Möller polarimeter in the Hall A Jefferson Lab after reconstruction
The Möller polarimeter in the Hall A of Jefferson Lab was reconstructed in order to expand of the energy range of the polarimeter to measure the polarization of the electron beam with an energy up to 11.5 GeV. The paper describes the main results of the Möller polarimeter testing after reconstruct...
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nasplib_isofts_kiev_ua-123456789-1153752025-02-09T20:53:59Z Möller polarimeter in the Hall A Jefferson Lab after reconstruction Мёллеровский поляриметр зала A лаборатории Джефферсона после реконструкции Мьоллерівський поляриметр залу А лабораторії Джефферсона після реконструкції Pomatsalyuk, R.I. Экспериментальные методы и обработка данных The Möller polarimeter in the Hall A of Jefferson Lab was reconstructed in order to expand of the energy range of the polarimeter to measure the polarization of the electron beam with an energy up to 11.5 GeV. The paper describes the main results of the Möller polarimeter testing after reconstruction. The measurements of the electrons polarization were provided by two data acquisition systems operating in parallel. The testing of the shielding insertion of magnetic dipole has been performed. The way to eliminate detected deviations in the operation of polarimeter during test is shown. В лаборатории им Т. Джефферсона (США) проведена реконструкция мёллеровского поляриметра зала А с целью расширения энергетического диапазона поляриметра для измерения поляризации пучка электронов с энергией до 11,5 ГэВ. Рассмотрены основные результаты тестирования мёллеровского поляриметра после реконструкции. Измерения поляризации электронов обеспечивали две системы сбора данных, работающие параллельно. Проведено тестирование защитной магнитной вставки диполя. Намечены возможные пути устранения отклонений в работе поляриметра, выявленных в процессе тестирования. У лабораторії ім Т. Джефферсона проведена реконструкція мьоллерівського поляриметра залу А з метою розширення енергетичного діапазону поляриметра для вимірювання поляризації пучка електронів з енергією до 11,5 ГеВ. Розглянуті основні результати тестування мьоллерівського поляриметра після реконструкції. Вимірювання поляризації електронів забезпечували дві системи збору даних, які працюють паралельно. Проведено тестування захисної магнітної вставки диполя. Намічено можливі шляхи усунення виявлених у процесі тестування відхилень у роботі поляриметра. 2016 Article Möller polarimeter in the Hall A Jefferson Lab after reconstruction / R.I. Pomatsalyuk // Вопросы атомной науки и техники. — 2016. — № 3. — С. 133-138. — Бібліогр.: 12 назв. — англ. 1562-6016 PACS: 29.25.Pj;29.27.Hj;29.85.Ca https://nasplib.isofts.kiev.ua/handle/123456789/115375 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Экспериментальные методы и обработка данных Экспериментальные методы и обработка данных |
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Экспериментальные методы и обработка данных Экспериментальные методы и обработка данных Pomatsalyuk, R.I. Möller polarimeter in the Hall A Jefferson Lab after reconstruction Вопросы атомной науки и техники |
| description |
The Möller polarimeter in the Hall A of Jefferson Lab was reconstructed in order to expand of the energy range
of the polarimeter to measure the polarization of the electron beam with an energy up to 11.5 GeV. The paper describes
the main results of the Möller polarimeter testing after reconstruction. The measurements of the electrons
polarization were provided by two data acquisition systems operating in parallel. The testing of the shielding insertion
of magnetic dipole has been performed. The way to eliminate detected deviations in the operation of polarimeter
during test is shown. |
| format |
Article |
| author |
Pomatsalyuk, R.I. |
| author_facet |
Pomatsalyuk, R.I. |
| author_sort |
Pomatsalyuk, R.I. |
| title |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction |
| title_short |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction |
| title_full |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction |
| title_fullStr |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction |
| title_full_unstemmed |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction |
| title_sort |
möller polarimeter in the hall a jefferson lab after reconstruction |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2016 |
| topic_facet |
Экспериментальные методы и обработка данных |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/115375 |
| citation_txt |
Möller polarimeter in the Hall A Jefferson Lab after reconstruction / R.I. Pomatsalyuk // Вопросы атомной науки и техники. — 2016. — № 3. — С. 133-138. — Бібліогр.: 12 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| first_indexed |
2025-11-30T16:33:28Z |
| last_indexed |
2025-11-30T16:33:28Z |
| _version_ |
1850233754980712448 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2016. №3(103) 133
MÖLLER POLARIMETER IN THE HALL A JEFFERSON LAB
AFTER RECONSTRUCTION
R.I. Pomatsalyuk
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: rompom@kipt.kharkov.ua
The Möller polarimeter in the Hall A of Jefferson Lab was reconstructed in order to expand of the energy range
of the polarimeter to measure the polarization of the electron beam with an energy up to 11.5 GeV. The paper de-
scribes the main results of the Möller polarimeter testing after reconstruction. The measurements of the electrons
polarization were provided by two data acquisition systems operating in parallel. The testing of the shielding inser-
tion of magnetic dipole has been performed. The way to eliminate detected deviations in the operation of polarime-
ter during test is shown.
