ALICE commissioning
21 Jun 2011
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ALICE Commissioning

 
 

Commissioning of the ALICE accelerator is a project in its own right, and continual optimisation and upgrades to the accelerator's performance is carried out in parallel with other projects.

The most intensive period of ALICE commissioning was the electron source and then the operation of the machine in energy recovery mode, which laid the foundation for all utilisation of the machine for other projects. Initially, the high-voltage DC photogun was commissioned in November 2007 and the beam was fully characterised at the nominal gun voltage of 350kV. Energy recovery was achieved in December 2008.

Commissioning then focussed on optimisation on the machine for other projects including the Compton backscattering project, the THz research programme, injection for the EMMA project, and the infra red free electron laser (IR-FEL).

During commissioning IR-FEL notable developments included the use of an electro-optic bunch profile monitor to confirm that the bunches were being compressed to provide sufficiently high peak charge. A significant modification was also made to the photoinjector laser so that a lower bunch repetition rate with higher bunch charge could be used. This proved to be a key step in achieving lasing in October 2010.  

Later, other improvements were made to the machine including the installation of a new high voltage ceramic insulator on the photogun for higher beam energy; a digital low level control system for the RF; and helium processing of the superconducting RF cavities to improve their performance.   

The initial achievement of energy recovery in 2008 is detailed below.

Energy recovery

In December 2008, a full energy recovery was demonstrated at a beam energy of 21MeV and bunch charges of up to ~20pC. This is illustrated by the LLRF signals (main linac RF power demand) shown below. Higher bunch charges were not attempted at the time because of beam loading effects in the superconductive linac cavities. The beam energy was limited by the field emission in the main linac cavities.

 Power demand LLRF signals without (left) and with (right) energy recovery

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