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DOE OSTI2013

Simulation of Scraping on the AGS Beam Dump

The AGS beam dump is described in reference [1]. Because there is no fast dipole magnet to kick the beam into the dump, the dump is used as a beam scraper into which circulating beam is moved over a period of many turns around the machine. To get a better understanding of what happens during scraping, a relatively simple model and computer code have been developed to simulate the process. We report here on the simulation results for protons at the nominal extraction kinetic energy of 22.874 GeV and for gold ions (Au77+) at the nominal extraction kinetic energy of 8.86 GeV per nucleon.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

The AGS Ggamma Meter and Calibrating the Gauss Clock

During AGS Polarized Proton acceleration periods, one output from the AGS Ggamma Meter, namely the energy (or Ggamma) calculated from the magnetic field in the AGS main magnets and the beam radius- both measured in particular instant, is used to figure out the times in the AGS magnet acceleration cycle when the beam passes through a particular set of depolarizing resonances. The resonance set occur whenever a particle’s Ggamma (energy*(G/m) becomes nearly equal to n*Qx (i.e. any integer multiplied by the horizontal betatron tune). This deliverable is why the machinery is referred to as the ''Ggamma Meter'' rather than the AGS energy meter. The Ggamma Meter takes as inputs a set of measurements of frequency (F(t)), radius (r(t)), and gauss clock counts (GCC(t)). The other energy (GgammaBr) assumes the field when the gauss clock starts counting is known. The change in field to time t is given by the measured accumulated gauss clock counts multiplied by the gauss clock calibration (gauss/GCC). In order to deal with experimental data, this calibration factor gets an added ad hoc complication, namely a correction dependent on the rate of change the counting rate. The Ggamma meter takes GCC(t) and together with the past history for this cycle calculates B(t).

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Simulations of Merging Helion Bunches on the AGS Injection Porch

During the setup of helions for the FY2014 RHIC run it was discovered that the standard scheme for merging bunches on the AGS injection porch required an injection kicker pulse shorter than what was available. To overcome this difficulty, K. Zeno proposed and developed an interesting and unusual alternative which uses RF harmonic numbers 12, 4, 2 (rather than the standard 8, 4, 2) to merge 8 helion bunches into 2. In this note we carry out simulations that illustrate how the alternative scheme works and how it compares with the standard scheme. This is done in Sections 13 and 14. A scheme in which 6 bunches are merged into 1 is simulated in Section 15. This may be useful if more helions per merged bunch are needed in future runs. General formulae for the simulations are given in Sections 9 through 12. For completeness, Sections 1 through 8 give a derivation of the turn-by-turn equations of longitudinal motion at constant magnetic field. The derivation is based on the work of MacLachlan. The reader may wish to skip over these Sections and start with Section 9.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Comments on Injector Proton Beam Study in Run 2014

During the entire period of injector proton study in run 2014, it seems that the beam transverse emittance out of Booster is larger than that in run 2013. The emittance measured at the BtA transfer line and also the transmission from Booster late to AGS late are presented for this argument. In addition to this problem, it seems that the multiturn Booster injection, which defines the transverse emittance, needs more attention. Moreover, for high intensity operations, the space charge effect may be already relevant in RHIC polarized proton runs. With the RHIC proton intensity improvement in the next several years, higher Booster input intensity is needed, therefore, the space charge effect at the Booster injection and early ramp may become a new limiting factor.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Pressure distribution along the AGS vacuum chambers with new types of pump out conduits

The AGS HEBT and ring vacuum system is monitored by the discharge current of the magnet ion pumps, which is proportional to the pressure at the inlet port of these ion pumps. The discharge current is measured and suitably calibrated to indicate the ion pump pressure. In order to calculate the vacuum chamber pressure from the ion pump pressure, a detailed analysis is essential to compute their difference in different scenarios. Such analysis has been carried out numerically in the past for the system with the older type of pump out conduits, and similar analysis using FEM in ANSYS is presented in this paper with the newer type of pump out conduit.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Run 16, eIPM Summary

Three problems with the eIPMs were corrected during the 2015 summer shutdown. These involved ac coupling and 'negative profiles', detector 'dead zone' created by biasing, and gain control on ramp. With respect to Run 16, problems dealt with included gain depletion on horizontal MCP and rf pickup on profile signals; it was found that the MCP was severely damaged over part of the aperture. Various corrective measures were applied. Some results of these measured obtained during Run 16 are shown. At the end of Run 16 there was a three-­day beam run to study polarized proton beams in the AGS. Attempts to minimize beam injection errors which increase emittance by using the eIPMs to measure the contribution of injection mismatch to the AGS output beam emittance are recounted. .

