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GSI-ACCELERATORS-16 GSI SCIENTIFIC REPORT 2009
Transversal Beam Dynamics Calculations for HITRAP ∗
J. Pfister † 1,2 , G. Clemente 2 , F. Herfurth 2 , O. Kester 3 , and U. Ratzinger 1
1 IAP, University of Frankfurt, Germany; 2 GSI, Darmstadt, Germany; 3 NSCL, East Lansing, MI 48824, USA
Until 2008 several transversal and longitudinal beam dynamics
simulation codes have been used for the calculation
of the transversal beam behavior in the HITRAP decelerator
and its connected beamlines. Since simulations
are an essential support during commissioning, the aim of
this project was to be able to simulate at least the complete
beam from the exit of the ESR through different optical elements
including the transversal effect of the Double-drift
buncher as well as the first deceleration stage (IH-structure)
shown in fig. 1 using only one code. This should result in
a fast code for transversal optimization down to the RFQ,
which can be used online during commissioning.
Elements taken into account are two big dipoles and
ESR
diaphragm
IH
RFQ
beam
Figure 1: Schematic of transversal optical elements:
dipoles (green), quadrupoles (red,blue), buncher (circles)
and IH-cavity (square).
a strong quadrupole doublet already used in the old reinjection
line. Furthermore new quadrupole triplets and
doublets as well as the double-drift buncher and the IHstructure
were installed in the linear deceleration beamline.
The problem has been approached using the COSY Infinity
software [1]. Algorithms for transversal influence of
an acceleration gap have been developed and extensively
tested and compared with LORASR calculations. A matrix
routine together with the knowledge of accelerating
fields and phase relations in each gap of bunchers and IHstructure
has been implemented.
Since the complete transversal beam dynamics can be
calculated within this code without interchanging data to
other codes an easy-to-use simulation tool including the deceleration
from 4 MeV/u down to 500 keV/u and injection
into the RFQ was achieved. It can be used for optimization
of the transversal beam properties.
An essential, but also critical part in the beamline is a
diaphragm (see fig. 1, length 150 mm with inner diameter
12 mm) inserted during and is staying there since the
first beamtime in May 2007 in between the ESR extraction
beamline and the HITRAP linear decelerator for vacuum
decoupling. This was not foreseen in the TDR [2] and
makes beam transport more difficult.
Studies which were carried out in 2009 show that
this makes an efficient transversal focusing into the IHstructure
impossible and then causes beam losses in the in-
144
∗ Founded by BMBF06FY160I and HITRAP-IH-Struktur
† j.pfister@gsi.de
tertank section resp. at RFQ injection due to too big RF
defocusing in the IH. At least 25% of the particles will be
lost with the presently possible magnet gradients. Fig. 2(a)
shows best possible beam transport from the IH to the RFQ
using the current intertank setup including the permanently
installed diaphragm in front of the first buncher. Phase
space distributions and acceptance of the RFQ are compared
in figs. 2(b) and (c).
Simulated beam transport from the ESR to the IH has
qudrupole rebuncher qudrupole
doublet 4 doublet 5
IH RFQ
15mm
(a) intertank beam transport
(b) horizontal phase space (c) vertical phase space
Figure 2: (a) Beam transport from IH to RFQ and injection
with diaphragm and current setup, (b) and (c) Best possible
phase space distributions and RFQ acceptance.
been experimentally proven. It shows discrepancies of only
up to a few percent, which is caused by the measurement
error of the beam diameter.
This problem could be solved by an adjusted intertank
section. If the two doublets could be pulsed to higher gradients
no physical adjustement would be necessary reaching
a transversal transmission of ≈ 98%. The corresponding
phase space is also shown in fig. 2 and compared to the
RFQ acceptance.
References
[1] K. Makino and M. Berz, “COSY INFINITY version 8”, Nucl.
Instrum. Methods A 427 (1999) 338-343.
[2] T. Beier, L. Dahl, H.-J. Kluge, C. Kozhuharov und W. Quint,
“HITRAP Technical Design Report”, Gesellschaft für Schwerionenforschung
mbH, Darmstadt (2003).