Beam losses and the resulting radio-activation of accelerator components are major considerations governing the operations and performance of mediumenergy, high-intensity proton accumulator rings using Hcharge exchange injection such as the Los Alamos Proton Storage Ring (PSR). Several beam loss mechanisms contribute including beam scattering (nuclear and large angle Coulomb scattering) in the injection foil, production of excited states of H0 in the Hinjection stripper foil that subsequently field strip in the magnetic fields down stream of the foil, halo growth from space charge effects, beam instabilities and losses from the fast extraction process. These are now well understood based on the progress in the diagnosis, measurement, and modeling of beam losses at PSR and related rings. The roles of the computer codes MAD8 [1], ORBIT [2], G4Beamline [3], and others used in modeling beam losses are discussed, and the modeling results are compared with relevant experimental data.

Independent component analysis (ICA) is a powerful blind source separation (BSS) method. Compared to the typical BSS method, principal component analysis, ICA is more robust to noise, coupling, and nonlinearity. The conventional ICA application to turn-by-turn position data from multiple beam position monitors (BPMs) yields information about cross-BPM correlations. With this scheme, multi-BPM ICA has been used to measure the transverse betatron phase and amplitude functions, dispersion function, linear coupling, sextupole strength, and nonlinear beam dynamics. We apply ICA in a new way to slices along the bunch revealing correlations of particle motion within the beam bunch. We digitize beam signals of the long bunch at the Los Alamos Proton Storage Ring with a single device (BPM or fast current monitor) for an entire injection-extraction cycle. ICA of the digitized beam signals results in source signals, which we identify to describe varying betatron motion along the bunch, locations of transverse resonances along the bunch, measurement noise, characteristic frequencies of the digitizing oscilloscopes, and longitudinal beam structure.

Low energy electrons (often referred to as "electron clouds") in the beam chambers of high intensity accelerators and storage rings can limit their performance. They can limit intensity by causing instabilities, unacceptable pressure increases or increases in beam size. Thus, reliable simulations of electron cloud generation in the Los Alamos high intensity Proton Storage Ring (PSR) and similar machines would be a most valuable tool for improving our understanding of its origin, the parameters that affect it and how it might be controlled. Such tools would provide cost-effective methods for designing mitigation measures and evaluating them before going to the expense of fabrication and experimental testing in an operating accelerator facility. In this project we have developed and tested several significant improvements to a widely used electron cloud simulation code, POSINST. In our version, LANLPOSINST V6, we have add several important features including the capability to model a multi-element section of the ring consisting of two quadrupole magnets with 3-dimensional magnetic fields, dipole magnet end fields, several drift spaces and various electron cloud diagnostics. Improvements were also added to the modeling of the initial primary or seed electrons from proton beam losses. One important conclusion from benchmarking these improvements was the need to include seed electrons produced from secondary particles resulting from the primary proton beam losses.

The Oak Ridge Spallation Neutron Source comprises a 1 GeV, 1.5 MW linear accelerator followed by an accumulator ring and a liquid mercury target. To manage the beam loss caused by the H^{0} excited states created during the H^{-} charge-exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming H^{-} beam, which circled around to strike the foil bracket and cause bracket failure. Another consequence is that convoy electrons can reflect back up from the electron catcher and strike the foil and bracket. An additional contributor to foil system failure is vacuum breakdown due to the charge developed on the foil by secondary electron emission. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them.

To accumulate high-intensity proton pulses, the Los Alamos Proton Storage Ring (PSR) uses the charge-exchange injection method. H− ions merge with already circulating protons in a bending magnet, and then are stripped off their two electrons in a carbon stripper foil. The circulating protons continue to interact with the foil. Despite efforts to minimize the number of these foil hits, like “painting” of the vertical phase space, they cannot totally be eliminated. As a result, foil heating and probably also radiation damage limit the lifetime of these foils. In recent years, LANL has collaborated with KEK to improve the carbon foils in use at PSR, and these foils now last typically for about 2 months. Recently, an alternative in the form of corrugated diamond foils has been proposed for use at SNS. These foils have now been tested in PSR production for a year, and have already shown to be at least as enduring as the LANL/KEK carbon foils. Advantages of the diamond foil concept, as well as some noteworthy differences that we observed with respect to the LANL carbon foils, will be discussed here.

A diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies with this diagnostic show that the electron flux striking the wall in the quadrupole is comparable to or larger than in an adjacent drift. In addition, the trapped electron signal, obtained using the sweeping feature of diagnostic, was larger than expected and decayed very slowly with an exponential time constant of 50 to 100 mus. Experimental results were also obtained which suggest that a significant fraction of the electrons observed in the adjacent drift space were seeded by electrons ejected from the quadrupole.