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Overview and analysis of the 2016 Gold Run in the Booster and AGS

Run 16 differed from preceding Au runs in that during most of it a 12:6:2 merge was employed in the AGS instead of an 8:4:2 merge. This was done to provide higher bunch intensities for RHIC. Since the approach to providing higher bunch intensities is, and has been, to merge more Booster bunches of the same intensity into one final bunch, detailing the longitudinal aspects of this setup seems quite relevant. So, aside from providing an overview of the Au portion of Run 16, this note also contains a series of emittance measurements in the Booster and AGS. Comparisons of these to similar measurements in previous runs are also made in hopes of gaining a better understanding of what factors contribute to the emittance of a bunch at AGS extraction. The note also tries to provide some context in which to understand the various merge schemes and describes a potential 8 to 1 type merge.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

AGS vertical beta function measurements for Run 15

One key parameter for running the AGS efficiently is by maintaining a low emittance. To measure emittance, one needs to measure the beta function throughout the cycle. This can be done by measuring the beta function at the ionization profile monitors (IPM) in the AGS. This tech note delves into the motivation, the measurement, and some strides that were made throughout Run15.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

On the image of AGS 3 He 2+ $\vec{n}$ 0 in the blue

This note addresses the transport of Helion spin $\vec{n}$ 0 vector, from its periodic orientation in the AGS to RHIC Blue ring injection kicker, via the AGS extraction system and the AtR line. The goal is to investigate optimal injection energy into RHIC, in the matter of Helion spin matching, in the hypothesis of equal warm and cold snake strengths in the AGS. The study uses recently computed OPERA 3-D field maps of the AGS cold snake, including possibility of independent solenoid and helix settings (as discussed in Tech. Note C-A/AP/485), together with the machinery of the AGS and AtR models developed in the stepwise ray-tracing code Zgoubi. Computing tools and methods employed are discussed as well, in order to facilitate possible further checks or investigations. They are however similar to those used in an earlier study regarding the image in RHIC Blue and Yellow of AGS $\vec{n}$ 0 via the AtR in the case of proton beam (Tech. Note C-A/AP/502), which can be referred to for additional details.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Simulation of 6 to 3 to 1 merge and squeeze of Au77+ bunches in AGS

In order to increase the intensity per Au77+ bunch at AGS extraction, a 6 to 3 to 1 merge scheme was developed and implemented by K. Zeno during the 2016 RHIC run. For this scheme, 12 Booster loads, each consisting of a single bunch, are delivered to AGS per AGS magnetic cycle. The bunch from Booster is itself the result of a 4 to 2 to 1 merge which is carried out on a flat porch during the Booster magnetic cycle. Each Booster bunch is injected into a harmonic 24 bucket on the AGS injection porch. In order to fit into the buckets and allow for the AGS injection kicker rise time, the bunch width must be reduced by exciting quadrupole oscillations just before extraction from Booster. The bunches are injected into two groups of six adjacent harmonic 24 buckets. In each group the 6 bunches are merged into 3 by bringing on RF harmonic 12 while reducing harmonic 24. This is a straightforward 2 to 1 merge (in which two adjacent bunches are merged into one). One ends up with two groups of three adjacent bunches sitting in harmonic 12 buckets. These bunches are accelerated to an intermediate porch for further merging. Doing the merge on a porch that sits above injection energy helps reduce losses that are believed to be due to the space-charge force acting on the bunched particles. (The 6 to 3 merge is done on the injection porch because the harmonic 24 frequency on the intermediate porch would be too high for the AGS RF cavities.) On the intermediate porch each group of 3 bunches is merged into one by bringing on RF harmonics 8 and 4 and then reducing harmonics 12 and 8. One ends up with 2 bunches, each the result of a 6 to 3 to 1 merge and each sitting in a harmonic 4 bucket. This puts 6 Booster loads into each bunch. Each merged bunch needs to be squeezed into a harmonic 12 bucket for subsequent acceleration. This is done by again bringing on harmonic 8 and then harmonic 12. Results of simulations of the 6 to 3 to 1 merge and the subsequent squeeze into harmonic 12 buckets are presented in this note. In particular, they provide a benchmark for what can be achieved with the available RF voltages.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Double and triple-harmonic RF buckets and their use for bunch squeezing in AGS

