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The readout of the LHC beam luminosity monitor: Accurate shower energy measurements at a 40 MHz repetition rate

Description: The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction create showers in the absorbers placed in front of the cryogenic separation dipoles. The shower energy, as it can be measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. This principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, detector and front-end electronics must comply with extremely stringent requirements. To make the bunch-by-bunch measurement feasible, their speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, in the actual operation the detector must stand extremely high radiation doses. The front-end electronics, to survive, must be located at some distance from the region of high radiation field, which means that a properly terminated, low-noise, cable connection is needed between detector and front-end electronics. After briefly reviewing the solutions that have been adopted for the detector and the front-end electronics and the results that have been obtained so far in tests on the beam, the latest version of the instrument in describe in detail. It will be shown how a clever detector design, a suitable front-end conception based on the use of a ''cold resistance'' cable termination and a careful low-noise design, along with the use of an effective deconvolution algorithm, make the luminosity measurement possible on a bunch-by-bunch basis at the LHC bunch repetition rates.
Date: May 10, 2003
Creator: Manfredi, P.F.; Ratti, L.; Speziali, V.; Traversi, G.; Manghisoni, M.; Re, V. et al.
Partner: UNT Libraries Government Documents Department

ALS-N - A candidate for a next-generation synchrontron light-source

Description: Judging from the experiments currently being pursued at the ALS, there is already a compelling case to be made for considering a future synchrotron radiation source that has a higher beam brightness than the third-generation facilities. For example, a large, and growing fraction of the ALS scientific program is based on soft x-ray microscopy experiments in materials science. Currently these experiments use high-brightness undulator radiation, on beam lines that are already oversubscribed. Dedicated beam lines from bend magnet sources would be useful for these techniques if the source brightness could be pushed to {approx}2{circ}10{sup 16} photons/(s {circ} mm{sup 2} {circ} mrad{sup 2} {circ} 0.1%b.w.), i.e., a factor of 20-100 higher (depending on wavelength), than currently available at the ALS. Another growing class of experiments uses microfocused beams for microanalysis, microdiffraction, microEXAFS, microXPS, and microNEXAFS. These are classic brightness experiments, but even at the high ALS brightnesses, require long exposure times. Finally there is a requirement to get to {approx}2 keV in the fundamental peak of the undulator spectrum, to access most transition- metal L-edges, and the rare-earth M-edges. This could be achieved with a machine energy of 2.5-3.0 GeV. An alternative strategy is to go to smaller gaps with a shorter period undulator - which is compatible with lower emittance beams.
Date: May 1, 1997
Creator: Jackson, A.; Byrd, J. & Decking, W.
Partner: UNT Libraries Government Documents Department


Description: To study CP violation, the HEM-B experiment uses an internal wire target in the transverse halo of the stored HERA proton beam. Operational experience shows that the resulting interaction rates are extremely sensitive to tiny orbit jitter amplitudes. Various methods have been studied to stabilize these interaction rates by increasing diffusion in the transverse proton beam tails without affecting the luminosity at the electron-proton collider experiments ZEUS and H1. Tune modulation was found to be a promising method for this task. Experiments performed in recent years will be reported.
Date: May 19, 2003
Creator: MONTAG,C.
Partner: UNT Libraries Government Documents Department

Single-top-squark production via baryon-number-violating couplings at the Fermilab Tevatron Collider.

Description: We consider the s-channel R-parity-violating production of a single light top squark {tilde t}{sub 1} and its subsequent R-parity-conserving decay. For masses in the range 180-325 GeV, and R-parity-violating couplings {lambda}{sub 3ij}{double_prime} > 0.02-0.05, we show that discovery of the top squark is possible with 2 fb{sup {minus}1} of integrated luminosity at run II. If no evidence for the top squark is found, the bound on {lambda}{sub 3ij}{double_prime} can be reduced by up to an order of magnitude with existing data from run I, and by two orders of magnitude at run II.
Date: April 29, 1999
Creator: Berger, E. L.; Harris, B. W. & Sullivan, Z.
Partner: UNT Libraries Government Documents Department

The polarized electron beam for the SLAC Linear Collider

Description: The SLAC Linear Collider has been colliding a polarized electron beam with an unpolarized positron beam at the Z{sup 0} resonance for the SLD experiment since 1992. An electron beam polarization of close to 80% has been achieved for the experiment at luminosities up to 8 {center_dot} 10{sup 29} cm{sup {minus}2} s{sup {minus}1}. This is the world`s first and only linear collider, and is a successful prototype for the next generation of high energy electron linear colliders. This paper discusses polarized beam operation for the SLC, and includes aspects of the polarized source, spin transport and polarimetry.
Date: October 1, 1996
Creator: Woods, M.
Partner: UNT Libraries Government Documents Department

