ESS Docs Document 36-v2

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Investigation of Different Pole Tips Geometries for the ESS RFQ, Part 1

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Tech Note
Submitted by:
Håkan Danared
Updated by:
Håkan Danared
Document Created:
21 Mar 2011, 11:50
Contents Revised:
21 Mar 2011, 12:01
Metadata Revised:
21 Mar 2011, 12:01
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21 Mar 2011, 11:53
The first stage of the radio-frequency (RF) acceleration through the ESS linear accelerator (linac) will be provided by a room temperature RF quadrupole (RFQ) of the 4-vane type. This latter will boost the energy of the proton beam from 75 keV at the ion source exit up to 3 MeV at the entrance of the drift tube linac (DTL). The presented note describes a method for the generation of the pole tip geometry and investigates then various RFQ designs considering various combinations of the generating parameters. The study shows that, for a given set of Kilpatrick value [6], K_p (which indicates the peak electric field on the poles), and beam current, an optimal performance geometry can be found: increasing the power consumption of the RFQ for this geometry adds a negligible contribution to the total transmission while running the RFQ with less power degrades substantially the performances. Two designs for the ESS RFQ are then detailed and proposed. They result in a total transmission better than 99 % for 50 mA and 75 mA (respectively the nominal current and a possible upgrade) for a 1 MW-class klystron. K_p = 1.8 is finally retained as a reference value for the ESS RFQ. Furthermore having a long pure bunching section is mandatory: this choice is the best strategy in order to pruduce high quality beams.
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