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Simulations of the longitudinal instability in the new SLC damping rings

Description: In 1992 a longitudinal, single bunch instability was observed in the SLC damping rings. Beyond a threshold current of 3 x 10{sup 10} a {open_quotes}saw-tooth{close_quotes} variation in bunch length and energy spread was observed, a phenomenon that made it practically impossible to operate the SLC collider above threshold. For the 1994 run a new, low-impedance vacuum chamber was installed in both damping rings both to alleviate this problem and to shorten the bunch length. According to recent measurements the bunch length has indeed become shorter, but the {open_quotes}saw-tooth{close_quotes} instability is still seen, now beginning at currents of 1.5-2.0 x 10{sup 10}. Fortunately, it appears to be benign and does not seem to limit SLC performance. In an earlier paper the authors investigated the single bunch behavior of the SLC damping rings with the old vacuum chamber using time domain tracking and a Vlasov equation approach. When compared to measurements they found: good agreement in the average values of bunch length, energy spread, and synchronous phase shift as functions of current; a 30% discrepancy in threshold current; in agreement, a mode with frequency near 2.5 times the synchrotron frequency (the so-called {open_quotes}sextupole{close_quotes} mode) as signature of the instability and the slope of the mode frequency as function of current. In the present paper they repeat the exercise of the earlier paper but with a new wakefield. The impedance which used to be inductive has become resistive, leading to different phenomena. In a recent paper the instability in a purely resistive ring is analyzed using a Vlasov equation approach. It is demonstrated that such an instability is a weak instability, with a growth rate proportional to intensity squared, and one that can be described as the coupling of two quadrupole modes with different radial mode numbers. The authors compare their results with ...
Date: June 1, 1995
Creator: Bane, K.L.F. & Oide, K.
Partner: UNT Libraries Government Documents Department

Properties of Z{sup 0} {yields} b{bar b}g events

Description: We present studies of e{sup +}e{sup -} {yields} b{bar b}g events recorded with SLC Large Detector(SLD) at the SLAC Linear Collider. The SLD precision vertex detector was exploited to select light quarks- (u,d, and s), c-, and b-enriched event samples. A comparison of the strong couplings of light, c, and b quarks was made using jet rates in these samples. We find: {alpha}{sub s}{sup uds} / {alpha}{sub s}{sup all} = 0.994 {+-} 0.018(stat) {+-} 0.025(syst), {alpha}{sub s}{sup c}/{alpha}{sub s}{sup all} = 1.021 {+-} 0.070 {+-} 0.081, and {alpha}{sub s}{sup b}/{alpha}{sub s}{sup all} = 1.007 {+-} 0.031 {+-} 0.032 (PRELIMINARY). We also investigated the structure of b{bar b}g events via the energy and polar-angle distributions of the gluon, and the forward-backward production asymmetry of the b-quark.
Date: May 1, 1997
Creator: Oishi, N.
Partner: UNT Libraries Government Documents Department

VXD3: The SLD vertex detector upgrade based on a 307 Mpixel CCD system

Description: The SLD Collaboration is building a new CCD vertex detector (VXD3) comprising 96 3.2 Mpixel CCDs of 13 cm{sup 2} each for a total of 307 million pixels. This system is an upgrade of the Pioneering CCD vertex detector VXD2 which has operated in SLD since 1992. The CCDs of VXD3 are mounted on beryllium ladders in three cylinders, providing three space point measurements along each track of about 5 microns resolution in all three coordinates. The design and construction of VXD3 builds on three years of successful performance of VXD2. Significant improvements are achieved with VXD3 in impact parameters resolution (about a factor of two) and acceptance ({approximately}20%) through optimized geometry and reduced material. New readout electronics have been developed for this system. This new vertex detector will be installed in late 1995 for the future runs of SLD.
Date: July 1, 1995
Creator: Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

A preliminary measurement of R{sub b} = {Gamma}({Zeta}{degrees} {yields} b{bar b})/{Gamma}({Zeta}{degrees} {yields} hadrons) at SLD

Description: We present a preliminary measurement of R{sub b}, the ratio of {Gamma}(Z{degree} - b{bar b}) relative to {Gamma}(Z{degree} {yields} hadrons) using the silicon CCD-pixel vertex detector of the SLD at the SLAC Linear Collider (SLC). An impact parameter method and a displaced vertex method are applied to all charged tracks, to efficiently tag Z{degree} - b{bar b} events. From the impact (displaced vertex) approach we find R{sub b} = 0.214 {plus_minus} 0.010 {plus_minus} 0.025 (R{sub b} = 0.204 {plus_minus} 0.010 {plus_minus} 0.030), consistent with the standard model value.
Date: November 1, 1992
Creator: Su, D. & Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

Highlights of SLD physics

Description: The SLAC polarized electron beam allows the SLD experiment a high-precision measurement of sin{sup 2}{theta}{sub W}{sup eff} using the parity violating cross section asymmetry A{sub LR} at the e{sup +}e{sup {minus}} {yields} Z{sup o} vertex. The SLD also uses the small luminous e{sup +}e{sup {minus}} collision region and CCD vertex detector to tag heavy quark final states for probing the Z{sup o} {yields} q{bar q} vertex. Results are presented on the following selected topics: A{sub LR}, the Z{sup o} {yields} the Z{sup o} {yields} b{bar b} branching fraction R{sub b}, and the parity violating cross section asymmetries A{sub b} and A{sub b} and A{sub c} for the Z{sup o} {yields} b{bar b} and Z{sup o} {yields} b{bar b} and Z{sup o} {yields} c{bar c} final states.
Date: August 1, 1995
Creator: Zapalac, G. & Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

Magnet Fiducialization with Coordinate Measuring Machines

Description: One of the fundamental alignment problems encountered when building a particle accelerator is the transfer of a component's magnetic centerline position to external fiducials. This operation, dubbed fiducialization, is critical because it can contribute significantly to the alignment error budget. The fiducialization process requires two measurements: (1) from magnetic centerline to mechanical centerline, and (2) from mechanical centerline to external fiducials. This paper will focus on methods for observing the second measurement. Two Stanford Linear Collider (SLC) examples are presented. The object of magnet fiducialization is to relate the magnet-defined beamline position to exterior reference surfaces. To be useful for later component alignment, this relationship must be established in a manner consistent with overall positioning tolerances. The error budget for the SLC's {+-} 100 {micro}m component to component alignment tolerance is as follows: magnetic centerline to mechanical centerline--{sigma} = {+-}30 {micro}m; mechanical centerline to fiducial marks--{sigma} = {+-}50 {micro}m; and fiducial marks to adjacent components--{sigma} = {+-}80 {micro}m; the TOTAL {sigma} = {+-}100 {micro}m. The offset between the mechanical and magnetic centerlines of well-known magnets is generally smaller than the {+-}30 {micro}m measurement tolerance. It is commonly assumed to be zero without measurement. When this tiny value must be measured, extreme care is necessary to avoid obscuring the offset with measurement tool registration errors. In contrast, the mechanical centerline to fiducial measurement must be performed on every magnet. The 50 {micro}m tolerance for this operation is only slightly larger and pushes conventional surveying technology to its limit.
Date: August 12, 2005
Creator: Friedsam, H.; Oren, W.; Pietryka, M. & /SLAC
Partner: UNT Libraries Government Documents Department

Z{sup 0} pole direct measurements of the parity violation parameters A{sub b} and A{sub c} at SLD

Description: This report presents three different techniques used at SLD to measure directly the parity violation parameters of Zb{bar b} and Zc{bar c} couplings from the left-right forward-backward asymmetries. The results have been obtained using 150,000 hadronic Z{sup 0} decays accumulated during the 1993-95 runs with high electron beam polarization.
Date: September 1, 1996
Creator: Mancinelli, G.
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

Studies of beam induced dipole-mode signals in accelerating structures at the SLC

Description: Beam emittance dilution by self induced transverse fields (wakefields) in accelerating structures is a key problem in linear accelerators. To minimize the wakefield effects the beam trajectory must be precisely centered within the structures. An efficient way to achieve this is to detect beam induced microwave signals in the lowest dipole mode band and to steer the beam by minimizing these signals. This paper briefly covers some experiences from SLC S-band structures, but mainly concentrates on results of a wakefield instrumentation scheme applied to a NLC prototype X-band structure and tested with beam in the SLC linac. A beam based in-situ structure straightness measurement is shown as well as results of beam steering experiments based on phase and amplitude detection of two separated modes in the structure. After centering the beam the reduction of the wakefield was demonstrated independently by probing it with a test bunch that is deflected by the residual wakefield at a short distance behind the drive bunch.
Date: June 1, 1997
Creator: Seidel, M.
Partner: UNT Libraries Government Documents Department

Updated measurement of the tau lifetime at SLD

Description: We present an updated measurement of the tau lifetime at SLD. 4316 {tau}-pair events, selected from a 150k Z{sup 0} data sample, are analyzed using three techniques: decay length, impact parameter, and impact parameter difference methods. The measurement benefits from the small and stable interaction region at the SLC and the precision CCD pixel vertex detector of the SLD. The combined result is: {tau}{sub {tau}} = 288.1 {+-} 6.1(stat) {+-} 3.3(syst) fs.
Date: July 23, 1996
Partner: UNT Libraries Government Documents Department

Measurements of longitudinal phase space in the SLC linac

Description: The electron and positron bunch distributions in the Stanford Linear Collider (SLC) linac have been measured using a Hamamatsu, model N3373-02, 500-femtosecond streak camera. The distributions were measured at the end of the SLC linac versus the bunch compressor RF voltage. The energy spread at the end of the linac was also measured using a wire scanner. The effects of the bunch compressor on the shape of the bunch distribution are also presented.
Date: June 1, 1995
Creator: Holtzapple, R.L.; Decker, F.J.; Jobe, R.K. & Simopoulos, C.
Partner: UNT Libraries Government Documents Department

Effects of temperature variation on the SLC linac RF system

Description: The rf system of the Stanford Linear Collider in California is subjected to daily temperature cycles of up to 15{degrees}C. This can result in phase variations of 15{degrees} at 3 GHz over the 3 km length of the main drive line system. Subsystems show local changes of the order of 3{degrees} over 100 meters. When operating with flat beams and normalized emittances of 0.3*10{sup {minus}5} m-rad in the vertical plane, changes as small as 0.5{degrees} perturb the wakefield tail compensation and make continuous tuning necessary. Different approaches to stabilization of the RF phases and amplitudes are discussed.
Date: June 1, 1995
Creator: Decker, F.J.; Akre, R.; Byrne, M.; Farkas, Z.D.; Jarvis, H.; Jobe, K. et al.
Partner: UNT Libraries Government Documents Department

Diagnostic beam pulses for monitoring the SLC linac

Description: The Stanford Linear Collider is a pulsed machine with a repetition rate of 120 Hz. By using fast devices such as kickers and triggers, individual pulses can be modified, measured and diagnosed, and then dumped to avoid any background in the experiment. For more than five years, a diagnostic pulse has been used to kick the beams onto off-axis screens at the end of the linac every 6 seconds. This provides a visual monitor of the beam size and loses about 0.14% of the rate or two minutes a day. The sensitivity of the linac optics to temperature and phase variations makes it desirable to monitor the phase advance between different locations in order to make local corrections. In principle, the feedback systems can measure the phase advance using the natural jitter of the beam. In practice, the phase jitter of the beam with respect to the rf may dominate the betatron jitter and distort the measurement. By using a large induced betatron oscillation, the two effects can be separated. To improve the monitoring of phase advance, a small kicker at the beginning of the linac is fired every few seconds and the orbit of this particular beam pulse measured and analyzed. The sensitivity, the measured variation and the correction scheme will be discussed.
Date: June 1, 1995
Creator: Decker, F.J.; Stanek, M.; Smith, H. & Tian, F.
Partner: UNT Libraries Government Documents Department

Ion effects in the SLC electron damping ring

Description: The authors report on the ion-related beam behavior in the electron damping ring during unusually poor vacuum conditions in the weeks that followed a catastrophic kicker chamber failure that contaminated the ring vacuum system. The vacuum gradually improved over several months of beam operation, during which time the vertical emittance remained blown up by a factor of 2. The emittance blowup was accompanied by a transverse instability that produced jitter in the extracted beam size. Both the characteristic spectrum of self-excited betatron sidebands and the emittance blowup exhibited a threshold behavior with beam current and vacuum pressure. This behavior depended strongly on the betatron tune and it was found that the ion effects could be minimized by operating just below the 1/2 integer resonance.
Date: May 1, 1997
Creator: Krejcik, P.; Pritzkau, D.; Raubenheimer, T.; Ross, M. & Zimmermann, F.
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

SLAC accelerator operations report: 1992-1995

Description: Operational statistics for the linear accelerator programs at SLAC are presented, including run-time records for the SLC, FFTB, and fixed target programs. Also included are summaries of reliability and maintenance-related statistics and a discussion of the analysis tools used to study error messages generated by the control system.
Date: May 1, 1995
Creator: Erickson, R.; Allen, C.W.; Inman, T.K.; Linebarger, W. & Stanek, M.
Partner: UNT Libraries Government Documents Department

Fast feedback for linear colliders

Description: A fast feedback system provides beam stabilization for the SLC. As the SLC is in some sense a prototype for future linear colliders, this system may be a prototype for future feedbacks. The SLC provides a good base of experience for feedback requirements and capabilities as well as a testing ground for performance characteristics. The feedback system controls a wide variety of machine parameters throughout the SLC and associated experiments, including regulation of beam position, angle, energy, intensity and timing parameters. The design and applications of the system are described, in addition to results of recent performance studies.
Date: May 1, 1995
Creator: Hendrickson, L.; Adolphsen, C.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T. et al.
Partner: UNT Libraries Government Documents Department

Design and performance of a new 307 Mpixel CCD vertex detector

Description: During the past year, the SLD Collaboration completed construction and began operation of a new vertex detector (VXD3) with 307,000,000 CCD pixels. This upgrade will improve the SLD measurement of the polarization-enhanced forward-backward asymmetry for b and c-quarks and the precision of the measurement of the b-fraction in hadronic Z decays and opens the possibility to observe B{sub s}{sup 0}-mixing. Full separation of primary, secondary and tertiary vertices is accessible.
Date: September 1, 1996
Creator: Brau, J.E. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department

