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The RF Power Consumption in the ESS Spoke Linac

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Document type:
Tech Note
Submitted by:
Håkan Danared
Updated by:
Håkan Danared
Document Created:
05 Feb 2013, 10:51
Contents Revised:
05 Feb 2013, 10:51
DB Info Revised:
05 Feb 2013, 10:51
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In the ESS LINAC the transition energy between the DTL and the spoke LINAC was changed by adding the fourth DTL tank in order to match the spoke LINAC in terms of the velocity acceptance. We present calculation of the RF power required to be fed to each spoke cavity to achieve the nominal acceleration gradient. The RF power overhead needed to compensate the beam loading and the Lorentz detuning is calculated and the peak and average values of the total RF power are presented. Overhead in terms of the power averaged over the pulse is only a few percents whereas the peak power overhead can reach 20% and lasts for around 200 microseconds. It turns out that the power overhead is mainly determined by the strong beam loading because of a high beam current whereas the Lorentz detuning is weak due to high stiffness of the spoke cavity and almost does not require extra power to the cavity. In our simulations the cavity voltage and phase are stabilized within nominal tolerances by feedback and feed-forward. A slow feed-forward is used to cure the Lorentz detuning whereas a fast feedback through a signal oscillator is applied to compensate the beam loading effect.
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