Abstract
Modern accelerator front ends almost exclusively include radio-frequency quadrupoles for initial capture and focusing of the low-energy beam. Dynamics in the RFQ define the longitudinal bunch parameters. Simulation of the SNS RFQ with PARMTEQ seeded with a realistic LEBT distribution produces a 2.5 MeV, 40 mA H- beam with root-mean-square emittance of 130 deg keV. In measurement, a detailed characterization of the longitudinal phase space is made, including a novel study of the dependence of longitudinal emittance on transverse coordinates. This work introduces a new virtual slit technique that provides subslit resolution in an energy spectrometer as well as an approach for visualizing 4D phase space data. Through simulation and measurement, the RFQ-formed bunch is confirmed to have significant internal correlated structure. The high-dimensional features are shown to be in qualitative agreement. However, the measured rms emittances are up to 30% lower than predicted, closer to the design value of 95 deg keV.
| Original language | English |
|---|---|
| Article number | 124201 |
| Journal | Physical Review Accelerators and Beams |
| Volume | 23 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 8 2020 |
Funding
The authors acknowledge the contributions of Brandon Cathey, who not only authored the initial high dimensional beam study but also the data collection software used here. We also thank Andrei Shishlo for useful discussion and assistance with the p y orbit code. We are also very grateful for the support of SNS operations during long study periods. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan .