Beam dynamics issues in undulator based PPA
The analysis of the beam dynamics simulation for an undulator based Positron Pre-Accelerator was carried out to produce a high positron capture with the reliable and reasonable design solution. From beam dynamics and taking into account a lot of parameters for optimization the attempt to ground th...
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irk-123456789-788772015-03-23T03:02:05Z Beam dynamics issues in undulator based PPA Moiseev, V.A. Paramonov, V.V. Flöttmann, K. Линейные ускорители заряженных частиц The analysis of the beam dynamics simulation for an undulator based Positron Pre-Accelerator was carried out to produce a high positron capture with the reliable and reasonable design solution. From beam dynamics and taking into account a lot of parameters for optimization the attempt to ground the proposal PPA design was done. The possible choice of any other design solution is discussed. Приведен анализ динамики пучка в позитронном предускорителе с целью получения значительного захвата позитронов при надежном и целесообразном решении конструкции ускорителя. Исходя из динамики пучка и принимая во внимание значительное число параметров оптимизации, сделана попытка обосновать предлагаемое решение предускорителя. Обсуждается возможный выбор любого другого решения конструкции предускорителя. Наведено аналіз динаміки пучка в позитронному передприскорювачі з метою одержання значного захвату позитронів при надійному і доцільному рішенні конструкції прискорювача. Виходячи з динаміки пучка і беручи до уваги значне число параметрів оптимізації, зроблена спроба обґрунтувати пропоноване рішення передприскорювача. Обговорюється можливий вибір будь-якого іншого рішення конструкції передприскорювача. 2006 Article Beam dynamics issues in undulator based PPA / V.A. Moiseev , V.V. Paramonov , K. Flöttmann // Вопросы атомной науки и техники. — 2006. — № 2. — С. 134-136. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 29.20.Bd http://dspace.nbuv.gov.ua/handle/123456789/78877 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Линейные ускорители заряженных частиц Линейные ускорители заряженных частиц |
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Линейные ускорители заряженных частиц Линейные ускорители заряженных частиц Moiseev, V.A. Paramonov, V.V. Flöttmann, K. Beam dynamics issues in undulator based PPA Вопросы атомной науки и техники |
| description |
The analysis of the beam dynamics simulation for an undulator based Positron Pre-Accelerator was carried out to
produce a high positron capture with the reliable and reasonable design solution. From beam dynamics and taking
into account a lot of parameters for optimization the attempt to ground the proposal PPA design was done. The possible
choice of any other design solution is discussed. |
| format |
Article |
| author |
Moiseev, V.A. Paramonov, V.V. Flöttmann, K. |
| author_facet |
Moiseev, V.A. Paramonov, V.V. Flöttmann, K. |
| author_sort |
Moiseev, V.A. |
| title |
Beam dynamics issues in undulator based PPA |
| title_short |
Beam dynamics issues in undulator based PPA |
| title_full |
Beam dynamics issues in undulator based PPA |
| title_fullStr |
Beam dynamics issues in undulator based PPA |
| title_full_unstemmed |
Beam dynamics issues in undulator based PPA |
| title_sort |
beam dynamics issues in undulator based ppa |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2006 |
| topic_facet |
Линейные ускорители заряженных частиц |
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http://dspace.nbuv.gov.ua/handle/123456789/78877 |
| citation_txt |
Beam dynamics issues in undulator based PPA / V.A. Moiseev , V.V. Paramonov , K. Flöttmann // Вопросы атомной науки и техники. — 2006. — № 2. — С. 134-136. — Бібліогр.: 4 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT moiseevva beamdynamicsissuesinundulatorbasedppa AT paramonovvv beamdynamicsissuesinundulatorbasedppa AT flottmannk beamdynamicsissuesinundulatorbasedppa |
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2025-07-06T02:58:33Z |
| last_indexed |
2025-07-06T02:58:33Z |
| _version_ |
1836864728434999296 |
| fulltext |
BEAM DYNAMICS ISSUES IN UNDULATOR BASED PPA
V.A. Moiseev1, V.V. Paramonov1, K. Flöttmann2
1INR RAS, Moscow, Russia
2DESY, Hamburg, Germany
E-mail: moiseev@inr.troitsk.ru
The analysis of the beam dynamics simulation for an undulator based Positron Pre-Accelerator was carried out to
produce a high positron capture with the reliable and reasonable design solution. From beam dynamics and taking
into account a lot of parameters for optimization the attempt to ground the proposal PPA design was done. The pos-
sible choice of any other design solution is discussed.
