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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

High Gradient Accelerating Structures for Carbon Therapy Linac

Carbon therapy is the most promising among techniques for cancer treatment, as it has demonstrated significant improvements in clinical efficiency and reduced toxicity profiles in multiple types of cancer through much better localization of dose to the tumor volume. RadiaBeam, in collaboration with Argonne National Laboratory, are developing an ultra-high gradient linear accelerator, Advanced Compact Carbon Ion Linac (ACCIL), for the delivery of ion-beams with end-energies up to 450 MeV/u for 12C6+ ions and 250 MeV for protons. In this paper, we present a thorough comparison of standing and travelling wave designs for high gradient S-Band accelerating structures operating with ions at varying velocities, relative to the speed of light, in the range 0.3-0.7. In this paper we will compare these types of accelerating structures in terms of RF, beam dynamics and thermo-mechanical performance.

Kutsaev, Sergey↗
DOE OSTI2025

Study on Electropolishing of N-Doped Niobium Surfaces and 650 MHz Cavity for High-Gradient Performance

This presentation provides an overview of the latest studies on electropolishing (EP) of nitrogen-doped niobium surfaces and 650 MHz cavities. The first study focuses on optimizing EP parameters to achieve a pit-free surface on N-doped niobium, highlighting the effects of process conditions on surface pitting and suggesting strategies for mitigation. The second study investigates the EP of 650 MHz cavities to achieve high-gradient performance comparable to that of 1.3 GHz niobium SRF cavities. Additionally, an example of a 650 MHz single-cell cavity is presented, demonstrating its record-high gradient achieved through optimized EP conditions.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Long lifetime of bialkali photocathodes operating in high gradient superconducting radio frequency gun

Abstract High brightness, high charge electron beams are critical for a number of advanced accelerator applications. The initial emittance of the electron beam, which is determined by the mean transverse energy (MTE) and laser spot size, is one of the most important parameters determining the beam quality. The bialkali photocathodes illuminated by a visible laser have the advantages of high quantum efficiency (QE) and low MTE. Furthermore, Superconducting Radio Frequency (SRF) guns can operate in the continuous wave (CW) mode at high accelerating gradients, e.g. with significant reduction of the laser spot size at the photocathode. Combining the bialkali photocathode with the SRF gun enables generation of high charge, high brightness, and possibly high average current electron beams. However, integrating the high QE semiconductor photocathode into the SRF guns has been challenging. In this article, we report on the development of bialkali photocathodes for successful operation in the SRF gun with months-long lifetime while delivering CW beams with nano-coulomb charge per bunch. This achievement opens a new era for high charge, high brightness CW electron beams.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

New results of development on high efficiency high gradient superconducting rf cavities

We report on the latest results of development on high-efficiency high-gradient superconducting radio frequency (SRF) cavities. Several 1-cell cavities made of large-grain niobium (Nb) were built, processed and tested. Two of these cavities are of the Low Surface Field (LSF) shape. Series of tests were carried out following controlled thermal cycling. Experiments toward zero-field cooling were carried out. The best experimentally achieved results are E acc = 41 MV/m at Q 0 = 6.5×10 10 at 1.4 K by a 1-cell 1.3 GHz large-grain Nb TTF shape cavity and E acc = 49 MV/m at Q 0 = 1.5×10 10 at 1.8 K by a 1-cell 1.5 GHz large-grain Nb CEBAF upgrade low-loss shape cavity.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Manufacturing Full-Scale High Gradient Copper Accelerators: Electron Beam Welding and Allied Processes

This DOE ARDAP-funded study examines the technical and business feasibility of manufacturing high-gradient normal conducting RF (NCRF) copper accelerating structures using electron beam welding (EBW) instead of conventional high-temperature brazing. The core motivation is material performance: brazing softens copper significantly, while hard copper alloys have demonstrated ~75% higher operational gradients in SLAC tests, making cold-joining techniques highly attractive. EBW, applied to split-cell (half or quadrant) structure designs, preserves copper hardness away from the weld joint and simplifies machining — but industrial process optimization remains immature and a substantial learning curve is expected. The business case was modeled for two scenarios: a greenfield EBW linac company (> $10M upfront costs, viable above ~30 units/year) and an EBW division added to an existing accelerator firm to reduce risk and upfront costs, at the expense of being less optimal structure for the higher volume production. The study concludes that without a significant increase in demand, private investment alone cannot sustain this capability, and recommends federal support through R&D grants, procurement incentives, and CAPEX cost-sharing to incubate domestic EBW-NCRF manufacturing — with the existing-company model.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Measurement of internal dark current in a 17 GHz, high gradient accelerator structure

