Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch
We present here the first experimental test of a singlepass non-destructive method of monitoring of longitudinal charge distribution in an intensive relativistic electron bunch. This method is based on the scanning of a thin electron beam within the energy range 20-100 keV in the electromagnetic fie...
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| Опубліковано в: : | Вопросы атомной науки и техники |
|---|---|
| Дата: | 1999 |
| Автори: | , , , , , , , , |
| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Онлайн доступ: | https://nasplib.isofts.kiev.ua/handle/123456789/81372 |
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| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Non-destruktive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch / P.V. Logatchov, P.A. Bak, A.A. Starostenko, N.S. Dikansky, V.S. Tupikov, K.V. Gubin, V.M. Mishnev, M.B. Korabelnikov, M.G. Fedotov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 57-59. — Бібліогр.: 2 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860036654893367296 |
|---|---|
| author | Logatchov, P.V. Bak, P.A. Starostenko, A.A. Dikansky, N.S. Tupikov, V.S. Gubin, K.V. Mishnev, V.M. Korabelnikov, M.B. Fedotov, M.G. |
| author_facet | Logatchov, P.V. Bak, P.A. Starostenko, A.A. Dikansky, N.S. Tupikov, V.S. Gubin, K.V. Mishnev, V.M. Korabelnikov, M.B. Fedotov, M.G. |
| citation_txt | Non-destruktive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch / P.V. Logatchov, P.A. Bak, A.A. Starostenko, N.S. Dikansky, V.S. Tupikov, K.V. Gubin, V.M. Mishnev, M.B. Korabelnikov, M.G. Fedotov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 57-59. — Бібліогр.: 2 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | We present here the first experimental test of a singlepass non-destructive method of monitoring of longitudinal charge distribution in an intensive relativistic electron bunch. This method is based on the scanning of a thin electron beam within the energy range 20-100 keV in the electromagnetic field of an intensive relativistic bunch.
|
| first_indexed | 2025-12-07T16:53:50Z |
| format | Article |
| fulltext |
NON-DESTRUCTIVE SINGLEPASS MONITOR OF LONGITUDINAL
CHARGE DISTRIBUTION IN AN ULTRARELATIVISTIC ELECTRON
BUNCH
P.V. Logatchov, P.A. Bak, A.A. Starostenko, N.S. Dikansky, V.S. Tupikov, K.V. Gubin,
V.M.Mishnev, M.B. Korabelnikov, M.G. Fedotov
BINP, Novosibirsk, Russia
We present here the first experimental test of a
singlepass non-destructive method of monitoring of
longitudinal charge distribution in an intensive
relativistic electron bunch. This method is based on the
scanning of a thin electron beam within the energy
range 20-100 keV in the electromagnetic field of an
intensive relativistic bunch.
The probe beam was injected across the path of
primary relativistic bunch. This type of an electron
beam probe is suitable for both circular or linear
accelerators. The prototype results obtained at VEPP-3
storage ring are in good agreement with the calculations
and give us a very high degree of confidence that this
single bunch diagnostic tool can be very useful not only
for accelerator tuning, but also for precise
measurements.
1 THEORY
The thin probe beam moves along X axis, is
orthogonal to the direction of the relativistic bunch
motion (Z axis) with the offset parameter ρ (Fig.1).
Z
Y
X
0
ρ}
β
Α
Β
Fig. 1.
The results of scanning are monitored on the
screen parallel to the Y-Z plane and positioned at the
distance L from Z axis. Let the center of the relativistic
bunch is located at the origin at time t=0 whereas the
testing beam has the uniform density along X and the
diameter d<< ρ . Here, we assume ρ exceeds the
typical transverse size of the relativistic bunch. At the
time t=0 every testing beam particle is corresponded to
the certain x -coordinate. The total deflecting angle in
Y direction for every particle under the influence of the
electric field of the relativistic bunch can be expressed
as:
θ
ρ
β ρ βy
ex
r n z dz
x z
( )
( )
( )
=
+ +− ∞
+ ∞
∫2
2 2 (1)
where re is the classical electron radius, β =vt/c – is a
relative velocity of the testing beam, c – is a velocity of
light, x - is a coordinate of testing beam particle at t=0,
n z( ) - is a relativistic bunch linear density along Z
axis. The expression for the deflecting angle of the
particle in Z direction due to magnetic field can be
written as:
θ
β
ρ βz ex r
x z n z dz
x z
( )
( ) ( )
( )
=
+
+ +− ∞
+ ∞
∫2 2 2 (2)
As a result, the testing beam traces the closed
curve on the screen. In assumption of the constant
current I of the testing beam one can derive the simple
correlation between the x -coordinate and the charge
distribution ( )q l along the indicated curve on the
screen from point A to point B (Fig. 1):
( )x
c
I
q l dl
A
B
= ∫
β
(3)
Integrating the charge along the curve from point
A up to point B (Fig.1) one can find the x -coordinate
(3) and correspond to it the certain angles θ z x( ) and
θ y x( ) at point B. Since the dependencies θ y x( ) and
θ z x( ) are determined, it is possible using any of this
functions to restore the dependence ( )n z :
( ) ( ) ( )n z
r
k e dk
e
ikz k=
− ∞
+ ∞
+ ⋅∫
β
π
θ β ρ
2
24 y (4)
where ( ) ( )θ θy yk x e dxikx=
− ∞
+ ∞
−∫ .
It is necessary to emphasize that dependencies
(1), (2) and (4) are valid only for ultra relativistic bunch
with γ>>1 and for θ Y
MAX < < 1 (5). The last condition
gives a small perturbation of probe beam longitudinal
motion by the electric field of relativistic bunch.
2 EXPERIMENTAL SETUP
The test of the electron beam probe was held at
VEPP-3 storage ring at the bunch energy 350, 1200 and
2000 MeV. We placed the device in the straight section
of the ring between two RF cavities. The probe system
was evacuated to a typical storage ring vacuum level of
10-9 Torr. The schematic diagram of the layout is shown
in Fig. 2. The probe electron gun had a flat diode
geometry with 0.2 mm diameter anode diaphragm. We
used 4 mm dispenser cathode with emission ability 3
A/cm2. The maximum pulse current of the probe
electron beam was 1 mA at the energy of 60 keV. Axial
magnetic focusing lens formed a minimal transverse
probe beam size as at the interaction region as on the
screen. Transverse correction coils was installed to
adjust the position of the probe beam on the screen. We
used to direct the probe beam to the thing strip placed
just before the Micro Channel Plate (MCP) of 20 mm
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 57-60.
57
diameter. It allowed to avoid the MCP saturation by 5 µ
s, 1mA probe beam and to measure its pulse current. We
also measured probe beam energy. These two
parameters gave us a possibility to restore the x value
(3) or time from the charge distribution on the MCP
entrance. The relativistic bunch duration was in the
range of one nanosecond, so all voltages on MCP,
screen and gun could be considered as constant during
this time period. The shortest pulse on the MCP served
as a gate pulse. It helped to make a single bunch picture
on the phosphor screen (the revolution frequency of the
bunch in the ring is 4.03 MHz). To digitise the screen
image we used the conventional black and white CCD
video camera and special ADC grabber of standard
video signal with external start. Synchronous start of the
camera is absolutely necessary to the brightness stability
of the screen image from pulse by pulse for brightness
to charge conversion.
-10 ..- 60 kV, 5µs
FC to ADC
0..- 800 V, 30 ns
+6.2 kV, 60 ns
1.2 GeV bunch
Probe electron beamCathode
MCP Screen
Camera
Synchro
Video
grabber
Electron gun
modulator
MCP
modulator
Screen
modulator
Bunch revol. freq.