PACS: 29.20.Bd
1. INTRODUCTION
The Positron Pre-Accelerator (PPA) will be the begin-
ning part of the positron branch of the International Linear
Collider (ILC). There are two main modes of positron pro-
duction. The first one is conventional and the second one is
undulator based. The conventional method uses multi-GeV
electrons impinging on a high-Z thick (in radiation length
units) target. Whereas the second method applies a very
high energy electron beam passing through undulator to
make multi-MeV photons (150…250 GeV electrons,
100 meter or more of undulators), which will hit a thin (in
radiation units also) target to yield the positrons [1]. The
undulator based method has a number of advantages with
respect to the conventional one. The main advantage is con-
siderably more compact transverse and longitudinal
positron momentum distributions. The next ones are the
possibility to produce polarized positrons and much lower
neutron activation. Improved initial positron momentum
distribution for undulator based PPA permits to get higher
positron capture efficiency, which is determined as ratio of
a number of positrons for further use to number of positrons
emitted from the target. For conventional positron produc-
tion schemes this parameter is about few percents whereas
for undulator based PPA the value more than 20% may be
reached [3].
There are few main requirements for PPA operation for
any type of positron production. At first, it needs to have
high positron capture efficiency in 6-dimensional phase
space for PPA beam output energy more than 250 MeV.
Secondly, it needs to have final positron beam quality: sin-
gle output positron bunch with minimum of useless
particles. And finally it needs to have the reliable
and reasonable PPA design solution. For TESLA
project the undulator based PPA scheme was de-
signed [2] and it is presented in Fig.1.
2. PPA COMPONENTS
For any PPA design there are main elements
used: base rf-klystron, magnetic device placed be-
hind the target to match the positrons beam from the
target with accelerator acceptance, room temperature
accelerating structure with rather high field gradient
embedded in a constant field long solenoid. Addi-
tionally, an insertion unit for particle separation and
collimation as well as an acceleration part with peri-
odic transverse focusing may be used [2].
2.1. MATCHING DEVICE
An adiabatic matching device (AMD) is suitable
decision for the PPA beginning. It consists of a ta-
pered solenoid field, which starts with a higher ini-
tial field and tapers down adiabatically to the con-
stant end field. Technically it is a special solenoid
with combined pulsed and time constant magnetic
field [2]. The AMD on-axis field law is
B(s)=B0/(1+gs), where s is the longitudinal coordi-
nate, Bo is the maximum magnetic field and g is the
taper coefficient. The final AMD field is equal to the
constant magnetic field of the PPA solenoid. The
modern reliable B0 value is ∼6 T [2]. The optimum
value for g is closed to 30 m-1. This result has been
received by simulation [3].
___________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.134-136.
134
mailto:moiseev@inr.troitsk.ru
Fig.1 The general PPA proposal
2.2. FOCUSING SOLENOID
To keep positrons in the PPA initial acceleration part
a focusing solenoid field has to be used. The value of
solenoid field Bsol is equal to the AMD downstream end
field. The acceptance of solenoid accelerating channel is
A0 ∼Bsola2, where a is the radius of an accelerating struc-
ture. In dependence of desired acceptance value (for
TESLA PPA A0 =0.036 π mrad) and taking into account
the technically reasonable Bsol (for 0.22 T and solenoid
length ∼11.5 m DC power consumption, which is ∼ Bsol
2,
will be ∼450 kW) the minimum radius of acceleration
section can be determined. It is evident that the higher
solenoid field is better. However, from some value of
Bsol the growth rate for the capture efficiency slows
down essentially. It results from the PPA acceptance ex-
ceeding the transverse emittance requirement for
positron beam [2].
In Fig.2 the positron capture efficiency is presented
in dependence on the accelerating section radius a. The
higher radius does not lead to essential growth for the
capture efficiency. The saturation of capture efficiency
begins when the acceptance of system becomes higher
than desired positron beam emittance. Due to the square
dependence of acceptance from aperture radius there is
not essential decreasing of aperture size with solenoid
field growth. Thus, there is a choice to have the large
solenoid field and moderate aperture radius or small
solenoid field and slightly higher aperture. For TESLA
PPA [2] the second solution was chosen taking in ac-
count the low DC power consumption in solenoid and
reduced influence of uniform solenoid field perturba-
tions on particle dynamics.