We report the measurement of the internal dark current in a 17 GHz, high gradient accelerator cavity and its comparison with theory. The cavities were fabricated from copper and had a sidewall that was either uncoated or coated with diamondlike carbon or TiN. The dark current was monitored by a downstream detector and by detectors behind two small slits made in the cavity sidewall. With an increasing gradient, the downstream current increased monotonically, as expected for field emission. The variation of the internal, side dark current was not monotonic but showed the onset of peaks at gradients near 45 and 65 MV / m . These were identified as the N = 2 and N = 1 single point multipactor resonances. The total internal dark current was estimated at ~ 15 – 30 A . The magnitude of the internal dark current and its dependence on the gradient were in good agreement with simulations using the cst code as well as an in-house code. Processing to a higher gradient, ~ 90 MV / m , eliminated the N = 2 mode, but the N = 1 mode persisted. The coated sidewall cavities showed the same multipactor resonances as the uncoated structure. However, at the highest gradient achieved in testing, the coated structures showed a modest reduction in the internal dark current.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Measurement of internal dark current in a 17 GHz, high gradient accelerator structure

We report the measurement of the internal dark current in a 17 GHz, high gradient accelerator cavity and its comparison with theory. The cavities were fabricated from copper and had a sidewall that was either uncoated or coated with diamond-like carbon or TiN. The dark current was monitored by a downstream detector and by detectors behind two small slits made in the cavity side wall. With an increasing gradient, the downstream current increased monotonically, as expected for field emission. The variation of the internal, side dark current was not monotonic but showed the onset of peaks at gradients near 45 and 65 MV/m. These were identified as the N = 2 and N = 1 single point multipactor resonances. The total internal dark current was estimated at ∼15–30 A. The magnitude of the internal dark current and its dependence on the gradient were in good agreement with simulations using the CST code as well as an in-house code. Processing to a higher gradient, ∼90 MV/m, eliminated the N = 2 mode, but the N = 1 mode persisted. The coated sidewall cavities showed the same multipactor resonances as the uncoated structure. However, at the highest gradient achieved in testing, the coated structures showed a modest reduction in the internal dark current.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

High-gradient magnetic filtration of UO 2 colloids from aqueous suspensions

Environmental samples often contain innocuous components that make trace actinide analysis difficult and expensive. Therefore, it is expedient to separate these materials from actinide particles. One characteristic of many actinides is that they are paramagnetic. High-gradient magnetic filtration (HGMF) is a non-destructive technique that selectively captures magnetic constituents from a matrix containing non-magnetic species. Here, in this work, a novel HGMF device made of a permanent magnet array was used to effectively separate UO 2 particles from undesirable soil species. Up to 88% of the UO 2 particles present in suspensions were effectively captured by HGMF, resulting in their enrichment and a substantial reduction in the concentrations of other constituents.

Actinide separations↗
DOE OSTI2026

Improved high-gradient performance for medium-velocity superconducting half-wave resonators: Surface preparation and trapped flux mitigation

A development effort to improve the performance of superconducting radio-frequency half-wave resonators (SRF HWRs) is underway at the Facility for Rare Isotope Beams (FRIB), where 220 such resonators are in operation. Our goal was to achieve an intrinsic quality factor (𝑄 0 ) of ≥ 2 × 10 10 at an accelerating gradient (𝐸 acc ) of 12 MV/m. FRIB production resonators were prepared with buffered chemical polishing. First trials of electropolishing (EP) and post-EP low-temperature baking of FRIB HWRs allowed us to reach higher gradient (15 MV/m, limited by quench) with a higher quality factor at high gradient, but 𝑄 0 was still below our goal. Trapped magnetic flux during the Dewar test was found to be a source of 𝑄 0 reduction. Three strategies were used to reduce the trapped flux: (i) adding a local magnetic shield (LMGS) to supplement the “global” magnetic shield around the Dewar for reduction of the ambient magnetic field; (ii) performing a “uniform cooldown” (UC) to reduce the thermoelectric currents; and (iii) using a compensation coil to further reduce the ambient field with active field cancellation (AFC). The LMGS improved the 𝑄 0 , but not enough to reach our goal. With UC and AFC, we exceeded our goal, reaching 𝑄 0 = 2.8 ×10 10 at 𝐸 acc = 12 MV/m.

