J. Seeman

RF Beam Deflection Measurements and Corrections in the SLC Linac

The requirements of RF acceleration in the SLC Linac to produce high energy beams are complicated by the presence of small transverse RF beam deflections which arise from several sources. These RF deflections place stringent tolerances on the phase and amplitude stability of the klystrons. They also force the use of special magnetic bumps to correct the trajectories of oppositely charged beams that will pass down the linac. If left unabated, RF deflections can limit the performance of the SLC. There are several methods to reduce the deflections. Many measurements of RF deflections have been made in the low energy part of the linac where the beams are most sensitive.

Performance of the PEP-II B-Factory Collider at SLAC

PEP-II is an e+e-asymmetric B-Factory Collider located at SLAC operating at the Upsilon 4S resonance (3.1 GeV x 9 GeV). It has reached a luminosity of 9.21×1033/cm2/s and has delivered an integrated luminosity of 710 pb-1in one day. PEP-II has delivered, over the past six years, an integrated luminosity to the BaBar detector of over 262 fb-1. PEP-II operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 2.45 A in 1588 bunches. Steady progress is being made in reaching higher luminosity. The goal over the next several years is to reach a luminosity of 2.1x1034/cm2/s. The accelerator physics issues being addressed in PEP-II to reach this goal include the electron cloud instability, beam-beam effects, parasitic beam-beam effects, high RF beam loading, shorter bunches, loweryinteraction region operation, and coupling control. Figure 1 shows the PEP-II tunnel.

Beam Steering in the SLC Linac

In order to control emittance growth due to transverse wakefields it will be necessary to transport electrons and positrons through the Stanford Linear Collider (SLC) linac to within a hundred ¿m of the centers of the linac irises. Beam centering will be accomplished using computer routines to read stripline beam position monitors and in turn correct the orbits with dipole magnets. Several different steering algorithms have been investigated using electrons in the first third of the SLC linac lattice. The most promising scheme is a cascade of modified three-bumps in conjunction with long spanning harmonic corrections. General features of the orbit correcting software are discussed along with the mathematical recipes for correction. Experimental results and a discussion of future plans are presented.

Accelerator Physics Measurements at the Damping Ring

Besides the optics measurements described elsewhere, machine experiments were done at the SLC damping ring to determine some of its parameters. The synchrotron radiation energy loss which gives the damping rates was measured by observing the RF-voltage dependence of the synchronous phase angle. The emittance was obtained from the synchrotron light monitor, scraper measurements and by extracting the beam through a doublet and measuring its size for different quadrupole settings. Current dependent effects such as parasitic mode losses, head tail instabilities, synchrotron and betatron frequency shifts were measured to estimate the impedance. RF-cavity beam loading and its compensation were also studied and ion collection was investigated. All results agree reasonably well with expectations and indicate no limitations to the design performance.

Generation and Acceleration of High Intensity Beams in the SLC Injector

A new gun pulser and substantially increased focusing have been added to the first 100 m of the SLAC linac in order to provide a pair of intense electron bunches to the SLC damping ring. Each bunch from this injector must have 5 x 1010 electrons, an invariant emittance ¿¿ ¿ 1.8 x 10-3 m-rad and the pair must have an energy spread of less than 2% . Wakefield instabilities present in earlier versions of this injector 1 have been controlled by reducing the transverse beam dimension by a factor of 3.

Test results of pre-production prototype distributed ion pump design for the PEP-II asymmetric B-Factory collider

We have built and tested a plate-type pre-production prototype distributed ion pump (DIP) for the PEP-II B-Factory High Energy Ring (HER). The design has been simplified from an earlier design to use less materials and to reduce overall costs. Penning cell hole sizes of 15, 18, and 21 mm have been tested in a uniform magnetic field of 0.18 T to optimize pumping speed. The resulting final DIP design consisting of a 7-plate, 15 mm basic cell size anode was predicted to give the best pumping speed results for the actual varying magnetic field of the HER dipole. A description of the final optimized DIP design will be presented along with the test results of the pumping speed measurements.

Observations of Accelerated High Current Low Emittance Beams in the SLC Linac

The Linac of the SLAC Linear Collider (SLC) is required to accelerate several intense single electron and positron bunches to high energy while not enlarging their small transverse emittances. The improvements needed by the SLAC Linac to meet these goals have very stringent design criteria. As partial systems have become available, beam tests have been performed to confirm the designs. The results of those beam tests are discussed. Future plans of the improvement program are described.

Recent Improvements in Luminosity at PEP

We will describe improvements which have led to new records for peak and average luminosity at PEP. Comparison of recent results with several earlier lattice and optical modifications shows rather good correlation with the predictions of a beam-beam simulation program.

Test results of a combined distributed ion pump/non-evaporable getter pump design developed as a proposed alternative pumping system for the PEP-II asymmetric B-factory collider

We have built and tested an all-in-one combination plate-type distributed ion pump/non-evaporable getter pump design (DIP/NEG) considered as a proposed alternative pumping system for the PEP-II B-Factory High Energy Ring (HER). The DIP portion of the design used a Penning cell hole size of 12 mm in a mostly uniform magnetic field of 0.18 T. The NEG portion of the design used commercially available non-evaporable getter material type St-707. A detailed description of the design is presented along with results of pumping speed measurements.

Beam dynamics issues in linear colliders

It is pointed out that the primary goal of present and future linear colliders is to maximize the integrated luminosity for the experimental program. Beam dynamics plays a central role in the maximization of integrated luminosity. It is the major issue in the production of small beam sizes and low experimental backgrounds and is also an important factor in the production of particle numbers, in the acceleration process, and in the number of bunches. Beam dynamics effects on bunches which are extracted from the damping rings, accelerated in the linac, collimated, momentum-analyzed, and finally delivered to the final focus are reviewed. The effects of bunch compression, transverse and longitudinal wakefields, BNS damping, energy definition, dispersion, emittance, bunch aspect ratio, and stability are shown to be important.<<ETX>>