For the past several years we have merged bunches in AGS in order to achieve the desired intensity per bunch prior to injection into RHIC. The merging is done on a flat porch at or above AGS injection energy. Because the merges involve the reduction of the RF harmonic number by a factor of 2 (for a 2 to 1 merge) and then a factor of 3 (for a 3 to 1 merge), one requires RF frequencies 6hf s , 3hf s , 2hf s and hf s , where f s is the revolution frequency on the porch and h = 4 is the fundamental harmonic number. The standard AGS RF cavities cannot operate at the lowest frequencies 2hf s and hf s ; these are provided by two modified cavities. Upon completion of the merges, the bunches are sitting in harmonic h buckets. In order to be accelerated they need to be squeezed into harmonic 3h buckets. This is accomplished by producing a double-harmonic bucket in which harmonics h and 2h act in concert, and then a triple-harmonic bucket in which harmonics h, 2h, and 3h act in concert. Simulations have shown that the squeeze presents an acceptance bottleneck which limits the longitudinal emittance that can be put into the harmonic 3h bucket. In this note the areas of the double and triple-harmonic buckets are calculated explicitly, and it is shown that these go through a minimum as the RF voltages are raised to the desired values. Several RF voltage ranges are examined, and the acceptance bottleneck is determined for each of these. Finally, the acceptance bottleneck for Au77+ bunches in AGS is calculated for several RF voltage ranges. The main result is that the RF voltages for the low-frequency harmonic h and 2h cavities both must be at least 22 kV in order to achieve an acceptance of 0:6 eV s per nucleon. If the harmonic h and 2h voltages are 15 and 22 kV, respectively, then the acceptance is reduced to 0:548 eV s per nucleon.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Comparing the effect on the AGS longitudinal emittance of gold ions from the BtA stripping foil with and without a Booster Bunch Merge

The aim of this note to better understand the effect of merging the Gold bunches in the Booster into one on the resulting AGS longitudinal emittance as compared to not merging them. The reason it matters whether they are merged or not is because they pass through a stripping foil in the BtA line. Data was taken last run (Run 17) for the case where the bunches are not merged, and it will be compared with data from cases where the bunches are merged. Previous data from Tandem operation will also be considered. There are two main pieces to this puzzle. The first is the ε growth associated with the energy spread due to ‘energy straggling’ in the BtA stripping foil and the second is the effective ε growth associated with the energy loss that occurs while passing through the foil. Both of these effects depend on whether or not the Booster bunches have been merged into one.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Booster and AGS transverse emittance during the 2006 and 2009 polarized proton runs

This note is an overview of issues relating to transverse polarized proton emittance in the Booster and AGS. It also compares the transverse emittance during the FY09 polarized proton run with it during the FY06 run as several changes were made for the FY09 run in an attempt to reduce the transverse emittance coming out of the AGS. The FY06 run is used for comparison because it was relatively long, and it's believed that the performance of the injectors for polarized protons, up until FY09, was best during that run. Over the shutdown just before the FY09 run work was done in LEBT and MEBT to reduce the emittance coming out of the Linac. Measurements of the beam coming out of Linac1 indicate that the horizontal normalized emittance was reduced from 11.0 {pi} to 4.5 {pi}mm mrad, and that the vertical normalized emittance was reduced from 12.1 {pi} to 5.5 {pi} mm mrad going from FY06 to FY09. There were 2 new types of stripping foil installed in the Booster, called descriptively the 'strip' (No.6) and 'stamp' (No.2) foil, both nominally 100 {micro}g/cm{sup 2}. Both foils are composed of a diamond like material, and designed to reduce the number of times the beam goes through the foil. Other than those, there are two standard 100 {micro}g/cm carbon foils (No.3 and 5), and one 200 {micro}g/cm{sup 2} carbon foil (No.4). Of the two 100 {micro}g/cm{sup 2} foils, one has shown some deterioration (No.3) in stripping efficiency. During the FY06 run a standard 100 {micro}g/cm{sup 2} foil was generally used, and during the FY09 run the strip foil was generally used, though the stamp foil was also used for the last 3-4 weeks of the run. Both the FY06 and FY09 runs were about 5 months long, starting in late January, FY06 ending in late June, and FY09 ending in early July. A new injection setup was used for about the last 3 months of FY09, from the beginning of April to the end of the run. This setup uses 1/2 integer stopband correctors with the tunes near, but slightly greater than, 4.5 to distort the {beta} functions at the foil in order to reduce the emittance blowup caused by scattering on the foil. New BtA quad settings, largely based on a MAD model of the BtA line and AGS were used for virtually the entire FY09 run (Feb 5 to the end) in an attempt to improve the matching into the AGS. Since, it has been thought for some time that there is emittance blowup in the vertical due to an injection mismatch. The nominal Linac pulse width was decreased from 400 {micro}s to 300 {micro}s in the latter part of february 09, so the vast majority of the FY09 run used a 300 {micro}s pulse width. The standard pulse width for FY06 was 400 {micro}s. This has some implications for comparing the data from FY06 with that from FY09, but they don't seem insurmountable.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