Foc. lens
Corrector
Electron
gun
Fig. 2 The scheme of installation.
Since built-in brightness to charge calibration
system was not ready at the first set of experiments we
used for that purpose longitudinal charge distribution
data obtained by dissector [2]. This stroboscopic device
works properly for operation with a stable bunch at the
time resolution level of 100 ps.
The maximum repetition rate for our system was
limited by the screen luminescence time (5 ms) and
video data acquisition time (500 ms). So all presented
measurements was made on 0.5 pps.
Probe beam focusing system, all modulators,
video and synchronous start system was controlled by
computer from the main control room.
3 EXPERIMENTAL REZULTS
At first we adjusted the synchronous start system
and modulators to reach a reliable operation with good
time stability (a maximum long time jitter was less then
1 ns). The pulse to pulse voltage stability at the moment
of relativistic bunch passing was better then 2% for each
modulator. Then we checked the surface uniformity of
MCP-Screen-Camera conversion system. The
nonuniformity less then 3% was detected. All presented
measurements was made with 60 keV, 1 mA probe
electron beam. The probe beam size was 0.5 mm at the
interaction point and 1 mm on the screen. To restore the
bunch shape according to (4) we need the ρ value. It
was measured directly by moving the probe beam up to
the crossing with relativistic bunch trajectory. One can
recognise the crossing picture very clearly.
After that we fulfilled the calibration
measurements with stable bunch in the ring in order to
have a real longitudinal charge distribution in the bunch
from the dissector (the longitudinal bunch shape is very
close to the Gaussian). Using this data one can calculate
the brightness to charge conversion coefficient,
pentium-133 can process the image for the time period
less then 1 second. Since the range of brightness
changing was not so big in comparison with dynamic
range of video signal (less then 10%) and MCP-Screen
system can be considered as linear within our range of
parameters it was possible to use that conversion
coefficient for the most of our measurements. Fig. 3
shows an example of calibration measurement with a
stable bunch state at the energy of 1200 MeV.
Fig.3. The calibration measurement with dissector at a
stable bunch state. The solid line is a result of the best
Gaussian fitting to the dissector data. Dots correspond
to our device measurement.
After calibration procedure we used our device
to monitor the longitudinal bunch instability. In this
case the signal from dissector was very wide and
unstable and it had two pikes with flashing amplitudes.
Fig.4 shows typical single bunch pictures for that
instability at the energy of 1200 MeV.
This is just an example to show the ability of the
method. But for detail instability analysis one need at
least few pictures: for example after 10th, 20th, 30th turn
and so on. Unfortunately at existing device we can not
make this shot. It need some changes in modulators, ad-
ditional horizontal scanning system and bigger MCP
with screen. We plan all this changes this year as a next
step.
58
a
a
b
c
Fig. 4. Typical single bunch pictures for longitudinal
instability: (a) - minimum bunch length, (c) - maximum,
(b) - intermediate state.
4 DISCUSSION
The basic idea of this diagnostic looks simple, but one
should be very careful evaluating the time resolution of
this method. At first we have a finite angle resolution
∆ θ Y due to a probe beam size on the screen or spatial
resolution of electron detecting system. An angle
resolution can be recalculated to a time resolution as
follows:
[ ]∆
∆
t
d x dx c
y
y MAX
1
1= ⋅
θ
θ β( ) (6)
From the other side the modulation of longitudinal
probe beam velocity due to x component of bunch
electric field increases the time error value. Total time
resolution is given by both effects. Assuming that
n z Ne e
z
( ) =
−
σ π
σ
2
2
22 ,
we can evaluate time resolution τ in two occurrence:
for
σ β
ρ
⋅
〉 〉1 ,τ
ρ
σ β
θ σ β
≈
⋅ ⋅
⋅ ⋅
+
⋅ ⋅
r Ne
c c r Ne
e y
e
3
2 2∆
(6); and
for
σ β
ρ
⋅
〈 〈1 , τ
θ ρ
β
ρ
β σ≈
⋅ ⋅
+
⋅ −
⋅
∆ y
e
e
c r Ne
r Ne
c
e
2
2
22
(7)
Our experiment fits the first case, the expression (7) is
suitable to linear accelerators. Taking into account the
final size of the screen, one can evaluate (6) the time
resolution value for our experiment (50 ps). To improve
time resolution significantly we plan to rearrange optic
and decrease the beam size on the screen. The
maximum vertical size of the loop on the screen can be
calculated for Gaussian bunch as follows:
h
Lr N
e erfe e
max = −
⋅2
1
22
2
2
2 2π
β σ
ρ
β σ
ρ
β σ (8)
where L is the distance between the interaction point
and the screen. So you can not decrease probe beam
energy to much in order to feet the image to the screen.
