In the fall of 1995, we successfully completed a major milestone in the RHIC (Relativistic Heavy Ion Collider) project: the first beam test of the AGS (Alternating Gradient Synchrotron) to RHIC (ATR) transfer line. The ATR serves as a test bed for the new RHIC control system. This transfer line is highly instrumented, with several types of instrumentation for characterizing the extracted beam from AGS and for matching the beam into RHIC. We describe the design and performance of ATR with gold ions with an eye to reaching the design criteria for RHIC operation, both in beam quality and controls

Ahrens, L.

Bennan, M.

Brown, K.

MacKay, W. W.

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5th European Particle Acclerator Conference BNL-6 2 650 Sitges (Barcelona) June 10-14, 1996 C ~ A )  - 4606&1--36 AGS TO RHIC TRANSFER LINE: DESIGN AND COMMISSIONING[l] W. W. MacKay, L. Ahrens, M. B R M ~ ,  K.Brown, 'E Clifford, R. COMOUY, E Dell, D. P. Deng, L. Hoff, I. Kewisch, G. Maldonado, B. Martin, R. Olsen, S. Peggs, E Pilat, T. Robinson, S. Sathe, T. Satogata, D. Shea, T. J. Shea, M. Tanaka, F! Thompson, S. Tepikian, C. G. Trahern, D. Trbojevils, N. Tsoupas, 3. Wei, R. Witkover, F! Zhou, BNL, Upton NY Abstract In the fall of 1995, we successfuIIy completed a major milestone in the RHlC project: the first beam test of the AGS to RHIC (MX) transfer line. The AIR serves as atest bed for the new RHtC control system. This transfer line is highly -ted, with several types of insbumenration for &mctenm ' g the extraaed beam from the AGS and for matching the beam into M C .  We describe the design and performance of the AIR with gold ions with an eye to reaching the design criteria for RHIC operation, both in beamqualityandamtrok 1 INTRODUCTION The Relativistic Heavy Ion Collidex (RHIC)[2][31 is a pair of intersectln ' g superconducting storage rings being built to study nuclear phenomena of heavy-ion collisions in the center-of-mass. The injector system for RHIC (see Fig. 1) consists of the AGS (Alternating Gradient Synchrotron), theAGS injectionBoosterandtwolinacs: atandemVan& Graaf for heavy ions, and a linac with an RFQ for protons. The Ani transfer lines consist of four pieces described in the next section. Beam will be injected into RHIC by single-bunch bucket-@bucket mfm. Multiplebun&es extracted dur- ing one AGS cycle will be injected into only one of the two RHIC Mgs however, it will be possible to switch rhgs be- liveen adjacent AGS ramps by reversing the polarity of a switch magnet between the X and Y-arcs. 2 DESIGN OF THE ATR LINE Over 770 m of transfer lines transport ions up to rigidi- ties of 100 Tm from the AGS tbroogh 80 dipoles, 31 quadntpoles, 35 a~rrectors, and 2 Lambertson magnets to the RHIC rings. All but four of the horizontal dipoles are combmed function magners. These transfet lines are di- 0 'he U-line matches the beam optics brn the AGS, and ends with zeto dispersion. There is a beam waist ofa, = & = 6mtolocateafoilforstrippingthefinal two electrons fmm gold ions (AU+~). An additional pair of switch dipolesalmosthalfway down theU-line are sometimes used to divert beam to a muon storage Mgexpe!imentlInlelatedtoRHIC. 0 The W-line tra~sports the beam fiom the end of the U- line onto a lee-right symmetry line of the two RHlC vided into fourregions as shown inFigm 1.: RHIC \-  AGS-RMC Complex figure 1: Layout of RHIC and the injector complex. Heavy ions originate at the beginning of the Tandem Van Graaf, and protons at the beginning of the linac. rings with a dispersion free c o m b d o n  of vertical and horizontal bends. A switch dipole after the W- line directs beam to either of the the RHIC rings, or if unpowered, into a beam dump just downstream of the switch. 0 The X-line bends almost 90° to the left with six tun- able quadrupoles at the end to match and inject vef- t i d y  into the clockwise (Blue) ring. In the second b a I f a U  of the clockwise ring after the Lambertson magnet, fourverticalkidsermagnetsbendtheiojected bunch onto the circulating orbit 0 The Y-line mirrors the X-line for the counterclockwise (Yellow) ring. Figure 2 shows the optical functions for the V, W, and Y-lioes. The functions for the x-line are identical to those of the Y-line, except that the horizontal dispersion, rhc is flipped in sign. 2.1 hsnslr~mentation[4] The charge in eacfi b c h  trausfd from the AGS to RHIC is measuted at five strategic points'aloag the trans- fer line, These are: (1) just after extraction from the AGS; (2) just after stripping and collimation; (3) immdht&' be- fore may into one of the two injection arcs; (4) at the end of each arc just before injection into RHIC. The detectors u ace current transformers, specmauy the