IMPROVING BEAM SET-UP USING AN ONLINE BEAM OPTICS TOOL
S. Richter, W. Barth, B. Franczak, U. Scheeler, D. Wilms, GSI, Darmstadt, Germany

Fig. 1: Layout of the existing accelerator facility at GSI. The universal linear accelerator Unilac, the heavy ion
synchrotron SIS and the Experimental Storage Ring ESR. The Unilac delivers from three sources heavy ion beams withenergies of up to 13 MeV/u, the SIS accelerates ion beams to up to 2 GeV/u.

Abstract
The GSI accelerator facility [1] consists of theUniversal Linear Accelerator (Unilac), the heavy ionsynchrotron SIS, and the Experimental Storage Ring
(ESR). Two Unilac injectors with three ion source
terminals provide ion species from the lightest such ashydrogen up to uranium. The High Current Injector (HSI)
for low charge state ion beams provides mostly highintense but short pulses, whereas the High Charge State
Injector (HLI) supplies long pulses with a high duty factorof up to 27%. Before entering the Alvarez section of theUnilac the ion beam from the HSI is stripped in asupersonic gas jet.
Up to three different ion species can be accelerated forup to five experiments in a time -sharing mode. Frequentchanges of beam energy and intensity during a single
beam time period may result in time consuming set-up
and tuning especially of the beam transport lines. To
shorten these changeover times an online optics tool(MIRKO EXPERT) had been developed. Based on online
emittance measurements at well-defined locations thebeam envelopes are calculated using the actual magnet
settings. With this input improved calculated magnet
settings can be directly sent to the magnet power supplies.
The program reads profile grid measurements, such that
an automized beam alignment is established and thatsteering times are minimized. Experiences on this tool
will be reported. At the Unilac a special focus is put onhigh current operation with short but intense beam pulses.
Limitations
likemissing
non-destructive beamdiagnostics, insufficient longitudinal beam matching, andinfluence of the hard edged model for magnetic fields will
be discussed. Special attention will be put on the limits
due to high current effects with bunched beams.

1 GSI ACCELERATOR COMPLEXThe GSI accelerator facility (shown in Fig. 1) consistsof the Unilac (Universal linear accelerator), the Heavy Ion
Synchrotron SIS, the Experimental Storage Ring ESR,and various experimental set-ups for low energy
experiments in the experimental hall (4 – 13 MeV/u) andin the High Energy Physics Area (100-2000 MeV/u).

The Unilac accelerates the full range of ion species
from hydrogen up to uranium. With three ion source
terminals (PIG , and high current operation sources
MEVVA and MUCIS at the High Current Injector HSI,
and the ECR ion source at the High Charge State Injector
HLI) a three beam operation is accomplished. The threeion beams are further accelerated to individual energies in
the Alvarez section in a pulse-switched mode, either forinjection into the SIS, or for low energy experiments
downstream from the Unilac. This mu lti-beam operationis shown exemplarily in Fig. 2. The administration of thedifferent ion beams is done in so called virtual
accelerators (up to 14 at Unilac and 14 at SIS). These
accelerators are treated by the control system asindependent accelerators.

elements. Space charge effects can be simulated by theintroduction of thin lenses which have a defocusing
effect.
Alternatively the user can switch between the ellipse
transformation notation and single particle tracing
calculations. Up to six parameters of the optical system
can be defined as variables to meet fitting constraints.
The input parameters are the beam-line (the opticssystem), and the characteristics of the ion beam, such as
mass number, charge, beam energy and emittance.
Additionally to the output of beam parameters at any
desired position in the beam transport system, MIRKO
also delivers graphical output. The beam envelopes in thetransverse or longitudinal plane can be displayed as wellas the phase space ellipse or the acceptance of the system.
To simulate the behavior of a particle distribution througha non-linear system, different particle distributions can begenerated and transported through the system in the single
particle mode.

3 MIRKO EXPERTFig. 2: Multi beam operation at the Unilac. On the left
side the pulse structure of the MEVVA and the PIG ion
source are indicated, running for the prestripper linac,
showing different repetition frequencies and duty cycles.
The ECR ion source is operated with a third ion species,
carbon, which is also operated with high duty cycle. The
different beams are switched into the Unilac experimental
hall and into the SIS injection line following the requestsof the experiments.

With frequent changes of ion species and energy –sometimes several times a week – the beam-line set-up
and tuning is elaborate (not possible) without a qualified
operating tool assisting these tasks. Since the design andtuning of a beam–line comprise many features incommon, the transition and development from MIRKO asa standalone design tool towards an operating tool MIRKO EXPERT - was the consequent step (Fig. 3).

The SIS further accelerates the ions provided by theUnilac with an energy of 11.4 MeV/u up to 2 GeV/u. It
can be operated at maximum magnetic bending power upof to 18 Tm with a ramp rate of 1,3 T/s. The beam caneither be extracted fast or slow from pulse to pulse. Likeat the Unilac, the energy, intensity and ion species canalso be changed from pulse to pulse.

