A Denker

B Martin

H Homeyer

J Röhrich

P Arndt

W Bohne

W Busse

W Pelzer

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ECR-Source and
5.5 MV 
Van-de-Graaff
Injector
14.5 GHz
ECR-Source
on a 200 kV
Platform
RFQ
90-360 keV/u
Eye-Tumour-Therapy
14 GHz
ECR-Source
Vertical-Beam Line
k=130
Cyclotron
Low-Energy
Target Area and
Dual-Beam Line
Magnetic
Spectrometer
Extremely
Slow Ions
 
Figure 1 : Layout of the facility 
STATUS OF ISL  
 
H. Homeyer, P. Arndt, W. Bohne, W. Busse, A. Denker, B. Martin*, W. Pelzer, J. Röhrich 
Ionenstrahllabor ISL, Hahn-Meitner-Institut Berlin, 
Glienicker Str. 100, 14109 Berlin, Germany  
 
Abstract 
During the last couple of years the scientific activities at 
the former VICKSI [1] facility have been switched to 
applications of ion beam techniques in medicine, 
modification of materials, and materials analyses. The 
nuclear physics programmes were no longer supported. 
With the new activities, the requirements on the 
accelerator specifications, beam guiding systems, and 
target areas have changed as well. The facility got the new 
name ISL1 (Ionen-Strahl-Labor). Within a period of 6 
years the facility has been rearranged. Major projects in 
this reorientation process were the installation of a new 
RFQ accelerator operating as injector for the cyclotron 
and the installation of a medical beam line to treat ocular 
melanoma with fast protons. 
1  INTRODUCTION 
Besides the limits set by the cyclotron specifications, 
the characteristics of the facility in terms of ion species 
and ion energies are determined by the ion sources and the 
injectors. With the development of powerful ECR ion 
sources, the original VICKSI concept of a high energy 
injector and a stripper before injection into the cyclotron  
became partly obsolete. In particular, this concept did not 
allow the production of very heavy ions and higher 
currents, two strong demands arising from the anticipated 
scientific programme. Stripping efficiencies for the 
necessary charge states become extremely low, and foil 
stripper live times decrease drastically with higher beam 
currents and heavier ions. To achieve the new goal - 
higher currents and heavier ion masses - a new injector 
has been installed. In addition, several measures were 
taken to improve the reliability and short as well as long 
term stability of the facility 
 
2  NEW ACCELERATOR EQUIPMENT 
The layout of the facility is shown in fig. 1. Two 
injectors, a 5.5 MV Van de Graaff and a RFQ, can 
alternatively inject their beams into a separated sector 
cyclotron. The first injector needs a stripper between both 
accelerators. Three low energy target areas can be 
supplied with van de Graaff beams. High energy beams 
are available at 12 stations. A so-called dual beam line 
                                                           
1 http://www.hmi.de/isl/ * diseased 4. April 2000 
allows irradiations of samples with both low and high 
energy beams simultaneously or consecutively. A special 
room is dedicated to eye tumour radiotherapy with fast 
protons. 
2.1   Van de Graaff Injector  
A first important step in the accelerator upgrade 
programme was the installation of new ion source 
operating on the high voltage terminal of the 5.5 MV Van 
de Graaff injector. It is a 5 GHz ECR ion source [2], fully 
equipped with permanent magnets operating at moderate 
RF power (100 Watts). After some improvements  of the 
ion source extraction system and the fast high voltage 
regulation system [3] this injector produces a very stable 
ion beam. 
2.2  RFQ Injector 
To reach final energies of 1.5 to 6 MeV/n after the 
cyclotron, ion charge to mass ratios between 1/8 and 1/5 
are necessary. These values can be achieved by powerful 
ECR ion sources for almost all ions. Possible accelerators 
acting as injectors for the ISL cyclotron are either a small 
compact injector cyclotron or a RFQ structure. After 
considering both solutions in detail [4,5] the RFQ option 
was chosen. In collaboration with A. Schempp a RFQ 
design [5] fulfilling the demands of continuous mode 
operation and the necessary energy variation has been 
developed. Basic features of this design are: i.) a relatively 
high injection energy, ii) a separate bunching system with 
CP600, Cyclotrons and Their Applications 2001, Sixteenth International Conference, edited by F. Marti
© 2001 American Institute of Physics 0-7354-0044-X/01/$18.00
105
RFQ Cyclotron
N
O
Beam Line from
Van de Graaff
Chopper
RFQ
Buncher
 