Collective effects in the NLC damping ring designs

Description: In this paper, we give an overview of collective effects and related issues in the damping rings for the NLC. The main damping ring will have a maximum average current of 1 A in four bunch trains which are separated by 60-80 ns, allowing the fast kickers to inject and extract individual trains. Each bunch train consists of 75-90 bunches, separated by 1.4 ns, with a maximum bunch population of 1.5 x 10{sup 10}. Because of the large average current, coupled bunch instabilities are a potential problem; these can be driven by the ring impedance or by a collective beam-ion instability. In addition, because the ring has a very small momentum compaction and synchrotron tune, potential well distortion and the microwave instability could be important. Finally, because of the very small beam emittances, the intrabeam scattering is significant. In the next sections, we will describe the present state of our calculations. We begin by describing the vacuum chamber design and RF cavities. We then discuss the longitudinal and transverse coupled bunch instabilities, the potential well distortion and the microwave instability, and finally, mode-coupling, ion effects, and intrabeam scattering.
Date: June 1995
Creator: Raubenheimer, T.; Bane, K. L. F.; Berg, J. S.; Byrd, J.; Corlett, J.; Furman, M. et al.
Partner: UNT Libraries Government Documents Department

Design and wakefield performance of the new SLC collimators

Description: The very small transverse beam sizes of the flat SLC bunches are 100-170 {mu}m in the horizontal and 30-50 {mu}m in the vertical near the end of the SLAC linac. Unexpectedly large transverse Wakefield kicks were observed from the collimators in this region during 1995. Upon inspection, it was found that the 20 {mu}m gold plating had melted and formed a line of spherules along the beam path. To refurbish the collimators, an improved design was required. The challenging task was to find a surface material with better conductivity than the titanium core to reduce resistive wakefields. The material must also be able to sustain the mechanical stress and heating from beam losses without damage. Vanadium was first chosen for ease of coating, but later TiN was used because it is more chemically inert. Recent beam tests measured expected values for geometric Wakefield kicks, but the resistive wall Wakefield kicks were four times larger than calculated.
Date: August 1, 1996
Creator: Decker, F.J.; Bane, K. & Emma, P.
Partner: UNT Libraries Government Documents Department

The Stanford Linear Collider

Description: The Stanford Linear Collider (SLC) is the first and only high-energy e{sup +}e{sup {minus}} linear collider in the world. Its most remarkable features are high intensity, submicron sized, polarized (e{sup {minus}}) beams at a single interaction point. The main challenges posed by these unique characteristics include machine-wide emittance preservation, consistent high intensity operation, polarized electron production and transport, and the achievement of a high degree of beam stability on all time scales. In addition to serving as an important machine for the study of Z{sup 0} boson production and decay using polarized beams, the SLC is also an indispensable source of hands-on experience for future linear colliders. Each new year of operation has been highlighted with a marked improvement in performance. The most significant improvements for the 1994-95 run include new low impedance vacuum chambers for the damping rings, an upgrade to the optics and diagnostics of the final focus systems, and a higher degree of polarization from the electron source. As a result, the average luminosity has nearly doubled over the previous year with peaks approaching 10{sup 30} cm{sup {minus}2}s{sup {minus}1} and an 80% electron polarization at the interaction point. These developments as well as the remaining identifiable performance limitations will be discussed.
Date: June 1, 1995
Creator: Emma, P.
Partner: UNT Libraries Government Documents Department

Feedback performance at the Stanford Linear Collider

Description: Many feedback loops are used at the Stanford Linear Collider (SLC) to control the orbit and energy of particle beams. Problems with corrector magnet slew rates, actuator calibrations, and computation of the beam transport matrix between loops have resulted in operation of many SLC feedback loops at lower than design gain. The response of various feedback loops to these errors is measured and analyzed in an attempt to improve performance.
Date: June 1, 1995
Creator: Minty, M.G.; Adolphsen, C.; Hendrickson, L.J.; Sass, R.; Slaton, T. & Woodley, M.
Partner: UNT Libraries Government Documents Department

The endcap Cherenkov ring imaging detector at SLD

Description: The authors present the Cherenkov Ring Imaging Detector in the endcap regions of the SLD detector and report initial performance. The endcap CRID was completed and commissioned in 1993 and is fully operational for the 1994 run. First Cherenkov rings have been observed. The endcap CRID detectors and fluid systems are described and initial operational experience is discussed.
Date: May 1, 1995
Creator: Abe, K.; Hasegawa, K.; Hawegawa, Y.; Iwasaki, Y.; Suekane, F.; Yuta, H. et al.
Partner: UNT Libraries Government Documents Department