An experimental study of microwave stability near transition in the PSR

We have undertaken a study of microwave stability in the PSR storage ring under a variety of beam conditions near transition, including variable intensity and machine impedance, which can be independently controlled in the PSR. Results indicate that the general features of a linear stability model are valid, namely that the instability threshold becomes very small sufficiently close to transition. In addition, many nonlinear features are apparent and the results suggest an extended operating regime is possible with saturated, but otherwise benign, longitudinal fluctuations. Details of the linear model experimental results and corresponding simulations will be presented

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

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 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

A compact layout for a 50 GeV proton radiography facility

We describe a new compact layout for a 50 GeV proton radiography facility. The more compact design utilizes two-point extraction from the main ring to drive an optimal 8 view imaging system. The lattice design of both the main ring, and of the corresponding 8.5 GeV booster ring is described. The rings have very good longitudinal stability, which is of interest for other applications of high current proton machines in this energy range

Characterization of the proton beam at the output of the 6.7MeV LEDA RFQ.

The present configuration of the Low-Energy Demonstration Accelerator (LEDA) consists of a 75-keV proton injector, a 6.7-MeV 350-MHz cw radio-frequency quadrupole (RFQ) with associated high-power and lowlevel rf systems, a 52-magnet periodic lattice followed by a short high-energy beam transport (HEBT) and highpower (670-kW cw) beam stop. The rms beam emittance was measured prior to the installation of the 52-magnet lattice, based on wire-scanner measurements of the beam profile at a single location in the HEBT. New measurements with additional diagnostic hardware have been performed to determine the rms transverse beam properties of the beam at the output of the 6.7-MeV LEDA RFQ. The 52-magnet periodic lattice also includes ten beam position monitors (BPMs) evenly spaced in pairs of two. The BPMs provide a measure of the bunched beam current that exhibits nulls at different locations in the lattice. Model predictions of the locations of the nulls and the strength of the bunched beam current are made to determine what information this data can provide regarding the longitudinal beam emittance

Longitudinal tracking studies for the AHF booster synchrotron

The greenfield site option for the Advanced Hydrotest Facility (AHF) contains a 157-MeV H- linac followed by two synchrotrons, a booster and a 50-GeV main ring. Several different lattice designs are under consideration for the main ring while two different booster designs are presently being studied. The first booster is a 4-GeV synchrotron operating at h=1 with a 5-Hz cycle. The second is a 9-GeV machine operating at h=2 with a 1-Hz cycle. Both designs are required to deliver {approx}3 x 1012 p/bunch. A longitudinal painting scheme was employed during injection to enhance beam quality and capture during the initial portion of the ramp. The longitudinal beam dynamics simulations were performed with the tracking code ESME. The purpose of these studies was to investigate parameter space and obtain estimates for the rf system requirements. This paper presents the results of these studies

Progress towards an RFQ-based front end for LANSCE

The LAN­SCE lin­ear ac­cel­er­a­tor at Los Alam­os Na­tion­al Lab­o­ra­to­ry pro­vides H− and H+ beams to sev­er­al user fa­cil­i­ties that sup­port Iso­tope Pro­duc­tion, NNSA Stock­pile Stew­ard­ship, and Basic En­er­gy Sci­ence pro­grams. These beams are ini­tial­ly ac­cel­er­at­ed to 750 keV using Cock­croft-Wal­ton (CW) based in­jec­tors that have been in op­er­a­tion for over 37 years. They have fail­ure modes which can re­sult in pro­longed op­er­a­tional down­time due to the un­avail­abil­i­ty of re­place­ment parts. To re­duce long-term op­er­a­tional risks and to re­al­ize fu­ture beam per­for­mance goals in sup­port of the Ma­te­ri­als Test Sta­tion (MTS) and the Mat­ter-Ra­di­a­tion In­ter­ac­tions in Ex­tremes (MaRIE) Fa­cil­i­ty, plans are un­der­way to de­vel­op a Ra­dio-Fre­quen­cy Quadrupole (RFQ) based front end as a mod­ern in­jec­tor re­place­ment for the ex­ist­ing CW in­jec­tors. Our progress to date will be dis­cussed

Characterizing proton beam of 6.7 MeV LEDA RFQ by fitting HEBT wire-scanner profiles to improved model.

Quadrupole scans in the HEBT of the 6.7 MeV LEDA RFQ were analyzed to characterize the transverse phase space at the RFQ exit. In previous work, the profiles measured by the wire scanner were fit to various models (HEBT simulations from the RFQ exit to the wire scanner) in an effort to determine the transverse Courant-Snyder parameters (a, p, and t) at the RFQ exit. Unfortunately, at the larger quadrupole settings, the measured profiles showed features that were not present in the simulations. This made good fits impossible. Here we describe our latest analysis, which resulted in very good fits by using an improved model for the beam at the RFQ exit. The model beam was generated by the RFQ simulation code TOUTATIS. In the 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. This present success indicates that there has not been any missing physics in the codes, which gives us increased confidence in our accelerator designs. In addition, we have learned that details in the RFQ beam can make a significant difference in observed behavior downstream of the RFQ

Electron cloud generation and trapping in a quadrupole magnet at the Los Alamos proton storage ring

Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the “prompt” electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the “swept” electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100  μs. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole