Abstracts Brochure - CERN

THPCH068
THPCH069
THPCH070
29-Jun-06 16:00 - 18:00 THPCH — Poster Session
(ATF). An infrared bolometer was used to detect the emitted infrared radiation in the 1-0.05 mm wavelength range
as a function of several beam parameters (beam current, RF power, extraction timing, photoinjector laser phase). The
beam energy spread was also recorded. We found that the mismatch between injected and equilibrium beam is the
source of the coherent signal detected concurrently with the bunch injection.
Experimental Study of the Fast Ion Instability in the ALS
The fast ion instability is an important effect,
C. Steier, J.M. Byrd, M. Venturini, A. Wolski (LBNL)
potentially limiting the performance of ILC
damping rings, future b-factories, as well as
future storage ring based light sources with smaller emittances. Very little quantitative data exist so far, to check the
growth rate prediction of the commonly used linear theory. Therefore experimental studies have been carried out at
the ALS studying the fast ion instability for very small vertical emittances and residual gas pressures similar to the
ones present in ILC damping rings.
BBU Calculations for Beam Stability Experiments on DARHT-2
Y. Tang (ATK-MR) K.C.D. Chan, C. Ekdahl (LANL) T.P. Hughes
(Voss Scientific)
406
The DARHT-2 (Dual-Axis Radiographic Hydrodynamics
Test) facility is expected to produce
a 2-kA, 20-MeV, 2-microsecond flattop
electron beam pulse. Normal operation re-
quires that the beam exit the accelerator with a normalized transverse emittance of less than 0.15-cm-rad. The beam
break up (BBU) instability is a potentially serious effect for a high current linear accelerator. It arises from the interaction
between the beam and the cavity modes of the accelerating cells. In support of the beam stability experiments,
simulations of BBU for DARHT-2 using the Lamda code have been carried out. The simulations used experimental
data for the transverse impedance of the cells. Lamda was benchmarked against results calculated with the LLNL code
BREAKUP. For nominal transport parameters, simulation results showed that the BBU growth was not significant in
changing the beam spot. For a magnetic field reduced by a factor of 5, BBU growth was over a factor of 100, and the
image displacement effect was significant.
Long-pulse Beam Stability in the DARHT-II Linear-induction Accelerator
C. Ekdahl, E.O. Abeyta, R. Bartsch, K.C.D. Chan, D. Dalmas, S.
Eversole, R.J. Gallegos, J. Harrison, E. Jacquez, J. Johnson, B.T. Mc-
Cuistian, N. Montoya, S. Nath, D. Oro, L.J. Rowton, M. Sanchez,
R. Scarpetti, M. Schauer (LANL) H. Bender, W. Broste, C. Carlson,
D. Frayer, D. Johnson, A. Tipton, C.-Y. Tom (Bechtel Nevada) R.J.
Briggs (SAIC) T.P. Hughes, C. Mostrom, Y. Tang (ATK-MR) M.E.
Schulze (GA)
The beam breakup instability has long been
a problem for linear induction accelerators
(LIAs). Although it is predicted to saturate
in the strong focus regime relevant to LIAs
most, if not all, LIAs have had pulse-widths
too short to observe this effect. We recently
completed BBU experiments on a 1.2 kA, 6.7-
MeV configuration of the DARHT-II LIA having
a 1600-ns pulse length much longer than
the saturation time. The saturated growth observed in these experiments when we reduced the magnetic guide-field
strength was in agreement with theory. We used these results to deduce that BBU growth will be insignificant in
the final 2-kA, 17-MeV DARHT-II configuration with the tunes that will be used. Another problematic instability