Quite good agreement has been achieved between computer modeling and actual
performance of the Brookhaven 200 MeV Linac. We will present comparisons
between calculated and measured performance for the beam transport through the
RFQ, the 6 meter transport from RFQ to the linac and meching and transport
through the linac.Comment: 3 page

Alessi, J. G.

Kponou, A.

Raparia, D.

English

arXiv

Quite good agreement has been achieved between computer modeling and actual performance of the Brookhaven 200 MeV Linac. We will present comparisons between calculated and measured performance for beam transport through the RFQ, the 6 m transport from RFQ to the linac, and matching and transport through the linac

Alessi, J.G.

UNT (University of North Texas) Digital Library

XVIII International Linac Conf., Geneva, Si+ALzerland, 8/26-30/96. BNL-62963 Comparisons Between Modeling and Measured Performance of the BNL Linac* A bstrailt D. Raparia, J.  G. Alessi, A. Kponou Upton, NY, 11973, USA [q E i,:': a \ f E OCT 1 0  4998 Brookhaven National Laboratory ra-8 Quite good agreement has been achieved between computer modeling and actual performance of the Brookhaven 200 MeV Linac. We will present compar- isons between calcuiated and measured performance for beam transport through the RFQ, the 6 m trans port from RFQ to the linac, and matching and trans- port through the linac. 1 INTRODUCTION The Brookhaven 200 MeV linac serves as the injector for the AGS Booster and as well delivers beam to the Brookhaven Isotope Resource Center. It consists of a 35 keV magnetron surface plasma source, a low energy beam transport (LEBT) [l], 201 MHz radio frequency quadrupole (RFQ) [2], medium energy beam transport (MEBT) and 200 MeV Linac [3]. In this last year we have gone through a linac upgrade to get 2.5 more average current (146 ,u A) [4]. This was achieved by increasing repetition rate 5 to 7.5 Hz and increasing peak current from 25 to 39 mA. In this paper we com- pare computer modeling with actual performance. 2 LEBTANDRFQ LEBT had two pulsed solenoids, two sets of x and y steerer, beam chopper, emittance probe, and two current toroids. The chopper was removed from the h e ,  making the line shorter by 70 cm. Computer modeling of this line showed that we should move the 1st solenoid as close to the ion source as possible to reduce the beam size in the 1st solenoid and the second solenoid as close to the RFQ as possible to increase the convergence angle required by the RFQ acceptance. Figure 1 shows the ion trajectories through this line and phase space at  the exit of the ion source, middle of the line and entrance of RFQ. The RFQ acceptance is shown as a solid line ellipse. This calculation assumed that the beam space charge is neutralized. Shortening of the line resulted in lower measured emittance. Due to lower emittance and better match- ing transmission through the FWQ was improved by about 10 percent. Figure 2 shows the transmission as a function of input beam current. ~~ Work performed under the auspices of the U. S. Department of Energy. O S T I  Figure 1: Ion trajectories through the LEBT and phase space at ion-source, middle of the line, and at the entrance of the RFQ. 95 f , t , I , 90 - h w .- S B S -  ;BO- ? 75 - V .  II) .- I- 70 , 1 I I I 40 50 60 70 a0 90 I( Input Current (ma) Figure 2: RFQ transmission as a function of input current. The solid line indicates the simulation and crosses the measured values. VSTFIIBtmQN OF THIS DOCUMENT IS UNtiMmb 0 Meas. Cal. Figure 3: MEBT, 750 keV Transport Line. I J Qz Pz Ez a y  I P, Ey -0.60 0.79 9.71 -1.59 I 1.61 13.82 '' -0.31 0.66 9.80 -1.79 1 1.67 14.00 3 MEBT AND LINAC Buncher MEBT Tank 1 This is where we have recovered most of the beam losses. This line is 6 meter long and is shown in Fig- ure 3. It consists of four triplets, three bunchers, one slow chopper, one fast chopper, two emittance mea- surement units, three current transformers, two sets of x, y steerers, and a dipole to accomodate polarized beam coming at 60 deg angle. The ideal match be- tween RFQ and DTL could have been obtained with a 5 PA long FODO lattice with quadrupole spacing about PA and at least two bunchers. But the require- ment of beam chopping and polarized beam dictated a triplet solution [5]. The first quadrupole after the RFQ was too far; by the time the beam reached the quadrupole it had gone through a waist in the x plane, hence was diverging in both planes. No matter which polarity quad one puts, beam size in the other direction is very big. Also the longitudinal beam size is too big before it reaches the first buncher. To improve the capture and trans- mission of the beam in MEBT, the RFQ end flange at the high energy end was modified to accommodate a permanent magnet quadrupole (PMQ). The PMQ was similar to one as used in the SSC DTL [SI. We have also rearranged the gate valve and current trans formers at the beginning of the line, and also measured and aligned all the quadrupoles very carefully. Mea- surement as well as simulation showed that as little as a 1.5 degree quadrupole rotation can increase the emittance by 50 %. The last quadruplet was changed to a triplet to reduce coupling. Figure 4, shows the measured and calculated phase spaces after the sec- ond buncher. Table 1 shows calculated (TRACE3D) and measured Twiss parameters for Figure 4. Table 2, compares measurements and PARMILA re- sults at various locations. We believe that lower values for currents after the second buncher and and at the entrance of the Linac are caused by the grids in the 50.0 41.0 62.9 57.8 42.4 37.3 62.9 53.2 27.4 28.4 37.1 37.7 Figure 4: Measured (upper two) and calculated (lower) phase space after the second buncher. 