US2020163199A1PendingUtilityA1
Source for Intra-Pulse Multi-Energy X-Ray Cargo Inspection
Assignee: AMERICAN SCIENCE & ENG INCPriority: May 16, 2014Filed: Jun 14, 2019Published: May 21, 2020
Est. expiryMay 16, 2034(~7.8 yrs left)· nominal 20-yr term from priority
Inventors:Aleksandr Saverskiy
H01J 35/00H05H 7/02H05H 2007/025H05G 2/00H05H 9/04H05H 2007/084H05H 7/08G01V 5/0041H01J 35/14G01V 5/224
58
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Claims
Abstract
Methods for generating a multiple-energy X-ray pulse. A beam of electrons is generated with an electron gun and modulated prior to injection into an accelerating structure to achieve at least a first and specified beam current amplitude over the course of respective beam current temporal profiles. A radio frequency field is applied to the accelerating structure with a specified RF field amplitude and a specified RF temporal profile. The first and second specified beam current amplitudes are injected serially, each after a specified delay, in such a manner as to achieve at least two distinct endpoint energies of electrons accelerated within the accelerating structure during a course of a single RF-pulse. The beam of electrons is accelerated by the radio frequency field within the accelerating structure to produce accelerated electrons which impinge upon a target for generating Bremsstrahlung X-rays.
Claims
exact text as granted — not AI-modifiedI claim:
1 . A method for generating a multiple-energy X-ray pulse, the method comprising:
a. generating a beam of electrons with an electron gun; b. modulating the beam of electrons prior to injection into an accelerating structure to achieve at least a first specified beam current amplitude and a first specified beam current temporal profile, and a second specified beam current amplitude and a second specified beam current temporal profile, the beam of electrons characterized by an electron beam pulse duration; c. applying to the accelerating structure a radio frequency field with a specified RF field amplitude and a specified RF temporal profile characterized by an RF pulse duration; d. injecting the beam of electrons at a first specified beam current amplitude and then at the second specified beam current amplitude after a specified delay, in such a manner as to achieve at least two distinct endpoint energies of electrons accelerated within the accelerating structure during a course of a single RF-pulse; e. optimizing a coupling coefficient between an RF source and the accelerating structure so as to achieve zero RF power reflection at the specified beam current; f. accelerating the beam of electrons with the radio frequency field within the accelerating structure to produce accelerated electrons; and g. impinging the accelerated electrons upon a target for generating X-rays by Bremsstrahlung.
2 . A method in accordance with claim 1 , wherein the electron beam pulse duration is shorter than the RF pulse duration by a sum of onset delays defined by a filling time of the accelerating structure.
3 . A method in accordance with claim 1 , wherein the first specified beam current temporal profile and the specified RF temporal profile begin substantially contemporaneously.
4 . A method in accordance with claim 1 , wherein the a beam of electrons is characterized by an amplitude of injection current, and wherein the amplitude of injection current decreases during the multiple-energy X-ray pulse.
5 . A method in accordance with claim 1 , wherein an end-point energy characterizing the beam of electrons increases during the multiple-energy X-ray pulse.
6 . A method in accordance with claim 1 , wherein applying the RF field includes modulating an RF source.
7 . A method in accordance with claim 6 , wherein modulating the RF source includes varying at least one of an input voltage and an input current to the RF source.
8 . A method in accordance with claim 1 , wherein applying the RF field includes modulating an RF modulator disposed between an RF source and the accelerating structure while the RF-source provides a constant level of power at a constant frequency.
9 . A method in accordance with claim 1 , wherein a high-energy portion of the multiple-energy x-ray pulse is characterized by a lower electron beam flux than a low-energy portion of the multiple-energy X-ray pulse.
10 . A method in accordance with claim 1 , wherein the accelerating structure includes a standing wave resonator.
11 . A method in accordance with claim 10 , wherein the RF source provides a constant level of RF-power;
wherein a temporal profile of the electron gun is characterized by at least two distinct levels of the amplitude of electron beam I n ; wherein each amplitude of the at least two distinct levels of amplitude is created in temporally descending order; and wherein the coupling coefficient of accelerating resonator β 0 is chosen to be optimal at a first level of beam current I 1 .
12 . A method in accordance with claim 11 , wherein breaking points of said at least two distinct levels include breaking points that are dynamically variable.
13 . A method in accordance with claim 11 ,
wherein a first portion of an electron beam current pulse starts with an optimum delay (t b1 ) relative to a beginning of an RF pulse; wherein said electron beam current pulse ends at a specified time (t 1 ); and wherein each successive portion of the electron beam current pulse is characterized by a distinct level I n and starts with a delay
t
bn
=
τ
·
ln
(
I
n
-
1
I
n
)
corresponding to an end of a previous pulse t n-1 , with representing a decay time of the accelerator structure.
14 . A method in accordance with claim 12 , wherein an end point of each pulse t n includes a dynamically variable end point.
15 . A method in accordance with claim 11 , further comprising:
a. supplying an RF-power pulse to the accelerating structure at two distinct energy levels, P L , P H , corresponding, respectively, to low and high energy portions of the beam of electrons; wherein an electron gun temporal profile is characterized by two distinct levels of the amplitude of electron beam, I L , I H , corresponding, respectively, to beam current levels for achieving low and high energy portion of the beam of electrons; and b. optimizing a coupling coefficient of accelerating resonator β 0 based upon parameters of the low energy beam.
16 . A method in accordance with claim 15 , further comprising:
c. forming an ascending order of two distinct X-ray energy levels by applying a corresponding ascending sequence of RF-power levels and a descending sequence of injection current pulses; d. delaying a low energy component of the pulse by a low energy current delay t bL defined by
t
bL
=
τ
·
ln
(
2
·
β
0
β
0
-
1
)
;
and
e. delaying a high energy component of the pulse by a high energy current delay t bH a defined by
t
bH
_
a
=
τ
·
[
ln
(
I
L
I
H
)
+
ln
(
1
+
2
·
β
0
β
0
-
1
P
H
P
L
-
1
)
]
.
17 . A method in accordance with claim 15 , further comprising:
c. forming a descending order of two energy levels by applying a corresponding descending sequence of RF-power levels and an ascending sequence of injection current pulses; d. delaying a high energy component of the pulse by a high energy current delay t bH defined by equation
t
bH
=
τ
·
ln
(
4
β
0
rLP
H
I
H
rL
)
;
and
e. delaying a low energy component of the pulse current delay t bL_d is defined by
t
bL
_
d
=
τ
·
[
ln
(
I
H
I
L
)
+
ln
(
1
+
4
β
0
rLP
H
I
H
rL
1
-
P
L
P
H
)
]
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