The 75-keV injector and 6.7-MeV RFQ that comprise the first portion of the
cw, 100-mA proton linac for the accelerator production of tritium (APT) project
have been built and operated. The LEDA RFQ has been extensively tested for
pulsed and cw output-beam currents <=100 mA. Up to 2.2 MW of cw rf power from
the 350-MHz rf system is coupled into the RFQ, including 670 kW for the cw
proton beam. The emittance for a 93-mA pulsed RFQ output beam, as determined
from quadrupole-magnet-scan measurements, is ex x ey = 0.25 x 0.31 (pi mm
mrad)2 [rms normalized]. A follow-on experiment, to intentionally introduce and
measure beam halo on the RFQ output beam, is now being installed.Comment: Paper TUD14 for the XX International Linac Conference (LINAC2000), 3
  pages, 10 figure

Schneider, J. David

Smith, Jr., H. Vernon

English

arXiv

The 75-keV injector and 6.7-MeV RFQ that comprise the first portion of the cw, 100-mA proton linac for the accelerator production of tritium (APT) project have been built and tested. The LEDA RFQ has been extensively tested for pulsed and cw output-beam currents {le} 100-mA. Up to 2.2 MW of cw rf power from the 350-MHz rf system is coupled into the RFQ, including 670 kW for the cw proton beam. The RFQ output beam emittance for a 93-mA pulsed RFQ output beam, determined from quadrupole-magnet-scan measurements, is {var_epsilon}{sub x} x {var_epsilon}{sub y} = 0.25 x 0.31 ({pi} mm mrad){sup 2} [rms normalized]. A follow-on experiment, to intentionally introduce and measure beam halo on the RFQ output beam, is now being installed

SMITH, H. V.

SCHNEIDER, J. D.