PACS: 29.25.Pj;29.27.Hj;29.85.Ca
INTRODUCTION
Jefferson Lab is one of the world's scientific centers,
where the properties of nuclei and nucleons using beams
of polarized electrons are being studied. The accelerator
of Jefferson Lab [1] is a recirculation superconducting
electron accelerator (Fig. 1) with beam energy
1…12 MeV and beam current up to 100 μA. Facililty
consists of an injector, two of linear accelerators
("northern" and "southern") bending and extracting
magnets, and is capable deliver a linearly polarized
electron beam in any three of four experimental halls
(A, B, C, D) at the same time.
Möller and Compton polarimeter are used when
conducting experimental studies with polarized electron
beam in Hall A of Jefferson Lab. Hall A Möller polar-
imeter was created as a result of cooperation Jefferson
Laboratory, KIPT and the University of Kentucky and it
was commissioned since 1997 [2]. Initially, Möller po-
larimeter was designed to measure the polarization of
the electron beam in the energy range of 0.8…6.0 GeV
[3].
Fig. 1. Jefferson Lab accelerator after reconstruction
During 2012-2013 years Jefferson Lab accelerator
was reconstructed to increase the maximum energy of
the electron beam from 6 to 12 GeV. Hall A Möller po-
larimeter was modernized at the same time to operate
with electron beams with energies up to 11 GeV.
1. ELECTRON BEAM POLARIZATION
MEASUREMENT
The operating principle of the polarimeter Møller
based on the use Möller scattering [4] е
→
+е
→
→е´+е´.
Möller scattering cross section depends on the polariza-
tion of the electron beam and target polarization:
0 (1 ),
Moll Moll
b t
Z
d d
A P P
d d
(1)
where
d
d Moll
0 – Möller scattering cross section of un-
polarized beam of electrons on unpolarized electrons of
the target,
bP и
tP – the polarization of the beam elec-
trons and electron targe, respectively, ZA – analyzing
power of the reaction of Möller scattering (the axis Z –
along the beam).
The asymmetry of the scattering beam of polarized
electrons by polarized electron target is measured with
polarimeter, which is described by the formula:
cos
tb
Zmeas PPA
NN
NN
A , (2)
where N and N – detector counting rates measured
in parallel and antiparallel direction of the longitudinal
component of the polarization vector of the target to the
direction of the longitudinal component of the polariza-
tion vector of the electron beam, respectively, α – angle
of the foil target to the direction of the electron beam.
The polarization of the beam is determined from the
expression (2) as:
cos
t
Z
measb
PA
A
P . (3)
The analyzing power ZA is also determined by the
geometry of the magnetic spectrometer and polarimeter
detector and it is calculated using the software toolkitt
GEANT [5]. Thus, to do measure of the beam polariza-
tion, asymmetry of scattering is to be measured and the
value and sign of the polarized electron target is to be
known.
2. POLARIMETER AFTER
RECONSTRUCTION
Möller polarimeter includes polarized electrons tar-
get (T), magnetic spectrometer and detector (Fig. 2).
Möller electrons resulting from the interaction of the
electron beam to the target are analyzed with a magnetic
spectrometer. The spectrometer after reconstruction
comprises four quadrupoles (Q1, Q2, Q3, Q4) and one
of the dipole magnets (Dipole). Scattered electrons are
focused by quadrupole magnets in the horizontal plane
at the entrance of the dipole magnet. The dipole magnet
deflects the electrons down to the detector. Shielding
ISSN 1562-6016. ВАНТ. 2016. №3(103) 134
insertion located in the center of the dipole magnet,
through which the primary electron beam is passing
without interaction with the magnetic dipole field.
Fig. 2. Diagram of Möllerr Polarimeter
after reconstruction: а – side view; b – top view
Electron detector consists of two full absorption cal-
orimeters, allowing to register the Möller events in co-
incidences. Möller events are registered by the coinci-
dence of signals from the left and right detectors, which
can significantly reduce the contribution of background
events.
