing for the first single room proton therapy machine by establishing a common set of acceptance testing and commissioning parameters with the manufacturer. The following work details the parameters tested and associated results. Methods: Dose rates in service mode were varied to ensure that when the threshold for maximum or minimum MU/min was met, the beam promptly shut off. The flatness parameter was tested by purposely assigning an incorrect secondary scatter, to ensure the beam shut off when detecting a heterogeneous profile. The beam symmetry parameter was tested by altering the steering coil up to 3.0A, thereby forcing the beam to be asymmetric and shut off. Lastly, the quench system was tested by ramping down the magnet to 5% capacity, whereby the quench button was engaged to bring down the magnet current to a safe level. Results: A dose rate increase or decrease in excess of 10% shut the beam off within 5 seconds as observed by the current on a Matrixx ionization chamber array (IBA Dosimetry, Bartlett, TN) A 3.0A change in the beam steering coil introduced a 2% change in the flatness and symmetry profiles with respect to baseline measurements resulting in the beam shutting off within 5 seconds. An incorrect 2nd scatterer introduced a flatness of 4.1% and symmetry of 6.4% which immediately triggered a beam shut off. Finally, the quench system worked as expected during the ramp down procedure. Conclusion: A fault testing plan to check dosimetric faults and the quench system was performed for the first single room proton therapy system. All dosimetric parameters and machine conditions were met to our satisfaction. We propose that the same type of fault testing should be applied to any proton system during commissioning, including scanning beam systems.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Varying stopping and self-focusing of intense proton beams as they heat solid density matter

Transport of intense proton beams in solid-density matter is numerically investigated using an implicit hybrid particle-in-cell code. Both collective effects and stopping for individual beam particles are included through the electromagnetic fields solver and stopping power calculations utilizing the varying local target conditions, allowing self-consistent transport studies. Two target heating mechanisms, the beam energy deposition and Ohmic heating driven by the return current, are compared. The dependences of proton beam transport in solid targets on the beam parameters are systematically analyzed, i.e., simulations with various beam intensities, pulse durations, kinetic energies, and energy distributions are compared. The proton beam deposition profile and ultimate target temperature show strong dependence on intensity and pulse duration. A strong magnetic field is generated from a proton beam with high density and tight beam radius, resulting in focusing of the beam and localized heating of the target up to hundreds of eV.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