RF Curves for Extraction from the Accumulator

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Since the start of Run IIa, the RF curves for the extraction process from the Accumulator have been based on an algorithm described in Pbar Note 636. There are a number of problems with this procedure that result in a dilution of the longitudinal phase space of the extracted beam. The procedure consists of a number of steps in which the frequency curve during each process is a linear time ramp. For a constant bend field, the synchronous phase angle is given as: {Lambda} = sin({phi}{sub s}) = -h/{eta} (1/f{sub rf}){sup 2}df{sub rf}/dt/qV/pc where h is the harmonic number of ... continued below

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669 pages

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McGinnis, Dav March 10, 2002.

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Description

Since the start of Run IIa, the RF curves for the extraction process from the Accumulator have been based on an algorithm described in Pbar Note 636. There are a number of problems with this procedure that result in a dilution of the longitudinal phase space of the extracted beam. The procedure consists of a number of steps in which the frequency curve during each process is a linear time ramp. For a constant bend field, the synchronous phase angle is given as: {Lambda} = sin({phi}{sub s}) = -h/{eta} (1/f{sub rf}){sup 2}df{sub rf}/dt/qV/pc where h is the harmonic number of the RF. Equation (1) shows that if the frequency curve consists of a number of linear time ramps with different slopes, there will be discontinuities in the synchronous phase. These discontinuities in the synchronous phase will lead to dipole oscillations of the beam in the RF bucket. The discontinuities observed for the present RF curves are about 10 degrees. In the procedure outlined in Pbar Note 636, the RF bucket is formed on the high energy edge of the rectangular momentum distribution. As the RF bucket is pulled away from the core, it is also programmed to increase in area. If the distribution is not perfectly rectangular, or if the bucket is not formed at the edge of the distribution, the growing bucket will gather up more particles at the edges of the bucket resulting in a substantial increase of longitudinal emittance. Finally, it is fairly difficult to prepare a rectangular momentum distribution and keep it rectangular for extended periods of time. Once the rectangular distribution is prepared, the core momentum cooling must be turned off. If there is a delay in the extraction process, the sharp edges of the rectangular distribution will soon diffuse. With the momentum cooling disabled, the longitudinal emittance of the core will grow resulting in larger longitudinal emittances for the extracted beam.

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669 pages

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  • Report No.: FERMILAB-PBAR-NOTE-669
  • Grant Number: AC02-07CH11359
  • DOI: 10.2172/984564 | External Link
  • Office of Scientific & Technical Information Report Number: 984564
  • Archival Resource Key: ark:/67531/metadc1014649

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  • March 10, 2002

Added to The UNT Digital Library

  • Oct. 14, 2017, 8:36 a.m.

Description Last Updated

  • Nov. 3, 2017, 9:26 p.m.

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McGinnis, Dav. RF Curves for Extraction from the Accumulator, report, March 10, 2002; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc1014649/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.