Engineering topics

Mihalcea, Daniel

Publications and source records attributed to Mihalcea, Daniel.

10 records

DOE OSTI2021

Recent Progress Toward a Conduction-Cooled Superconducting Radiofrequency Electron Gun

High-repetition-rate electron sources have widespread applications. This contribution discusses the progress toward a proof-of-principle demonstration for a conduction-cooled electron source. The source consists of a simple modification of an elliptical cavity that enhances the field electric field at the photocathode surface. The source was cooled to cryogenic temperatures and preliminary measurements for the quality factor and accelerating field were performed. Additionally, we present future plans to improve the source along with simulated beam-dynamics performances.

43 PARTICLE ACCELERATORS↗

DOE OSTI2020

Field-Emission Electron Source Embedded in a Field-Enhanced Conduction-Cooled Superconducting RF Cavity

We present simulations and experimental progress toward the development of a high-current electron source with the potential to deliver high charge electron bunches at GHz-level repetition rates. To achieve these goals electrons are generated through field-emission and the cathode is immersed in a conduction-cooled superconducting 650-MHz RF cavity. The field-emitters consist of microscopic silicon pyramids and have a typical enhancement factor of about 500. To trigger field-emission, the peak field inside the RF cavity of about 6 MV/m is further enhanced by placing the field-emitters on the top of a superconducting Nb rod inserted in the RF cavity. So far, we cannot control the duration of the electron bunches which is of the order of RF period. Also, the present cryo-cooler power of about 2 W limits the beam current to microamp level.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

Simulations and Experimental Plans for a High-Repetition-Rate Field-Enhanced Conduction-Cooled Superconducting RF Electron Source

We present a novel RF design for a field enhanced electron source driven by field emission cathodes. The proposed electron source relies on the enhanced high electric field gradients at the cathode to simultaneously extract and accelerate electrons. The system will be tested in a conduction-cooled superconducting radio-frequency cavity recently demonstrated at Fermilab. In this paper, we present electromagnetic and thermal simulations of the setup that support the feasibility of the design.

43 PARTICLE ACCELERATORS↗

DOE OSTI2018

Coherent Stacking Scheme for Inverse-Compton Scattering at MHz Repetition Rates

An experiment to produce 1-MeV gamma rays via Compton back-scattering of infrared photons on 250-MeV electron bunches is currently in preparation at the Fermilab Accelerator Science & Technology (FAST) facility. To increase the gamma-ray flux the energy of the infrared laser pulses are planned to be amplified within the interaction region using a resonant cavity. This passive amplifier composed of a Fabry-Perot cavity will allow the laser pulse bunches to coherently and constructively stack. Our estimates, based on theoretical models, show that the laser pulse energy can be increased from approximately 1-2 mJ at the exit of the last active amplifier to 5 -10 mJ at the interaction point when the laser repetition rate is set at the nominal value of 3 MHz. This paper details the cavity design option(s) and associated wave-optic simulations.

43 PARTICLE ACCELERATORS↗

DOE OSTI2018

Time-Resolved Electron-Bunch Diagnostics Using Transverse Wakefields

The development of future free electron lasers (FELs) requires reliable time-resolved measurement of variable ultra-short electron-bunchs characteristics. A possible technique is to streak the bunch in the transverse direction by means of time-dependent external fields. In this paper we explore the possible use of self-generated electromagnetic fields *. A passive deflector, consisting of a dielectric-lined waveguide, is used to produce wakefields that impart a time-dependent transverse kick to the relativistic electron bunch passing off-axis. We investigate the technique and its performances and explore its possible application at the Fermilab Accelerator Science & Technology (FAST) facility.

43 PARTICLE ACCELERATORS↗

DOE OSTI2018

High Spectral Density Compton Back-Scattered Gamma-Ray Sources at Fermilab

A ~1 MeV gamma-ray source is planned to be built at Fermilab following the completion of the ~300 MeV superconducting linac. The high-energy photons are back-scattered from the interactions between electrons and high-intensity IR laser pulses. In this contribution, we discuss some of the experiment design challenges and evaluate the performances of the gamma-ray source. We expect the peak brilliance to be of the order of 10²² photons/s-(mm-mrad)²-0.1\% BW and the spectral density of the radiation in excess of 3x10⁵ photons/s/eV.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

High brightness gamma-ray production at Fermilab Accelerator Science and Technology (FAST) facility

Electron beams with energies of the order of a few 100's of MeV and low transverse emittance, in combination with powerful infrared lasers, allow for the production of high quality gamma rays through Inverse Compton Scattering (ICS). At Fermilab Accelerator Science and Technology (FAST) facility, a 300 MeV beam will be used to generate gamma rays with maximum photon energies of up to ~1.5 MeV and brightness of the order of 10 21 photons/[s-(mm-mrad) 2- 0.1%BW]. Due to the low electron-beam transverse emittance, the relative bandwidth of the scattered radiation is expected to be ≤ 1%. A key challenge toward the production of high radiation dose and brightness is to enhance the energy of the infrared 3 ps laser pulses to the joule level. Finally, in this contribution, we present the plans for the experimental setup, along with comprehensive numerical simulations of the ICS process.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Numerical simulations of early-stage dynamics of electron bunches emitted from plasmonic photocathodes

High-brightness electron sources are a key ingredient to the development of compact accelerator-based light sources. The electron sources are commonly based on (linear) photoemission process where a laser pulse with proper wavelength impinges on the surface of a metallic or semiconductor photocathode. Very recently, the use of plasmonic cathodes - cathodes with a nano-patterned surface - have demonstrated great enhancement in quantum efficiencies (Li et al., 2013 [1]). Alternatively, this type of photocathodes could support the formation of structured beams composed of transversely-separated beamlets. In this paper we discuss numerical simulations of the early-stage beam dynamics of the emission process from plasmonic cathodes carried out using the Warp (Friedman et al., 2014 [2]) framework. Furthermore, the model is used to investigate the properties of beams emitted from these photocathode and subsequently combined with particle-in-cell simulations to explore the imaging of cathode pattern after acceleration in a radiofrequency gun.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Expected Results From Channeling Radiation Experiments at Fast

The photoinjector at the new Fermilab FAST facility will accelerate electron beams to about 50 GeV. After initial beam commissioning, channeling radiation experiments to generate hard X-rays will be performed. In the initial stage, low bunch charge beams will be used to keep the photon count rate low and avoid pile up in the detector. We report here on the optics solutions, the expected channaling spectrum including background from bremmstrahlung and the use of a Compton scatterer for higher bunch charge operation.

43 PARTICLE ACCELERATORS↗

DOE OSTI2015

Simulations of Field-Emission Electron Beams from CNT Cathodes in RF Photoinjectors

Average field emission currents of up to 700 mA were produced by Carbon Nano Tube (CNT) cathodes in a 1.3 GHz RF gun at Fermilab High Brightness Electron Source Lab. (HBESL). The CNT cathodes were manufactured at Xintek and tested under DC conditions at RadiaBeam. The electron beam intensity as well as the other beam properties are directly related to the time-dependent electric field at the cathode and the geometry of the RF gun. This report focuses on simulations of the electron beam generated through field-emission and the results are compared with experimental measurements. These simulations were performed with the time-dependent Particle In Cell (PIC) code WARP.

43 PARTICLE ACCELERATORS↗