[en] The Spallation Neutron Source (SNS) has been in operation since 2006 and routinely operates at 1 MW of beam power. At 1 MW, the High Voltage Converter Modulators (HVCMs) are delivering 8-11 MW pulsed power to the Klystrons for up to 1185 us at 60 Hz. The pulsed output of the modulator has a substantial voltage droop operating in open-loop mode. Achieving 1.4 MW operations require an increase in the output pulse width of the HVCM, resulting in loss of LLRF control margin due to modulator voltage reduction at the end of the pulse. Initially, the HVCM was designed with a pulse width modulation scheme for droop compensation but early operations at full duty revealed this technique unreliable. Increasing the output voltage of the modulator would likely compromise system reliability. This paper proposes the use of alternate modulation schemes to address the voltage droop. The effect of frequency modulation and phase modulation on voltage droop is studied. Experimental results will also be presented.

[en] The response of particles trapped in one-dimensional resonance islands to betatron tune modulation resembles, yet is not equivalent to, that of a parametric resonant system. Experimental data obtained at Indiana University Cyclotron Facility for the fourth-order resonance islands have confirmed this characteristic feature. The beam, driven by betatron tune modulation, was observed to travel from near the center of resonance islands toward the separatrix. The experimental data are characterized by the onset of a large response at a critical modulation amplitude and frequency, which are compared with theoretical models. Possible future experiments are suggested

No abstract available

No abstract available

[en] The modulation transfer function of a microdensitometer was measured by scanning a transmission sinusoidal test pattern by means of the microdensitometer and modulations at the various discrete spatial frequencies were measured from the profile of the image. The modulation versus spatial frequency data were fitted to a sin function and the MTF of the microdensitometer was estimated from the fitted curve. The MTF of the microdensitometer was sin (aφμ)/(aφμ) where a=0.0155 mm and μ is the spatial frequency in cycles/mm. Correction factor for the MTF of screen-film system at 10 cycles/mm was 1.04 suggesting only small error would result if one neglects the degradation by the microdensitometer (author)

[en] For intensity-modulated radiation therapy (IMRT), a simple technique is described which splits any NxN matrix I of fluences into two mathematically equivalent matrices I_A and I_B summing to 2I, each of which requires considerably fewer segments to deliver IMRT using the jaws-plus-mask technique (Webb 2002b). When I_A and I_B are delivered alternately at fractions throughout the treatment, the total number of field segments required is between 1/2 and 2/3 that of delivering matrix I when unadjusted. (author)

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No abstract available

[en] A chromaticity tracker based on a method by D. McGinnis is proposed. This method starts with the slow modulation of the accelerating RF which causes the beam to respond to it. This beam modulation can be detected transversely with a Schottky pickup which after phase demodulation, the chromaticity can be calculated from it. However, to perform phase demodulation, the carrier frequency which is the betatron tune needs to be identified. The identification of the carrier frequency falls naturally onto the phase locked loop tune tracker which when locked to the betatron tune outputs this value in real time

No abstract available