Upgrade of the high current heavy ion front-end system of the GSI UNILAC
The FAIR Project requires an U⁴⁺ beam current above 18 emA behind the heavy ion high current RFQ. The measured intensity was a factor of two lower. The beam dynamics in the front-end system has been simulated with the DYNAMION code. New RFQ electrodes with an improved quality of the surface and...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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Yaramyshev, S. Barth, W. Dahl, L. Kolomiets, A. 2015-03-20T20:04:24Z 2015-03-20T20:04:24Z 2006 Upgrade of the high current heavy ion front-end system of the GSI unilac / S. Yaramyshev , W. Barth , L. Dahl , A. Kolomiets // Вопросы атомной науки и техники. — 2006. — № 2. — С. 64-66. — Бібліогр.:8 назв. — англ. 1562-6016 PACS: 29.17.+w, 41.75.Lx https://nasplib.isofts.kiev.ua/handle/123456789/78766 The FAIR Project requires an U⁴⁺ beam current above 18 emA behind the heavy ion high current RFQ. The measured intensity was a factor of two lower. The beam dynamics in the front-end system has been simulated with the DYNAMION code. New RFQ electrodes with an improved quality of the surface and a redesigned matching section were fabricated. Beam experiments after the RFQ upgrade confirmed the calculated gain in beam current. Для проекта FAIR после сильноточного RFQ нужен ток пучка U⁴⁺ больше 18 emA. Измеренная интенсивность была в два раза меньше. В начальной части динамика пучка моделировалась по программе DYNAMION. Были изготовлены новые RFQ электроды с улучшенным качеством поверхности и реконструирована согласующая секция. Эксперименты с пучком после модернизации RFQ подтвердили расчетное увеличение тока пучка. Для проекту FAIR після сильнострумового RFQ потрібний струм пучка U⁴⁺ більше 18 emA. В той же чаc інтенсивність пучка до реконструкції структури RFQ була в два рази менше. В початковій частині динаміка пучка моделювалась за допомогою програми DYNAMION. Виготовлені нові RFQ електроди, що мають підвищену якість поверхні, і реконструйована узгоджуюча секція. Експерименти з пучком після модернізації RFQ підтвердили розраховане збільшення струму пучка. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Линейные ускорители заряженных частиц Upgrade of the high current heavy ion front-end system of the GSI UNILAC Модернизация сильноточной начальной части ускорителя тяжелых ионов UNILAC, GSI Модернизація сильноточної начальної частини прискорювача важких іонів UNILAC, GSI Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC |
| spellingShingle |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC Yaramyshev, S. Barth, W. Dahl, L. Kolomiets, A. Линейные ускорители заряженных частиц |
| title_short |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC |
| title_full |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC |
| title_fullStr |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC |
| title_full_unstemmed |
Upgrade of the high current heavy ion front-end system of the GSI UNILAC |
| title_sort |
upgrade of the high current heavy ion front-end system of the gsi unilac |
| author |
Yaramyshev, S. Barth, W. Dahl, L. Kolomiets, A. |
| author_facet |
Yaramyshev, S. Barth, W. Dahl, L. Kolomiets, A. |
| topic |
Линейные ускорители заряженных частиц |
| topic_facet |
Линейные ускорители заряженных частиц |
| publishDate |
2006 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Модернизация сильноточной начальной части ускорителя тяжелых ионов UNILAC, GSI Модернизація сильноточної начальної частини прискорювача важких іонів UNILAC, GSI |
| description |
The FAIR Project requires an U⁴⁺ beam current above 18 emA behind the heavy ion high current RFQ. The
measured intensity was a factor of two lower. The beam dynamics in the front-end system has been simulated with
the DYNAMION code. New RFQ electrodes with an improved quality of the surface and a redesigned matching
section were fabricated. Beam experiments after the RFQ upgrade confirmed the calculated gain in beam current.
Для проекта FAIR после сильноточного RFQ нужен ток пучка U⁴⁺ больше 18 emA. Измеренная интенсивность была в два раза меньше. В начальной части динамика пучка моделировалась по программе DYNAMION. Были изготовлены новые RFQ электроды с улучшенным качеством поверхности и реконструирована согласующая секция. Эксперименты с пучком после модернизации RFQ подтвердили расчетное увеличение тока пучка.