A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback.

At the 39 th ICFA Advanced Beam Dynamics Workshop HB 2006 and the 23 rd INTDS World Conference we reported on first results of a test of nanocrystalline diamond foils developed at ORNL under operational conditions at the Los Alamos Proton Storage Ring (PSR) (1). We have continued these tests during the 2006 and 2007 run cycles and have been able to compare the diamond foils with the foils that are normally in use in PSR, which were originally developed by Sugai at KEK. We have gathered valuable information regarding foil lifetime, foil related beam losses and electron emission at the foil. Additional insight was gained under unusual beam conditions where the foils are subjected to higher temperatures. In the 2007 run cycle we also tested a Diamond-like-Carbon foil developed at TRIUMF. A Hybrid-Boron-Carbon foil, also developed by Sugai, is presently in use with the PSR production beam. We will summarize our experience with these different foil types.

In order to better understand the two stream e-p instability issue in the LANSCE Proton Storage Ring (PSR), a new diagnostic instrument has been developed to measure the electron cloud formation and trapping in a quadrupole magnet at the LANSCE PSR. The device called the Electron Cloud Detector (ECD) was fabricated and has successfully been installed in the PSR. Along with the Electron Cloud Detector, an additional device was developed to manipulate electrons ejected from the quadrupole and allow additional information to be obtained from ECD measurements. This paper will discuss the mechanical design and fabrication issues encountered during the course of developing both devices.

The PSR (Proton Storage Ring) at LANSCE has observed an E-P (electron-proton) instability. A wideband analog feedback damper system was designed and implemented that has shown it is possible to correct this instability. The damper system consists of two 180 degree hybrids, low level amplifiers, a delay line, comb filter, power amplifiers, and adjustable delay lines. The system bandwidth is about between 10-300 MHz, and was developed and implemented in stages showing improvement in the e-p threshold of the buncher voltage. The system takes advantage of fiber optic technology for delays as well as for the comb filter. A system description and some measurement results are presented.

Simulations have indicated that electron clouds generated by beam-induced multipactor can be trapped in the mirror-like fields of magnetic quadrupoles and thereby contribute significantly to the electron cloud buildup in high intensity accelerators and storage rings. This could be a very important source of electrons driving the two-stream (e-p) instability at the Los Alamos Proton Storage Ring (PSR) and may also play a significant role in electron cloud effects at some of the new high intensity accelerator projects. We describe the physics design and optimization of an electron-sweeping detector designed to measure the trapped electrons at various times after the beam pulse has passed. The instrument can also serve as an electro-magnetically shielded detector which provides a signal obtained from electrons striking the wall during the passage of beam bunches.

A puzzling aspect of the e-p instability at PSR is the “1st Pulse” instability phenomenon. It shows up on the first beam pulse after a beam-off period of a few minutes or more. This pulse has a significantly lower instability threshold than beam pulses at regular repetition rate with a much shorter time separation. While the standard PSR operation for the Lujan Center spallation neutron source is unaffected by this phenomenon, it does interfere with some high intensity, single pulse experiments using PSR beam to another external beam area (WNR). We summarize the present experimental data characterizing this phenomenon as compared with the typical e-p instability observed at higher repetition rates and suggest some possible explanations.

The 31st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects ''ECLOUD'04'' was held April 19-23, 2004 at Napa, CA, USA. A broad range of current topics in this field were illuminated by 53 talks in 7 sessions plus 6 session summaries at the final summary session. These covered a variety of experimental methods and results, along with progress on understanding of the topic obtained from simulations and analytic theory, and evaluations of the effectiveness of various methods/mechanisms for mitigation of the adverse impact on accelerator performance. In addition, a panel discussion was held on ''Future Needs and Future Directions''. A summary of progress on the major themes covered at ECLOUD'04 is presented.

The mechanism of electron multipacting in long bunched proton machine has been quantitatively described by the electron energy gain and electron motion. Some important parameters related to electron multipacting are investigated in detail. It is proved that multipacting is sensitive to beam intensity, longitudinal beam profile shape and transverse beam size. Agreements are achieved among our analysis, simulation and experiment. The possible remedies to clearing electron cloud are also investigated.

We show that, due to inaccurate calculations with a Volterra integral equation, the results obtained in the commented paper are not true. Such an awkwardness could be avoided if the authors would retain in their calculations initial conditions for the proton bunch centroid.