Cryogenics & vacuum technology↗
DOE OSTI2023

High-gradient magnetic separation of colloidal uranium oxide particles from soil components in aqueous suspensions

The separation of uranium oxide (UO 2 ) particles from soil-surrogate particles in aqueous suspensions was achieved using filtration enhanced by a magnetic field. Enhanced attraction of paramagnetic UO 2 colloids to a ferromagnetic stainless-steel filter placed in a strong magnetic field arises because of the positive magnetic susceptibility of the particles and the high-gradient field generated near ferromagnetic fibers. Enhanced uptake of smaller particles over larger ones occurs through Brownian motion that promotes the collision of particles with the ferromagnetic fibers of the filter. Hence, this work focused on UO 2 particles in the colloidal size range. Experiments used a water-cooled electromagnet and an array of permanent magnets. Chemical analysis showed that the magnetic field increased the capture efficiency of uranium particles from a range of 27–53% with the magnet off up to 98% with the magnet on after a single pass of the suspension through the filter. Further, the recovery of the UO 2 particles from the filter, however, was more difficult to achieve. Small amounts of UO 2 , together with significant amounts of background SiO 2 particles, were removed from the filter during a first flush with the magnetic field on. A much larger recovery of UO 2 was not observed until a second out-of-field flush was performed, which also released some SiO 2 . The degree to which particle separation was enhanced through the use of multi-stage filtration compared to single pass-through filtration was also examined. A design was suggested that could be used to optimize the separation efficiency for a continuous process.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

High gradient tests of metallic mm-wave accelerating structures

This study explores the physics of vacuum rf breakdowns in high gradient mm-wave accelerating structures. We performed a series of experiments with 100 GHz and 200 GHz metallic accelerating structures, at the Facility for Advanced Accelerator Experimental Tests (FACET) at the SLAC National Accelerator Laboratory. This paper presents the experimental results of rf tests of 100 GHz travelling-wave accelerating structures, made of hard copper-silver alloy. The results are compared with pure hard copper structures. The rf fields were excited by the FACET ultra-relativistic electron beam. The accelerating structures have open geometries, 10 cm long, composed of two halves separated by a variable gap. The rf frequency of the fundamental accelerating mode depends on the gap size and can be changed from 90 GHz to 140 GHz. The measured frequency and pulse length are consistent with our simulations. When the beam travels off-axis, a deflecting field is induced in addition to the decelerating longitudinal field. We measured the deflecting forces by observing the displacement of the electron bunch and used this measurement to verify the expected accelerating gradient. We present the first quantitative measurement of rf breakdown rates in 100 GHz copper-silver accelerating structure, which was 10 –3 per pulse, with peak electric field of 0.42 GV/m, an accelerating gradient of 127 MV/m, at a pulse length of 2.3 ns. The goal of our studies is to understand the physics of gradient limitations in order to increase the energy reach of future accelerators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Recent development on nitrogen infusion work towards high Q and high gradient

A quality factor as high as 2 × 1010 at 1.5 GHz was achieved at a gradient of 35 MV/m by 800 °C annealing and N-infusion at 140 °C. A comparison of the field dependence of the surface resistance after N-infusion with a recent theoretical model that extends the calculation of the BCS surface resistance to high rf fields suggests an increase in the quasiparticles¿ relaxation time with increasing infusion temperature, which could be due to a decreasing density of subgap states. Nb coupons treated similarly showed the formation of thicker oxynitride layer on the surface beneath thin dielectric Nb2O5 layer. A plausible explanation for the improved Q0 is that the oxynitride layer on the Nb surface adds additional electron scattering within RF penetration depth.

Dhakal, P.↗
DOE OSTI2023

Design Criteria for High-Gradient Radio-Frequency Linacs

This article will review methods used at the SLAC National Accelerator Laboratory and other world accelerator laboratories to design high-gradient normal conducting accelerating structures. A quest for compact radio-frequency linacs fueled decades of studies toward a higher accelerating gradient. A major phenomena limiting the increase of the gradient is vacuum radio-frequency breakdown; therefore, this paper will address the breakdown physics and discuss approaches that reduce the breakdown probability. This discussion will cover both the electrical design and fabrication technology of the accelerating structures to achieve practical operating accelerating gradients in excess of 100 MV/m. Most of the data described here were obtained during the development of 11 GHz linacs for electron–positron linear colliders, so extrapolation of the results to other frequencies should be performed cautiously.

