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Yichao Jing

Publications and source records attributed to Yichao Jing.

9 recordsLinked to original sources
arXiv2026

Long Term Dynamics and Stability Studies for the High-energy Electron Cooler

The Ring Electron Cooler (REC) is being developed for the Electron-Ion Collider to provide cooling at the top proton energy of 275GeV to reduce emittance growth from intra-beam scattering (IBS) and other effects. Cooling electrons circulate in a 150 MeV storage ring equipped with strong damping wigglers. While these wigglers counteract emittance degradation driven by intra-beam scattering and proton-electron beam-beam scattering, they introduce significant nonlinear dynamics which can affect electron beam lifetime. In this paper we present the nonlinear optimization of the REC, including optimized focusing wiggler fields, chromatic correction, misalignments and orbit correction and space-charge studies. A novel sextupole-like wiggler field configuration is shown to substantially reduce chromatic aberrations compared with quadrupole-like focusing. Transverse and longitudinal dynamic apertures exceeding 5$\sigma$ are achieved in the presence of realistic alignment and BPM errors. Space-charge simulations for a Gaussian beam using the Bassetti-Erskine model show manageable tune spread and limited equilibrium emittance growth. These results demonstrate the feasibility of REC operation under the required cooling parameters.

physics.acc-ph↗
arXiv2025

CW SRF Gun generating beam parameters sufficient for CW hard-X-ray FEL

SRF CW accelerator constructed for Coherent electron Cooling (CeC) Proof-of-principle (POP) experiment at Brookhaven National Laboratory has frequently demonstrated record parameters using 1.5 nC 350 ps long electron bunches, typically compressed to FWHM of 30 ps using ballistic compression. We report experimental demonstration of CW electron beam with parameters fully satisfying requirements for hard X-ray FEL and significantly exceeding those demonstrated by APEX LCLS II electron gun. This was achieved using a 10-year-old SRF gun with a modest accelerating gradient of $\sim$15 MV/m, a bunching cavity followed by ballistic compression to generate 100 pC, $\sim$15 ps FWHM electron bunches with a normalized slice emittance of $\sim$0.2 mm-mrad and a normalized projected emittance of $\sim$0.25 mm-mrad. Hence, in this paper, we present an alternative method for generating CW electron beams for hard-X-ray FELs using existing and proven accelerator technology. We present a description of the accelerator system settings, details of projected and slice emittance measurements as well as relevant beam dynamics simulations.

physics.acc-ph↗
arXiv2022

3D Theory of Microscopic Instabilities Driven by Space-Charge Forces

Microscopic, or short-wavelength, instabilities are known for drastic reduction of the beam quality and strong amplification of the noise in a beam. Space charge and coherent synchrotron radiation are known to be the leading causes for such instabilities. In this paper we present rigorous 3D theory of such instabilities driven by the space-charge forces. We define the condition when our theory is applicable for an arbitrary accelerator system with 3D coupling. Finally, we derive a linear integral equation describing such instability and identify conditions when it can be reduced to an ordinary second order differential equation.

physics.acc-ph↗
arXiv2022

First experience with He conditioning of an SRF photoinjector

The recent achievements in the performance of superconducting RF (SRF) photoinjectors have opened a new era in the development of the reliable high-brightness CW electron sources. While the SRF guns become one of the most promising technologies, the compatibility of SRF environment with the complex photocathodes remains on the forefront of the modern accelerator science. The SRF cavities operate at cryogenic temperatures providing the ultra-high vacuum (UHV) environment highly beneficial for the photocathode performance. However, the necessity to keep the photocathodes at room temperature while being surrounded by the cavity walls that are kept at cryogenic temperatures creates an additional complexity for the SRF gun design and operation. The complex and volatile chemical compounds used for photocathodes have a high chance of contaminating the surfaces of an SRF cavity. When deposited, such compounds could create centers for cold electron emission which degrade performance of the SRF guns. Such a circumstance would require development of the in-situ processing techniques for restoring the SRF cavity performance. This paper presents the results of the successful implementation and application of the He conditioning method for cavity restoration using the existing SRF photoinjector at Brookhaven National Laboratory (BNL). The method has proven to be extremely effective and resulted in a dramatic improvement of the BNL gun performance.

physics.acc-ph↗
arXiv2019

Solenoid: universal tool for measuring beam parameters

Solenoids are frequently used for focusing of the low energy electron beams. In this paper we focus on using these magnets as a nearly universal tool for measuring beam parameters including energy, emittance, and the beam position and angle with respect to the solenoid axis. We describe in detail corresponding procedures as well as experimental results of such measurements.

physics.acc-ph↗
arXiv2015

High-gradient High-charge CW Superconducting RF gun with CsK2Sb photocathode

High-gradient CW photo-injectors operating at high accelerating gradients promise to revolutionize many sciences and applications. They can establish the basis for super-bright monochromatic X-ray free-electron lasers, super-bright hadron beams, nuclear- waste transmutation or a new generation of microchip production. In this letter we report on our operation of a superconducting RF electron gun with a record-high accelerating gradient at the CsK2Sb photocathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (i.e., 3 nC). We briefly describe the system and then detail our experimental results. This achievement opens new era in generating high-power electron beams with a very high brightness.

physics.acc-ph↗
arXiv2015

Model Independent Description of Amplification and Saturation Using Green's Function

High-gain Free Electron Laser (FEL) is one of the many electron-beam instabilities that have a number of common features linking the shot noise, the amplification and the saturation. In this paper, we present a new, model-independent description of the interplay between these effects. We derive a simple formula for a maximum attainable gain before instability saturates. Application of this model-independent formula to FELs is compared with FEL theory and simulations. We apply the limitations resulting from these findings to FEL amplifiers used for seeded FELs and for Coherent electron Cooling.

physics.acc-ph↗