ICAP-2002 Abstracts and Posters

ICAP 2002 Abstracts and Posters

High order beam features and fitting quadrupole scan data to a particle code model

Abstract

Quadrupole scans in the HEBT of the 6.7 MeV LEDA RFQ were analyzed to characterize the RFQ output beam. In previous work, profiles measured by the wire scanner were fit to models (beam parameterizations and HEBT simulations) to determine the transverse Courant-Snyder parameters alpha, beta, and epsilon at the RFQ exit. Unfortunately, at the larger quadrupole settings, the measured profiles showed features (shoulders or tails) that were not present in any of our simulations. Here we describe our latest analysis, which resulted in very good fits by using an improved model for the RFQ output beam. The model beam was generated by the RFQ simulation code TOUTATIS. In our fitting code, this beam was distorted by linear transformations that changed the Courant-Snyder parameters to whatever values were required by the nonlinear optimizer while preserving the high-order features of the phase-space distribution. No new physics in the HEBT was required to explain our quad-scan results, just an improved initial beam. High order features in the RFQ output beam apparently make a significant difference in behavior downstream of the RFQ. While this result gives us increased confidence in our codes, we still have a mystery: exactly what high-order features in the beam are responsible for the the strange behavior downstream. Understanding this phenomenon may be helpful to understanding our halo experiment data. We have begun to study this by comparing higher order moments of the TOUTATIS distribution with other distributions.

WP Lysenko, RW Garnett, JD Gilpatrick, J Qiang, LJ Rybarcyk, RD Ryne, JD Schneider, HV Smith, LM Young, and ME Schulze

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