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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Vertical Coupled Bunched-Beam Breakup Due to Resistive-Wall Wake

We estimate in this note the magnitude of the vertical rigid coupled-bunch mode of Courant and Sessler at NSLS-II. If the proposed mini gap undulators (MGUs) are operated at the room temperature, the threshold current is calculated to be about 10 mA; this is to be compared to the designed beam current of 500 mA. If the MGUs are operated at 4.2° Kelvins, the threshold current is about 120 mA. In either case, a feedback damper is needed in order to operate NSLS-II at 500 mA.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Redistribution of cooling rates for electron bunch with nonuniform density

In this paper we derive explicit formulas for the friction force and the cooling rates in non-magnetized electron coolers in the presence of redistribution of cooling decrements. In the derived formulas we take into account that the density of the electron bunch can be non-uniform.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Illustration of bunch merge simulation in RHIC

Following are examples of a 4 to 2 to 1 merge of proton bunches in RHIC obtained by running the simulation code rhic2mrg23. As the code runs, the user is prompted to enter several numbers. For these examples, RF harmonic number 1440.0 is entered. An RF frequency of 112.597 696 626 MHz at this harmonic is entered. This gives a proton energy of 100 GeV. The merge simulation starts with a uniform distribution of unbunched protons. 2.0 eV-s is entered for the longitudinal emittance of the distribution. The code will recommend a voltage to capture the unbunched protons into 4 harmonic 1440 buckets. A capture voltage of 142.390 kV is recommended. 144.0 kV is entered. It is desirable to capture the protons as “adiabatically” as possible. A capture time of 3318 ms is recommended by the code. 3320.0 ms is entered. A 4 to 2 merge time of 1659 ms is recommended by the code. 1660.0 ms is entered. A 2 to 1 merge time twice that of the 4 to 2 merge is recommended by the code. 3320.0 ms is entered. The code requests a “time fraction” FQMRG to be entered. This is a number (from 0.1 to 1.0) that determines the time at which data are recorded during the 4 to 2 merge. The number 0.5 is entered. This encodes the recording of data halfway through the 4 to 2 merge.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Illustration of bunch merge simulation in AGS

Following are examples of a 4 to 2 to 1 merge of proton bunches in AGS obtained by running the simulation code ags2mrg23. As the code runs, the user is prompted to enter several numbers. For these examples, RF harmonic number 12.0 is entered. An RF frequency of 4.453 913 448 73 MHz at this harmonic is entered. This gives proton G γ = 45.5. The merge simulation starts with a uniform distribution of unbunched protons. 2.0 eV-s is entered for the longitudinal emittance of the distribution. The code will recommend a voltage to capture the unbunched protons into 4 harmonic 12 buckets. A capture voltage of 0.0527 kV is recommended. 0.053 kV is entered. It is desirable to capture the protons as “adiabatically” as possible. Because of the long synchrotron period (372 ms), a capture time of 74,707 ms is recommended by the code. A shorter time, 10,000 ms, is entered to reduce the running time of the code. A 4 to 2 merge time of 37,353 ms is recommended by the code. 4000.0 ms is entered. A 2 to 1 merge time twice that of the 4 to 2 merge is recommended by the code. 8000.0 ms is entered. The code requests a “time fraction” FQMRG to be entered. This is a number (from 0.1 to 1.0) that determines the time at which data are recorded during the 4 to 2 merge. The number 0.5 is entered. This encodes the recording of data halfway through the 4 to 2 merge.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Reconstruction of the BNB and NuMI Neutrino Bunch Structure with ICARUS

ICARUS serves as the Far Detector of the Short Baseline Neutrino (SBN) program at Fermilab, sitting on-axis on the Booster Neutrino Beam (BNB) and 6$^\circ$ off-axis from the Neutrinos at the Main Injector (NuMI) beam. Neutrinos from both beams inherit the timing sub-structure of their parent proton spills, which is in turn derived from either the Booster's or the Main Injector's synchrotron acceleration. Since neutrino propagation introduces only a constant offset, their timing structure is preserved as they travel. Identifying this structure in data represents a powerful tool for selecting neutrino events and searching for physics beyond the Standard Model (BSM). This poster presents the preliminary reconstruction of the BNB and NuMI neutrino bunch structure with ICARUS data, exploiting only the precise timing of ICARUS optical readout system to both locate and assign a time to each interaction.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Single-Bunch Instabilities at the Fermilab Recycler Ring

Understanding and characterizing collective instabilities is critical for high-intensity operation at the Fermilab Recycler Ring. This work presents an application of the the Nested Head-Tail (NHT) formalism for modeling single-bunch transverse instabilities, incorporating analytical solutions to the resistive wall impedances in the absence of space charge. Predicted growth rates and mode structures are benchmarked against PyHEADTAIL simulations and ongoing experimental measurements. The experimental program includes studies of bare-machine instabilities at different machine parameters. These results support the understanding of naturally-occurring instabilities in the Recycler and contribute to the development of predictive tools for beam stability in future high-intensity configurations.

