Engineering topics

Pokharel, S.

Publications and source records attributed to Pokharel, S..

4 records

DOE OSTI2023

Modeling for the phased injector upgrade for 12 GeV CEBAF

The upcoming Jefferson Lab K-Long experiment at Hall D will require unique beam conditions with a much lower bunch repetition rate and atypically high bunch charge. To optimize the Continuous Electron Beam Accelerator Facility (CEBAF) injector for this experiment, we performed Multi-Objective Genetic Optimization (MGO) using General Particle Tracer (GPT) to determine the magnetic elements and RF settings necessary for the K-long bunch charge (0.64 pC) at 200 kV. We also investigated the transmission and beam characteristics of low to high charge per bunch electron beams through the injector for simultaneous operations of all four CEBAF Halls and characterized the transmission as a function of the photocathode laser spot size and pulse length. Our findings provide valuable insights into optimizing the CEBAF injector for the Jefferson Lab K-Long experiment, as well as for other experiments with similar beam conditions

Kazimi, R.↗

DOE OSTI2022

Bunch Length Measurements at the CEBAF Injector at 130 kV

In this work, we investigated the evolution in bunch length of beams through the CEBAF injector for 8?770 fC charge per bunch. Using the software General Particle Tracer (GPT), we have simulated beams through the beamline of the CEBAF injector to predict bunch lengths at the location of a beam chopper for comparison with measurements and to validate the model. We performed these simulations with the existing injector using a 130 kV gun voltage. The mea- surements have been done using chopper phase scanning technique for two injector laser drive frequencies 499 MHz and 249.5 MHz. Acknowledgement This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.

Pokharel, S.↗

DOE OSTI2022

Modeling a Nb3Sn Cryounit in GPT at UITF

Nb₃Sn is a prospective material for future superconducting RF (SRF) accelerator cavities. The material can achieve higher quality factors, higher temperature operation and potentially higher accelerating gradients (E_{acc} 96 MV/m) compared to conventional niobium. In this work, we performed modeling of the Upgraded Injector Test Facility (UITF) at Jefferson Lab utilizing newly constructed Nb₃Sn cavities. We studied the effects of the buncher cavity and varied the gun voltages from 200-500 keV. We have calibrated and optimized the SRF cavity gradients and phases for the Nb₃Sn five-cell cavities energy gains with the framework of General Particle Tracer (GPT). Our calculations show the beam goes cleanly through the unit. There is full energy gain out of the second SRF cavity but not from the first SRF cavity due to non-relativistic phase shifts.

Pokharel, S.↗

DOE OSTI2022

B-flavor tagging at Belle II

We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom (B) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic B decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8fb -1 , collected at the Υ(4S) resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be ε eff = (30.0 ± 1.2(stat) ± 0.4(syst))% for a category-based algorithm and ε eff = (28.8 ± 1.2(stat) ± 0.4(syst))% for a deep learning-based algorithm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