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Shih, K.

Publications and source records attributed to Shih, K..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Confinement performance predictions for a high field axisymmetric tandem mirror

This paper presents Hammir tandem mirror confinement performance analysis based on Realta Fusion's first-of-a-kind model for axisymmetric magnetic mirror fusion performance. This model uses an integrated end plug simulation model including, heating, equilibrium, and transport combined with a new formulation of the plasma operation contours (POPCONs) technique for the tandem mirror central cell. Using this model in concert with machine learning optimization techniques, it is shown that an end plug utilizing high temperature superconducting magnets and modern neutral beams enables a classical tandem mirror pilot plant producing a fusion gain Q > 5. The approach here represents an important advance in tandem mirror design. The high fidelity end plug model enables calculations of heating and transport in the highly non-Maxwellian end plug to be made more accurately. The detailed end plug modelling performed in this work has highlighted the importance of classical radial transport and neutral beam absorption efficiency on end plug viability. The central cell POPCON technique allows consideration of a wide range of parameters in the relatively simple near-Maxwellian central cell, facilitating the selection of more optimal central cell plasmas. These advances make it possible to find more conservative classical tandem mirror fusion pilot plant operating points with lower temperatures, neutral beam energies, and end plug performance requirements than designs in the literature. Despite being more conservative, it is shown that these operating points have sufficient confinement performance to serve as the basis of a viable fusion pilot plant provided that they can be stabilized against MHD and trapped particle modes.

FOS: Physical sciences↗
DOE OSTI2023

Improved calibration of rf cavities for relativistic electron beams: Effects of secondary corrections and experimental verification

In the aspect of longitudinal beam bunching, the bunching strength can be controlled by the rf cavity phase and voltage. However, these machine parameters are different from those that interact with the beam itself. In order to gain control of the beam-cavity interaction, cavity calibration must be performed. Furthermore, it relies on fitting the beam energy gain versus cavity phase to a calibration function. Under the conventional assumption of relativistic beam conditions, the calibration function is a first harmonic sinusoidal function (a sinusoidal function with a period of 2π). However, this expression is insufficient for a high-voltage bunching cavity. Due to beam acceleration inside the cavity, an energy bias and a second harmonic function should be included to modify the conventional calibration function, even for a relativistic electron beam. In this paper, we will derive this modification and provide a comparison to both the Coherent Electron Cooling Experiment and the IMPACT T simulation, respectively.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Summary of the CeC Experiment in RHIC Run 21

The coherent electron cooling (CeC) experiment at RHIC is crucial for determining the feasibility of this technique for cooling the hadron beam in the electron-ion collider (EIC) and reaching the luminosity of 10 34 cm -1 s -1 . During RHIC Run 21, various progresses have been made including successfully commissioning the time resolved diagnostic beam line (TRDBL), achieving the key performance parameters (KPP) of the system and the development of novel methods for accurate alignment of the electron beam with the ion beam. While the longitudinal cooling of the ion beam with cooling time of 100 hours was observed during Run 21, it was related to the traditional electron cooling since the cooling rate was not as sensitive to the energy of the electron beam as what one would expect from the CeC. In Run 21, we were not able to observe the longitudinal cooling of the ion beam caused by CeC and the main challenges are identified as the insufficient stability of the electrons' energy. The sources of the energy jitter have been identified and we are making improvements to the stability of the CeC system for Run 22.

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 OSTI2020

High-Brightness Continuous-Wave Electron Beams from Superconducting Radio-Frequency Photoemission Gun

Continuous-wave photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic x-ray free electron lasers, high-brightness hadron beams, or a new generation of microchip production. In this Letter we report on the record-performing superconducting rf electron gun with CsK 2 Sb photocathode. The gun is generating high charge electron bunches (up to 10 nC / bunch ) and low transverse emittances, while operating for months with a single photocathode. As such, this achievement opens a new era in generating high-power beams with a very high average brightness.

43 PARTICLE ACCELERATORS↗
NASA NTRS1978

Flat-plate liquid solar collector

Report presents test procedures and results of program to obtain thermal performance data on liquid, incident-angle-modifier, heat-loss-coefficient, and stagnation tests.

Shih, K.↗
NASA NTRS1978

Performance evaluations of a liquid solar collector

Report presents procedures and results of thermal performance tests on single-covered liquid solar collector under simulated comditions. Test conditions and data are given in tables and graphs for stagnation tests and thermal performance test. In addition, time-constant test and incident-angle modifier test were conducted to determine transient effect and incident-angle effect. Results of collector load tests are also given.

Shih, K.↗
NASA NTRS1978

Indoor and outdoor tests of a liquid solar collector

Two reports describe thermal-performance data obtained on double-covered liquid solar collector. One report describes data obtained during outdoor testing and the other describes indoor test data obtained by using Marshall Space Flight Center solar simulator. Indoor data were taken to verify performance of solar simulator.

Losey, R.↗
NASA NTRS1977

Indoor test for thermal performance evaluation of Sunworks (liquid) solar collector

Test procedures used and test results obtained from an evaluation test program conducted on a single covered liquid solar collector under simulated conditions are presented. The test article was a flat plate solar collector using water as the heat transfer medium. The absorber plate was copper with copper tubes bonded by soft solder. The plate was coated with Enthone selective black with an absorptivity factor of .87 approximately .92 and an emissivity factor of .10 approximately .20. A time constant test and incident angle modifier test were conducted to determine the transient effect and the incident angle effect on the collector.

Shih, K.↗
NASA NTRS1977

Indoor test for thermal performance evaluation of Libbey-Owens-Ford solar collector

The thermal performance of a flat plate solar collector that uses liquid as the heat transfer medium was investigated under simulated conditions. The test conditions and thermal performance data obtained during the tests are presented in tabular form, as well as in graphs. Data obtained from a time constant test and incident angle modifier test, conducted to determine transient effect and the incident angle effect on the collector, are included.

Shih, K.↗
NASA NTRS1977

Indoor test for thermal performance evaluation of Lenox-Honeywell solar collector

The test procedures used and the test results obtained from an evaluation test program conducted on a double-covered liquid solar collector under simulated conditions are presented. The test article was a flat plate solar collector using liquid as the heat transfer medium. The absorber plate was steel with the copper tubes bonded on the upper surface. The plate was coated with black chrome with an absorptivity factor of .95 and emissivity factor of .12. A time constant test and incident angle modifier test were conducted to determine the transient effect and the incident angle effect on the collector.

Shih, K.↗