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Microsphere Macroscopic Traps |
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We have constructed several macroscopic charged particle traps. The purpose of these traps is to simulate ion trap physics in order to demonstrate our research to visitors and to easily experiment with various traps and difficult trapping processes. The physics of the particle traps mirrors that of the ion traps, except that the traps are used to confine hollow glass microspheres, about three microns in diameter, instead of ions, and the size of the trapping volume is on the order of millimeters. We have produced several functioning trap designs. The first trap constructed is of the ring and endcap geometry, and is composed of a copper ring and rod electrodes made from optics mounts. The other three are made up of tungsten rod electrodes arranged in four-rod square, four-rod planar, and six-rod geometries. The most recent development is a trap made from a printed circuit board. This type of design allows us to shuttle the microsphere between several trapping zones by manipulating voltages of various DC electrodes.
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 A single microsphere confined in the 1/8" wide trapping region in the expanding trap. |
 View of a microsphere confined in the first circuit board trap, called the expanding trap. The purpose of the trap was to test different trapping volume aspect ratios; the widest gap is 1/4", the next is 1/8", and the smallest is 1/16". The circuit board is 1/16" in thickness. |
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 Four-rod square geometry: two microspheres trapped.
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 Four-rod planar geometry: several microspheres trapped. |
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 Six-rod geometry: several microspheres are trapped not in the anticipated trapping region, but above the two ground electrodes on the top side of the trap. |
 Ring and endcap geometry: single microsphere trapped. |
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| The traps
are all variations of the Paul trap design. AC potential is
applied to two electrodes in a quadrupole geometry while the other
two are grounded; the potential at the center of the quadrupole is
always zero and the microsphere is confined there. We use AC
potential ranging from 400 to 1000 volts at 60 Hz, with lower
voltages for smaller trapping volumes. The high AC voltage is achieved by
stepping up voltage from a Variac using a transformer from a
household microwave oven. DC electrodes with potential of 20
to 150
volts confine the microspheres in the third dimension. Each
trap is enclosed either in acrylic cylinders or a box with an
acrylic lid to protect the microspheres
from air currents that knock them out of the trapping volume and
protect the electrodes from human contact. The microspheres are illuminated by
lasers that make them appear pink for increased visibility, though
under normal lighting they
look like fine white powder. When trapped, the microspheres look like tiny fibers. This is because of their
micromotion: they oscillate at the trapping frequency of 60 Hz in
one dimension.
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 Six-rod trap holding a few trapped microspheres.
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 Two microspheres in the ring and endcap trap. |
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 A single microsphere in the planar trap.
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 At least four microspheres in the square trap. |
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 The early (and more dangerous) trap set-up.
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 The experiment workstation. |
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Movies: |
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| Description | Length (min:sec) | WMV | Other |
| Reversing the order of several microspheres in the t-trap. | 2:07 | MVI_02442.wmv (2.4 MB) |
2teetrap.m1v (3.7 MB) 18 sec edited version |
| Preliminary t-trap corner-rounding movie. | 1:50 | MVI_02421.wmv (2.0 MB) |
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| First circuit board trap shuttling demo. | 2:03 | MVI_02232.wmv (2.3 MB) |
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| Three microspheres orbiting in the ring and endcap trap. | 0:30 |
MVI_01571.wmv (594 KB) |
MVI_0157.avi
(4.8 MB) |
| Microspheres in the four-rod square geometry while the endcap voltage is increased, then decreased. | 1:16 |
MVI_01421.wmv (1.4 MB) |
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| Microsphere drops into the planar trap from another trapping region. | 0:37 |
MVI_01541.wmv (712 KB) |
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| Zero, then three, then two microspheres in the planar trap. | 0:37 |
MVI_01551.wmv (702 KB) |
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| Single microsphere blowing around in the ring and endcap trap. | 0:21 |
MVI_01591.wmv (410 KB) |
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| Several microspheres in the ring and endcap trap. | 0:21 |
MVI_01731.wmv (414 KB) |
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