High intensity performance and upgrades at the Brookhaven AGS

Description: For the last two years the Brookhaven AGS has operated the slow extracted beam program at record proton intensities. This high beam intensity allowed for the simultaneous operation of three high precision rare kaon decay experiments. The record beam intensities were achieved after the 1.5 GeV Booster was commissioned and a transition jump system, a powerful transverse damper, and an rf upgrade in the AGS were completed. Recently even higher intensity proton synchrotrons are studied for neutron spallation sources or proton driver for a muon collider. Implications of the experiences from the AGS to these proposals and also possible future upgrades for the AGS are discussed.
Date: December 31, 1996
Creator: Roser, T.
Partner: UNT Libraries Government Documents Department

Performance optimization of synchrotron light sources

Description: This paper will present work done at the NSLS to tailor the electron beam properties so as to maximize the performance of the photon beamlines. The electron beam properties of most importance to photon users are the total stored current, emittance, lifetime, and transverse stability. Recent and planned improvements in each of these properties will be discussed as well as the ultimate limits for each. The discussion of transverse stability will include high frequency motion, which can reduce the effective brightness, as well as slow drift during a fill and fill-to-fill reproducibility.
Date: Summer 1996
Creator: Safranek, J
Partner: UNT Libraries Government Documents Department

Beam-beam collisions and crossing angles in RHIC

Description: This paper evaluates the strength of head on and parasitic beam-beam collisions in RHIC when the crossing angle is zero. A non-zero crossing angle is not required in normal operation with 120 bunches, thanks to the early separation of the two beams. The RHIC lattice is shown to easily accommodate even conservatively large crossing angles, for example in beam dynamics studies, or in future operational upgrades to as many as 360 bunches per ring. A modest loss in luminosity is incurred when gold ions collide at an angle after 10 hours of storage.
Date: June 1, 1999
Creator: Peggs, S.
Partner: UNT Libraries Government Documents Department

A proton driver for the muon collider source with a tunable momentum compaction lattice

Description: The future Muon Collider will have a luminosity of the order of 10{sup 35} cm{sup {minus}2{minus}1} during 1,000 turns when the muons decay. This requires 10{sup 12} muons per bunch. The muon source is a 30 GeV proton driver with 2.5 10{sup 13} protons per pulse. The proton bunch length should be of the order of 1 ns. Short bunches could be created by a tunable momentum compaction lattice which would bring the momentum compaction to zero in a short time. This isochronous conduction would allow bunches to shear and become very short in time. The authors present a lattice where the momentum compaction is a tunable parameter at fixed horizontal and vertical betatron tunes. The values of the maxima of the dispersion function are kept small. They examine two kinds of lattices, with combined function as well as normal dipole and quadrupole magnets.
Date: July 1, 1997
Creator: Trbojevic, D.; Brennan, J.M.; Courant, E.D.; Roser, T.; Peggs, S.; Ng, K.Y. et al.
Partner: UNT Libraries Government Documents Department

Coherent synchrotron radiation in the isochronous muon collider ring

Description: To achieve the luminosity of L = 10{sup 35} cm{sup {minus}2}s{sup {minus}1} in a {mu}{sup +}{mu}{sup {minus}} collider, two bunches per sign of N = 2 {times} 10{sup 12} particles each and a betatron function of {beta}* = 3 mm at the interaction point (IP) are required. This small {beta}* at the IP constrains the size of the bunch to be {sigma}{sub z} {approximately} {beta}*. To maintain this rather short bunch without excessive rf power consumption, an isochronous lattice has been chosen for the final collider ring. One of the important advantages of muons as opposed to electrons is that at up to at least TeV energy it is possible to accelerate muons in circular machines as their synchrotron radiation is reduced by a factor of (m{sub e}/m{sub {mu}}){sup 2} {approximately} 23 {times} 10{sup {minus}6} with respect to electrons. Nevertheless, the large number of muons in a short bunch suggests the possibility of strong shielded coherent synchrotron radiation. First, the author uses the well known formulae to evaluate the power of shielded coherent synchrotron radiation in the isochronous muon collider ring. Finally, following the results obtained by Kheifets and Zotter for a bunch with a Gaussian longitudinal charge distribution the author shows that the coherent synchrotron radiation in the isochronous {mu}{sup +}{mu}{sup {minus}} collider ring is negligible if the rms bunch length is larger than {approx} 0.3 mm.
Date: October 1, 1996
Creator: Gallardo, J.C.
Partner: UNT Libraries Government Documents Department