 
Figure 3: Beam transport from the RFQ to the 
Cyclotron 
The upper part shows the beam envelope and the 
time evolution of the beam pulses. The total path 
length from the RFQ to the cyclotron is about 20 m.
the cyclotron frequency in front of the RFQ and iii.) 
frequency variability and 2-stage operation of the RFQ 
allowing a total energy variation of a factor of 4. The 
layout of the RFQ injection system is shown in figure 2. 
The RFQ is described in detail in ref. [6] and [7]. It was 
manufactured by the German company NTG (Neue 
Technologien) under the supervision of the Frankfurt 
Group [8] and was delivered to HMI by the end of 97. 
After an installation period of 5 months, the first beam 
was accelerated in May 98, two hours after the power had 
been switched on. This confirmed the basic correctness of 
the design and the construction of the electrodes 
immediately. In fall 1998, the first beam was injected into 
the cyclotron. The first tests disclosed the basic tuning 
problems connected with the existing design. The 
injection of the RFQ beam into the cyclotron imposes 
severe constraints on the energy stability of the beam from 
the platform, the phase relation between the buncher and 
the RFQ, and the phase relation of the two RFQ stages 
with respect to each other. Small deviations in phase 
influence both the energy and the rotation of the phase 
ellipse at the exit of the RFQ. The long flight path from 
the RFQ to the cyclotron (shown in detail in fig. 3) 
amounts to more than 100000 in cyclotron RF-phase. 
Thus, small changes in energy at the exit of the RFQ lead 
to considerable phase shifts of the beam pulses arriving at 
the first acceleration gap of the cyclotron. 
In a series of detailed measurements properties of 
accelerated and transported beams have been investigated 
[9]. An example of energy shifts depending on the RFQ1-
RFQ2 phase relation is shown in figure 4. With 
comparable transmissions (see insert in fig.4) completely 
different energy distributions are observed. It is obvious 
that both phase settings require a different tuning of the 
beam guiding elements in the injection path from the RFQ 
to the cyclotron. The strong interdependence of the 
longitudinal and transversal phase space impedes a fast 
tuning. To overcome the problems a very careful and 
accurate calibration of all parameters is necessary. This 
work is currently under way. Total beam transmissions 
from the ion source to the target of 15 to 20% are usual 
though tuning times are sometimes rather long. The 
maximum transmission observed so far was 30%. These 
numbers include the 50% bunching efficiency of the 
bunchers in front of the RFQ. With these transmission 
values the system provides an excellent injector solution 
for the cyclotron, in particular for very heavy ion beams. 
3 SCIENTIFIC PROGRAMME 
Ion beams at ISL are more or less exclusively used for 
ion beam applications in different fields of research and 
technology. The major active fields are medical 
applications (~15%), modification of materials (~35%), 
and materials analyses (~25%). More than 60% of the 
beam time is given to outside users. 
 
