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

Abstract

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.

Authors:
; ;
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
296798
Report Number(s):
LA-UR-98-2423; CONF-980827-
ON: DE99001210; TRN: 99:003044
DOE Contract Number:  
W-7405-ENG-36
Resource Type:
Conference
Resource Relation:
Conference: 19. international linac conference, Chicago, IL (United States), 23-28 Aug 1998; Other Information: PBD: [1998]
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; PROTON SOURCES; BEAM CURRENTS; MODULATION; LINEAR ACCELERATORS; MAGNETRONS; OPERATION; POWER; PERFORMANCE; ION SOURCES

Citation Formats

Balleyguier, P, Sherman, J, and Zaugg, T. Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source. United States: N. p., 1998. Web.
Balleyguier, P, Sherman, J, & Zaugg, T. Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source. United States.
Balleyguier, P, Sherman, J, and Zaugg, T. 1998. "Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source". United States. https://www.osti.gov/servlets/purl/296798.
@article{osti_296798,
title = {Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source},
author = {Balleyguier, P and Sherman, J and Zaugg, T},
abstractNote = {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.},
doi = {},
url = {https://www.osti.gov/biblio/296798}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Dec 01 00:00:00 EST 1998},
month = {Tue Dec 01 00:00:00 EST 1998}
}

Conference:
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