1 . TT Planes I X I Y II Tank 9 I 26.2 I 26.7 I 36.4 I 35.9 ' Emittance, (nor,RMS) A mm mrad RFQ 0.400 0.400 0.375 0.375 Buncher 0.44 0.56 0.47 0.57 200 MeV 1.32 2.8 1.85 1.92 Table 1: Calculated and measured Twiss parameters after the second buncher. p is in mm/mrad and E (unnor.,RMS) in A mm mrad. buncher drift tubes (four in each buncher). These grids are placed in the bunchers to reduce RF defocusing ef- fects. Emittance measurements at 200 MeV are done using profiles at five places. Agreement between cal- culations and measured Twiss parameters a t  200 MeV is poor because there are 295 quadrupoles, and cali- bration and misalignment errors are not known to a good accuracy. Table 2: Comparison between simulations and mea- sured beam parameters. 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 account 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 responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process, or service by trade name, trademark, manufac- turer, 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 henin do not necessarily state or reflect those of the United States Government or any agency thereof. 4 ALGEBRAIC RECONSTRUCTION TECHNIQUE (ART) A radiograph of the beam at the BLIP target taken last year showed a tilted ellipse in the x-y plane. Sources of this coupIing can be quad rotation or vertical offset in the dipole. This triggered the need for an x-y density profile. We found that algebraic reconstruction tech- nique (ART) could help us. ART was introduced by Gordan, Bender and Herman [7] for solving the prob- lem, of three dimensional reconstruction from projec- tions. The ART algorithms have a simple intuitive ba- sis. Each projected density is thrown back across the reconstruction space in which the densities are itera- tively modified to bring each reconstructed projection into agreement with the measured projection. The r e  construction space is an n x n array of smalI pixeis, p is grayness or density number which is uniform within the pixel but different from other pixels. Assume P is a matrix of m x n2 and the m component column vector R Let p i j  denote the (i j) th element of P , and & demote the ith element of reconstructed projection vector R. For 1 5 i 5 rn, Ni is number of pixels under projection K, defined as Ni = c jp t j .  The density number p j  denotes the value of p j  after q iterations. After q iterations the intensity of the ith recon- structed projection ray is R! = CPijP;, j and the density in each pixel is with starting value pTo = 0 p;g+l = pj'+pi j  & - R: N, where is the measured projection and, m,if (q+l) is divisible m the remainder of dividing (q+I)by m, otherwise i =  { and, It is necessary to determine when an iterative a lge  rithm has converged to a solution which is optimal ac- cording to some criterion. We are using as the criteria of convergence the discrepancy between the measured and calculated projection elements We have added a third wire at 45 degree in wire scanners in two places. Figure 5 compares the mea- sured and reconstructed profiles in the BLIP transfer line [8] after the 1st octupole and figure 6 shows the reconstructed 3D density distribution. Figure 5: Beam projection on x, y, and 45 degree planes. Figure 6: Reconstructed 3D density distribution using ART. 5 REFERENCES [l] J. G. Alessi, et a1,"The AGS H- RFQ Preinjedor" Proc. 1988 Linear Accelerator Conference , CEBAF- Report-8%OOl, pp196. (1989). [2] R A. Gough, et al, "Design of an RFQ Based H- Injec- tor for the BNL/FNL 200 MeV Proton Linacs", Proc. 1986 Linear Accelerator Conference, SLAC-Report- 303, pp303 (1986). [3] G. W. Wheeler, et 01, "The Brookhaven 200 MeV Pro- ton Linear Accelerator", Particle Accelerator, VoI. 9, [4] J. G. Alessi, et 01, "Upgrade of the Brookhaven 200 MeV Linac", these Proceeding. [SI D. Raparia, "RFQ-DTL Matching Solution For Dif- fereat Requirements" Proc. 1995 Particle Accelerator Conference,ppl385 (1995). SSC Drift-'ILbe Linac Design", Proc. 1992 Linear Accelerator Conference, AECG 10728, Voll , pp199 (1992). [7] R Gordon, e t  al, "Three-Dimensional Reconstruction from Projections: A Review of Algorithms", Interna- tional Review of Cytology, Vol. 38, pp 111, (1974). PP 1, (1979). [6] D. Raparia, et al, [SI A. Kponou, e t  al, these proceeding. 