Contributions to the mini-workshop on beam-beam compensation in the Tevatron

Description: The purpose of the Workshop was to assay the current understanding of compensation of the beam-beam effects in the Tevatron with use of low-energy high-current electron beam, relevant accelerator technology, along with other novel techniques of the compensation and previous attempts. About 30 scientists representing seven institutions from four countries--FNAL, SLAC, BNL, Novosibirsk, CERN, and Dubna were in attendance. Twenty one talks were presented. The event gave firm ground for wider collaboration on experimental test of the compensation at the Tevatron collider. This report consists of vugraphs of talks given at the meeting.
Date: February 1, 1998
Creator: Shiltsev, V.
Partner: UNT Libraries Government Documents Department

Beam-based optical tuning of the final focus test beam

Description: In order to reduce the SLAC 46.6 GeV beam to submicron sizes, the Final Focus Test Beam (FFTB) must meet tight tolerances on many aberrations. These aberrations include: mismatch and coupling of the incoming beam; dispersion; chromaticity; lattice errors in the chromatic correction sections; lattice coupling; and residual sextupole content in the quadrupoles. In order to address these aberrations, the authors have developed a procedure which combines trajectory analysis, use of intermediate wire scanners, and a pair of novel beam size monitors at the IP. This procedure allows the FFTB IP spot to be reduced to sizes under 100 nanometers.
Date: May 1, 1995
Creator: Tenenbaum, P.; Burke, D.; Hartman, S.; Helm, R.; Irwin, J.; Iverson, R. et al.
Partner: UNT Libraries Government Documents Department

Disruption effects on the beam size measurement

Description: At the SLC Final Focus with higher currents and smaller beam sizes, the disruption parameter D{sub y} is close to one and so the pinch effect should produce a luminosity enhancement. Since a flat beam-beam function is fit to deflection scan data to measure the beam size, disruption can affect the measurement. Here the authors discuss the quantitative effects of disruption for typical SLC beam parameters. With 3.5 10{sup 10} particles per pulse, bunch length of 0.8 mm and beam sizes of 2.1 {mu}m horizontally and 0.55 {mu}m vertically, the measured vertical size can be as much as 25% bigger than the real one. Furthermore during the collision the spot size actually decrease, producing an enhancement factor H{sub D} of about 1.25. This would yield to a true luminosity which is 1.6 times that which is estimated from the beam-beam deflection fit.
Date: June 1, 1995
Creator: Raimondi, P.; Decker, F.J. & Chen, P.
Partner: UNT Libraries Government Documents Department

Beam tube vacuum in 100 TeV hadron colliders

Description: Bounds on the beam tube gas pressure and the required pumping speed are estimated for {approximately} 2 T low field (LF) and {approximately} 12 T high field (HF) 100 TeV center-of-mass hadron colliders. In both cases photodesorption by synchrotron radiation is the dominant source of gas. Assuming beam-gas scattering limited luminosity lifetime five times the IP scattering lifetime, the required CO equivalent beam tube pressure is 0.25 nTorr for LF and 1.8 nTorr for HF, ambient room temperature equivalent. The CO equivalent pumping speeds required to achieve this pressure within a reasonable beam conditioning time (a few tenths of an operational year at design intensity) are estimated to be {approximately} 300 l/s-m for LF and {approximately} 40 l/s-m for HF. For the LF case with a superferric warm iron magnet, the beam tube is at ambient room temperature and a distributed NEG plus lumped ion or cryo pump system is considered. The size of antechamber needed, ID {approximately} 6 cm, requires that it be located outside the {approximately} 2 cm C-coil magnet gap. Lumped pumps for pumping CH{sub 4} need to be spaced at {approximately} 20 m intervals on the antechamber. For the HF case the likely beam tube temperature is 15--20 K and cryopumping with a beam screen system is considered. The necessary pumping speed can be achieved with slots covering {approximately} 2% of the beam screen surface.
Date: April 1, 1997
Creator: Turner, W.C.
Partner: UNT Libraries Government Documents Department

