As part of the efforts to increase polarization and luminosity in RHIC during polarized proton operations we have modified the injection optics and stripping foil geometry in the AGS Booster in order to reduce the emittance growth during H{sup -} injection. In this paper we describe the modifications, the injection process, and present results from beam experiments

Ahrens, L.

Brown, K. A.

Gardner, C.

Gassner, D.

Raparia, D.

Steski, D.

Theiberger, P.

Zeno, K.

UNT Digital Library

BROONATION1\LBNL..81800~2009-CPMinimizing emittance growth during He. injection inthe AGS boosterK. A. Brown, L. Ahrens, C. Gardner, D. Gassner,D. Raparia, D. Steski, P. Thieberger, K. ZenoPresented at the Particle Accelerator Conference (PAC09)Vancouver, B.C., CanadaMay 4-8, 2009CoUider-Accelerator DepartmentBrookhaven National LaboratoryP.O. Box 5000Upton, NY 11973-5000www.bnLgovNotice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC underContract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting themanuscript for publication acknowledges that the United States Government retains a non-exclusive, paid··up,irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow othersto do so, for United States Government purposes.This preprint is intended for publication in a journal or proceedings. Since changes may be made beforepublication, it may not be cited or reproduced without the author's permission.DISCLAIl\1ERThis report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United States Government nor anyagency thereof, nor any of their employees~ nor any of their contractors,subcontractors, or their employees, makes any warranty, express or implied, orassun1es any legal liability or responsibility for the accuracy, completeness, or anythird party's use or the results of such use of any information, apparatus, product,or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specific commercial product, process, or serviceby trade name~ trademark, Inanufacturer, or otherwise, does not necessarilyconstitute or imply its endorsenlent, recommendation~ or favoring by the UnitedStates Government or any agency thereof or its contractors or subcontractors.The views and opinions of authors expressed herein do not necessarily state orreflect those of the United States Government or any agency thereof.MINIMIZING EMITTANCE GROWTH DURING Hoo INJECTION IN THEAGS BOOSTER *K. A. Brown t , L. Ahrens, C. Gardner, D. Gassner, D. Raparia, D. Steski~P. Thieberger, K. ZenoC-AD Dept., BNL, Upton, NYAbstractAs part of the efforts to increase polari7Ation and lumi~nosity in RHIC during polarized proton operations we havemodified the injection optics and stripping foil geometry inthe AGS Booster in order to reduce the emittance growthduring H'" injection. In this paper we describe the mod~itkations, the injection process. and present results frombeam experiments.INTRODUCTIONThe RHle complex consists of a 200 MeV LINAC,a Booster synchrotron that takes polarized protons up to2.16 GeVIc (G'Y = 4.5). the AGS that takes the beamsup to 23.8 GeV/c (G"Y = 45.5). and the two RHIC syn·chrotron rings. that take polarized protons up to 250 GeVIc(Or = 477.7). The LINAC was upgraded with a newlow energy transport system this year [1]. As a resultit now delivers a factor of two smaller polarized protonbeam emittance in both planes I:1]. Nominal ernittancesin the past were on the order of 10 1TJ1m, 95%. normal-ized. With smaller emittances. the percentage of emit-tance growth from Coulomb scattering on the injection foilin the Booster represents a significant fraction of the finalemittance delivered to the AGS. To reduce this growth wehave introduced thinner stripping foils and new foil geome-tries. In an attempt to further reduce the growth, we havechanged the optics at injection to reduce the ,8-functions atthe foil..BOOSTER INJECTIONThe lJNAC produces an 1I- beam. which is stripped ofboth electrons when injected into the: Booster. The strip-ping foil is located on the inside acceptance of the Boosterjust downstream of the CS main Booster sector bend. TheC5 magnet has a channel in the backleg through which theH'" 'beam enters the field. and is bent to the left. Circulat-ing beam is bent to the right. Figure 1 shows this geometry.A set of orbit deformation dipoles create a closed bump atthe foil. such that beam is kept on the foil only during theinjection pulse. Ibe LINAC pulse is about 350 psec long.while the booster revolution period is about 1 psec. After350 'lsec the bump is collapsed and beam no longer hits thefoil.~ Work performed un.der Contract Number DE-AC02-98CH10886 withthe auspices of the US Department of Energy.t kbrown@.>onl.goYFigure 1: Injected beam trajectory through the Booster C5main sector bend.El\tUTTANCE GROWTH IN THEBOOSTERThe emittance growth in the booster is mainly causedby injection processes such as muJtiple scattering in thecharge exchange foil and injection mis·match. The emit-tance growth due to multiple scattering can be approxi-mated by(1)where n is the number of traversals through the foil anddepends on the linac pulse length and shape of the foil. fJ( s)is the matched f3-function at the foil, and eis the rms multi-ple scattering per turn. which depends on the foil thicknessand material To reduce the emittance growth we try tominimize each of the..