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GSI-ACCELERATORS-06 GSI SCIENTIFIC REPORT 2009
SIS18 Status Report
P. Spiller, R. Balss, O. Boine-Frankenheim, U. Blell, Y. El-Hayek, H. Eickhoff, G. Franchetti, P. Hülsmann,
M. Kirk, H. Klingbeil, H.G. König, H. Kollmus, U. Laier, C. Mühle, A. Parfenova, D. Ondreka,
H. Ramakers, H. Reich-Sprenger, M. Schwickert, J. Stadlmann, H. Welker
INTRODUCTION
Beside the main upgrade program dedicated to the acceleration
of low charge state heavy ions for FAIR [1], several measures
have been initiated and completed which improve the
beam performance for the running experimental program. The
machine development program for high intensity operation and
nonlinear dynamics studies has been intensified [2, 3, 4, 5].
TRANSFER OF UNILAC BEAMS
Low energetic (4 MeV/u) Xe-beams from the UNILAC
could be transferred without acceleration through SIS18 to the
ESR. By means of a slightly modified tune, setting of horizontal
steerer magnets and switched-off bumper magnets, the
UNILAC beam could be guided directly from the injection
channel towards the extraction channel to the high energy beam
transport system. SIS18 has only been used as a transport system
and the UNILAC beams could be sent to the ESR [6] for
potential use at the HITRAP experiment.
BEAM LOSS AT MULTITURN INJECTION
Depending on the emittance of the injected UNILAC beam
and the actual settings of the injection devices, beam loss of the
order of typically 30% is unavoidable during the transverse
multi turn injection process. In order to minimize the multi turn
injection losses, the scraper system in section 6 and 7 of the
transfer channel may be used to cut of the tails of the injected
beam. Precondition is an imaging optical system in between the
scrapers and the injection septum, including three turns of revolution.
Such an optical setting could be realized by means of
emittance measurements with an updated MIRKO model of the
beam transport and injection system. In the frame of machine
experiments, it could be demonstrated that the beam intensity
may be maintained in the SIS after cutting 25 % percent of the
total intensity of the injected beam [7].
BEAM OPTICS STUDIES
The development of the Nonlinear Tune Response Matrix
method (NTRM) for the reconstruction of nonlinear field errors
was continued. The first attempts have been performed to reconstruct
the natural sextupolar field components of the ring's
main dipoles. The β-functions of the machine were systematically
measured to determine the tune response of quadrupole
and sextupole magnets [8]. According to the carried out measurements
and simulations, the β-functions may be affected by
the CO induced β-beating. The initial CO distortion in the presence
of sextupoles leads to a β-beating via the feed-down of
quadrupolar components. The uncontrolled β-beating, affects
the nonlinear field error reconstruction and may also affect the
efficiency of the multiturn injection and slow extraction. Therefore,
it is important to correct the CO at the best in order to
keep the β-functions symmetric. The new SISMODI closed
orbit correction software was tested. However, the horizontal
CO correction suffers from missing bipolar power converters.
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GSI Darmstadt, Germany
BUNCH COMPRESSION
The first bunch compressor cavity based on magnetic alloy
ring cores as inductive load has been installed in the SIS18
synchrotron and commissioned with beam [9]. The new cavity
provides a compression voltage of up to 40 kV in Rf pulses
with a length of 500 ns. So far, one of the Fe-loaded acceleration
cavities with a maximum voltage of 14 kV, has been used
for compression for e.g. plasma physics experiments. Although
the implementation of the new cavity in the accelerator control
system was not completed, first compression experiments could
be performed on the injection plateau and at final energy. The
experiments at final energy were partly performed in combination
with one of the Ferrit-loaded acceleration systems.
BUNCH TRIMMING
For a further reduction of the pulse length on the target and
especially for a removal of the leading and following beam
tails, the extraction kicker system may be used. This method is
based on the fact that the acceptance angle of the extraction
channel is a small fraction of the total kick angle. By igniting
the kicker after the leading tail and shortening before the following
tail, only the core of the bunch is extracted. However,
the particles of the tails are dumped and distributed in the synchrotron.
It could be shown, that by means of the extraction
kicker trimming, the core of a compressed bunch may be cut
out and pulse lengths of a few ten nanoseconds may be
achieved on the target (Figure 1). See also [10].
Figure 1: Intensity profiles of extracted single bunches
measured with the fast transformer in TE1, without compression
(long), with compression (medium) and with compression
and extraction kicker trimming (short peaked).
REFERENCES
[1] P. Spiller et al, this annual report
[2, 3, 4, 5] S. Appel, G. Franchetti, S. Sorge, this annual report
[6] J. Stadlmann, internal note,
www.gsi.de/beschleuniger/sis18/einstellung_steuerung.html
[7] Y. El-Hayek, Masterthesis, GSI Master 2009-01 (2010)
[8] A. Parfenova et. al., internal note,
https://www.gsi.de/documents/DOC-2009-Nov-94-1.pdf.
[9] P. Hülsmann et al, Proc. of the EPAC04, Lucerne (2005)
[10] A. Tauschwitz et al, this annual report