Linac2 - 50th anniversary of the CERN Proton Synchrotron

eam, so far the highest intensity reached by an operational RFQ. Longitudinal matching to the
Alvarez DTL is performed by two bunching cavities. Fig. 3 shows the RFQ as installed in front of the
Linac2 tanks.
Fig. 3: RFQ2 and Linac2 tanks.
During the first years after installation, the RFQ was operated at voltages slightly below
nominal in order to limit RF breakdowns to levels compatible with the reliability required for the
CERN injector. This in turn limited the beam current from the RFQ to values around 180 mA. The
progressive upgrade and cleaning of the vacuum system allowed reaching the design voltage a few
years after installation, with the RFQ delivering beam currents in excess of 200 mA, which correspond
to currents in excess of 180 mA at the exit of the linac.
Other improvements to Linac2 after construction were mainly aimed at keeping the required
reliability and to adapt to the evolving technologies. These included the commissioning of a new
control system in 1993, the installation of new low-power solid state amplifiers and the replacement of
the interlocks and of the electronics of the high-power amplifiers on the RF systems.
4 Conclusions
It was the rapid progress in linac technology that made possible the replacement of Linac1 after 20
years of operation with the new Linac2, providing a factor 2 increase in both current and pulse length,
with the additional advantages of increased reliability and reduced maintenance.
In the same way Linac2 has been now operating smoothly and reliably for more than 30 years,
but now shows similar limitations to those that led to the replacement of Linac1. On one hand, the
exploration of possible options for an LHC luminosity upgrade indicates that the first bottleneck for
achieving a higher intensity in the PS complex is the PSB injection, where the space charge tune shift
at 50 MeV energy limits the total intensity. The only way to go beyond this limitation is by increasing
the linac energy, which in turns requires the construction of a new linac, an appreciable energy
increase of Linac2 being prevented by the lack of space at the end of the linac. On the other hand, over
the last years Linac2 has developed serious vacuum problems due to its now “old-fashioned”
construction technology, which constitute a serious threat for operation. Moreover, procurements of
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