Integrating cur- I 0.0 s tml 583.2 Figure 2: Optical functions for the U-W-Y beam lines from the AGS into the countefclockwise ring of RHIC. The tall elements are quadrupoles, and the shorter elements are dipoles. rent Transformer type developed by UnserlS] for LEP and purchased off-the-shelf h m  Bergoz, ?his design incor- porates two toroidal transformer cores and is particularly suited to measuring the charge in short beam bunches. Beam loss monitoring is one of the most important di- agnostic tools in setting up the LUX. Beam loss monitors for the MX and RHIC are argon filled ion chambers of es- sentially the same design as used in the Tevawn at FNAL. Ion chambers mounted on the vacuum flange downstream of each magnetic element detect the ionizing radi ion pro- duced by beam loss. Because the number of readout chan- nels is limited, some detectors are daisy-cbined on a sin- gle si@ cable. The ionization current is collected by a low leakage gated integrator and read out using the stan- dard multi-channel ADC designed by the RHIC Controls Section. Special non-tribo4e.dric cable is used to reduce noise due to mechanical motion which would compromise the pi-amp sensitivity of the system. An input circuit stretches the electron signai's rise time to milliseconds thus reducing induced noise from the kicker magnets which are time coincident with the beam. The shield of the ion cham- ber signal connectot is isolated from the enclosure to pre- vent a ground loop with the HV connector shield. The re- sult of these precautions is that a noise level of under 10 PA was observed during the All2 commissioning, allow- ing measurement of the beam 2 decades beIow the nominal design intensity. Striplinebeam position monitors (BPMs) are distributed along the AiX with 24 planes in the U and W-lines and another 12 planes in each of the X and Y-lines. The sig- naIs h m  these BPMs are canid throughphased-matchen heliax cables out of the tunnel to a V7U-basa-l sample-ad- hold systeml6l. The outputs of the analog circuits are then digitized and converted to positions which are written into VME memory. The position resolution is about lop for bunches of 2 lo7 charges. Beam profile information is measured by digitizing im- serted into the beam at various locations along the AIR one (UFl) at the beginning of the U-he, one (UF2) near beam waist in both the horizontal and vertical about 50 m into the U-line, three (UF3, UF4, UF5) at the end of the U- line, three (WF1, WF2, WF3) at the end of the W-line, two at the end the X-line, and another two at the end the Y-line. The first nvo flags in the U-line are 1 mm thick Al2Q:Cr and are designed to withstand high current beams (6 x l O I 3  protons per AGS cycle) for the muon ring experiment. The remaining 10 flags are made of 1 mil thick Al coated with 2 mils of Gd202S:Tb phosphor and are designed to with- stand RHIC beam intensities. These thin flags are designed so that up to four profiles might be taken for a single ex- tracted bunch with minimal blowup from multiple scatm- ing. Profiles are read by CCD cameras except for the first location where a CID camera is used because of its higher tolerance for radiation. Up to four !lags may be simulta- neously digitized with VME frame grabbers. The follow- ing paperr81 discusses emittance measurements using these For future running a thin gold foil for stripping the final elearons from the extracted ions will be installed in the U-line just downstream of flag UF2. Three pairs of collimator jaws will also be installed in the U-line to aid in momentum spread measurements. a g e ~  on phosphorescent flagS[l  which  an be ~ ~ t e l y  in- flags. 2.2 AGS Extraction Figure 3: Schematic of the extraction orbit. Single bunches are extracted horizontally from the AGS as .shown in Fig. 3. During the fiattop of the acceleration cy- de, two horizontal bumps are ramped to move the orbit into the gap of a fast kicker magnet at the peak of the first bump and close to a septum magnet at the peak of the sec- ond bump. At the maximum bump amplitude the septum magnet is then pulsed. Finally the kicker is fked to kick the desired bunch inward so that after 3/4 of a betatron pe- DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. DISCLAIMER This report was prepared as an amount of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. riod the imsh will arrive at the extrmion chanoel of the 3 COMMIssloNING In the fall of 1995, we COmmiSSiOned the U and W- lines, taking beam beam to the dump just downstream of the switch magnet with gold ions of momentum 1 1 2  Gevlclnucteoa (7 = 12.1). The beam intensityat thebeginning of them SMrtedat about 5 x lo6 ionsper pulse from the AGS. At the endof