Modelling the Fermilab Collider to determine optimal running

Description: A Monte Carlo-type model of the Fermilab Collider has been constructed, the goal of which is to accurately represent the operation of the Collider, incorporating the aspects of the facility which affect operations in order to determine how to run optimally. In particular, downtime for the various parts of the complex are parameterized and included. Also, transfer efficiencies, emittance growths, changes in the luminosity lifetime and other effects are included and randomized in a reasonable manner. This Memo is an outgrowth of TM-1878, which presented an entirely analytical model of the Collider. It produced a framework for developing intuition on the way in which the major components of the collider affect the luminosity, like the stacking rate and the shot set-up time, for example. However, without accurately including downtime effects, it is not possible to say with certainty that the analytical approach can produce accurate guidelines for optimizing the performance of the Collider. This is the goal of this analysis. We first discuss the way the model is written, describing the object-oriented approach taken in C++. The parameters of the simulation are described. Then the potential criteria for ending stores are described and analyzed. Next, a typical store and a typical week are derived. Then, a final conclusion on the best end-of-store criterion is made. Finally, ideas for future analysis are presented.
Date: December 1, 1994
Creator: McCrory, E.
Partner: UNT Libraries Government Documents Department

Improvement to the D0 luminosity monitor constant

Description: The D0 experiment has previously calculated its luminosity using the visible cross section (luminosity monitor constant) for its Level 0 trigger, {sigma}{sub L0} = 48.2 mb, based on the world average {ovr p}p inelastic cross sections at {radical}s = 1.8 TeV. The error on luminosity had been set at 12%. Recent studies using the MBR and DTUJET Monte Carlo event generators and unbiased D0 data samples have resulted in a more precise determination of the D0 luminosity monitor constant. The result, {sigma}{sub L0} = 46.7 {+-} 2.5 mb, lowers the central value by 3.1% and reduces the error to 5.4%. 12 refs., 7 figs., 9 tabs.
Date: March 1, 1996
Creator: Bantley, J.
Partner: UNT Libraries Government Documents Department

The D-Zero luminosity monitor constant for {radical} {ital s} = 630 GeV

Description: D0 has calculated the luminosity monitor constant for {radical}s= 630 GeV. The inelastic p{anti p} cross section was interpolated between measurements performed at {radical}s = 546 and 1800 GeV. The geometric acceptance, hardware efficiency, and luminosity-dependent corrections are similar to those previously published for the full Tevatron energy. We find a luminosity-weighted value of {sigma}{sub L0} = 34.04 {+-} 1.05 mb, yielding a precision of {+-} 3.08%.
Date: June 1, 1997
Creator: Krane, J.; Barnly, J. & Owen, D.
Partner: UNT Libraries Government Documents Department

Beam-beam studies for the Tevatron

Description: In the first stage of Run II, the Tevatron will be operated with 36 bunches in each beam with bunch separations of 396 nanoseconds. The expected peak luminosity is L = 8.6 x 10{sup 31}cm{sup {minus}2}sec{sup {minus}1} with an average number of 2.3 interactions per bunch crossing. In the second stage of Run II, the goal is to increase the luminosity to about 1.5x10{sup 32} cm{sup {minus}2}sec{sup {minus}1}. If the bunch spacing were kept constant, the average number of interactions per bunch crossing would increase to about 4. This is thought to be unacceptably large and might saturate the efficiency of the detectors. This is the main reason for decreasing the bunch spacing at higher luminosities. One possibility is to reduce the bunch spacing to 132 nanoseconds which lowers the average number of interactions to an acceptable value of 1.4. This shorter bunch spacing though has several consequences on beam dynamics. Collisions between bunches will now occur every 19.78m. This is shorter than the distance of the nearest separators from the main IPs at B0 and D0. Consequently the beams will not be separated at the parasitic collisions nearest to the IPs if the geometry of the orbit is left unchanged. A sketch of this orbit is seen in the top part of Figure 1. This will lead to unacceptably large beam losses and background. Moving the separators closer to the detectors does not separate the beams sufficiently at the locations PC1L and PC1R. The phase advance from the first available position for the separators to these points is too small for the separator strengths that are available. One way to increase the transverse separation between the beams is to make the beams cross at an angle at the IPs. The optimum crossing angle depends upon a number of issues ...
Date: June 13, 2000
Creator: Sen, Tanaji
Partner: UNT Libraries Government Documents Department

Calculating luminosity for a coupled Tevatron lattice

Description: The traditional formula for calculating luminosity assumes an uncoupled lattice and makes use of one-degree-of-freedom lattice functions, {beta}{sub H} and {beta}{sub v}, for relating transverse beam widths to emittances. Strong coupling requires changing this approach. It is simplest to employ directly the linear normal form coordinates of the one turn map. An equilibrium distribution in phase space is expressed as a function of the Jacobian`s eigenvectors and beam size parameters or emittances. Using the equilibrium distributions an expression for the luminosity was derived and applied to the Tevatron lattice, which was coupled due to a quadrupole roll.
Date: May 1, 1995
Creator: Holt, J.A.; Martens, M.A.; Michelotti, L. & Goderre, G.
Partner: UNT Libraries Government Documents Department