This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Klasen, M.

Lash, J.

Pollock, R.

English

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FIELD-IMMERSED TARGETS (CE-30) 
M. Klasen, J. Lash, R. Pollock, T. Sloan 
Indiana Universi ty  Cyclotron Facility, Bloornington, Indiana 4 74 08 
An experiment to develop and explore the potential of a charged particle trap as a 
target in a cooling ring has been initiated. A solenoid magnet of 48 pancake coils and a steel 
frame, with interior diameter 0.24 rn, length 0.83 m and field 0.23 T has been constructed 
and field-mapped. The outer 4+4 coils are excited from a separate power supply, allowing 
the field to be adjusted either for maximum uniformity or with a mirroring enhancement 
at the ends. Pancakes are assembled with a 72' azimuthal phase advance between the 
current leads of adjacent pancakes. This results in a five-fold symmetry that reduces the 
effect of conductor cross-over length of 0.50 m. Field lines in this central region are found 
to differ from a straight line by less than 0.3 mm. 
A bakeable cylindrical vacuum chamber with several ports for feedthroughs has been 
constructed. A vacuum of 20 nTorr has been reached when pumping with a small turbo- 
pump, and 8 nTorr when installed in the S region of the Cooler ring with no pump closer 
than 3 m. 
In a first application of this system, an electron gun, a set of electrostatic deflectors 
and steerers, and position-sensing collectors have been installed within the chamber. A 
10 eV-0.1 pA electron beam from a hairpin Tungsten filament is guided onto a path which 
can be made to coincide with a stored ion beam. The electromagnetic interaction between 
the beams is observed as a position shift at the collector. In a five shift run ending 6 May 
1992, it was demonstrated that the position and intensity of a coasting stored cooled beam 
of 45 MeV protons could be monitored with this setup. (The normal beam positioning 
pickups only function when the beam has rf structure imposed.) A 30 keV decrease in 
the stored beam energy which occurred during each cooled stripping injection phase was 
discovered through a small position shift (4.2 m dispersion) at this detector and later 
confirmed with Schottky scans. An electron beam of smaller diameter is being developed 
to permit non-destructive monitoring of the cooled beam emittance. 
The system will be reconfigured for electron accumulation studies as an anharmonic 
Penning trap with a bathtub-shaped longitudinal confinement potential. The system is a 
synchrotron analog, and particles may be captured by an rf modulation below transition 
energy and decelerated onto a stack. Transverse multi-turn accumulation may also be 
possible using an rf signal applied to steerer fields. A small enclosure north of the S region 
has been fitted out as an off-line test area for these trap studies. 
A long-term goal is to be able to store a quantity of electrons sufficient to serve as 
a free electron target for the Cooler. Studies of loss processes (CE-17) have shown that 
electrons bound to atoms in internal targets can be a significant cause of beam heating and 
loss. Electrons bound to the field lines of a trap have a larger Coulomb logarithm. Their 
effect on the beam should be observable at thicknesses of order 1 0 ~ ~ / c m ~ .  However the 
stability of a dense cloud of trapped electrons interacting with a stored beam is uncertain. 
Certainly the ion beam will undergo a tune shift from the collective electric field of the 
electron lens, and may serve as a useful diagnostic for the trap. 
Figure 1. The diamond symbols show the expected in-plane electric force exerted on a 
charge by a stored beam with a Gaussian density profile. The square symbols are data 
from CE-30 on May 6, 1992 showing the difference between the outputs of two logarith- 
mic amplifiers connected to a split-plate collector. The abscissa is proton beam position 
spanning about 30 mm. The ordinate reflects horizontal beam deflection. The data are 
corrected to a typical proton current of 0.5 mA. 


Field-Immersed Targets (CE-30)

https://scholarworks.iu.edu/dspace/bitstream/2022/636/1/iucf1991-1992_181-182.pdf

Field-Immersed Targets (CE-30)

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