Electron Bypass Line (EBL) Design: Electrons to A-line bypassing LCLS

Forty one years ago, September 20, 1966, the first beam entered End Station A, passed on through, and was terminated in Beam Dump East. This beam had an energy of 18.4 GeV, a record for the time. Since then, the SLAC ESA has been a mainstay facility for many high-energy physics and test beam experiments involving countless hours of data taking. Heretofore, it was assumed that with the completion and commissioning of the LCLS facility, beams from the main injector would no longer be available to this well equipped experimental facility. Fortunately, it has become clear that a bypass beamline design calling for modest modifications and using existing, soon to be surplus, components will enable continued utilization of this important facility

Transport construction status and commissioning plans

Installation of the PEP-II electron and positron Injection beamlines in the SLAC linac housing is now underway. Utilization of the existing high power, low emittance beams available at SLAC required that a great portion of the systems for pulsed extraction and transport of 9.0 GeV electrons and 3.1 GeV positrons for injection into the PEP-II rings will reside in the existing linac housing. Approximately 4.7 kilometers of these beamlines will be completed during the summer of 1995. All components, including orbit correctors and diagnostic instruments, required for extraction and transport of the electron beam will be in place and ready for commissioning as soon as this fall. The positron transport line in the housing will also be complete except for the pulsed extraction system. These systems are described, along with the status of the construction and installation of the important subsystems such as magnets and power supplies, vacuum systems, instrumentation and controls. The plan for commissioning is discussed

Studies of anomalous dispersion in the SLC second order achromat

Certain causes of anomalous dispersion in the second order achromats of the SLC arcs are investigated. For matched dispersion, transverse displacements of combined function magnets do not introduce anomalous dispersion. This is shown by deriving a non-dispersive condition connecting the average of the matched dispersion function with the quadrupole and sextupole components of the field. In the SLC Arcs, however, the achromats are rolled producing a dispersion mismatch. In this case, the horizontal (vertical) dispersion is affected linearly by vertical (horizontal) displacement of magnets. The integral condition connecting the dipole and quadrupole fields and the matched dispersion is also derived. Combining this with the non-dispersive condition and the analytic expression of the matched dispersion gives two simple relationships for the fields of second order achromats constructed of combined function magnets. The effects of the dispersion mismatch in the SLC Arcs is investigated using computer simulations. The results show that this mismatch will increase the sensitivity to transverse errors. We report the effects of certain systematic errors

Online monitoring of dispersion functions and transfer matrices at the SLC

The symmetries of the chromatic correction sections in the SLC Final Focus System allow a high-resolution determination of the pulse-to-pulse energy fluctuations by exploiting the information from beam position monitors (BPMs) in regions of large dispersion. By correlating this signal with other BPMs, one can infer the dispersion function as well as spatial components of transfer matrices anywhere in the arcs and the Final Focus System without interrupting normal machine operation. We present results from data recorded during either periods of stable operation or periods when the linac energy was intentionally varied. 6 refs., 7 figs

Observation of Target Electron Momentum Effects in Single-Arm M\o ller Polarimetry

In 1992, L.G. Levchuk noted that the asymmetries measured in M\o ller scattering polarimeters could be significantly affected by the intrinsic momenta of the target electrons. This effect is largest in devices with very small acceptance or very high resolution in laboratory scattering angle. We use a high resolution polarimeter in the linac of the polarized SLAC Linear Collider to study this effect. We observe that the inclusion of the effect alters the measured beam polarization by -14% of itself and produces a result that is consistent with measurements from a Compton polarimeter. Additionally, the inclusion of the effect is necessary to correctly simulate the observed shape of the two-body elastic scattering peak.Comment: 29 pages, uuencoded gzip-compressed postscript (351 kb). Uncompressed postscript file (898 kb) available to DECNET users as SLC::USER_DISK_SLC1:[MORRIS]levpre.p

Bunch compression for the TLC: Preliminary design

A preliminary design of a TLC bunch compressor as a two-stage device is described. The main parameters of the compressor, as well as results of some simulations, are presented. They show that the ideal system (no imperfections) does the job of transmitting transverse emittances without distortions (at least up to the second-order terms) producing at the same time the desired bunch length of 50 m. 9 refs., 6 figs., 4 tabs

Recent commissioning experience on the SLC Arcs

The Arc transport line, which brings high-energy, high-intensity electron and positron bunches from the SLAC linac to the Stanford Linear Collider final focus section, has been in operation for the past few years. In this paper, we will review the techniques developed for the optical tune-up and diagnostics, recent performance, and on-going improvement programs. 13 refs., 4 figs., 1 tab

Observation of Parity Nonconservation in Moller Scattering

We report a measurement of the parity-violating asymmetry in fixed target electron-electron (Moller) scattering: A_PV = -175 +/- 30 (stat.) +/- 20 (syst.) parts per billion. This first direct observation of parity nonconservation in Moller scattering leads to a measurement of the electron's weak charge at low energy Q^e_W = -0.053 +/- 0.011. This is consistent with the Standard Model expectation at the current level of precision: sin^2\theta_W(M_Z)_MSbar = 0.2293 +/- 0.0024 (stat.) +/- 0.0016 (syst.) +/- 0.0006 (theory).Comment: Version 3 is the same as version 2. These versions contain minor text changes from referee comments and a change in the extracted value of Q^e_W and sin^2\theta_W due to a change in the theoretical calculation of the bremsstrahulung correction (ref. 16

Precision Measurement of the Weak Mixing Angle in Moller Scattering

We report on a precision measurement of the parity-violating asymmetry in fixed target electron-electron (Moller) scattering: A_PV = -131 +/- 14 (stat.) +/- 10 (syst.) parts per billion, leading to the determination of the weak mixing angle \sin^2\theta_W^eff = 0.2397 +/- 0.0010 (stat.) +/- 0.0008 (syst.), evaluated at Q^2 = 0.026 GeV^2. Combining this result with the measurements of \sin^2\theta_W^eff at the Z^0 pole, the running of the weak mixing angle is observed with over 6 sigma significance. The measurement sets constraints on new physics effects at the TeV scale.Comment: 4 pages, 2 postscript figues, submitted to Physical Review Letter

Recent Improvements in the SLC Positron System Performance

The positron system is very specific to the SLC in that the positrons are accelerated in the same linac as the electrons that produce them and the electrons with which they collide. Some of the difficulties in tuning this system to peak performance are thus unlikely to be encountered in future linear colliders, but many of the lessons learned in beam matching are useful for future machines. The design and commissioning of this system has been previously reported so we only briefly describe the major subsystems before detailing the tuning and diagnostics involved in optimizing the performance of the overall system