Following elements of the polarimeter have been
modified [6]:
- Magnetic Spectrometer;
- Shielding box of the detector and the detector;
- The elements of beamline;
- Data acquisition system.
2.1. MAGNETIC SPECTROMETER
The most significant changes required for a magnet-
ic spectrometer of polarimeter. The first quadrupole
magnet Q1 was moved down along the beam by 40 cm
and an additional quadrupole magnet Q4 was installed
in 70 cm from the target (Fig. 3).
2.2. DIPOLE
Reconstruction of the dipole magnet was performed
to improve the protection of the main beam of electrons
from the magnetic field of the dipole magnet. For this
purpose a additional shielding insertion type of tube
made from steel AISI-1006 with an internal diameter of
2.5 cm and thickness of 0.9 cm and length of 212.4 cm
has been manufactured and installed in the dipole
(Fig. 4).
Q1
shifted off 40 см
Q4
new
Support
beam
Fig. 3. New quadrupole magnet Q4 installed behind
the target
The power supply provides a maximum dipole cur-
rent 550 A, which is only enough for the beam energy
up to 8 GeV at Möller electron deflection angle of 10°.
This limitation has led to reduce the maximum deflec-
tion angle of Möller electrons from 10 to 7.3° for elec-
tron energy 11 GeV.
Fig. 4. Photo: shielding insertion of dipole
2.3. DETECTOR
As the deflection angle Möller electrons has been
reduced from 10 to 7.3°, the detector with a shielding
housing box was also raised to 7 cm (Fig. 5).
Input
Window
Detector
Support
beam
7 см
Doors
Detector
Shielding
Box
Fig. 5. Detector shielding box and detector
after reconstruction
The vertical corrector to compensate the deflection
of the electron beam after the dipole has been added
also. An additional beam position monitor has been
added for more precise positioning of the beam on the
polarimeter target.
2.4. POLARIZED ELECTRON TARGETS
Two types of polarized targets are used in Möller
polarimeter for measurements of the beam polarization:
1) the target with a low magnetic field (0.03 T) and po-
larization along the plane of the target ("Low Field")
(Fig. 6) [7]; 2) target with a large magnetic field (4 T)
and polarization across the plane of the target ("High
Field") (Fig. 7) [8].
Fig. 6. The schematic diagram of the target with polari-
zation along the longitudinal plane of the target:
1 – polarized electron beam; 2 – electrons scattered
by the target; 3 – magnetic coil with field of 0.05 T;
4 – target (foil)
ISSN 1562-6016. ВАНТ. 2016. №3(103) 135
Fig. 7. The schematic diagram of the target with
the polarization transverse plane of the target.
The notation is the same as in Fig. 6
"Low Field" target of polarized electrons comprises
ferromagnetic foil set that inclined at an angle of 20.5°
to the direction of the electron beam and the magnetic
field. The foils have a different thickness (7…10 μm)
and made of pure iron (99.95%) or supermendur
(49% Fe, 49% Co, 2% V) (Fig. 8).
Fig. 8. Holder of polarized electrons target ("Low Field")
The design of "High Field" target of polarized elec-
trons of Möller polarimeter in the Hall A is shown in
Fig. 9. The target consists of:
- Superconducting magnet with a maximum field up
to ± 4 T;
- Target holder with a set of four targets. All targets
are made of pure iron with a purity of 99.85% and
99.99% and thicknesses of 1, 2, 4, and 10 μm to the
study of possible systematic errors;
- Adjustment mechanism for the orientation of the
plane of the target relative to the direction of the
magnetic field;
- Unit for movement and control targets position;
- The target chamber with orientation mechanism to
the direction of the magnetic field along the electron
beam.
Fig. 9. The scheme of polarized electrons target of Hall
A Möller polarimeter. The diagram shows:
superconducting magnet, the target unit and the target
chamber. The photo shows the target holder with a set
of iron foils
2.5. DATA ACQUISITION SYSTEM
Hall A Møller polarimeter has two data acquisition
and data processing systems:
1. The old system, based on the modules in the
standard CAMAC, VME and NIM, since 1997.
2. A new system VME-based flash-ADC module F-
250, commissioned since 2009.
The old data acquisition system of Möller polarime-
ter is used more than 15 years [9]. It is fully functional
for all targets polarimeter and well studied. At the same
time it has a low rate of events logging, system modules
occupy several racks, as well as a large number of con-
nections and interconnect cables, which reduces the
reliability of the data acquisition system. In addition,
some modules of the system are out from production
and can not be replaced in case of failure.