Dolgashev, Valery A. (ORCID:0000000166715402)↗
DOE OSTI2018

Effect of High-Gradient Magnetic Field on Electrical Property of Carbon Nanotube-Polypyrrole Composite; Nanotube Separation Mechanism

High- and low-gradient magnetic fields are produced by resistor-inductor-capacitor (RLC) discharge apparatuses. The maximum magnetic field is 12.5 Tesla with 1-ms pulse duration. Multiwall carbon nanotube–polypyrrole composite is prepared. The samples are exposed to high- and low-gradient magnetic fields. To understand the behavior of carbon nanotubes (CNTs) in high-gradient magnetic fields (HGMFs), we theoretically calculated the equivalent magnetic susceptibility of a CNT in the gradient magnetic field. We found that the gradient force which is exerted on a CNT could be repellent or absorbent depending on the parallel and perpendicular susceptibilities of the CNT, as well as on the initial orientation of the CNT with respect to magnetic field direction. Four-probe studies show that the electrical conductivity of CNT composites decreases after exposure to a high-gradient magnetic field. Microscopic observation of the electrical current profile of composites reveals rearrangement of CNTs under HGMF.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

R&D Towards High Gradient CW SRF Cavities

This talk will discuss Fermilab’s recent progress in the surface engineering of superconducting radio-frequency (SRF) cavities geared toward producing simultaneously high quality factors and high accelerating gradients in cryomodules. We investigate possible microscopic mechanisms that drive improved performance by carrying out sequential RF tests on cavities subjected to low temperature baking. We compare performance evolution to observations made with material science techniques and find correlations with material parameters. We also discuss other key advancements that enable high gradient operation in cryomodules.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Interstrand Coupling Properties of LARP High Gradient Quadrupole Cables in Response to Variations in Cable Design and Heat Treatment Condition

Calorimetric measurement of coupling loss versus frequency has been measured on two sets of cored and uncored large Hadron Collider Accelerator Research Program high gradient quadrupole Nb 3 Sn Rutherford cables. Studied are the responses of the resulting interstrand contact resistances (ICR) to variation of stainless-steel (SS) core width and position and to variation of reaction-heat-treatment (RHT) condition. One pair of cables (an early HQ-series type) with and without core had received RHT under 20-MPa uniaxial face-on pressure. Another set of cables (recent QXF type) furnished with SS cores of various widths had received RHT under ambient pressure. The results were displayed as cable-cross-sectional micrographs and plots of ICR versus percent core coverage (W). The HQ cables were tightly compacted and produced results consistent with a previously expected continuous ICR versus W variation. Furthermore, the QXF cables were uncompacted such that their upper and lower layers were separated by what is referred to as a full-width 'pseudocore;' as a result, their ICRs were independent of the widths of the SS cores. Compaction versus noncompaction is discussed and future research directions are suggested.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Field Harmonic Measurement of High-Gradient Permanent Magnet Quadrupoles for NSLS- II Upgrade

The National Synchrotron Light Source II (NSLS-II) is preparing for a major upgrade based on a new lattice concept, known as “Complex Bend,” to replace its existing double bend achromat (DBA) lattice. Here, this novel lattice will use high-gradient permanent magnet quadrupoles (PMQs) with small apertures in the range of 16–22 mm. A prototype complex bend branch with PMQs has been installed in the NSLS-II linac to evaluate the lattice's performance. An accurate and precise magnetic measurement system is required for field harmonic characterization and magnetic tuning of these PMQs. As part of this project a Rotating-Coil bench, based on a Printed Circuit Board (PCB) coil with a 12 mm diameter, has been configured to measure nine PMQs with bore diameter of 12.7 mm. This PCB coil has an active length of 270 mm, and is able to measure fields up to the 15th harmonic of the main field at a reference radius of 5 mm, while maintaining field quality levels within 10 ppm of the main field. This article presents the PCB coil setup, the harmonic measurement results and their temperature dependencies and repeatability. Simulation results on compensation of undesired multipoles using “IDBuilder”, a genetic algorithm-based optimizer code for magnetic tuning is included for field harmonic corrections.

36 MATERIALS SCIENCE↗