UNT Digital Library

P..Appmvedforpubl;craleese;dkdribtdionisurrlimifed.Title: Status Report onthe Low-Energy Demonstration Accelerator (LEDA)Author(s): H. Vernon Smith, Jr.J. David SchneiderSubmitted to: XX International Linac Conference (LINAC2000)Monterey, California USA21-25 August 2000Los AlamosNATIONAL LABORATORYLosAlamosNationalLaboratory,an afr%mativeationlequal opportunityemployer,laoperatedby the UniveraityofCaliforniaforthe U.S.Departmentof EnergyundercontractW-7405-ENG-36. Byacceptanceofthisarticle,the publisherracognuea thatthe U.S. Governmentretelrraa nonexclusive,royalty-freekense to publishorreproducethe publishedformofthiscontribution,orto allowotheratodo so,for U.S.Governmentpurposes.LosAlamosNationalLeboratoryrequestathatthe publisher[dentifyfhisartideaswotl( performedundertheauspicesoftie U.S. Deparbnentof Energy.LosAlamosNationalLaboratorystmnglysupportsacademlcfreadom and a researcher’srighttopublish;as an institution,however,the Laboratotydoesnotendoraethe viewpointofa publicationorguaran~- itstechnicalcareotneas.Form836 (8/00).— -—.-, —.— .. . . . . . ... .DISCLAIMERThis report was prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof..—.- ——— ,——...smy.,m.-. ,... . . . . ..W ->-+7. <,* ., . . -,.,-. , . . . ,., --; ----~ -. —--. — ,2 . .,,,. ,-. . . . . .DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.. .. --—-— ..—..—..—r— ---- ‘. .—..,m-.- ?.. .,— ..-,.. ..---e----’: ----- ,.r%-..; --; r - .-. .STATUS REPORT ON THE LOW-ENERGY DEMONSTRATIONACCELERATOR (LEDA)*REcElv~pJH. Vernon Smith, Jr. and J. D. Schneider,Los Akunos National Laboratory, Los Alamos, NM 87545, USA DEL’ t 32800 ~Abstract ‘The 75-keV injector and 6.7-MeV RFQ that comprisethe first portion of the cw, 100-mA proton Iinac for theaccelerator production of tritium (APT) project have beenbuilt and tested. The LEDA RFQ has been extensivelytested for pulsed and cw output-beam currents <100-mA.Up to 2.2 MW of cw rf power from the 350-MHZ rfsystem is coupled into the RFQ, including 670 kW for thecw proton beam. The RFQ output beam ernittance for a93-mA pulsed RFQ output beam, determined fromquadrupole-magnet-scan measurements, is EX X &y =0.25 X 0.31 (n mm mad)’ [rms normalized]. A follow-onexperimen~ to intentionally introduce and measure beamhalo on the RFQ output beam, is now being installed.1 INTRODUCTIONThe LEDA RFQ [1] is a 100% duty factor (CW)linacthat delivers >100 mA of W beam at 6.7 MeV [2-4]. The8-m-long, 350-MHz RFQ structure [5] accelerates the dc,75-keV, 110-mA II beam from the LEDA injector [6]with -94% trans~ssion. The primary objectives ofLEDA are to verify the design codes, gain fabricationknowledge, understand beam operation, measure outputbeam characteristics, learn how to minimize the beam-tripfrequency, and improve pre&ction of costs andoperational availability for the full 1000- to 1700-MeVAPT accelerator. This paper summarizes the RFQcommissioning results given in Refs. [1, 3,4, 7-13].2 LEDA CONFIGURATION -The accelerator configuration for beam commissioningof the LEDA RFQ is shown in Fig. 1. Major subsystems—- A.. .RFQ ~ HE,BT —Figure 1. LEDA conf@ration for RFQ commissioning.* Worksupportd by the US Departmentof Energy.Ion Source SolmoldSxtmior ~ M+ 1& y.12Figure 2. The LEBT beamline with optics and diagnostics.are the injector [6], ion source and low-energy beamtransport (LEBT); RFQ [1, 4, 5]; high-energy beam &ans-port (HEBT) [14]; and the beamstop [15]. The injector(Fig. 2) matches the 75-keV, 110-mA dc proton beam intothe RFQ. Simulations of offline injector measurements[16] indicate the RFQ input beam rms normalizedernittance is <0.23 n mm mrad [6]. A current modulatorfeedkg the microwave magnetron provides beam pulsing[17] for commissioning and beam-tuning activities. Theon-line LEBT diagnostics include a pulsed-current toroid,located directly before the RFQ (AC toroid 3), that is usedin deterr&dng the RFQ transmission.A complete description of the LEDA RFQ, includingthe RFQ x-f-fieldtuning procedure, resonance control, andoperation with the high-power rf (HPRF) and low-level rf(LLRF) systems, is given in [1, 4,5, 9, and 11] and thereferences contained therein. A schematic of the LEDAHEBT showing the location of beamline optics anddiagnostics is given in Fig. 3. The fi.mction of the LEDAHEBT is to characterize the properties of the beam andtransport the 6.7-MeV, 100-mA RFQ output beam withlow losses to a water-shielded ogive beamstop [15]. Thebeamhe optics consist of four quadrupole-singlet andtwo X-Y steering magnets.Capadtive Pmba1Ban! Profiledngha unit wlm scanner.