465 research outputs found
Feedback Between Accelerator Physicists and Magnet Builders
Our task is not to record history but to change it. (K. Marx (paraphrased)) How should Accelerator Physicists set magnet error specifications? In a crude social model, they place tolerance limits on undesirable nonlinearities and errors (higher order harmonics, component alignments, etc.). The Magnet Division then goes away for a suitably lengthy period of time, and comes back with a working magnet prototype that is reproduced in industry. A better solution is to set no specifications. Accelerator Physicists begin by evaluating expected values of harmonics, generated by the Magnet Division, before and during prototype construction. Damaging harmonics are traded off against innocuous harmonics as the prototype design evolves, lagging one generation behind the evolution of expected harmonics. Finally, the real harmonics are quickly evaluated during early industrial production, allowing a final round of performance trade-offs, using contingency scenarios prepared earlier. This solution assumes a close relationship and rapid feedback between the Accelerator Physicists and the magnet builders. What follows is one perspective of the way that rapid feedback was used to `change history` (improve linear and dynamic aperture) at RHIC, to great benefit
Grazing function g and collimation angular acceptance
The grazing function g is introducedâa synchrobetatron optical quantity that is analogous (and closely connected) to the Twiss and dispersion functions ÎČ, α, η, and ηâČ. It parametrizes the rate of change of total angle with respect to synchrotron amplitude for grazing particles, which just touch the surface of an aperture when their synchrotron and betatron oscillations are simultaneously (in time) at their extreme displacements. The grazing function can be important at collimators with limited acceptance angles. For example, it is important in both modes of crystal collimation operationâin channeling and in volume reflection. The grazing function is independent of the collimator typeâcrystal or amorphousâbut can depend strongly on its azimuthal location. The rigorous synchrobetatron condition g=0 is solved, by invoking the close connection between the grazing function and the slope of the normalized dispersion. Propagation of the grazing function is described, through drifts, dipoles, and quadrupoles. Analytic expressions are developed for g in perfectly matched periodic FODO cells, and in the presence of ÎČ or η error waves. These analytic approximations are shown to be, in general, in good agreement with realistic numerical examples. The grazing function is shown to scale linearly with FODO cell bend angle, but to be independent of FODO cell length. The ideal value is g=0 at the collimator, but finite nonzero values are acceptable. Practically achievable grazing functions are described and evaluated, for both amorphous and crystal primary collimators, at RHIC, the SPS (UA9), the Tevatron (T-980), and the LHC
ZACK : a computerized farm budgeting program
Developed by the Department of Agriculture, ZACK enables farmers to throw away their pencils, rubbers, calculators and cash-flow forms and use a computer to prepare their annual farm plans and cash-flow budgets
Simulation results for crystal collimation experiment in SPS UA9
The UA9 experiment will first take place in 2009 at the CERN-SPS and will evaluate the feasibility of silicon crystals as primary collimators for a storage ring. A crystal placed at 6 Ï from the beam core will deviate protons towards two Roman Pots and a tungsten absorber (TAL). In this paper the authors show simulations of the expected beam dynamics and of the capture efficiency into the secondary collimator. The result of these simulations will guide us in interpreting the experimental data expected in UA9
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Rf Voltage Modulation At Discrete Frequencies With applications To Crystal channeling Extraction
RF voltage modulation at a finite number of discrete frequencies is described in a Hamiltonian resonance framework. The theory is applied to the problem of parasitic extraction of a fixed target beam from a high energy proton collider, using a bent crystal as a thin ``septum`` within an effective width of about one micron. Three modes of employment of discrete resonances are proposed.First, a single relatively strong static ``drive`` resonance may be used to excite a test proton so that it will penetrate deeply into the channeling crystal. Second, a moderately strong ``feed`` resonance with a ramped modulation tune may be used to adiabatically trap protons near the edge of the beam core, and transport them to the drive resonance. Third, several weak resonances may be overlapped to create a chaotic amplitude band, either to transport protons to the drive resonance, or to provide a ``pulse stretching`` buffer between a feed resonance and the drive resonance. Extraction efficiency is semi- quantitatively described in terms of characteristic ``penetration,`` ``depletion,`` and ``repetition`` times. simulations are used to quantitatively confirm the fundamental results of the theory, and to show that a prototypical extraction scheme using all three modes promises good extraction performance
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Thorium Energy Futures
The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options â liquid or solid, with or without an accelerator â can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice
Channeling and Volume Reflection Based Crystal Collimation of Tevatron Circulating Beam Halo (T-980)
The T980 crystal collimation experiment is underway at the Tevatron to
determine if this technique could increase 980 GeV beam-halo collimation
efficiency at high-energy hadron colliders such as the Tevatron and the LHC.
T980 also studies various crystal types and parameters. The setup has been
substantially enhanced during the Summer 2009 shutdown by installing a new
O-shaped crystal in the horizontal goniometer, as well as adding a vertical
goniometer with two alternating crystals (O-shaped and multi-strip) and
additional beam diagnostics. First measurements with the new system are quite
encouraging, with channeled and volume-reflected beams observed on the
secondary collimators as predicted. Investigation of crystal collimation
efficiencies with crystals in volume reflection and channeling modes are
described in comparison with an amorphous primary collimator. Results on the
system performance are presented for the end-of-store studies and for entire
collider stores. The first investigation of colliding beam collimation
simultaneously using crystals in both the vertical and horizontal plane has
been made in the regime with horizontally channeled and vertically
volume-reflected beams. Planning is underway for significant hardware
improvements during the FY10 summer shutdown and for dedicated studies during
the final year of Tevatron operation and also for a "post-collider beam physics
running" period.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10,
23-28 May 2010: Kyoto, Japa
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