The main goal of introduction of the new data acqui-
sition system is to reduce systematic errors of polariza-
tion measurement by increasing the rate of events and
reduce the dead time.
The new data acquisition system is based on the
flash-ADC F250, which was developed in the Jefferson
Laboratory [10]. This data acquisition system allows to
register and record the data flow at speeds up to
50 MB/s for events rate in the coincidence of the left
and right arms of detector is about 160 kHz.
Detailed description of the structure and operation of
both data acquisition systems is given in [11].
Software for analysis and processing of measured
data is built on the package ROOT (package object-
oriented programs and libraries developed by the Euro-
pean Center for Nuclear Research (CERN)) [12].
The software package consists of programs for
online monitoring of the data and the program for of-
fline processing. The monitoring program allows one to
control the quality of incoming information by display-
ing the current values of the coincidence scalars, the
digitized analog signals from each detector unit, ampli-
tude spectra of signals from the detector. Program off-
line processing allows to convert data files from the
CODA format to root file format, perform data analysis
and obtain results of the beam polarization measure-
ments.
The both data acquisition systems operated in paral-
lel during measuring of the polarization. Thus, that al-
lows an additional study of systematic errors of the
measurements.
3. DIPOLE TESTING
Testing of the dipole shielding insertion was per-
formed using the beam position monitor, which is locat-
ed behind the dipole magnet and a polarimeter detector.
Three measurements of the vertical beam position were
done:
with disabled dipole and vertical corrector;
dipole is ON and vertical corrector is OFF;
dipole and vertical corrector are both ON.
The test results are shown in Fig. 10. One can see
that the switch on of dipole leads to a displacement of
the vertical beam position of about 1.4 mm. This value
agrees well to the estimated value for the beam energy
of 6.05 GeV and dipole with a shielding insertion.
ISSN 1562-6016. ВАНТ. 2016. №3(103) 136
Fig. 10. Test of operation of dipole shielding insertion
Fig. 11 shows the results of simulation with TOSCA
software the displacement value of the primary electron
beam on the physical target of Hall A (the left – 13 m
from the center of the dipole) and at the beam dump
(right – 63 m from the center of the dipole) due to the
influence of the dipole magnetic field with shielding
insertion. Turning on the vertical corrector is fully com-
pensate the deflection of the beam due to the dipole
magnetic field. Thus this test is checked the operation of
dipole shielding insertion.
Fig. 11. Main electron beam deflection at the target
(left) and at the beam dump (right) due to magnetic field
of dipole with shielding insertion
Also, operation dipole tests, with maximum current
of 500 A were conducted. During these tests it was
found that the dipole power supply instability appears at
current of 450 A (Fig. 12). Further research of operation
of the power supply has shown that stable operation of
the power supply is provided only with a maximum
current up to 440 A. It was planned during the recon-
struction of the polarimeter that the operation of the
polarimeter with a maximum energy of electron beam of
11 GeV the dipole current has to be set at 500 A. It was
decided to reduce the angle of deflection of the electron
by dipole from 7.3 to 6° to provide the operation of the
polarimeter with a maximum beam energy and with a
maximum dipole current of 440 A. This requires to lift
up the detector with a shielding box for another 3.5 cm.
Fig. 12. Instability of dipole power supply
with current set at 450 A
4. OPTIMIZATION OF POLARIMETER
OPERATION
All tests of the polarimeter and tuning its systems
were carried out using target with low magnetic field
and the polarization along the plane of the target.
Detector setup, optimization of the magnetic elements
of the spectrometer were performed during test trials of
polarimeter. The polarization of the electron beam with
an energy of 6.05, 7.375, and 9.57 GeV was measured.
Both data acquisition systems operated in parallel at the
time of tests and measurements of the polarization.
The detector tuning carried out in several stages. Ini-
tially, setting of the high voltage supply for the PMT
was performed to provide that the amplitude of the sig-
nal for all channels was the same and corresponded to
the middle of the input range of the ADC. Then the
thresholds of discrimination signals from the detector
were determined to provide optimum rate of events and
minimize random events for data acquisition systems of
polarimeter. The detector tuning process was controlled
in on-line mode using the amplitude spectrum of signals
from the detector (Fig. 13).