Comparisons between modeling and measured performance of the BNL Linac

Quite good agreement has been achieved between computer modeling and actual performance of the Brookhaven 200 MeV Linac. We will present comparisons between calculated and measured performance for the beam transport through the RFQ, the 6 meter transport from RFQ to the linac and meching and transport through the linac

Raparia, D

Alessi, J G

Kponou, A E

CERN Document Server

1Comparisons Between Modeling and Measured Performance of theBNL LinacD. Raparia, J. G. Alessi, A. KponouBrookhaven National LaboratoryUpton, NY, 11973, USAAbstractQuite good agreement has been achieved betweencomputer modeling and actual performance of theBrookhaven 200 MeV Linac. We will present compar-isons between calculated and measured performancefor beam transport through the RFQ, the 6 m trans-port from RFQ to the linac, and matching and trans-port through the linac.1 INTRODUCTIONThe Brookhaven 200 MeV linac serves as the injectorfor the AGS Booster and as well delivers beam to theBrookhaven Isotope Resource Center. It consists of a35 keV magnetron surface plasma source, a low energybeam transport (LEBT) [1], 201 MHz radio frequencyquadrupole (RFQ) [2], medium energy beam transport(MEBT) and 200 MeV Linac [3]. In this last year wehave gone through a linac upgrade to get 2.5 moreaverage current (146  A) [4]. This was achieved byincreasing repetition rate 5 to 7.5 Hz and increasingpeak current from 25 to 39 mA. In this paper we com-pare computer modeling with actual performance.2 LEBT AND RFQLEBT had two pulsed solenoids, two sets of x andy steerer, beam chopper, emittance probe, and twocurrent toroids. The chopper was removed from theline, making the line shorter by 70 cm. Computermodeling of this line showed that we should move the1st solenoid as close to the ion source as possible toreduce the beam size in the 1st solenoid and the secondsolenoid as close to the RFQ as possible to increase theconvergence angle required by the RFQ acceptance.Figure 1 shows the ion trajectories through this lineand phase space at the exit of the ion source, middle ofthe line and entrance of RFQ. The RFQ acceptance isshown as a solid line ellipse. This calculation assumedthat the beam space charge is neutralized.Shortening of the line resulted in lower measuredemittance. Due to lower emittance and better match-ing transmission through the RFQ was improved byabout 10 percent. Figure 2 shows the transmission asa function of input beam current.Work performed under the auspices of the U. S. Departmentof Energy. Sol.dat | 8-24-95 | em solenoids                                               -10.00 10.00  -225.00225.00  ...............................................................................................A= -0.52  B= 0.019  E=0.853E-04  N=474                                          15:30:59-50.00 50.00  -20.0020.00  ........................................................... .................................................................................................. .................................................................................................................................................... ................... ................................................ ..............A= -0.69  B= 1.083  E=0.132E-03  N=474                                          29-AUG-95-10.00 10.00  -125.00125.00  ................................................................ ......................................................................................................................................... ..................................................................................................A= 2.53 B= 0.090 E=0.610E-04  N=474                                          Npt=474  Ngood=474  Alpha= 2.495  Beta= 0.087  Emit=0.3250E-03  MMF=0.034       0.00 161.11 322.22 483.33 644.44 805.56 966.67 1127.78 1288.89 1450.00  -50.0050.00  Figure 1: Ion trajectories through the LEBT andphase space at ion-source, middle of the line, and atthe entrance of the RFQ.Figure 2: RFQ transmission as a function of inputcurrent. The solid line indicates the simulation andcrosses the measured values.Figure 3: MEBT, 750 keV Transport Line.3 MEBT AND LINACThis is where we have recovered most of the beamlosses. This line is 6 meter long and is shown in Fig-ure 3. It consists of four triplets, three bunchers, oneslow chopper, one fast chopper, two emittance mea-surement units, three current transformers, two setsof x, y steerers, and a dipole to accomodate polarizedbeam coming at 60 deg angle. The ideal match be-tween RFQ and DTL could have been obtained witha 5  long FODO lattice with quadrupole spacingabout  and at least two bunchers. But the require-ment of beam chopping and polarized beam dictateda triplet solution [5].The rst quadrupole after the RFQ was too far; bythe time the beam reached the quadrupole it had gonethrough a waist in the x plane, hence was divergingin both planes. No matter which polarity quad oneputs, beam size in the other direction is very big. Alsothe longitudinal beam size is too big before it reachesthe rst buncher. To improve the capture and trans-mission of the beam in MEBT, the RFQ end angeat the high energy end was modied to accommodatea permanent magnet quadrupole (PMQ). The PMQwas similar to one as used in the SSC DTL [6]. Wehave also rearranged the gate valve and current trans-formers at the beginning of the line, and also measuredand aligned all the quadrupoles very carefully. Mea-surement as well as simulation showed that as littleas a 1.5 degree quadrupole rotation can increase theemittance by 50 %. The last quadruplet was changedto a triplet to reduce coupling. Figure 4, shows themeasured and calculated phase spaces after the sec-ond buncher. Table 1 shows calculated (TRACE3D)and measured Twiss parameters for Figure 4.Table 2, compares measurements and PARMILA re-sults at various locations. We believe that lower valuesfor currents after the second buncher and and at theentrance of the Linac are caused by the grids in theFigure 4: Measured (upper two) and calculated (lower)phase space after the second buncher.Planes X YxxxyyyMeas. -0.60 0.79 9.71 -1.59 1.61 13.82Cal. -0.31 0.66 9.80 -1.79 1.67 14.00Table 1: Calculated and measured Twiss parametersafter the second buncher.  is in mm/mrad and (unnor.,RMS) in  mm mrad.buncher drift tubes (four in each buncher). These gridsare placed in the bunchers to reduce RF defocusing ef-fects. Emittance measurements at 200 MeV are doneusing proles at ve places. Agreement between cal-culations and measured Twiss parameters at 200 MeVis poor because there are 295 quadrupoles, and cali-bration and misalignment errors are not known to agood accuracy.Location 94-95 95-96Sim. Meas. Sim. Meas.Current mARFQ 50.0 50.0 62.9 62.9Buncher 50.0 41.0 62.9 57.8MEBT 42.4 37.3 62.9 53.2Tank 1 27.4 28.4 37.1 37.7Tank 9 26.2 26.7 36.4 