Для проекту FAIR після сильнострумового RFQ потрібний струм пучка U⁴⁺ більше 18 emA. В той же чаc інтенсивність пучка до реконструкції структури RFQ була в два рази менше. В початковій частині динаміка пучка моделювалась за допомогою програми DYNAMION. Виготовлені нові RFQ електроди, що мають підвищену якість поверхні, і реконструйована узгоджуюча секція. Експерименти з пучком після
модернізації RFQ підтвердили розраховане збільшення струму пучка.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/78766 |
| citation_txt |
Upgrade of the high current heavy ion front-end system of the GSI unilac / S. Yaramyshev , W. Barth , L. Dahl , A. Kolomiets // Вопросы атомной науки и техники. — 2006. — № 2. — С. 64-66. — Бібліогр.:8 назв. — англ. |
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UPGRADE OF THE HIGH CURRENT HEAVY ION
FRONT-END SYSTEM OF THE GSI UNILAC
S. Yaramyshev1,2, W. Barth1, L. Dahl1, A. Kolomiets2
1 Gesellschaft fuer Schwerionenforschung (GSI), Darmstadt, Germany
2 Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia
E-mail: S.Yaramishev@gsi.de
The FAIR Project requires an U4+ beam current above 18 emA behind the heavy ion high current RFQ. The
measured intensity was a factor of two lower. The beam dynamics in the front-end system has been simulated with
the DYNAMION code. New RFQ electrodes with an improved quality of the surface and a redesigned matching
section were fabricated. Beam experiments after the RFQ upgrade confirmed the calculated gain in beam current.
PACS: 29.17.+w, 41.75.Lx
1. INTRODUCTION
For the Facility for Antiproton and Ion Research
(FAIR) at Darmstadt the present GSI-accelerator
complex, consisting of the UNIversal Linear
ACcelerator (UNILAC) and the heavy ion synchrotron
SIS 18, is foreseen to serve as a high current
injector [1]. The UNILAC [2] was designed to
accelerate all ion species with mass over charge ratio of
up to 8.5. As shown in Fig.1, the main parts of the
UNILAC are the 36 MHz High Current Injector (HSI), a
gas stripper section at an energy of 1.4 MeV/u and a
108 MHz Alvarez type post-stripper (11.4 MeV/u).
Fig.1. Schematic overview of the GSI UNILAC
The HSI consists of two ion source terminals (PIG
and MUCIS/MEVVA), the Low Energy Beam
Transport line (LEBT), a Radio Frequency Quadrupole
accelerator (RFQ), a short matching section (superlens),
and two Interdigital H-structure (IH) tanks. In the FAIR
scenario the HSI has to deliver 18 emA of U4+.
The HSI-RFQ is in operation since 1999 [3]. During
operation with U4+ beam (Vrf = 125 kV), the measured rf
power was about factor of two higher than calculated.
The design voltage of 137 kV, required for the ions with
higher mass to charge ratio, was not reached. New
electrodes were fabricated and additionally copper-
plated. A dedicated procedure for the control of the
copper-plating and rf tuning of the RFQ resulted in an
improvement of the rf-performance [4].
Additionally the new design of the first electrodes
was implemented to improve the beam dynamics in the
whole front-end system. The achieved uranium beam
transmission through the RFQ was 55% (design
value 90%). The design current of medium ions behind
the RFQ has been obtained, but with a significant
surplus of primary intensity.
2. BEAM MATCHING TO THE RFQ
Beam matching to the HSI-RFQ is carried out with
four magnetic quadrupole lenses (Fig. 2).
Fig.2. Matching line to the HSI-RFQ
Transverse beam emittances can be measured with a
slit-grid device placed about 3 m before the RFQ. Due
to the limited space between the Quadrupole
Quartet (QQ) and the RFQ, beam transmission can be
measured only for the whole front-end system.
A detailed beam dynamics study of the front end-
system showed a significant gain in the particle
transmission with only minor modification of the Input
Radial Matcher (IRM), which length is about 1% of the
total RFQ structure length.
3. BEAM DYNAMICS
Well-known codes for beam dynamics simulations
PARMTEQM and PARMTRA don't provide the
required accuracy of calculations due to intrinsic
simplifications, namely paraxial approximation for the
particle motion, calculations of the external field in the
RFQ for ideal shape of electrodes and the representation
of the space charge forces by a charged ellipsoid. The
DYNAMION code has been chosen to provide for
higher accuracy and reliability of the calculations.
3.1. MULTIPARTICLE CODE DYNAMION
The multiparticle code DYNAMION (DYNAMics
of IONs) was written in ITEP for precise end-to-end
beam dynamics simulations in high current linear
accelerators and was implemented world-wide as for
linac design and for study of linacs in operation as well.
In collaboration between GSI and ITEP the
DYNAMION code is in use since many years for the
investigation of operation of the GSI high current heavy
ion linac UNILAC. Significant development of the code
was done under GSI support.
One of the main features of the DYNAMION code
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PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.64-66.
