Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source

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Earlier operation of a microwave proton source exhibited an approximate 1-MHz modulation in the beam current. This oscillation could cause instabilities at higher energies in the linac, as the low-level RF control for linac operation rolls off at 200 kHz. Tests on a dummy load show the modulation is created by the magnetron itself: at a typical power level required for the source operation (680W), the 1-MHz sideband level was as high as {minus}4 dB from carrier. Since the magnetron exhibited better behavior at higher levels, a RF power attenuator is inserted to force the magnetron to run at a ... continued below

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10 p.

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Balleyguier, P.; Sherman, J. & Zaugg, T. December 1, 1998.

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Description

Earlier operation of a microwave proton source exhibited an approximate 1-MHz modulation in the beam current. This oscillation could cause instabilities at higher energies in the linac, as the low-level RF control for linac operation rolls off at 200 kHz. Tests on a dummy load show the modulation is created by the magnetron itself: at a typical power level required for the source operation (680W), the 1-MHz sideband level was as high as {minus}4 dB from carrier. Since the magnetron exhibited better behavior at higher levels, a RF power attenuator is inserted to force the magnetron to run at a 50% higher power level for the same final power in the load. This attenuator is made of two antennas plunged in the waveguide and connected to dummy loads by a coaxial line. As the antenna are separated by a quarter of the guided wavelength, mismatching effects approximately cancel each other. The antenna length is experimentally adjusted to obtain the {minus}1.8 dB attenuation required. Magnetron operation at the higher power level gives a beam current spectrum free of the 1-MHz modulation, showing the coherent beam noise is not generated by plasma chamber phenomena.

Physical Description

10 p.

Notes

INIS; OSTI as DE99001210

Source

  • 19. international linac conference, Chicago, IL (United States), 23-28 Aug 1998

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  • Other: DE99001210
  • Report No.: LA-UR--98-2423
  • Report No.: CONF-980827--
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 296798
  • Archival Resource Key: ark:/67531/metadc684174

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  • December 1, 1998

Added to The UNT Digital Library

  • July 25, 2015, 2:20 a.m.

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  • Feb. 26, 2016, 6:34 p.m.

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Balleyguier, P.; Sherman, J. & Zaugg, T. Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source, article, December 1, 1998; New Mexico. (digital.library.unt.edu/ark:/67531/metadc684174/: accessed September 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.