Los Alamos Proton Storage Ring Research Articles

Independent component analysis applied to long bunch beams in the Los Alamos Proton Storage Ring

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.

Comparison of carbon and corrugated diamond stripper foils under operational conditions at the Los Alamos PSR

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.

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 $100\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$. 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.

Active damping of the e-p instability at the Los Alamos Proton Storage Ring

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.

Electron cloud instabilities in the Proton Storage Ring and Spallation Neutron Source

Electron cloud instabilities in the Los Alamos ProtonStorage Ring (PSR) and those foreseen forthe Oak Ridge SpallationNeutron Source (SNS) are examined theoretically, numerically, andexperimentally.

Calculations of the conditions for bunch leakage in the Los Alamos proton storage ring

Observations are consistent with the possibility of an “ep” instability in the Los Alamos Proton Storage Ring (PSR) with both bunched and unbunched beam. The instability requires electrons to be trapped within the beam, and calculations have shown that such trapping requires leakage of beam into the interbunch gap. Observationally, leakage of beam into the gap appears necessary for the onset of the instability. In this paper we present results of studies of the longitudinal beam dynamics at PSR parameters. The studies indicate that the combined effects of the rf buncher, longitudinal space charge, and injection mismatch are sufficient to cause the observed bunch leakage. Simulation results are presented and compared with PSR observations. Variations of PSR performance parameters are considered, and methods of improving bunch confinement are suggested and studied.

Observations of a fast transverse instability in the PSR

Abstract A fast instability with beam loss is observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam current exceeds a threshold value, with both bunched and unbunched beams. Large coherent transverse oscillations occur prior to and during beam loss. The threshold depends strongly on rf voltage, beam-pulse shape, beam size, nonlinear fields, and beam environmental. Results of recent observations of the instability are reported; possible causes of the instability are discussed. Recent measurements and calculations indicate that the instability is an “e-p”-type instability, driven by coupled oscillations with electrons trapped within the proton beam. Future experiments toward further understanding of the instability are discussed, and methods of increasing PSR beam storage are suggested.

Providing common data access for the LAMPF and PSR control systems

The merging of the Los Alamos Meson Physics Facility (LAMPF) and the Los Alamos Proton Storage Ring (PSR) controls and operations groups in early 1988 motivated planning for a common, probably workstation-based, operator interface. Application programs driving this interface must be able to communicate with both LAMPF and PSR devices in a uniform manner. We would like this communication to be implemented with minimal changes to the current LAMPF and PSR control systems. A common device-naming scheme has made it possible for remote systems to acquire both LAMPF and PSR data through the use of server processes residing in the appropriate network nodes. Remote supervisory control of LAMPF devices has been provided in a similar manner. Incompatibilities between information in the LAMPF and PSR database has made remote supervisory control of PSR devices somewhat more difficult. This paper discusses our experience providing this common access and plans for providing future common communications.

Determination of beam position and angle to minimize beam loss in the Los Alamos proton storage ring

A beam of negatively charged hydrogen ions passes through a stripper magnet to produce a neutral hydrogen beam before it is injected into the proton storage ring at the Los Alamos Meson Physics Facility. Inside the ring the injected beam passes through a carbon foil which strips off the remaining electrons to produce a proton beam. It is desirable to position the foil where it will minimize beam losses due to multiple Coulomb scattering in the ring. Beam loss is also decreased if the position and angle of the injected beam are chosen so that the phase ellipse of the injected beam has the best match with the phase ellipse of the ring beam. To achieve these two objectives, the position and angle of the injected beam must be determined at the foil. This is done by describing the beam path in the ring, and interpolating at the foil. A number of beam-position monitors placed at intervals around the ring provide data on the position of the beam at these points. A multiple-regression algorithm uses the data from the beam-position monitors to estimate the position and angle of the injected beam at the foil, along with correlation coefficients and confidence limits.

Transmission-line impedance measurements for an advanced hadron facility

High-intensity synchrotrons such as the proposed Advanced Hadron Facility (AHF) [1] and the Los Alamos Proton Storage Ring (PSR) [2] must have a low beam-coupling impedance for stability. The conflicting requirement of low eddy-current effects in the rapid cycling AHF makes the AHF beam-pipe design a particularly difficult problem. A ceramic pipe deposited with conducting stripes has been proposed for AHF. It can have adequately small eddy currents, but it may have an unexpectedly large coupling impedance. Therefore, a facility for measuring transmission-line impedances has been established and is described in this paper. Measurements of transverse and longitudinal coupling impedances for ceramic/metal and other beam-pipe segments are reported; a ceramic/metal chamber can have adequately small impedance. Results of impedance measurements for other AHF and PSR devices, such as a PSR beam pickup and bumper magnet, are also reported.

New Method for Inverting the Closed Orbit Distortion Problem

A certain class of magnet misalignments in storage rings and other accelerators produces closed orbit distortions (CODs). Quite often the CODs are measured at a fewer number of locations (N) than the number of misalignment parameters (M). There is a linear relation between COD measurements, u(j), j= l, ..., N and the misalignment parameters e(k), k= l, ..., M. Hence the c(k)' s are underdetermined. If M < 2N, one can obtain an overdetermined set of equations by measuring the COD at two quadrupole settings. There are several ways of inverting the COD measurements to get the misalignment parameters that are fairly insensitive to errors in the measured CODs. A computer program called CODINV has been written to test some of these schemes. Two schemes give fairly good results when applied to the lattice of the Los Alamos Proton Storage Ring (PSR). The first scheme requires measurements at two nearby tunes and the use of singularvalue decomposition methods. The second scheme requires measurements of the CODs in the FODO and DOFO cell arrangements but is easier mathematically.

Laser photoionization of Ho beams for charge-changing injection

The two-step charge-changing injection used in the Los Alamos Proton Storage Ring (PSR) requires stripping of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> to H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> by high magnetic fields and subsequent stripping of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> to H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> by a carbon foil. We consider single-and multiphoton laser ionization as alternatives to using a fragile foil. The multiphoton case is of possible interest for selection of practical lasers, which tend to have increased power output at higher wavelengths. The formulas derived express the necessary laser powers for ionization of monoenergetic H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> beams; they also hold for beams of particles other than atomic hydrogen. The numerical examples given are for the 800-MeV PSR beam with momentum spread taken into account. Additionally, we discuss selective stripping as an implication of the inherent energy selectivity of the photoionization process.