2 MIRKO -- INTRODUCTION
At GSI the program MIRKO [3] was developed
originally to support beam-line-design and the analysis of
1. order beam-dynamics. The following key-features are
implemented:•Various beam transport elements•
Multipole approximation through thin lenses•
Misalignments•
Arbitrary matrices
The code is based on the matrix formalism (6x6matrices) to describe the beam as well as the opticalFig. 3: Screenshot of MIRKO EXPERT. The selection of
the accelerator (Unilac or SIS), the virtual accelerator
number and the beam-line part is needed to start withMIRKO EXPERT. A graphical output window starts up,
where the beam-line together with the transverse beamenvelope is displayed.
This tool is integrated into the control system of theGSI accelerator complex. The operators can access
MIRKO EXPERT out of their console environment.
When it starts the operation mode is default. There is no3.2 Scope of MIRKO EXPERT
To assist the operators in beam-line set-up and tuning,
MIRKO EXPERT is used in beam transport lines such as
the transport lines into the experimental hall, the Transfer
Channel to the SIS and the high energy transport lines.
It gives support to tune the beam-lines and to achievecertain conditions at well defined positions (e.g. focus ontarget). In the Unilac accelerating sections semi-empiricalsettings are used for the periodic focusing in the rf tanks,since MIRKO EXPERT does not yet cover sufficiently
the various accelerating elements in a linac. To tune thesynchrotron, MIRKO (as beam optics tool) is
implemented in the optics model for the data supply, sothat there is no need to use MIRKO EXPERT for thattask.
UnilacThe use of MIRKO EXPERT at the Unilac is limited tobeam transport sections in the experimental hall and theTransfer Channel. As input for the calculations theinformation about the emittance size and orientation isneeded. This data is obtained either by emittancemeasurements with slit-grid devices or by themeasurement of at least three profile grids.
One beam-line in the experimental hall is equippedwith octupoles [4] which require a careful preparation of
the beam to show the desired effect. MIRKO EXPERT is
essential to set-up this beam-line. In the Transfer Channel
beam-line MIRKO EXPERT supports the use ofcollimators to cut off the emittance to adjust the beam for
SIS injection.

3.3 Beam Alignment
Beam alignment is a typical example for the applicationof MIRKO EXPERT. The following figure displays in asequence the different steps, the operator has to performin order to align the beam as best as possible.
100.

axyx y xx y

Quadrupoles

Quadrupoles

Quadrupoles-x[mm].. +x[mm]MIRKO EXPERT has access to different componentsof the controls. When a virtual accelerator is selected, theprogram has read access to the database that administrates
the different virtual accelerators and gets the information
about the ion species, charge state, energy and source andrespectively target of the beam. To get the missing beamline data from the actual setting, the values of the magnet
settings are read out. To set the changed values resulting
from calculation, MIRKO EXPERT also has write accessto any magnet in the selected beam-line. The translation
between the physical values – focusing values (focalvalues) – and the manipulated variables which a power
supply can process is supported by function calls thecontrol system supplies. Additionally, read access toprofile grid measurements is granted. Implemented asconsole program, no authorization mechanisms areincluded.

-100.

b-x[mm].. +x[mm]3.1 Integration into the Control System

High Energy Beam-Lines
The assistance of MIRKO EXPERT in the High Energy
Beam-Lines is widely used by operators and by theexperimentalists. The assumption that the orientation ofthe phase space ellipse is well known after SIS extraction
is used to deduce standard input parameters forcalculations. The emittance size is not measured directly,
since the information obtained about the beam size (readout from profile -grids) is sufficient to have an adequate
description of the beam in MIRKO EXPERT being very
close to the actual beam size in the machine.

ProfileGrid

ProfileGrid100.

c-x[mm].. +x[mm]command line interface present. All required input
parameters are accessible via mouse clicks. To make useof the full complexity of MIRKO EXPERT an expert
mode with an additional command line interface isaccessible. MIRKO EXPERT can be used to tune any ofthe virtual accelerators independently.

Steering
Magnet-100.
0.

Steering
MagnetPath lenght [mm]60142.

Fig. 4: Screenshots taken during the beam alignmentprocedure. Only the graphical output for the horizontal
beam envelope is shown. See text for explanation.
Part (a) shows the result of the envelope determination
with actual magnet settings. No information about
eventual misalignment is included yet. Measurementswith profile grids provide the information about themisalignment. Then MIRKO EXPERT calculates theactual beam envelopes and beam steering (b). An
automized beam alignment can be used now. A

predefined correlation between profile grids and steering
magnets is used to calculate the steering magnet settings
and to align the beam. An example of this correlation isshown in the following figure.

Fig. 5: Screenshot of the beam alignment window.
The underlying basic calculation algorithm is thesolution of two differential equations. The matrix
elements from the beginning of the system to the firstresp. second profile grid are known. With the information
about the misalignment a backward calculation isperformed.

