Experimental results of the instability studies are being reported. The system built gives a BPM-derived single bunch 'instability signal". The signal was recorded simultaneously with the longitudinal density bunch profiles obtained from the synchroton light with the high resolution Hamamatsu streak camera. Correlation of the instability signal with the streak camera profiles has been found. For the strongly developed instability state the dominant mode structure was obtained.

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Sawtooth instability studies in the Stanford Linear Collider damping rings

The SLC damping rings function to provide low emittance, short bunches for injection into the linac. As the beam intensity in the rings was raised, as part of the SLC luminosity improvement program, we observed a threshold above which beam jitter would occur in the linac. Frequent machine trios, caused by beam loss on some bunches, were associated with the jitter. These erratic "flier" pulses were traced to extraction phase errors from the damping rings. This paper covers the diagnosis of this condition and the observations of the transient bunch length instability phenomena. The evidence of this turbulent (microwave) bunch length instability is seen in both time domain and in frequency domain measurements. The instability has been dubbed the "sawtooth" because of the characteristic time dependent nature of the phase and bunch length signals. It is present in both the SLC electron and positron damping rings at about the same threshold of 3/spl times/10/sup 10/ particles per bunch. There is also some evidence in numerical simulations of transient bunch lengthening phenomena, which is discussed later in this paper.<<ETX>>

High intensity bunch length instabilities in the SLC damping rings

We present a summary of the main topics discussed in the Accelerator Working Group during the ``Workshop on the Physics at the First Muon Collider``. The discussions centered on critical design issues for a high-intensity, medium-energy proton synchrotron that would replace the present Fermilab 8 GeV Booster early in the next century. Such a machine is intended both to serve the hadron program with an order of magnitude increase in average proton current and to be compatible as a source for a future muon collider. Particular issues discussed at length include rf system design, control of longitudinal space-charge effects, bunching of proton beams and beam instabilities.

/pdf/summary-of-the-accelerator-working-group-13bm6hziq9.pdf

Summary of the accelerator working group

The longitudinal phase space distribution of the SLC beams is affected by many different machine parameters and constraints. By using a technique of over-compression in the ring to linac transfer line, a small energy spread of 0.12% can be achieved at the end of the linac for a bunch length of 1.2 mm (/spl sigma/). In the final focus a small energy spread is desirable to reduce emittance dilution due to chromatic effects. Optimization of the bunch length is also important as a longer bunch of 1.2 mm can contribute up to 40% luminosity enhancement due to disruption. If there is a correlated energy variation along the bunch, for example due to mistuning of the optimal rf phase with respect to the beam, the bunch will be further compressed as it passes through the SLC Arcs. The resulting bunch can be too short to produce the desired disruption enhancement, but will radiate more beamstrahlung during collisions giving a false indication of higher luminosity. This paper discusses the interplay of these issues from the damping ring to the interaction point.

/pdf/longitudinal-phase-space-setup-for-the-slc-beams-31fjwkz6wd.pdf

Longitudinal phase space setup for the SLC beams

In this paper, we will first review the status of the Stanford Linear Collider (SLC). In particular, we will discuss the luminosity and performance issues and the accelerator studies that relate to future linear colliders. Next, we will describe the present state of the Next Linear Collider (NLC) design and the ongoing RD detailed descriptions of the NLC design can be found in Refs. [1, 2, 3].

/pdf/slc-status-and-nlc-design-and-r-d-1mtd3dxd0p.pdf

SLC Status and NLC Design and R&D

The pulse-to-pulse behavior of the beams in the SLC linac is dominated by wakefields which can amplify any other sources of jitter. A strong focusing lattice combined with BNS damping controls the amplitude of oscillations which otherwise would grow exponentially. Measurements of oscillation amplitude along the linac show beam motion that is up to six times larger than that expected from injection jitter. A search for possible sources of jitter within the linac uncovered some problems such as structure jitter at 8 to 12 Hz, pump vibrations at 59 Hz and 1 Hz aliasing by the feedback systems. These account for only a small fraction of the observed jitter which is dominantly white noise. No source has yet been fully identified but possible candidates are dark current in the linac structures (not confirmed by experiment) or subtle correlations in injection jitter. An example would be a correlated x-z jitter with no net offset visible on the beam position monitors at injection. Such a correlation would cause jitter growth along the linac as wakefields from the head of the bunch deflect the core and tail of the bunch. Estimates of the magnitude of this effect and some possible sources are discussedmore » in this paper.« less

/pdf/higher-order-beam-jitter-in-the-slc-linac-4efoexgcpu.pdf

P. Raimondi

Papers

Higher Order Beam Jitter in the SLC Linac