A discussion on possibilities for timing-based experiments at the MAX IV rings has been initiated by the user community. Several workshops have been held to identify the requirements set by the beamline instrumentation and/or the processes that are to be studied, but also accelerator schemes to be able to serve both high-intensity and timing users simultaneously at the rings [1, 2].

Both MAX IV rings are planned to operate in multibunch mode, but several research areas have been identified that would benefit from modes with other repetition rates and/or pulse lengths than those provided by the multibunch mode. These experiments include e.g. time-of-flight and pump-probe experiments. The work to gather input from interested users is underway.

So far, the focus of the studies [3] has been on the ability to provide the repetition rates requested by the users. These studies concern three areas:

  • Non-uniform fill patterns in the MAX IV rings, e.g. fill patterns with a camshaft bunch placed in a gap
  • Pulse picking by resonant excitation (PPRE)
  • Pseudo single bunch (PSB)

In addition to the accelerator physics studies, a science case for a single-bunch mode at the MAX IV 1.5 GeV storage rings has been submitted to the the MAX IV directors by the user community [4].

Both MAX IV rings employ a 100 MHz RF system and passive harmonic cavities. The purpose of the harmonic cavities is to increase Touschek lifetime and damp instabilities. Studies at other rings have shown that non-uniform fill patterns cause transients in the harmonic cavities that give rise to a variation of bunch phase and bunch length along the bunch train. bunchlength_no_camshaftThe purpose of these studies is to evaluate such effects on the performance of the MAX IV rings. The initial results at the 3 GeV
ring indicate that schemes where the gap in the fill pattern is minimized would be advantageous [5].

Measurements have been conducted at the now decommissioned MAX II ring to evaluate simulations codes and the measurement method for future measurements at the MAX IV rings [6,7].

Two methods that have the potential to reduce the gap requirement in the fill pattern are PPRE and PSB. PPRE has been developed at BESSY-II [8], pulse pickingwhere the emittance of a single bunch in the bunch train is increased by an incoherent excitation. Part of the light from this bunch can then be separated by an aperture in the beamline, giving rise to single pulse light in this beamline while all other beamlines make use of the multibunch pattern.

PSB has been developed at ALS [9]. psbThis method involves a single bunch being kicked onto another orbit using a fast kicker. The light from the bunch can then be separated in a beamline in a similar way to PPRE. This method could provide higher intensity and more flexibility than PPRE, but it is also technically more demanding.

Plans for measurements using PPRE and first simulations of PSB are in place. The purpose of these studies is to identify opportunities and challenges for implementing and operating such schemes at MAX IV.


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Last updated: January 31, 2017


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