BNL, Upton, Long Island, New York, USA
RHIC operation as the polarized proton collider presents unique challenges since both luminosity and spin polarization are important. With longitudinally polarized beams at the experiments, the figure of merit is LP4. A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system has been installed to improve longitudinal match at injection and to increase luminosity. The beam dumps were upgraded to allow for increased bunch intensities. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control has also been improved this year. Additional efforts were put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point was chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper.
BNL, Upton, Long Island, New York, USA
The use of fluorescent screens for beam profile monitors provides a simple and widely used way to obtain detailed two dimensional intensity maps. For high precision measurements many possible error contributions need to be considered that have to do with properties of the fluorescent screens and of the CCDs. Saturation effects, reflections within and outside the screen, non-linearities, radiation damage, etc are often mentioned. Here we concentrate on an error source less commonly described, namely erroneous baseline subtraction, which is particularly important when fitting projected images. We show computer simulations as well as measurement results having remarkable sensitivity of the fitted profile widths to even partial suppression of the profile baseline data, which often arises from large pixel-to-pixel variations at low intensity levels. Such inadvertent baseline data suppression is very easy to miss as it is usually not obvious when inspecting projected profiles. In this report we illustrate this effect and discuss possible algorithms to automate the detection of this problem as well as some possible corrective measures.
BNL, Upton, Long Island, New York, USA
A horizontal tune jump system has been installed to overcome the horizontal intrinsic spin resonances, which requires jumping the horizontal tune 0.04 units 82 times, 41 up and 41 down. Two quadruple magnets have been installed in AGS ring to do this. The pulsed magnet currents range from about 140 amps near injection to about 1400 amps late. Current pulse rise and fall times are around 100 micro-sec and flat tops time are around 4mS. These quadruples have separate supplies. This tune jump pulse power supply employees all semiconductor parts as the main switches. During dummy load and magnet testing, the test result showed that the power supply could meet the specification. This article will describe some detail of power supply simulation, design and testing. Some test waveform and pictures are presented in this paper.
BNL, Upton, Long Island, New York, USA
Two partial snakes overcome the vertical depolarizing resonances in the AGS. But a new type of depolarizing intrinsic resonance from horizontal motion appeared. We reduce these using horizontal tune jumps timed to these resonances. We gain a factor of five in crossing rate with a tune jump of 0.04 in 100 micro-sec. Two quadrapoles, we described in 2009 *, pulse 42 times, the current matching beam energy. The power supplies for these quads will be described in this conference**. The controls for the Jump Quad system is based on a BNL designed Quad Function Generator. Two modules are used; one for timing, and one to supply reference voltages. Synchronization is provided by a proprietary serial bus, the Event Link. The AgsTuneJump application predicts the times of the resonances during the AGS cycle and calculates the power supply trigger times from externally collected tune and energy verses time data and the Low and High PS voltage functions from a voltage to current model of the power supply. The system was commissioned during runs 09 & 10. Beam effects are described elsewhere in this conference***. Details of improvements, operation and the feed forward software will be described.
* JW Glenn, et al “AGS Fast Spin Resonance,-” PAC-09
** JL Mi, et al “AGS Tune Jump Power-” these proceedings
*** L.A.Ahrens, et al "Recent RHIC Motivated Polarized-" these proceedings
BNL, Upton, Long Island, New York, USA
A large distortion of the vertical beta function became evident in the Brookhaven AGS during the 2010 polarized proton run. This paper describes the beam measurements and model calculations made to verify the distortion of the optics, to infer possible sources and to explore correcting strategies. The optics distortion is only apparent when operating with a betatron tune very near the integer (as required for polarization preservation during acceleration in the AGS) and with the lattice chromaticity sextupoles powered. The measurements indicate a small (on the order of millimeters) unexpected systematic horizontal closed orbit displacement in the sextupoles that is not evident in beam position monitor measurements. Motivated especially by these observations a complete survey of the AGS was performed during the 2010 shutdown period.&nb sp; The results of that survey and their impact on the observed optical errors in the AGS are included.
BNL, Upton, Long Island, New York, USA
A model of the Alternating Gradient Synchrotron is being developed based on stepwise ray-tracing numerical tools. It provides a realistic representation of the lattice, and accounts for the two helical partial Siberian snake insertions. The aim is to make this stepwise ray-tracing based model an aid for the understanding of the AGS, in matter of both beam dynamics and polarization transmission.
BNL, Upton, Long Island, New York, USA
The RHIC polarized proton physics program requires high luminosity and high polarization which depends directly on the intensity, emittances and polarization delivered to RHIC by the injector chain. In the AGS, two partial snakes create gaps in the realized spin-tune around the integers which allows an accelerating beam with sufficiently small vertical emittance and near-integer vertical tune to avoid the imperfection and vertical intrinsic resonances. The same strategy strengthens the many (82) weak horizontal intrinsic resonances crossed during AGS acceleration. A system speeding up these resonance crossings – the AGS JumpQuad system: 82 tiny (0.04) fast (100usec) betatron tune shifts – has been commissioned and evolved during RHIC Runs 09, 10, and 11. Subtle properties of the AGS geometry and lattice, magnified into relevance by the high vertical tune can result in polarization-damaging emittance growth when combined with the Jump Quad gymnastics. Orbit stability is critical. Some aspects of the JumpQuad system, of this commissioning effort and related developments will be described.