* Work supported by INTAS (Project 03-54-3543)
64
is the possibility to simulate the 3D particle motion
under space charge conditions in the whole linac,
potentially consisting of RFQs, different types of DTLs,
transport lines and other elements. The required
accuracy and reliability were reached by an improved
description of the external fields inside the code.
Additionally, data from measurements or from
calculations performed with external codes (e.g.
focusing and accelerating fields, beam emittance,
misalignments, etc.) are usable.
3.2. HSI PERFORMANCE BEFORE UPGRADE
First DYNAMION calculations of the particle
motion in the RFQ were carried out with a design beam
current of 16.8 emA for the uranium case. A beam
transmission of 82% was shown, whereas the
PARMTEQ code predicted up to 95% in the design
stage [6]. Although the measured transmission was even
lower.
Recent beam dynamics simulations in the front-end
system were done with a beam current of 15 emA,
which was measured before the matching quadrupoles.
Results of the emittance measurements in the LEBT, the
measured distribution of the magnetic field in the
quadrupole lenses, the geometry of the electrodes "as
fabricated" and measured misalignments of the ten RFQ
sections were implemented. External electrical fields in
the IRM as well as in the regular RFQ cells, were
precisely calculated solving the Laplace equation for the
potential in the area, formed by the surfaces of the
electrodes and the tank. Behind the RFQ a beam current
of 8.7 emA was calculated; the measured current was
8.3 emA.
The low transmission (55%) was caused by
significant particle losses in the RFQ and 50% higher
beam emittance (compare to the design value).
Additionally, narrow matching conditions require strong
beam convergence at the RFQ entrance. This leads to a
significant deformation of the 6D beam phase volume, a
large diameter of the beam in the QQ and remarkable
particle losses. Therefore, machine settings were
optimized to provide for maximum transmission
through the whole front-end system (but not for the
beam matching).
4. STUDY OF UPGRADE MEASURES
Strong magnetic fields in the QQ are required to reach
high beam convergence simultaneously in both transverse
planes at the HSI-RFQ entrance. The integration of the
full 3D equation of the particle motion takes interaction
of magnetic field in quadrupoles into account; not only
with longitudinal, but also with transverse components of
the particle velocity [5]. The transverse velocity of the
outer particles inside the QQ reaches 20% of the
longitudinal one. Even beam dynamics simulations in
linear external magnetic field show a significant
deformation of the 6D phase volume (Fig.3).
A lower beam convergence at the RFQ entrance
should lead to easier beam matching, lower beam
emittance perturbation and smaller particle losses in the
quadrupole channel. Varying apertures (i.e. focusing
strength) along the IRM change matched beam
parameters at the RFQ entrance.
Fig.3. Vertical beam emittances before (left) and after
(right) magnetic quadrupoles (linear magnetic field, no
space charge effects, "open" apertures)
5. NEW IRM DESIGN
Originally the length of the electrodes with changing
aperture was only 3 cells (3 βλ/2). The following
10 cells were designed with small modulation
(amplitude less than 5 μm) not influencing the
longitudinal particle motion. The aperture along the new
increased IRM (13 cells) follows the special law to
provide for improved beam matching (Fig.4); not in
accordance with the classical model.
Fig.4. Apertures along IRM for original (1999) and for
new (2004) design. Z=0 corresponds to the tank flange.
Dashed line represents the RFQ axis
Several variants of the IRM design were considered
and investigated with different codes: DYNAMION,
TRACE-3D, DRAMA [7], and ABC [8]. In the original
design width and rounding of the electrodes were
constant in the original design. In the new design these
parameters were changed in accordance with the
aperture [4]. Correspondent modifications were
introduced into DYNAMION field calculations.
Matched Twiss-parameters for the 15 emA U4+ beam at
the beginning of the regular part of the RFQ were
obtained by the code ABC. The aperture in the IRM was
defined in accordance with the required electrical
rigidity along the channel. Beam Twiss-parameters were
transformed back to the RFQ entrance by means of the
code DRAMA including the distance from electrodes to
the flange.
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PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.64-66.
64
Fig.5. Beam envelopes and emittances in the LEBT for
original (1999) and for new (2004) IRM design
Starting at the position of emittance measurement
device the beam was matched to the RFQ entrance with
four quadrupole lenses, optimized with TRACE-3D
code (Fig.5). Finally, the particle motion in the whole
front-end system was simulated with the DYNAMION
code. For the final design a 15% higher transmission
was predicted by calculations for the 15 emA U4+ beam.
6. EXPERIMENTAL RESULTS
After recommissioning of the RFQ, measurements
for a high current argon beam (16 emA) and a low
current uranium beam (< 0.5 emA) had been carried out.