#lC & DICTomId BIF Pmflle I h+ YRFQt.-RGA L-Z Bum StopFigure 3. Layout of HEBT bearnline optics anddiagnostics. Beam direction is from left to right.4J.worn 12076-3 1?/17/39 1#17n9 !2n7m W17.S9 Wtzw la17J5s w17m161s 16,49 17.16 17X5 m14 im.Y I*12 Isa 2==TimeFigure 4. Archived RFQ output beam current (30-s inter-vals) for a 3.3 hr period on Dec. 17, 1999. Any beaminterruptions during the last 118 min are <30-s long.The HEBT beam diagnostics [18] allow pulse&beam-current, dc-bearn-curren~ and bunched-beam-current aswell as transverse centroid, longitudinal centroid (i.e.,beam energy from time-of-flight and beam phase), andtransverse beam profile (wire scanner and beam-inducedfluorescence) measurements.3 BEAM COMMISSIONING RESULTSAND DISCUSSIONWe have accumulated 21 hr of LEDA RFQ operationwith >99 mA of cw output beam current and >110 hr with>90 mA of cw output beam current [11] since modifyingthe injector and increasing the RFQ rf fields to 5-10%above the design values as described in [1], [4], and [11].For one run of 118 min (Fig. 4), most of the beaminterruptions were 1-6 s in duration (Fig. 5). Recoveryfrom these interruptions, most of them arising from short-duration injector and/or rf-system sparks, was automatic(no operator intervention).We find that during pulsed beam operation for RFQ rf-field levels at the design value, for pulse Iengths >200 W,1#17m Ilmxca30I25-az:20.aL%15.5z ) --J310- —E% ~. -048121620242832 364044’43525660Trip Duration (see)Figure 5. The number of beam trips vs. trip duration (dataarchived in 1s intervals) for a 9-hr time period thatincludes the 3.3-hr interval displayed in Fig. 4.10080 -2&60-E: 40-520 -0-0 100 200 300 400Time (p)Figure 6. RFQ output beam current vs. time into a 300-p.seclong pulse for the design RFQ rf-field level.and for RFQ output beam currents >90 mA, the RFQtransmission drops abruptly about 100 w into the beampulse [11]. The transmission then remains constant at thelower value for the duration of the pulse, including cwoperation. The RFQ output beam current for a 300-Wec-long beam pulse is shown in Fig. 6. The current abruptlydrops by -10% about 125 p.sec into the pulse. Figure 7shows the measured values for the total beamtransmission at the start and end of a 500+s, 2-Hz, 90-mA beam pulse. At the end of the pulse the totaltransmission deviates from the PARMTEQM predictionfor 108-mA output beam current over the field-level range88-98% of the design (Fig.7). The total transmission at thestart of the pulse follows the PARMTEQM prediction forthe range 0.91-1.1 of the design rf-field level. For outputbeam currents >90 mA, e.g. 100 mA, the RFQ trans-mission over the whole pulse is increased to the designvalue by increasing the rf-fieId level to 105-110% of thedesign field. Both the rf power system and the RFQcooling system allow this increase —the only drawback isthat the RFQ requires 10-20% more input power.The LEDA RFQ output beam emittance is determined[12,13] from quadrupole-magnet scan measurements [12].For a 93-mA puked beam, three x quad scans are given inFig. 8 and three y quad scans in Fig. 9: also shown are thequad-scan simulations obtairikd using the particle-optics1.00-0.90-2 0.80-$Eg 0.70 -/g #m=a —PAPJ.47EQM 10Sm4eakulaKorI0.50- - Total rramm&h (end of puke)/.+ TotalLrammsslen(Mst100 IS@0.407 1 ! I0.s5 0.s 0.95 1 1$5 1.1 1.15RFQ Cavity Field Amplitude(1.00= design)Figure 7. RFQ total and accelerated beam transmissionvs. rf cavity field level at the start (crosses) and at the end(dashes) of a 500-W-long, 90-mA beam pulse.“,k-4,4/E — — —J 6“ t),4 \4 ‘.x ● Measured mm width2 “~ LNAC014.5 5.5 6.5 7.5 8.5 9.6 10.5QZ (T/m)Figure 8. 