Fig.2 Capture efficiency in dependence of rf-section ra-
dius
2.3. ACCELERATION
The main goal of the PPA beginning part is as fast as
possible to accelerate positron beam up to high energy
where the bunch lengthening will be negligible and the
transverse momentum becomes much less than longitu-
dinal one. For L-band operation (1.3 GHz) both Stand -
ing Wave (SW) Coupled Cells (CC) structures and
Traveling Wave (TW) structures may be used in depen-
dence on the ILC operation. However, it was shown [4]
that for TESLA operation the SW structures are more
preferable. The first TESLA PPA part consists of the
four Accelerating Cavities (ACs) embedded in a focus-
ing solenoid. The first two ACs have a high accelerating
gradient (<14.5 MV/m) to reduce the bunch lengthen-
ing, whereas the others have a moderate gradient (<8.5
MV/m) to diminish the rf-power consumption. Each AC
is powered by one standard TESLA 10 MW klystron.
There are some reasons for this solution. At first, energy
increase per section is less for higher gradients (Lsec∼E0
-2
whereas energy gain per AC ∼ E0Lsec∼E0
-1). The beam dy-
namics simulation has shown [3] that bunch lengthening
effect becomes small for bunch energy more than
40 MeV. Therefore, further acceleration can be done
with lower gradients and higher energy gain per AC.
The higher accelerating gradient in first ACs will in-
crease the number of klystrons and ACs. Also there will
be additional perturbations in uniform solenoid field due
to AC feeding lines and alignment equipment. More-
over, the using of 20 MV/m gradient in first ACs leads
only to ∼2.5% growth of positron capture efficiency on
the level of ∼25%, but electron losses were risen in
1.5 times in these ACs. Additionally adjusting the
bunching rf-phase (optimum value is ∼-200 for a refer-
ence particle) in high gradient ACs it is possible, reduc-
ing the final energy, to prevent the large lengthening in
ACs. In this case the capture efficiency growth will be ∼
2%.
2.4. TRANSVERSE PERIODIC FOCUSING
There is positron beam energy when it is possible to
change the solenoid focusing on transverse periodic fo-
cusing by quadrupoles. The advantages of this solution
are smaller DC power consumption in short solenoid
and better maintenance for ACs and diagnostics. For
TESLA requirements beam energy more than 100 MeV
is acceptable for transition [3]. The triplet periodic
structure was chosen because of the maximum of free
space to place ACs and moreover a beam will be practi-
cally round in ACs. In addition, the periodic structure
can be used for beam cleaning from electrons and
positrons with large energy deviation due to the mis-
matching of the dynamic parameters of the useless parti-
cles with periodic focusing.
2.5. SEPARATION AND COLLIMATION
There is a problem to separate positrons, electrons
and photons for undulator based PPA. And it is neces-
sary to clean 6-dimention positron phase space to have
beam quality acceptable for further operation. These
problems can be solved in any PPA point except the
solenoid part. At least two solutions may be proposed.
The first one is to make separation and collimation at
the PPA exit. And the second one is to place special in-
sertion at the transition point from solenoid to periodic
focusing if it exists. The advantages of the last solution
are lower power of useless accelerated electron beam (∼
15 kW for TESLA PPA proposal [2]) and lower require-
ments for equipment misalignments with respect to the
photon beam. However, at lower energy for separation it
will be stronger nonlinear chromatic effects that can
lead to the abrupt drop of positron beam quality [2]. The
main requirements for special insertion for separation
and collimation the positron beam are to be achromatic
or isochronous system and to have small optical func-
tions to reduce the nonlinear chromatic effects (not good
for collimation) [2].
3. BEAM DYNAMICS SIMULATION
For TESLA PPA proposal (Fig.1) the following pa-
rameters and decisions were accepted. The PPA is a
standing wave normal conducting linac. Its first part
126
consists of the four ACs embedded in a focusing
solenoid with Bsol = 0.22 T. Behind the first PPA part
(final positron energy ~114 MeV) there is a magnetic
insertion to separate the positron and electron beams.
Additionally it serves to collimate the positron beam.
The insertion has a standard achromatic design with two
bending dipoles and matching sections on both ends [2].