A high current uranium beam was not available at that
time.
For the U4+ beam 100% transmission was reached
for the first time since commissioning in 1999. Before
the upgrade the transmission was up to 85%.
On Fig. 6 the Ar1+ transmission before and after the
upgrade is presented as a function of the intervane
voltage. As shown, the calculated gain of up to 15% is
verified.
Fig.6. Measured transmission for a high current argon
beam before and after the upgrade of the RFQ
CONCLUSION AND OUTLOOK
The main goal of the RFQ upgrade has been
achieved: the measured rf power for the acceleration of
the 180Ta3+ beam decreased from 650 to 380 kW. A
detailed computer study for the improvement of the
beam dynamics in the HSI front-end system was done
by means of the DYNAMION code. Small changes of
the aperture in the beginning of the RFQ electrodes had
been proposed, investigated and realized. Experiments
with high current beam verified the calculated gain of
up to 15% in transmission and in brilliance.
Nevertheless the existing front-end system can not
provide the beam current of 18 emA for the FAIR
requirements. Recently the design of a compact LEBT
and new RFQ is under investigation.
REFERENCES
1. W. Henning. An International Accelerator Facility
for Research with Ions and Antiprotons. Proc. of the
EPAC-04, Luzerne. 2004, p.50-53.
2. W. Barth et al. Development of the UNILAC
Towards a Megawatt Beam Injector. Proc. of the
LINAC-04, Luebeck. 2004, p.246-250.
3. W. Barth. Commissioning of the 1.4 MeV/u High
Current Heavy Ion Linac at GSI. Proc. of the
LINAC-2000, Monterey. 2000, p.1033-1035.
4. S. Minaev et al. Matching of the capacity
distribution for the new HSI-RFQ electrodes by
individual copper plating: Preprint IAP Nr: IAP-
ACC-080604, Frankfurt, 2004.
5. A. Kolomiets et al. DYNAMION - The Code for
Beam Dynamics Simulation in High Current Ion
Linac. Proc. of the EPAC-98, Stockholm. 1998,
p.1201-1203.
6. J. Klabunde et al. Beam Dynamics Simulations for
the GSI High Current Injector with the New
Versatile Computer Code DYNAMION. Proc. of the
PAC-2001, Chicago. 2001, p.2899-3001.
7. I.A. Vorobyov. Program ABC. Programs for
calculation and simulation in accelerator
techniques. Information fond of algorithms and
programs on accelerator beam. Moscow, 1992,
p.159.
8. A.I. Balabin. Numerical field calculation in RFQ
structure with special shape of electrodes: Preprint
ITEP Nr: 107, Moscow, 1981.
МОДЕРНИЗАЦИЯ СИЛЬНОТОЧНОЙ НАЧАЛЬНОЙ ЧАСТИ
УСКОРИТЕЛЯ ТЯЖЕЛЫХ ИОНОВ UNILAC, GSI
С. Ярамышев, В. Барт, Л. Дагл, А. Коломиец
Для проекта FAIR после сильноточного RFQ нужен ток пучка U4+ больше 18 emA. Измеренная интенсив-
ность была в два раза меньше. В начальной части динамика пучка моделировалась по программе
DYNAMION. Были изготовлены новые RFQ электроды с улучшенным качеством поверхности и реконстру-
ирована согласующая секция. Эксперименты с пучком после модернизации RFQ подтвердили расчетное
увеличение тока пучка.
МОДЕРНИЗАЦІЯ СИЛЬНОТОЧНОЇ НАЧАЛЬНОЇ ЧАСТИНИ ПРИСКОРЮВАЧА ВАЖКИХ ІОНІВ
UNILAC, GSI
С. Ярамишев, В. Барт, Л. Дагл, А. Коломієць
56
Для проекту FAIR після сильнострумового RFQ потрібний струм пучка U4+ більше 18 emA. В той же чаc
інтенсивність пучка до реконструкції структури RFQ була в два рази менше. В початковій частині динаміка
пучка моделювалась за допомогою програми DYNAMION. Виготовлені нові RFQ електроди, що мають
підвищену якість поверхні, і реконструйована узгоджуюча секція. Експерименти з пучком після
модернізації RFQ підтвердили розраховане збільшення струму пучка.
___________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.64-66.
64
1. INTRODUCTION
2. BEAM MATCHING TO THE RFQ
3. BEAM DYNAMICS
3.1. MULTIPARTICLE CODE DYNAMION
3.2. HSI PERFORMANCE BEFORE UPGRADE
4. STUDY OF UPGRADE MEASURES
5. NEW IRM DESIGN
6. ExPERIMENTAL RESULTS
CONCLUSION and outlook
REFERENCES
|