93-mA x-scan data (diamonds) taken on threedifferent days. The LINAC calculation (triangles, line)has Twiss parameters as described in the text.code LINAC. The LINAC curves in Figs. 8 and 9 aredetermined by starting with the RFQ output beam Twissparameters calculated using PARMTEQM, then adjustingthese Twiss parameters to give the “fits” to the datashown in Figs. 8 and 9 [12]. The resulting RFQ outputbeam Twiss parameters are ~ = 1.8, ~ = -2.5, (3X= 36cm, (3Y= 89 cm, &X=0.25 nmmmrad, and EY=0.31 nmmmrad (rms normalized) [12]. The beam-optics codeIMPACT, which, like LINAC, includes non-linear space-charge effects, is used to calculate the beam profiles foreach of the quadruple magnet settings used in the quadscans [13]. LINAC has 2-D (r-z) space charge; IMPACT,3-D. The Twiss parameters given above are used in thesecalculations. In Fig. 10 samples for 3 points in the x quadscan are given as a) - c) @3g. 8] and for 3 points in the yquad scan as d) - f) [Fig. 9]. A computer program thatadjusts the Twiss parameters to obtain the best global fitto the measured beam profiles is being considered.4 SUMMARYThe LEDA RFQ has operated with >99-mA cw outputbeam for 21 hr cumulative: it has operated >110 hrcumulative with >0-mA cw output beam. The RFQoutput beam emittance for a 93-mA pulsed beam, deter-mined from quadrupole-magnet-scan measurements, is~ X&, = 0.25X 0.31 (n mm mrad)’ [rms normalized]. Weare now preparing to intentionally introduce and measurethe beam halo in a 52-magnet FODO lattice [19, 20].16-14-LA12-d)~lo -k w T~6- \ / ~ ~.} 6- 11 ●4-● Measuredrms width2- 4-L[NAc6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5QI (?’/m)Figure 9. Same as Fig 8, except a y scan.Figure 10. IMPACT calculation (dashed) of the meas-ured (solid lines) 93-mA x- (top) and y-scan (bottom)profiles using the Twiss parameters in the text [12,13].[1][2][3][4][5][6][7][8][9]REFERENCESL. M. Young et al., “High Power Operations of LEDA,” thisConf.J. D. Schneider, et al., “LEDA – A High-Power Test Bed ofInnovation and Opportunity,” this conference.H. V. Smith, Jr., et al., ‘TJpdate on the Commissioning ofthe Low-Energy Demonstration Accelerator (LEDA) Radio-Frequency Quadruple (RFQ),” Proc. 2nd ICFA AdvancedAccelerator Workshop on the Physics of High-BrightnessBeams (Los Angeles, 9-12 November 1999) (in press).L. M. Young, et al., “Low-Energg DemonstrationAccelerator (LEDA) Radio-Frequency Quadru@e (RFQ)Results,” ibid (in press).D. Schrage et al., “CW RFQ Fabrication and Engineering,”Proc. LINAC98 (Chicago, 24-28 Aug. 1998), pp. 679-683.J. Sherman et al., “Status Report on a dc 130-mA, 75-keVProton Injector; Rev. Sci. Instrum. 69 (1998) pp. 1003-8.K. F. Johnson et al., “Commissioning of the Low-EnergyDemonstration Accelerator (LEDA) Radio-FrequencyOuadruoole (RlO,” Proc. PAC99 (New York, 29 March -2~pril 1999) Pp. 3~28-3530.J. D. Schneider. “Ooeration of the Low-Enerw Demon-stration Accele~toc ‘the Proton Injector for A@T,” Proc.PAC99 (New York, 29 March -2 April 1999) pp. 503-507.H. V. Smith, Jr., et al., “Commissioning Results from the.Low-Energy Demonstration Accelerator (LEDA) Radio-Frequency Quadruple (RFQ),” Proc. EPAC2000 (Viem&26-30 June 2000) (in press).[10] J. D. Schneider, “Overview of High-Power CW ProtonAccelerators,” ibid. (in press).[11] L. J. Rybarcyk et al., “LEDA Beam Operations Milestone& Observed Beam Transmission Characteristics,” this conf.[12] M. E. Schu@e et al., “Beam Emittance Measurements forthe Low-Energy Demonstration Accelerator Radio-Frequency Quadruple,” this conf.[13] W. P. Lysenko et al., “Determining Phase-Space Propertiesof the LEDA RFQ Output Beam,” this conf.[14] W. P. Lysenko et al., “High Energy Beam TransportBeamline for LEDA.” Proc. LINAC98 (Chica~o, 24-28August 1998) pp. 4961498..-[15] T. H. Van Hagan et aL, “Design of an Ogive-ShapedBearnstop,” ibid., DD. 618-620.[16] H. V. S~t.lL Jr.; ;tal., “Comparison of Simulations withMeasurements for the LEDA LBBT W Beam,” Proc.PAC99 (New York, 29 March -2 April 1999) pp. 1929-31.[17] T. Zaugg et al., “Operation of a Microwave Proton Sourcein Pulsed Mode;’ Proc. LINAC98 (Chicago, 24-28 August1998) RD.893-895.[18] J. D: Gilpatrick et al., “Beam DMgnostic Instrumentationfor the Low-Energy Demonstration Accelerator (LEDA):Commissioning and Operational Experience,” Proc.EPAC2000 (Vienna, 26-30 June 2000) (in press).[19] P. L. Colestock et al., “The Beam Halo Experiment at theLEDA Facility: a First Test of the Core-Halo Model;’ this[20] ~% Wangler, “Beam Halo in Proton Llnac BearosV ibid.

Status Report on the Low-Energy Demonstration Accelerator (LEDA)

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