Transcript poster

A Pyroelectric Crystal Particle Accelerator
Amanda Gehring, Rose-Hulman Institute of Technology
Dr. Rand Watson, Texas A&M Cyclotron Institute
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Results
The purpose of this experiment was to instigate d + d
fusion and optimize the neutron output by varying the
D2 gas pressure, optimize parameters that determine
the intensity and energy of the particle beam, and to
examine the feasibility of using the system as a
neutron generator. Runs were conducted at 0.5 A, 1.0
A, 1.5 A, and 2.0 A heating currents under vacuum
condition with a Zr target. As heating currents
increased, beam intensity and energy also increased.
CdS and ZnS coating was added to the target wheel
so that the beam could be seen.
Current vs Heating Accelerating Potential
Energy (keV)
70
60
50
40
30
0.0
0.5
1.0
1.5
2.0
2.5
Heating
Current
Current
(A) (A)
160
2.0 A Temperature Cycle
140
Heating
Cooling
o
Temperature ( C)
120
80
60
40
20
104
103
102
101
100
0
100
200
300
400
500
600
Counts per Channel
Counts per Channel
Counts per ten seconds
105
Zr K
Cu K
104
103
102
103
102
100
100
10
20
30
40
50
60
70
Zr K
Cd K
101
0
Zn K
104
101
Time
(10 (s)
s Interval)
Time
0
10
20
30
40
Energy (keV)
50
60
70
80
90
Energy (keV)
A 2.0 A current produced the highest beam intensity and energy. The
maximum energy reached was 88 keV. This heating current was used in the
deuterium gas experiments.
14000
60
160
140
Deuterium Max Heating X Ray Count Rates
Deuterium Heating Accelerating Potentials
0.1 mTorr Deuterium
12000
55
o
120
100
10000
50
Energy (keV)
80
60
40
Heating
Cooling
45
40
0
Neutron Counts
6000
35
2000
40
30
0
Counts
8000
4000
50
1
2
3
Pressure (mTorr)
30
4
5
6
0
0
1
2
3
4
5
6
Pressure (mTorr)
Runs were carried out at deuterium pressures
ranging from 5x10-3 to 1x10-4 Torr, but in all cases
the observed neutron counting rates were never
above the background rate.
Future research may involve minimizing discharges, running additional deuterium
gas pressures, and adding another pyroelectric crystal to the system in order to
double the accelerating potential.
20
10
0
0
100
200
Time (10 s Interval)
Entire System
2.0 A Cooling Cycle X-ray Spectrum
105
105
20
Inner Chamber
2.0 A Heating Cycle X-ray Spectrum
Cu K
X-Ray Counts
Temperature ( C)
Experimental Setup and Principles
The lithium tantalate pyroelectric crystal
is attached to a copper block, to which
two heating resistors are attached. The
front face of the crystal becomes
positively charged causing the creation
D +D  3He +
n
of positive ions due to field ionization of
(820 KeV) (2.45 MeV)
gas molecules in the vicinity. The
D+DT
+
p
(1.01 MeV) (3.02 MeV)
positive ions are accelerated toward the
target by the electrostatic field.
Simultaneously, electrons from the target are accelerated toward the crystal where
they collide with atoms at the surface producing x rays and bremsstrahlung which
are measured with a Si(Li) x ray detector. When the crystal is cooled, the polarity
reverses and the electrons are accelerated toward the target. If the accelerating
potential reaches ~100 keV, the d + d fusion reaction can be initiated. Deuterium
gas must be introduced to the chamber, and a deuterated polyethylene target must
be added as well. A liquid scintillation neutron detector is used to measure the
neutron output.
100
X-ray Counts/s
Why use a pyroelectric crystal?
Pyroelectric crystals can be used to produce a
large electrostatic field. Once heated, the
random crystal lattice dipole moments of the
crystal align, creating oppositely charged
surfaces that produce the electrostatic field.
Upon cooling, the polarity of the crystal reverses.
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