35.9Emittance, (nor,RMS)  mm mradRFQ 0.400 0.400 0.375 0.375Buncher 0.44 0.56 0.47 0.57200 MeV 1.32 2.8 1.85 1.92Table 2: Comparison between simulations and mea-sured beam parameters.4 ALGEBRAICRECONSTRUCTIONTECHNIQUE (ART)A radiograph of the beam at the BLIP target taken lastyear showed a tilted ellipse in the x-y plane. Sources ofthis coupling can be quad rotation or vertical oset inthe dipole. This triggered the need for an x-y densityprole. We found that algebraic reconstruction tech-nique (ART) could help us. ART was introduced byGordan, Bender and Herman [7] for solving the prob-lem of three dimensional reconstruction from projec-tions. The ART algorithms have a simple intuitive ba-sis. Each projected density is thrown back across thereconstruction space in which the densities are itera-tively modied to bring each reconstructed projectioninto agreement with the measured projection. The re-construction space is an n x n array of small pixels, is grayness or density number which is uniform withinthe pixel but dierent from other pixels. Assume Pis a matrix of m x n2and the m component columnvectorR. Let pi;jdenote the (i,j)th element of P , andRidemote the ith element of reconstructed projectionvector R. For 1  i  m, Niis number of pixels underprojection Ri, dened as Ni=Pjp2i;j. The densitynumber qjdenotes the value of jafter q iterations.After q iterations the intensity of the ith recon-structed projection ray isRqi=Xjpi;jqj;and the density in each pixel isq+1j= qj+pi;jRi RqiNiwith starting value 0j= 0where Riis the measured projection and,i =m,if (q+1) is divisible mthe remainder of dividing (q+1)by m, otherwiseand,qj=8<:0; if q 0qj; if 0  qj 11; if qj 1It is necessary to determine when an iterative algo-rithm has converged to a solution which is optimal ac-cording to some criterion. We are using as the criteriaof convergence the discrepancy between the measuredand calculated projection elementsDq=(1mmXi=1(Ri Rqi)2Ni)12We have added a third wire at 45 degree in wirescanners in two places. Figure 5 compares the mea-sured and reconstructed proles in the BLIP transferline [8] after the 1st octupole and gure 6 shows thereconstructed 3D density distribution.Figure 5: Beam projection on x, y, and 45 degreeplanes.Figure 6: Reconstructed 3D density distribution usingART.5 REFERENCES[1] J. G. Alessi, et al,\The AGS H RFQ Preinjector"Proc. 1988 Linear Accelerator Conference , CEBAF-Report-89-001, pp196. (1989).[2] R. A. Gough, et al, \Design of an RFQ Based H Injec-tor for the BNL/FNL 200 MeV Proton Linacs", Proc.1986 Linear Accelerator Conference, SLAC-Report-303, pp303 (1986).[3] G. W. Wheeler, et al, \The Brookhaven 200 MeV Pro-ton Linear Accelerator", Particle Accelerator, Vol. 9,pp 1, (1979).[4] J. G. Alessi, et al, \Upgrade of the Brookhaven 200MeV Linac", these Proceeding.[5] D. Raparia, \RFQ-DTL Matching Solution For Dif-ferent Requirements" Proc. 1995 Particle AcceleratorConference,pp1385 (1995).[6] D. Raparia, et al, \ SSC Drift-Tube Linac Design",Proc. 1992 Linear Accelerator Conference, AECL-10728, Vol1 , pp199 (1992).[7] R. Gordon, et al, \Three-Dimensional Reconstructionfrom Projections: A Review of Algorithms", Interna-tional Review of Cytology, Vol. 38, pp 111, (1974).[8] A. Kponou, et al, these proceeding.

Comparisons Between Modeling and Measured Performance of the BNL Linac

Abstract

Similar works

Full text

Available Versions

UNT (University of North Texas) Digital Library

CERN Document Server