Coherent betatron instability in the Tevatron

Conference · Thu Jun 09 04:00:00 EDT 1988

OSTI ID:7198889

Bogacz, S A; Harrison, M; Ng, K Y

The coherent betatron instability was first observed during the recent 1987-88 Tevatron fixed target run. In this operating mode 1000 consecutive bunches are loaded into the machine at 150 GeV with a bunch spacing of 18.8 /times/ 10/sup -9/ sec (53 MHz). The normalized transverse emittance is typically 15 ..pi.. /times/ 10/sup -6/ m rad in each plane with a longitudinal emittance of about 1.5 eV-sec. The beam is accelerated to 800 GeV in 13 sec. and then it is resonantly extracted during a 23 sec flat top. As the run progressed the bunch intensities were increased until at about 1.4 /times/ 10/sup 10/ppb (protons per bunch) we experienced the onset of a coherent horizontal oscillation taking place in the later stages of the acceleration cycle (>600 GeV). This rapidly developing coherent instability results in a significant emittance growth, which limits machine performance and in a catastrophic scenario it even prevents extraction of the beam. In this paper we will present a simple analytic description of the observed instability. We will show that a combination of a resistive wall coupled bunch effect and a single bunch slow head-tail instability is consistent with the above observations. Finally, a systematic numerical analysis of our model (growth-time vs chromaticity plots) points to the existence of the greater than or equal to1 slow head-tail modes as a plausible mechanism for the observed coherent instability. This last claim, as mentioned before, does not have conclusive experimental evidence, although it is based on a very good agreement between the measured values of the instability growth-time and the ones calculated on the basis of our model. 4 refs., 3 figs.

• Research Organization: Fermi National Accelerator Lab., Batavia, IL (USA)
• DOE Contract Number: AC02-76CH03000
• OSTI ID: 7198889
• Report Number(s): FNAL/C-88/69; CONF-880695-10; ON: DE88012677
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
430200* -- Particle Accelerators-- Beam Dynamics
Field Calculations
& Ion Optics
ACCELERATORS
BEAM DYNAMICS
BEAM POSITION
BETATRON OSCILLATIONS
CYCLIC ACCELERATORS
DIFFERENTIAL EQUATIONS
EQUATIONS
EQUATIONS OF MOTION
FERMILAB TEVATRON
IMPEDANCE
INSTABILITY
OSCILLATIONS
PARTIAL DIFFERENTIAL EQUATIONS
SYNCHROTRONS