X1 = A1x0 + B1 x0`
X 2 = A2 x0 + B2 x´0
After that automatic procedure of which the result isshown in part (c) of Fig. 4, the beam is aligned.
Sometimes this procedure must be repeated once or twice.
This is due to the inaccuracy of the profile gridmeasurements. If the beam is far off axis the beam centercan not be determined with adequate accuracy. This
uncertainty can be due to the fact that the beam may bewider than the profile grid or the calculation of the centerof mass is inaccurate because the wire distance of theouter wires is larger. The measurement gets more accurate
if the beam is near the axis.

4 LIMITATIONS OF MIRKO EXPERTThis paragraph focuses on the limitations of MIRKO
EXPERT in daily operation and in the high current
operation for the future project.

4.1 Operation at the Unilac
As the transverse emittance size and - orientation ofUNILAC beams cannot be treated as a constant as after
SIS extraction, a measurement must precede all
calculations. These measurements are beam destructive,that do not just disturb one beam in one virtual accelerator
but also the beam in all other virtual accelerators. For amachine that is characterized by its high grade of parallel
operation, this condition should be avoided.
Since emittance growth is not covered in MIRKO, itsuse is limited to support the beam matching between thepre- and the poststripper section. The HSI operates with afrequency of 36 MHz whereas the Alvarez with 108
MHz. This source of emittance growth due to bunch
compression cannot be handled adequately for the time
being. As a partly solution to that problem an insert of amatrix that blows up the emittance by a fixed factor could
be seen as a workaround.

4.2 High intensity operation at the Unilac
The Unilac was not originally designed as an injector
for a synchrotron, filling the SIS up to the space charge
limit even for the highest mass numbers. The HSI
commissioned in 1999 was designed to provide anintensity increase by 2.5 orders of magnitude. Table 1
summarizes the design parameters for high intense
uranium operation [5].
With the introduction of high current operation, the way
and the means how to operate and to handle those beams
had to be modified compared to the operation with low
and medium intense beams. Beam destructive diagnostics
cannot be used under these conditions. With the immense
power that is stored in the beam, the diagnostics elements
could be destroyed within a macro pulse of 150 µs withfull intensity. To avoid destruction, the pulse is shortened.
Providing incomplete information about the beam being
not representative for the whole beam.
Table 1: Specified beam parameters at UNILAC and SIS
injection, exemplary for a uranium beam.
HSI
entrance
238 4+
Ion species
U
El. Current [mA]
16.5
Part. per 100µs pulse 2.6⋅1012
Energy [MeV/u]
0.0022∆W/W
0.3
εn,x [mm mrad]
0.3εn,y [mm mrad]

HSIexit238 4+
U
152.3⋅1012
1.4±4⋅10 -3
0.5
0.5

Alvarezentrance
238 28+U
12.5
2.8⋅1011
1.4±2⋅10 -3
0.75
0.75

SISinjection
238 73+U
4.6
4.2⋅1010
11.4±2⋅10 -30.8
2.5

Additionally the handling of space charge effects is notconsidered as adequate any more, the assumption of
faultless magnetic fields must be dropped. If theenvisaged high intensities are reached, the physics model
behind MIRKO with its linear space charge model has tobe revised in order to provide the required accuracy toserve as an online tool or if multi-particle tracking codes
have to be used instead.

5 CONCLUSION AND OUTLOOKMIRKO EXPERT has proven to be a valuable tool forbeam-line set-up and tuning in many transport sections ofthe GSI accelerator facility. This time consuming task
was reduced significantly employing the code. For thestandard high current operation envisaged for the future
project, the use of MIRKO EXPERT has to be revised.
The use of a complementary multi-particle code must beconsidered. If such a tracking program will be developed
as an operations tool or if it will be an offline tuning aid,
must still be discussed.

6 ACKNOWLEDGEMENTS
The authors acknowledge the operations team of theaccelerator complex for the support in developingMIRKO EXPERT as an operations tool and in beam-line
tuning
The authors thank R. Müller for the help preparing thefigures.

7 REFERENCES[1] Conceptual Design Report “An InternationalAccelerator Facility for Beams of Ions and Anitprotons”,
GSI, Darmstadt, Germany, (2001). P. 493-499[2] R. Steiner, C. Riedel, W. Rösch, Realtime Aspects ofPulse-to-Pulse Modulation, Proceedings of theInternational Conference on Accelerator and Large

Experimental Physics Control Systems , Tsukuba, Japan,(1991)[3] B. Franczak, MIRKO – An Interactive Program for
Beam Lines and Synchrotrons, Proceedings of theEurophysics Conference on computing in Accelerator
Design and Operation, Berlin, Germany, (1983)[4] S. Richter, W. Barth, Development and progress in theUnilac High Intensity Upgrade Program, Proceedings ofEPAC2002, Paris, France, (2002)[5] W. Barth, Commissioning of the 1.4 MeV/u Highcurrent Heavy Ion Linac at GSI, LINAC2000, Monterey,
U.S.A., p. 1033 (2000)