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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Continuous bunch-by-bunch spectroscopic investigation of the microbunching instability

Electron accelerators and synchrotrons can be operated to provide short emission pulses due to longitudinally compressed or substructured electron bunches. Above a threshold current, the high charge density leads to the microbunching instability and the formation of substructures on the bunch shape. These time-varying substructures on bunches of picoseconds-long duration lead to bursts of coherent synchrotron radiation in the terahertz frequency range. Therefore, the spectral information in this range contains valuable information about the bunch length, shape and substructures. Based on the KAPTURE readout system, a 4-channel single-shot THz spectrometer capable of recording 500 million spectra per second and streaming readout is presented. First measurements of time-resolved spectra are compared to simulation results of the Inovesa Vlasov-Fokker-Planck solver. Finally, the presented results lead to a better understanding of the bursting dynamics especially above the micro-bunching instability threshold.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Late-time structure of the Bunch-Davies de Sitter wavefunction

We examine the late time behavior of the Bunch-Davies wavefunction for interacting light fields in a de Sitter background. We use perturbative techniques developed in the framework of AdS/CFT, and analytically continue to compute tree and loop level contributions to the Bunch-Davies wavefunction. We consider self-interacting scalars of general mass, but focus especially on the massless and conformally coupled cases. We show that certain contributions grow logarithmically in conformal time both at tree and loop level. We also consider gauge fields and gravitons. The four-dimensional Fefferman-Graham expansion of classical asymptotically de Sitter solutions is used to show that the wavefunction contains no logarithmic growth in the pure graviton sector at tree level. Finally, assuming a holographic relation between the wavefunction and the partition function of a conformal field theory, we interpret the logarithmic growths in the language of conformal field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Transverse modes and instabilities of a bunched beam with space charge and resistive wall impedance

Transverse instability of a bunch in a ring accelerator is considered with space charge and wakefield taken into account. It is assumed that space charge tune shift significantly exceeds the synchrotron tune. Bunch spectrum, instability growth rate, and effects of chromaticity are studied with different bunch and wake forms. Fast instability caused by coupling of transverse modes is studied in detail. It is shown that, for monotonic wakes, the transverse mode coupling instability is possible only with a certain sign of the wake. Its threshold and growth rate are calculated precisely over a wide range of parameters.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Analysis on Achieving a Minimum Bunch Length in LCLS Bunch Compressor One

An ultra-short bunch is required by different applications in many aspects. In this paper, the condition to achieve a minimum bunch length at the Linac Coherent Light Source (LCLS) [1] bunch compressor one (BC1) is analyzed analytically and evaluated by simulation. The space charge, wake field and coherent synchrotron radiation (CSR) effects are not discussed here.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Superimposed coherent terahertz wave radiation from mono-energetically bunched multi-beam

Intense coherent radiation is obtained from multiple electron beams monochromatically bunched over the wide higher-order-mode (HOM) spectral band in the THz regime. The overmoded waveguide corrugated by dielectric-implanted staggered gratings superimposes evanescent waves emitted from the low energy electron beams. The dispersion and transmission simulations of the three-beam slow wave structure show that the first two fundamental modes ($TE_{10}$ and $TE_{20}$) are considerably suppressed ($\sim-50$ dB) below the multi-beam resonating mode ($TE_{30}$) at the THz regime (0.8–1.24 THz). The theoretical calculations and particle-in-cell simulations show that with significantly higher interaction impedance and power growth rate radiation of the $TE_{30}$ mode is $\sim$23 dBm and $\sim$50 dBm stronger than the $TE_{10}$ and $TE_{20}$ modes around 1 THz, respectively. As a result, this highly selective HOM multi-beam interaction has potential applications for power THz sources and high intensity accelerators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Ion motion in the wake driven by long particle bunches in plasmas

In this paper, we explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Bunch-by-bunch measurement of transverse coherent beam-beam modes in the Fermilab Tevatron collider