the heavy-ion nm the inrmsity was inueased to about 2.5 x lo8 iarsperhuch. several things were done to impvethe intenSity, in patti&, doubling the tandem output and two IeveIs of bunch coalescing in the Booster and AGS. More ?brk wil l  be done during the next heavy-ion run to increase the desired intensity per bunch to the RHIC design value of lo9 gold ions per bunch. A very important change in the AGS complex was devel- switching between AGS cycfes, With amtext-switching we were able to do most of the commissioning by stealing only an ocsasional AGS cycle for the ATR. The result was that the ATR tests had an almost negligible impact on the fixed very useful for other marhine studies of the Booster and AGS. Setring up extraction from the AGS took about four hours with dedicated beam time. Next the AGS and Booster were switched into a context-switching "ping- pong" mode where only one of every 11 cycles were ex- tracted to the ATR; the remaining 10 cydes were used for slow extracted beam to the fixed-target experiments. Later this mode of operation was shifted to a "puise-on-demand" context-switching. In the puise+ndemand mode, we used fewer than 200 cycles per 8-hour shift (< 2.5%) throughout the rest of the AGS heavy-ion run. - Initial threading of beam down the U-line was very quick, although some time was taken to adjust timing and settings for the instrumentation. Due to the smaU beam currents, only the tlags and loss monitors were used. The beginning of the W-line took longer to thread since there are a combination of horizontal and vertical bends without any flags. There is a 20° bend of 8 widely spaced gradient dipoles with a namw-aperture vertical bend between the SeCcHld and third, 'Ihe night shift made an aperture scan versus Current in the horizontal bend and were able to de termine the c o w  current setting for the momentum. Oped and ~ e r y  SUcceSSfully tested during this ~ n :  context- targe-t program. context-switching has aIS0 proven to be 3.1 AGS extraction stability After beam C o a l e g  was introduced there were only two bunches in the AGS, one with half the cutrent of the other. 'Ibis limitation was due to the pulse length of the extrac- tion kicker in the booster. 'Ihe larger current bunch was then extracted into the ATR for further studies. In tbis mn- ning mode, the radial feedback loop to the rf system within the AGS would not lock if the bunch intensity was smaller i! ."- I I - 1 . 0 " ' ~ ~ ' ' ~ ' ' '  0.0 m.0 400.0 600.0 800.0 1ooo.o CIlmnr at dl fxld. ioos) Figure 4: Stabiity of AGS exmctioa position measwed on flag UM at the beginning of the ATR versus intensity. than about 4 x lo' ions (indicated by the dashed line in Fig. 4). Fig. 4 shows the position measured on the fiag, UFI, at the begiMing of the U-line versus bunch inten- sity. "%e vertical position of the extracted beam is very stable, but the horizontal position shows some jitter, and even an apparent current dependence. We believe that this current dependence may be related to the radial feedback loop. If the ament dependence is unfolded, then the or- bit variations appear to be within f0.5 mm at UFl. This Variation should be cozrectable by the transverse dampirig system which allows for a 2 mm injection variation of the transverse orbit at a pmaX = 150 m, which when translated back to UFl corresponds to errors of about f0.7 mm. More information about the controls and physics analy- sis will be found in the following paperr81. 4 ACKNOWLEDGMENTS This paper is dedicated to the memory of Horst Foelsche who inspired much of the design and construction of the KlR. We would also like to acknowledge the h e  work of the installationand operations groups. 5 REFERENCES [ 11 Work supported by the US DOE. [2] 'RHIC Design Manual", October 1994. [3] "RHIC', M. Harrison et at., These Proceedings [4] T. J. Shea et al, 9eamInsbumentation for the RHIC Sextaot Test", p. 1521, Proc. of EPAC94, London. [5] K B. Unser, "Measuring Bunch Intensity, Beam Loss and Bunch Lifetime in LEP", h c .  IEEE part ACC. Conf., EPAC 90, p.786, Nice, France, June 1990. [6] W. A. Ryan and T. J. Shea. "An Sampling Detector for the RHIC BPM Electrunics", Proc. of the 1995 Part Acc. Conf., Dallas, to be published. [q R. L. Witkover, "Design of the Beam Profile Monitor for the RHIC Injection Line", Proceedings of the 1995 Particie AC- ceIerator Conference, to be published. [8] L. Satogata et al.. "Physics During the 1995 AGS-tO-WC Transfer Line Commissioning", "kese Proceedings. 

AGS to RHIC transfer line: Design and commissioning

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AGS to RHIC transfer line: Design and commissioning

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