Gonzalez-Ortiz, Cristhian [Fermilab]↗
DOE OSTI2026

Thermal and electromechanical response of ultra-thin carbon-strip polarimeter targets in relativistic bunched beams

Thin carbon-strip targets provide fast relative hadron beam polarimetry, but their response in intense relativistic bunched beams is not governed by local stopping-power heating alone. We develop a coupled response model that combines beam-target overlap, secondary-electron escape, retained heat, target motion, transient heat transport, RF-induced strip-end heating, beam-induced forces, resistance changes, and slack-strip deformation. RHIC target observations constrain the relevant motion, force, and nonlocal-heating scales and show that target survival depends on both beam-center heating and electromagnetic boundary conditions near the strip ends. Applying the model to Booster, AGS, RHIC, and EIC proton and 3 He cases shows that the RHIC proton lifetime scale is reproduced at the order-of-magnitude level, while the RHIC target-holder fin results require the additional RF/end-heating mechanism. For EIC proton flattop operation, carbon-strip polarimetry may remain viable only with reduced dwell time, sufficient detector acceptance, and suppression of RF-induced end heating. For cooled-emittance 3 He, the calculated sublimation-loss scale is far beyond a straightforward RHIC-like carbon-strip extrapolation. Conventional carbon strips are therefore unlikely to remain viable for the most demanding EIC light-ion cases without major changes in target motion, target technology, or diagnostic concept.

43 PARTICLE ACCELERATORS↗
NASA NTRS1969

Enhancement of photon-bunching effects.

Photon bunching effect in spatially coherent noise field enhanced by superposing monochromatic coherent signal and/or shaping incident noise spectra

Aldridge, M. D.↗
NASA NTRS1974

Phase-bunching and other non-linear processes occurring in gyroresonant wave-particle interactions

Consideration of the movement of individual electrons in a magnetized plasma in which a monochromatic wave is propagating in the whistler mode. Simple expressions are derived which give the displacement of the electrons as a function of time, the phase angle that their velocity vector makes with the magnetic component of the wave, their pitch angle, and energy changes. A useful formula is obtained which gives the velocity range over which particles remain trapped inside the wave, as a function of the wave intensity and of the initial phase angle of the particle. It is shown that even strictly resonant particles can escape from the wave when their initial phase angle is very small. From the derived expressions, it is possible to compute the phase-bunching effect which occurs approximately at one trapping wavelength behind the leading edge of the interaction region.

Gendrin, R.↗
NASA NTRS1985

SAR imaging of waves in water and ice - Evidence for velocity bunching

Synthetic aperture radar (SAR) images collected over the Arctic marginal ice zone show gravity wave patterns in both the open water and the ice. Diffuse wave patterns are visible in the water at near range (small incidence angles), while most distinct wave patterns are visible in the ice across the entire swath. The wave patterns in the ice appear as bright lines rather than sinusoidal intensity variations. Additionally, the images show a periodic displacement of the ice/water boundary, apparently due to Doppler shift effects associated with the gravity wave orbital motions. These observations are interpreted as evidence for the velocity bunching effect and also illustrate the effects of random scatterer motions in the open water.

Lyzenga, D. R.↗
NASA NTRS1985

A component of nongyrotropic (phase-bunched) electrons upstream from the earth's bow shock

The count rates of 1.5- and 6-keV electrons measured on ISEE 1 and ISEE 2 are at times strongly spin modulated despite the fact that the axes of the detectors lie along the spin axis of the spacecraft. Spatial gradients in the guiding center density are ruled out as a cause of the spin modulation. The characteristics of the spin modulation can be explained if the electron velocity distribution is nongyrotropic. The procedure is to show that the direction of the plasma flow velocity during times of spin modulation does not lie along the direction of the local magnetic field when both are projected onto the ecliptic plane. While a gyrotropic distribution will cause spin modulation, the count rate maximum will correspond to the direction of the local magnetic field. Gyrophase-bunched electrons are seen within a few tens of kilometers of the shock and as far upstream as 30,000 km from the shock, suggesting that a wave is associated with their propagation. The magnetosheath electrons in the same energy range are also nongyrotropic at times.

Anderson, K. A.↗
DOE OSTI2011

Subpicosecond electron bunch train production using a phase-space exchange technique

Our recent experimental demonstration of a photoinjector electron bunch train with sub-picosecond structures is reported in this paper. The experiment is accomplished by converting an initially horizontal beam intensity modulation into a longitudinal phase space modulation, via a beamline capable of exchanging phase-space coordinates between the horizontal and longitudinal degrees of freedom. The initial transverse modulation is produced by intercepting the beam with a multislit mask prior to the exchange. We also compare our experimental results with numerical simulations.

43 PARTICLE ACCELERATORS↗