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GSI-UPGRADE-ACC-02 GSI SCIENTIFIC REPORT 2009
146
GSITemplate2007
HSI-Frontend Upgrade
W. Barth, L. Dahl, M.-S. Kaiser, A. Kolomiets*, S. Mickat, S. Minaev*, W. Vinzenz, H. Vormann,
S. Yaramyshev
GSI, Darmstadt, Germany; *ITEP, Moscow, Russia.
Overview HSI-Frontend Upgrades
To fulfil the requirements of FAIR (15 emA of U 28+
with min. 70 µs pulse length to be injected into SIS18),
the UNILAC has to be upgraded in several sections: the
LEBT [1], the HSI-RFQ [2], the Alvarez main accelerator
[3], and high current beam diagnostics [4].
Corresponding to the requirements of FAIR, the High
Current Injector HSI has to deliver 18 mA U 4+ at HSI
output. This cannot be achieved with the RFQ and the
LEBT as existing up to 2008. Therefore a three-step upgrade
of this HSI-Frontend is scheduled: The RFQ-
Upgrade has been realized in 2009, the LEBT-upgrade I
(quadrupole quartet and switching magnet) is foreseen for
2010, followed by LEBT-upgrade II with an additional
linear source branch (Compact LEBT), as a part of the
FAIR-UNILAC upgrade.
Figure 1: HSI-Frontend upgrade, including new ion
source terminal and Compact LEBT.
HSI-RFQ Upgrade
In a prior upgrade of the HSI-RFQ (2004), a modified
input radial matching section (IRM) was installed, resulting
in significantly increased high current transmission,
confirmed by simulations [5].
In 2009, the HSI-RFQ has been upgraded again, now
with a completely new beam dynamics design of the new
electrodes [2]. With an enlarged aperture and higher voltage
(155 kV instead of 125 kV at Uranium level, but max.
surface peak field held lower than the old design), the
acceptance is increased. With an improved IRM design
the emittance in the radial matching section is keeping
small.
A constant average aperture, transverse electrode vane
shape and carrier ring dimension along the whole RFQ
was chosen from simulations to meet the resonance frequency
and a flat voltage distribution. After machining
and reassembly of the RFQ, first measurements during the
RF tuning period confirmed the predicted properties. As
expected from the comparison of simulations and measurements
of existing resonator sections, only six fixed
plungers were needed.
Besides mechanical modifications, the power supply
for the RF transmitter has been equipped with bigger capacitors,
to provide for the higher total RF power and for
acceptable reliability. RF conditioning took only four days
to reach the argon level (104 kV, 330 kW), and three more
weeks to reach uranium level (155 kV, 1.2 MW). Conditioning
for uranium level was proceeded for additional six
weeks, until the necessary RF-power decreased
(1.0 MW).
HSI-RFQ New Design Existing Design
Electrode voltage / kV 155 125
Average aperture radius / cm 0.6 0.5245 – 0.7745
Electrode width / cm 0.846 0.9 – 1.08
Maximum field / kV/cm 312.0 318.5
Modulation 1.012 – 1.93 1.00 – 2.09
Synch. Phase, degrees -90 0 - -28 0 -90 0 - -34 0
Minimum aperture radius, cm 0.410 0.381
Number of cells with modulation 394 343
Length of electrodes, cm 921.74 921.74
Table 1: Design parameters of the HSI-RFQ.
Figure 2: New RFQ electrodes, with new IRM.
Electrodes and carrier rings
July 2008
fabrication, assembly
- April 2009
RF tuning (prelim. assembled) May 2009
Re-assembly in beamline June 2009
Beam-commissioning with argon July 2009
Beam-commissioning with uranium,
routine heavy ion high current operation
since September 2009
Table 2: RFQ upgrade schedule.
Beam-commissioning started in July 2009 with Ar 1+ .
For this an emittance measurement device was installed
behind the RFQ. Transmission measurements showed a
gain of 50 % compared to the previous RFQ-design: After