The second PPA part consists of five ACs with moder-
ate gradient (<8.5 MV/m). The quadrupole triplets carry
out the transverse focusing. AMD has the following pa-
rameters: g = 29.5 m-1, length ∼ 0.9 m.
Fig.3 Longitudinal positron beam phase spaces
In Fig.3 the longitudinal positron beam phase spaces
are presented at PPA exit with different design solu-
tions. In Fig.3,a the simulation results are presented for
PPA with solenoid focusing only. There is a train of
positron bunches. The first one includes ∼90% of accel-
erated positrons. In Fig.3,b the results are for PPA with
combined transverse focusing (solenoid + periodic
triplet focusing). There is an obvious cleaning of low
energy train momentum region. In Fig.3,c the simula-
tion results are presented for TESLA PPA proposal
(Fig.1) with magnetic insertion [2]. Negligible number
of positrons is in tail train (∼0.7% of total positron num-
ber) and the first bunch is more compact compared with
previous cases.
In Table the simulation results for different PPA de-
signs are presented.
Comparison of different PPA designs
Parameter Solenoid Solenoid &
triplets
Solenoid &
separator &
triplets
Final energy, MeV 274 278 287
Capture efficiency, % 24.8 24.3 21.3
Solenoid length, m 34 11.4 11.4
Number of klystrons 9 9 9
Total length, m 34.3 45 55.5
DC power consump-
tion, kW ∼ 1350 ∼ 450 ∼ 480
4. CONCLUSIONS
The undulator based PPA permits to get output
positron beam with satisfied parameters. It is possible to
design the flexible PPA proposal in dependence on the
required purposes and existing equipments.
REFERENCES
1. www-project.slac.stanford.edu/ilc/acceldev/injector
/parameters.htm
2. Conceptual Design of a Positron Injector for the
TESLA Linear Collider. DESY, TESLA 2000-12,
Hamburg, 2000.
3. V.A. Moisev, V.V. Paramonov, K. Flottmann.
Beam Dynamics Studies in a TESLA Positron Pre-
Accelerator // Problems of Atomic Science and
Technology. Series: Nuclear Physics Investiga-
tions. 2001, №3(38), p.147-149.
4. Conceptual design of a Positron Pre-Accelerator
for the TESLA Linear Collider. DESY, TESLA 99-
14, Hamburg, 1999.
АНАЛИЗ ДИНАМИКИ ПУЧКА В ПОЗИТРОННОМ ПРЕДУСКОРИТЕЛЕ
НА БАЗЕ ОНДУЛЯТОРА
В.А. Моисеев, В.В. Парамонов, К. Флеттманн
Приведен анализ динамики пучка в позитронном предускорителе с целью получения значительного за-
хвата позитронов при надежном и целесообразном решении конструкции ускорителя. Исходя из динамики
пучка и принимая во внимание значительное число параметров оптимизации, сделана попытка обосновать
предлагаемое решение предускорителя. Обсуждается возможный выбор любого другого решения конструк-
ции предускорителя.
АНАЛІЗ ДИНАМІКИ ПУЧКА В ПОЗИТРОННОМУ ПЕРЕДПРИСКОРЮВАЧІ
НА БАЗІ ОНДУЛЯТОРА
В.А. Моісеєв, В.В. Парамонов, К. Флоттманн
Наведено аналіз динаміки пучка в позитронному передприскорювачі з метою одержання значного
захвату позитронів при надійному і доцільному рішенні конструкції прискорювача. Виходячи з динаміки
пучка і беручи до уваги значне число параметрів оптимізації, зроблена спроба обґрунтувати пропоноване
рішення передприскорювача. Обговорюється можливий вибір будь-якого іншого рішення конструкції
передприскорювача.
___________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.134-136.
134
2.1. MATCHING DEVICE
Fig.1 The general PPA proposal
2.2. FOCUSING SOLENOID
2.3. ACCELERATION
2.4. TRANSVERSE PERIODIC FOCUSING
2.5. SEPARATION AND COLLIMATION
АНАЛИЗ ДИНАМИКИ ПУЧКА В ПОЗИТРОННОМ ПРЕДУСКОРИТЕЛЕ
НА БАЗЕ ОНДУЛЯТОРА
АНАЛІЗ ДИНАМІКИ ПУЧКА В ПОЗИТРОННОМУ передприскорювачі
|