5 CONCLUSION
The design of the monitor essentially depends on
the relativistic beam parameters. We just note the
general useful qualities of the method:
1. Ability of simultaneous measurement not
only longitudinal distribution of beam density, but the
transverse position of its center of mass also [1] (two
testing beams - above and below the relativistic beam).
2. Testing beam has practically no influence on
the relativistic bunch, so its parameters don't get worse.
3. Small slots for testing beam transit in main
vacuum chamber don't change its impedance.
In this year the monitor will be installed either in
the (VEPP-4) storage ring and in the linear accelerator
(VEPP-5 injector).
6 ACKNOWLEDGMENTS
The authors wish to thank Dr. A.V. Burov,
Dr. D.V. Pestrikov and Dr. V.A. Kiselev of the Budker
Institute of Nuclear Phisics for very usefull discussions.
REFERENCES
1. John A. Pasour and Mai T. Ngo «Nonperturbing
electron beam probe to diagnose charged-particle
beams», Rev. Sci. Instrum. 63 (5), May 1992.
2. Zinin E.I. «Stroboscopic method of electro-optical
58
picosecond-resolution chronography and its
application in synchrotron radiation
experiments», NIM, 208 (1983) 439-441.
58
58
|
| id | nasplib_isofts_kiev_ua-123456789-81372 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:53:50Z |
| publishDate | 1999 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Logatchov, P.V. Bak, P.A. Starostenko, A.A. Dikansky, N.S. Tupikov, V.S. Gubin, K.V. Mishnev, V.M. Korabelnikov, M.B. Fedotov, M.G. 2015-05-14T20:50:19Z 2015-05-14T20:50:19Z 1999 Non-destruktive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch / P.V. Logatchov, P.A. Bak, A.A. Starostenko, N.S. Dikansky, V.S. Tupikov, K.V. Gubin, V.M. Mishnev, M.B. Korabelnikov, M.G. Fedotov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 57-59. — Бібліогр.: 2 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/81372 We present here the first experimental test of a singlepass non-destructive method of monitoring of longitudinal charge distribution in an intensive relativistic electron bunch. This method is based on the scanning of a thin electron beam within the energy range 20-100 keV in the electromagnetic field of an intensive relativistic bunch. The authors wish to thank Dr. A.V. Burov,
 Dr. D.V. Pestrikov and Dr. V.A. Kiselev of the Budker
 Institute of Nuclear Phisics for very usefull discussions. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch Неразрушающий однопролетный датчик продольного распределения заряда ультрарелятивистского электронного сгустка Article published earlier |
| spellingShingle | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch Logatchov, P.V. Bak, P.A. Starostenko, A.A. Dikansky, N.S. Tupikov, V.S. Gubin, K.V. Mishnev, V.M. Korabelnikov, M.B. Fedotov, M.G. |
| title | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| title_alt | Неразрушающий однопролетный датчик продольного распределения заряда ультрарелятивистского электронного сгустка |
| title_full | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| title_fullStr | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| title_full_unstemmed | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| title_short | Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| title_sort | non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/81372 |
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