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At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

DOE OSTI2017

High Average Current Bunched Electron Source for RF Accelerators

High-average current high-quality electron beams are imperative for high-power RF accelerators used in various energy and environmental applications in industry, medicine, and national security as well as for advanced existing and future accelerator systems such as PIP II, particle colliders (eRHIC BNL) for cooling high-energy proton, ion, and hadron beams, storage rings, wakefield accelerators (AWA), and energy recovery linacs. The most common current approach to generate high-peak current high-brightness short electron bunches uses photoemission excited by intense laser radiation. However, to avoid overheating photocathodes are operated at a subharmonic of the linac frequency that in turn restricts the average beam current. There are also limitations in the electron-beam average current due to the average power available from drive lasers. On the other hand, the state of the art thermionic sources that produce high average current electron beams do not have yet good emission gating methods to realize sufficiently short and good quality electron bunches. We develop a robust thermionic electron source (e-source) of >1 A average current with advanced gating of the emission at the linac-frequency and its 3rd harmonic. Central to the approach is a novel scheme for energy efficient feeding of the 3rd-harmonic power in the RF gap. The cathode is attached to the gun cavity through this small emission-gating gap in which the RF modes are excited. The use of thermionic emission allows for the desired high-average current CW electron beams. Adding the 3rd emission gating harmonic shortens the electron bunches and by this means lessens impact of the RF curvature on the beam quality resulting in the smaller energy spread and bunch emittances. Such high current electron beam is suitable for injection into high-power normal- or superconducting linacs in CW mode at a high repetition rate of the linac frequency. In Phase I, we performed modeling and beam dynamics, parametric, and optimization studies. A >1A average current e-source with 200,000hrs lifetime expectancy has been demonstrated in the simulations. We have developed baseline design of the e-source and its components. It is anticipated that the e-source will be in demand for normal- and superconducting particle accelerators and will benefit many commercial and energy and environmental applications such as treating waste and potable water, sludge, stack gases, and medical waste as well as X-ray sources for medicine, sterilization, materials processing, geology, and non-intrusive imaging.

43 PARTICLE ACCELERATORS↗

NASA NTRS1975

A no-load RF calorimeter

The described device can be used to measure the output of any dc powered RF source. No dummy load is required for the measurements. The device is, therefore, called the 'no-load calorimeter' (NLC). The NLC measures the power actually fed to the antenna or another useful load. It is believed that the NLC can compete successfully with directional coupler type systems in measuring the output of high-power RF sources.

Chernoff, R. C.↗

DOE OSTI2021

Novel Magnetron Operation and Control Methods for Superconducting RF Accelerators

High power magnetrons designed and optimized for industrial heating, being injection-locked, have been suggested to power superconducting RF cavities for accelerators due to lower cost and higher efficiency. However, standard operation methods do not provide high efficiency with wideband control suppressing microphonics. We have developed and experimentally verified novel methods of operating and controlling the magnetron that provide stable RF generation with higher efficiency and lower noise than other RF sources. By our method the magnetrons operate with the anode voltage notably lower than the self-excitation threshold improving its performance. This is also a promising way to increase tube reliability and longevity. A magnetron operating with the anode voltage lower than the self-excitation threshold, in so-called stimulated coherent generation mode has special advantage for pulse operation with a gated injection-locking signal. This eliminates the need for expensive pulsed HV modulators and additionally increases the magnetron RF source efficiency due to absence of losses in HV modulators.

43 PARTICLE ACCELERATORS↗

NASA NTRS1999

A LIS Validation Study at the KSC-ER using LDAR and Field Mill Data

The chance of having the TRMM satellite pass over east central Florida when there is lightning over the NASA Kennedy Space Center (KSC) and USAF Eastern Range (ER) is small; however, such a condition did occur on September 21, 1998 (Day 264). Starting at about 20:40 GMT, the Lightning Imaging Sensor (LIS) reported 5 flashes during a 90 second interval that the KSC-ER was within the sensor field of view. Ground-based instrumentation, the Lightning Detection and Ranging (LDAR) system and a network of electric field mills (FM), detected 6 flashes in the same interval. In this paper, we will compare the times and locations of the optical pulses that were detected by LIS with the times and locations of RF sources (LDAR) and the charges that were deposited by the flash (FM network). We will show that LIS responded to all flashes that the LDAR and FM network detected; however, two discharges that were separated by less than 1 second in time and by about 10 km in space were grouped as one flash by the LIS data processing algorithm. In spite of the fact that all flashes occurred near the edge of the LIS field of view, the locations of the LIS events were consistent with both the LDAR and FM locations (the latter are usually within 1-2 kilometers of each other and often are co-located). Two of the 5 flashes reported by LIS were shifted north by about 8 km from the corresponding LDAR and FM locations. The LIS flash times tended to be after the first LDAR pulse was detected and before the last, and the integrated light signal (per LIS event) was surprisingly constant over the 5 flashes that were detected by LIS. In the future, we plan to study more correlated events and will try to determine whether and how the LIS light signal is related to the charge transfer in the flash and/or the number and spatial extent of RF sources.

Koshak, William J.↗

DOE OSTI2018

Demonstration of fast-electron populations in a low-pressure, low-power, magnetized RF plasma source

Using x-ray spectroscopy, we demonstrate the existence of 0.3–6 keV electrons in a low-pressure, low-power, magnetized plasma source, heated by an external radio-frequency antenna located at one end of an axisymmetric tandem mirror. X-ray measurements on low-bulk-temperature, T e,b ~ 4 eV, hydrogen, neon, argon, and gas-mixture plasmas show spectra with high-energy tails having a near-Maxwellian form with T e,f up to 650 eV. Furthermore, the fast electrons producing these x-rays have densities in the range of 10 7 –10 9 cm –3 0.01%–1% of the bulk plasma density (up to 3 × 10 11 cm –3 ), and so carry a significant fraction of the plasma energy and represent an important mechanism relevant to power coupling and heat flow in similar plasma sources.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019