Fig. 13. Amplitude spectrum of left
and right calorimeters (flash-ADC)
A
n
a
ly
z
in
g
p
o
w
e
r 0.75
0.74
0.73
0.72
0.71
0.70
0.69
0.68
1200
1100
1000
900
800
700
600
500
400
300
C
o
in
c
id
e
n
c
e
r
a
te
Fig. 14. Quadrupole magnet Q4 current scan (top) and
calculated analyzing power of polarimeter (bottom)
Optimization of the magnetic elements of the spec-
trometer was carried out by measuring the dependence
of the frequency of events in the coincidence of the left
and right arms of the detector from the set magnetic
field (current) of the magnetic element. The measure-
ments were performed for the quadrupole magnets Q1,
Q2, Q4, and the dipole. The obtained data were com-
pared with calculations made in the GEANT. Fig. 14 (at
ISSN 1562-6016. ВАНТ. 2016. №3(103) 137
the top) shows the measurement of the Q4 quadrupole
magnet, and at the bottom is the calculated values of the
analyzing power of polarimeter for the given currents in
the magnetic element Q4. Optimization was performed
to set such magnetic current of element that would cor-
respond to the maximum rater of events in coincidence.
Measurements of the polarization of the electron
beam were carried out for several sets of the electron
energy. As noted previously, both data acquisition sys-
tems operated in parallel during the measurements.
Fig. 15 shows the results of measurements of the asym-
metry of polarized electron beam with an energy of
6.05 GeV made with four polarimeter targets.
Fig. 15. The asymmetry of polarized electron beam
for four targets, as measured by two data acquisition
systems of the polarimeter
Measurements of the beam polarization for given
energy was (-55±0.11)%.
Fig. 16 shows the results of measurements of the
beam polarization with an energy of 7.375 GeV for the
three polarimeter targets. The value of the beam polari-
zation (average) was (86.1±0.25)%.
Fig. 16. Polarization of electron beam with energy
7.375 GeV for different polarimeter targets
Fig. 17. Polarization of electron beam with energy
9.573 GeV for different polarimeter targets
Fig. 17 shows the results of measurements of the
beam polarization with an energy of 9.573 GeV for dif-
ferent polarimeter targets. The beam polarization aver-
aged over the four targets was (80.5±0.16)%.
CONCLUSIONS
The paper presents the main results of the Møller po-
larimeter testing after reconstruction. Operation and
tests of polarimeter with electron beam showed that all
systems and polarimeter generally working well. The
measurements of the electron beam polarization with
energies of 6.05, 7.375, and 9.573 GeV have been per-
formed. The polarimeter is a unique setup with two dif-
ferent types of polarized targets, and two types of data
acquisition systems working in parallel. Measurements
with two data acquisition systems showed quite good
agreement with each other. The slight difference in the
data is due to the different in thresholds set of signal
discrimination from the detector and the difference in
the analyzing software for each data acquisition system.
This work was supported by contract DE-AC05-
06OR23177 the U.S. Department of Energy on the basis
of which Jefferson Science Associates operates the Jef-
ferson Lab.
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Article received 03.03.2016
МЁЛЛЕРОВСКИЙ ПОЛЯРИМЕТР ЗАЛА А ЛАБОРАТОРИИ ДЖЕФФЕРСОНА
ПОСЛЕ РЕКОНСТРУКЦИИ
Р.И. Помацалюк
В лаборатории им Т. Джефферсона (США) проведена реконструкция мёллеровского поляриметра зала А
с целью расширения энергетического диапазона поляриметра для измерения поляризации пучка электронов
с энергией до 11,5 ГэВ. Рассмотрены основные результаты тестирования мёллеровского поляриметра после
реконструкции. Измерения поляризации электронов обеспечивали две системы сбора данных, работающие
параллельно. Проведено тестирование защитной магнитной вставки диполя. Намечены возможные пути
устранения отклонений в работе поляриметра, выявленных в процессе тестирования.
МЬОЛЛЕРІВСЬКИЙ ПОЛЯРИМЕТР ЗАЛУ А ЛАБОРАТОРІЇ ДЖЕФФЕРСОНА
ПІСЛЯ РЕКОНСТРУКЦІЇ
Р.I. Помацалюк
У лабораторії ім Т. Джефферсона проведена реконструкція мьоллерівського поляриметра залу А з метою
розширення енергетичного діапазону поляриметра для вимірювання поляризації пучка електронів з енергі-
єю до 11,5 ГеВ. Розглянуті основні результати тестування мьоллерівського поляриметра після реконструкції.
Вимірювання поляризації електронів забезпечували дві системи збору даних, які працюють паралельно.
Проведено тестування захисної магнітної вставки диполя. Намічено можливі шляхи усунення виявлених у
процесі тестування відхилень у роботі поляриметра.
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