~ parameters. We have used new foilgeometries. different linac pulse lengths. thinner foils. anddifferent injection optics.INJECTION FOILSEach of tlve carbon foils mounted on a foil wheel maybe selectively rotated into the aperture for .H'- stripping.The available foils are given in table L There are basi-cally 4 types of foils to choose from. Two of them are100 fl'9 / em.2 full frame foils, which have been the standardfoil used for polarized proton operdtion. There is one 200J19 / cm2 foil, which is what we have used for high intensityunpolarized operation. Then there are two special foils. astrip foil. shown in l1g. 2. and a stamp shapt-xi foil, shownin fig. 3. These foils are designe.d to reduce the number oftimes the beam hits the foil during the injection process.The specialty foils are made by gluing a diamond like car·bon (DLC) foil [2] to a frame and then using a la'ier cutterto produce the desired. geometry [3].Figure 4: Relative yeilds of H- , and NT as a functionof foil thickness for a 200 MeV, H ,- incident beanl.Table 1: Available foils on foil wheeL40354517"==<:::l<:I::===:r.r.TTnTnrTTrTTnTiTTTITTTTI., - Foil ~ll = 11.075 m-- Foil ~v ~ 5.337 m- Distork'(il3g = 4.671 m-- Distorted l\ = 2.629 miNo. _._--~---_.~._,-----Thickness Edge location Typei (pg/crn2) Inches from RfjL1 No Foil na2 130 -1.00 stamp3 100 -1,00 full4 200 -l.tX) full5 100 -LOO full6 130 -1.00 stripthe same quadrupoles such that they increase the distortionrather than correct it.Figure 4 shows the relative yields of H- .Ho. and H+ asa function of foii thickness. For high intensity unpolarizedoperation in the past. concern over radiation damage re-quired that we use the very efficient 200 tty / cm2 foiL Butfor polarized protons. the relatively low intensity allows usto optimize beam parameters by trading off some intensityto achieve smaller emittances.Figure 2: Diamond like strip foiLFigure 3: Diamond like stamp shaped foil.REDUCED j3-FUNCTIONS AT THE FOILThe distortion of the O-functions in an accelerator due toquadrupole gradient errors is wen known [4]. The amountof distortion is a function of the working point, the magni-tude of the errors, and the distribution of th.e errors. Usu-any we want to reduce the distortion by exciting latticequadrupoles such that the 2Q= N resonance can be ap-proached or crossed without any beam loss or emittancegrowt.h. Driving a distortion is just a matter of excitingFigure 5: ,a-functions with and without the half-integerstop band distortion at Booster injection.Figure 5 shows the injection lattice structure of theBooster for polarized. protons with and without the half-integer stop band correctors exciting a distortion. Figure 6shows the l:~-functions near the foiL Figure 7 shows howthe horizontal distortion d.epends on horizontal tune.35 .45 rr-----r=======::;-'r--,--l1li-""""T-.....-- Foil ~H=] 1.075 m- - Foil i3v = 5.337 m- Distorted~H=4.671 m-- Distorted I'v= 2.629 mofti:--_-L-...--ii-.-_a:Figure 6: !3-functions near the injection foil.jection dynamics and to reduce the emittance growth fromthe foUs.40 r:=:::::::::=J::~=:::r.:-~r--'--r--'--~r----'-----,~Thin, distorted optics~ '" TIlick, distorted optics.~ 1 <> stam.p, distorted optics§.. 30 ~ • S~P, di~l~rted opticsJ~ f:i Tllm,ongmm.,~ i" Thick, original0; i ~ Slrip. original[20'-~9.3±0.56.3±0.514.2±O.5lO.9±O.51.- 1..--.Table 2: Measured emittances for two different injectionoptics.Figure 8: Emittance as a function of time spent on the foil,for different types of foils, with and without the distorted/3~function lanice.458Nonna! ~-furrction at foil.......... QVSTR'g & QHSTR's [ow CUTrmts (02·0.6 amp)~ QVSTR's & QHSTR's high currents (4-10 amp)~i.-5_~_""'4.LS2"""--'-- 454 4.56Horiz.. Tune at InjectionHgure 7: Tune dependence of distortion, for two differentfixed stop band corrector strengths.SUMMARYEXPERIMENTAL RESULTSOur primary diagnostic for these studies is a beam profilemonitor located at the start of the Booster to AGS transferline. This profile monitor has wire spacing's of 1.5 mm,a horizontal f3~function of 3.14 meters, and a vertical ;3-function of 16 meters. We studied emittance growth fromthe foil by scanning the amount of time the beam was heldon the foil by making the LINAC pulse width very short(50 p,sec) and adjusting the timing of the injection bumps.Figure 8 shows the horizontal emittances for different foilsas a function of time spent traversing the foils.Although this shows the predicted linear response to thetime on the foil, the change in the slopes due to the changein optics is not consistent with predictions. While the emit-tance growth was reduced in the horizontal. the verticalemittance growth was not reduced. Nevertheless. the finaloverall emittances were smaJler for the distorted injectionoptics. Some of that improvement is due to the new optics,but some is likely due to improved injection matching. Theemittances for the two sets of optics are given in table 2.We have many questions still to answer. Because thetunes are so close together during injection. large couplingis observeli, resulting in mixing of the emittances. We con-tinue to perform experiments to better understand the in-The emittance growth due to Coulomb scattering in theinjection H- stripping foil has been reduced by using thin-ner foils and by reducing the ~-function at the foil. Theseimprovements have also resulted in improved machine per-formance, with as much as 15% higher transmission effi-ciencies.ACKNOWLEDGEMENTSThe DeL films were supplied to us by TRIUMF (Micro-matter ® [5]). Rolf BeuttenmuHer operated the laser cutterand produced the specialty foils.REFERENCES[1] D. Raparia, et aI, "Results of LEET/MEBT Upgrade at BNL200 MeV Lina..:", These proceedings.[2J P. Maier-Komar, G. Dollinger, CoM, Fr~y and H,J. KIner,NucL Instr. and Metfi. A561 (2006) 4[3] D. Steski, P. Thieberger, Proceedings ofthe 24th World Conf.of the lut. Nuclear Target Dev. Soc.[4] E. D. Courant and H. S. Snyder, Annals Phys. 3, 1 (1958)[Annais Phys. 281, 360 (2000)].[5] Micromatter, 4004 Wesbrook Mall, Vancouver, Be. V6t 2A3,Canada (www.micromatter.com)

Minimizing emittance growth during H- injection in the AGS booster

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Minimizing emittance growth during H- injection in the AGS booster

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