A simple crunching of the AGS 'bare' machine ORM data - February 2007 - to extract some aspects of AGS transverse coupling at injection and extraction

The objective of this note is to (once again) explore the AGS 'ORM' (orbit response matrix) data taken (by Operations) early during the 2007 run with an AGS bare machine and gold beam. Indeed the present motivation is to extract as much information about the AGS inherent transverse coupling as possible - from general arguments and the copious ORM data. And taking this one step further, (though not accomplished yet) the goal really should be to tell the model how to describe this coupling. 'Bare' as used here means the AGS with no quadrupole, sextupole or octupole magnets powered. Only the main (combined-function) magnet string and dipole bumps necessary to optimize beam survival are powered. 'ORM data' means the systematic recording of the equilibrium orbit beam position monitor response to powering individual dipole corrector magnets. The 'matrix' results from looking at the effect of each of the (12 superperiods X 4 dipoles per superperiod) 'kicks' on each of the (12 X 6) pick up electrodes (pues) in each transverse plane. So then we have two (48 X 72) matrices of numbers from the ORM data. (Though 'pue' usually refers to the hardware in the vacuum chamber and 'bpm' to the beam position monitoring system, the two labels will be used casually here.) The exercise is carried out at two magnet rigidities, injection (AGS field {approx}434 Gauss) and extraction to RHIC ({approx}9730 Gauss), - a ratio of rigidities of about 22.4. Since we stick with a bare machine, we are also stuck with the bare tunes which means the tunes are rather close together and near 8.75. Injection: (h,v) {approx} (8.73, 8.76).

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

AGS tune jump power supply design and test

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 perform this. The pulsed magnet current ranges from about 140A near injection to about 1400A later. The current pulse rise and fall time are around 100uS and flat tops time is around 4mS. These quadruples have separated supplies. This tune jump pulse power supply employees all semiconductor parts as well as the main switches. During dummy load and magnet testing, the test results showed that the power supply could meet the specification. This article will describe some details of power supply simulation, design and testing. Some test waveforms and pictures are presented in this paper.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

AGS tune jump system to cross horizontal depolarization resonances overview

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 six in crossing rate with a tune jump of 0.05 in 100 {micro}s. Two quadrapoles, we described in 2009, pulse 42 times, the current matching beam energy. The power supplies for these quads are described in detail elsewhere 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 versus 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 and is operational. Many beam effects are described elsewhere. The TuneJump system has worked well and has caused little trouble save for the perturbations in the lattice having such a large effect due to our need to run with the vertical tune within a few thousandths of the integer tune. As these problems were mostly sorted out by correcting the 6th harmonic orbit distortions which caused a large 18 theta beta wave. Also running with minimal chromaticity reduces emittance growth. There are still small beta waves which are being addressed. The timing of the pulses is still being investigated, but as each crossing causes minimal polarization loss, this is a lengthy process.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Near integer tune for polarization preservation in the AGS

The high energy (T = 250 GeV) polarized proton beam experiments performed in RHIC, require high polarization of the beam. In order to preserve the polarization of the proton beam, during the acceleration in the AGS, which is the pre-injector to RHIC, we have installed in AGS two partial helical magnets which minimize the loss of the beam polarization caused by the various intrinsic spin resonances occurring during the proton acceleration. The minimization of the polarization loss during the acceleration cycle, requires that the vertical tune of the AGS is between the values of 8.97 and 8.985 during the acceleration. With the AGS constrained to run at near integer tune {approx}8.980, the perturbations to the beam caused by the partial helical magnets are large and also result in large beta and dispersion waves. To mitigate the adverse effect of the partial helices on the optics of the AGS, we have installed in specified straight sections of the AGS compensation quads and we have also generated a beam bump at the location of the cold partial helix. In this paper we present the beam optics of the AGS which ameliorates the adverse effect of the two partial helices on the beam optics.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

A model of the AGS based on stepwise ray-tracing through the measured field maps of the main magnets

Two-dimensional mid-plane magnetic field maps of two of the main AGS magnets were produced, from Hall probe measurements, for a series of different current settings. The analysis of these data yielded the excitation functions [1] and the harmonic coefficients [2] of the main magnets which have been used so far in all the models of the AGS. The constant increase of the computation power makes it possible today to directly use a stepwise raytracing through these measured field maps with a reasonable computation time. We describe in detail how these field maps have allowed the generation of models of the 6 different types of AGS main magnets, and how they are being handled with the Zgoubi ray-tracing code [3]. We give and discuss a number of results obtained regarding both beam and spin dynamics in the AGS, and we provide comparisons with other numerical and analytical modelling methods.

43 PARTICLE ACCELERATORS↗