200 kV Platform 
14 GHz ECR Source 
To the
Cyclotron
RFQ1 RFQ2Buncher
 
Figure 2 : RFQ injection. 
Ions from the ECR source are preaccelerated, bunched
and injected into the RFQ. The beam envelopes are
shown at the left-hand side and at the lower part of the
figure. 
3.1  Medical applications  
In cooperation with the medical partners from the 
university hospitals of the Freie Universität Berlin and the 
Universität Essen radiotherapy with fast protons is applied 
to ocular melanomas. Starting in July 1998 [10] 200 
patients have been treated up to now. In addition to 
routine therapy, research and development aiming at 
improvements of treatment planning is performed.  
3.2  Materials Analyses  
The materials analyses activities involve both the 
heaviest and the fastest ions available. At high energy 
ERDA (elastic recoil detection analysis) heavy ions with 
energies up to 2 MeV/n are utilised [11] to analyse the 
composition profile of thin layers. With fast protons 
(68MeV) employing high energy PIXE (Proton induced 
X-ray emission) [12] heavy elements in or hidden 
underneath thick layers are determined.  
3.3  Modification of materials  
Effects of the high energy deposition involved with the 
heavy ion impact such as strong electronic excitations [13] 
and the subsequent modification of the solid state 
structure [14] are studied to uncover the track formation 
process. The irradiation of polymer foils for microfilter 
production is the strongest field of direct applications. 
4  OPERATIONS 
The accelerators operate 18 to 19 days per month with 
three major shutdowns in spring, summer, and fall. Until 
1998 increased shutdown periods were necessary for the 
renewal of the infrastructure and the installation of the 
RFQ. For the proton therapy 10 five-day periods per year 
are foreseen. Details of the operation statistics are 
displayed in figure 5. 
5  FUTURE PLANS  
Ion source development is the major issue for the near 
future. This involves a new 10 GHz ECR source on the 
Van de Graaff terminal and a second platform with 14.5 
GHz ECR source for the RFQ injector. 
For the study of modifications of materials two new target 
areas are foreseen, one of them allowing in-situ X-ray 
diffraction analysis of irradiation induced structural 
modifications.  
REFERENCES 
[1] W. Busse. B. Martin, R. Michaelsen.,W. Pelzer, 
K.Ziegler, Proceedings of the EPAC 88, Rome 7.-11. 
6 1988, Editor: S. Tazzari, World Scientific 
Publishing, 1988, pp. 448-450 
[2] P. Arndt, N. Golovanivski,, H. Homeyer, B. Martin, 
Nucl. Instr. & Meth B 89, 1994, pp. 14-16 
[3] P. Arndt et al., Nucl. Instr. & Meth., A268, 1988, 
pp.442-444 
[4] W. Pelzer, Proc. 13th. Int. Conf. Cycl. 1992, 
Vancouver, World Scientific Publishing 1993, 
Editors: G. Dutto and M. K. Craddock, 519-522 
[5] W. Pelzer, A. Schempp, Nuc. Instr. &Meth. A 346, 
1994, 24-30. 
[6] O. Engels, J. Häuser, F. Marhauser, W. Pelzer, A. 
Schempp, Nucl. Inst. & Meth. B113, 1996, 16-20 
[7] A. Schempp, Invited paper to this Conference 
[8] O. Engels, PhD. Thesis, University of Frankfurt/M, 
1998 
[9] F. Höllering, Diploma Thesis, University of 
Frankfurt/M, 1999 
[10] H. Fuchs et al., Annual Report Bereich 
Festkörperphysik, 65-70, ISBN1437-1464  
[11] W. Bohne, J. Röhrich, and G. Röschert, ., Nucl. Instr. 
&Meth B 136-138, 1998, pp. 633-637 
[12] A. Denker, K. H. Maier, Nucl. Instr. & Meth. B150  
[13] G. Schiwietz et al., Nucl. Instr. & Meth. B146, 1998, 
131-136 
[14]A. Benyagoub,  S.Klaumünzer, and M. Toulemonde, 
Nucl. Instr. & Meth. B146, 1998, 44 
0.24 0.25 0.26
0
25
50
75
100
-180 -120 -60 0 60 120 180
0
25
50
75
100
 
 
 Measurement
 SimulationTr
an
sm
iss
io
n 
%
Phase RFQ2 [°]
 RFQ2 -600
 RFQ2 -800
Io
n 
C
ur
re
nt
Magnet Current
 Figure 4: Selected energy spectra for different 
phases of RFQ2 
1995 1996 1997 1998 1999 2000
0
1000
2000
3000
4000
5000
 
ISL Operations
H
ou
rs
 Break Downs
 Total Tuning
 Beam Tests
 Beam on Target
 
Figure: 5 ISL Operations 
An average of 3000 h/year of beam time on target has 
been delivered during the last six years. The increase 
of beam time after 98 reflects the .start of the RFQ 
operation. 


Status of ISL

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