A system for bunch-by-bunch detection of transverse proton and antiproton coherent oscillations in the Tevatron is described. It is based on the signal from a single beam-position monitor located in a region of the ring with large amplitude functions. The signal is digitized over a large number of turns and Fourier-analyzed offline with a dedicated algorithm. To enhance the signal, band-limited noise is applied to the beam for about 1 s. This excitation does not adversely affect the circulating beams even at high luminosities. The device has a response time of a few seconds, a frequency resolution of 1.6e-5 in fractional tune, and it is sensitive to oscillation amplitudes of 60 nm. It complements Schottky detectors as a diagnostic tool for tunes, tune spreads, and beam-beam effects. Measurements of coherent mode spectra are presented to show the effects of betatron tunes, beam-beam parameter, and collision pattern, and to provide an experimental basis for beam-beam numerical codes. Comparisons with a simplified model of beam-beam oscillations are also described.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Design of 162-MHz CW Bunch-by-Bunch Chopper and Prototype Testing Results

The PIP-II program of upgrades proposed for the Fermilab accelerator complex, is centered around a 800 MeV, 2 mA CW SRF linac. A unique feature of the PIP-II linac is the capability to form a flexible bunch structure by removing a pre-programmed set of bunches from a long-pulse or CW 162.5 MHz train, coming from the RFQ, within the 2.1-MeV Medium Energy Beam Transport (MEBT) section. The MEBT chopping system consists of two travelling-wave kickers working in sync followed by a beam absorber. The prototype components of the chopping system, two design variants of the kickers and a 1/4-size absorber, have been installed in the PIP-II Injector Test (PIP2IT) accelerator and successfully tested with beam of up to 5 mA. In part, one of the kickers demonstrated a capability to create an aperiodic pulse sequence suitable for synchronous injection into the Booster while operating at 500 V and average switching frequency of 44 MHz during 0.55 ms bursts at 20 Hz. This report presents the design of the PIP-II MEBT chopping system and results of prototypes testing at PIP2IT.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Notes on the 2 to 1 bunch merge with application to polarized proton bunches in AGS

A simple and useful program to produce a 2 to 1 bunch merge is developed in these notes and applied to polarized proton bunches in AGS. The notes are summarized in Sections 1 through 4. The reader may refer to the additional sections as needed. Given the large number of pages and references to various sections, it is recommended that the document viewer be set up to increment and decrement the page number with single key strokes. This gives fast access to the sections and allows sequences of figures to be viewed as movies.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Simulation Studies of Intra-Train, Bunch-by-Bunch Feedback Systems at the International Linear Collider

The International Linear Collider (ILC) is a proposed electron-positron collider targeting collision energies from 250 GeV to 1 TeV. With design luminosities of order 10³⁴ cm²s⁻¹, a beam-based, intra-train feedback system would be required near the Interaction Point (IP) to provide nanometre-level stabilisation of the beam overlap in the collisions. Here we present results from beam-tracking simulations of the 500 GeV ILC, including the impact of beam-trajectory imperfections on the luminosity, and the capability of the IP feedback system to compensate for them. Effects investigated include the position jitter introduced by the damping ring extraction kicker, short-range and long-range wakefields, and ground motion. The feedback system was shown to be able to correct for beam-beam offsets of up to 200 nm and stabilise the collision overlap to the nanometre level, within a few bunch crossings.

Ramjiawan, R. L.↗
DOE OSTI2019

X-Ray Monitor for SuperKEKB HER/LER to Monitor Vertical Beam Size Bunch-by-Bunch

The beginning of the period of performance for this grant began after we had designed a Printed Circuit Board (PCB) for biasing and transporting signals from a new, thin Silicon strip sensor made at the Stanford Nanofabrication facility. This complex PCB was manufactured in mid-2017, and then work began on a preamplifier design that would take signals from the sensor and provide sufficient gain while maintaining fidelity, in terms of noise figure and signal speed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