Emittance Dilution Dilution In Emittance In HERA-p: HERA-p: Lessons Lessons and and Overview Overview R. R. Wanzenberg Wanzenberg DESY, Notkestr. 85, 22603 Hamburg, Germany DESY, Notkestr. 85, 22603 Hamburg, Germany Abstract. Protons of an energy of 920 GeV collide with positrons or electrons (energy 27.5 GeV) in the HERA Abstract. of anToenergy 920 luminosity GeV collideanywith positrons or electrons 27.5Different GeV) in sources the HERA acceleratorsProtons at DESY. obtain of a high emittance dilution must be(energy minimized. of accelerators at DESY. To are obtain a high Effects luminosity anyfrom emittance dilution mustoscillation be minimized. Differentofsources potential emittance growth discussed. arising a coherent injection or a mismatch the beta-of potential growth are discussed. Effects arisingdilution from a coherent oscillation or a mismatch of the betafunctionsemittance are the main sources of transverse emittance at HERA.injection In addition a longitudinal emittance growth functions are the main sources of transverse emittance dilution at HERA. In addition a longitudinal emittance growth during the acceleration of the protons has been observed in HERA. Finally the emittance growth due to intra-beam during the isacceleration of the protons has been observed in HERA. Finally the emittance growth due to intra-beam scattering briefly discussed. scattering is briefly discussed. oscillation, aamismatch mismatchofofthe thelinear linearbeam beamoptics optics(beta(betaoscillation, function or dispersion), nonlinear fields or coherent function or dispersion), nonlinear fields or coherent beam instabilities. instabilities. The The different different effects effects are areestimated estimated beam in the following sections for the HERA-p ring based in the following sections for the HERA-p ring based on the data and formulas from Ref. [2]. on the data and formulas from Ref. [2]. TABLE1.1.HERA HERAparameters parameters(pre (preupgrade). upgrade). TABLE Parameter HERA-p HERA-e Parameter HERA-p HERA-e 920 27.5 EE/GeV / GeV 920 27.5 I/mA 100 50 I / mA 100 50 bunches 180 189 ##bunches 180 189 10 7.3 3.5 NN/10 / 1010 7.3 3.5 41 5.0 8 /nm x 5.0 41 εx / nm 0.1 11 0.1 εy/εx 1.1 19 19 1.1 σoz z//cm cm Scattering of particles, such as residual gas Scattering of particles, such as residual gas scattering or intra-beam beam scattering also results scattering or intra-beam beam scattering also results inin an emittance emittance growth. growth. Intra-beam Intra-beamscattering scattering(IBS) (IBS)isisa a an multiple Coulomb Coulombscattering scatteringprocess processofofthe theparticles particlesinin multiple the bunch, bunch, which which cause cause an an emittance emittance growth growth ofofthe the the beam inin all all three three beam beam dimensions. dimensions. The Thelongitudinal longitudinal beam emittance growth growth due due toto IBS IBS isisaagood good candidate candidatefor for emittance the observed observed generation generation ofofcoasting coastingbeam, beam,which whichmay may the resultinto intobackground backgroundproblems problemsfor forHERA-B HERA-B[3]. [3]. result INTRODUCTION INTRODUCTION HERA, circumference of of about about 6.3 6.3 km, km, isis HERA, with with aa circumference the largest accelerator facility at DESY in Hamburg. A the largest accelerator facility at DESY in Hamburg. A 920 GeV proton beam and a 27.5 GeV polarized 920 GeV proton beam and a 27.5 GeV polarized positron electron beam beam are are provided provided for for four four high high positron or or electron energy physics experiments. HI and ZEUS are e/p energy physics experiments. H1 and ZEUS are e/p collider while two two fixed fixed target target collider experiments, experiments, while experiments use of of the the polarized polarized ee++ (or (or ee")-beam experiments make make use )-beam (HERMES) or the halo of the p-beam (HERA-B). The (HERMES) or the halo of the p-beam (HERA-B). The two accelerator rings for the p and e-beam are shown two accelerator rings for the p and e-beam are shown in 1. The beam parameters parameters which which were were used used in Fig. Fig. 1. The basic basic beam until the year 2000 are listed in Table 1. During until the year 2000 are listed in Table31 1. During aa -2 -11 and a typical luminosity of of 1.8 1.8 10 1031 cm cm'V typical run, run, aa peak peak luminosity s and a 30 2 -2 -1 specific of 0.8 0.8 10 1030 cm^s^mA" have been been specific luminosity luminosity of cm s mA-2 have achieved 6). In In 2001 2001 the the interaction interaction regions regions achieved (see (see Fig. Fig. 6). were upgraded for an increase in the the specific specific luminosity by a factor factor of 2.76. Ref. Ref. [1] [1] presents presents further HERA parameters and and future future further details on these HERA plans. 8y/8X TRANSVERSEEMITTANCE EMITTANCE TRANSVERSE DILUTION DILUTION The The emittance emittance dilution dilution ininthe thetransverse transverseplanes planesisis mainly mainly caused caused from from injection injection errors errors atat HERA. HERA.After After each each magnet magnet cycle cycle aa careful careful adjustment adjustmentofofthe thetunes, tunes, energy energy and and injection injection trajectory trajectoryisis necessary necessarysince sincethe the magnetic magnetic fields fields inin the thesuperconducting superconductingmagnets magnetsdiffer differ from from cycle-to-cycle cycle-to-cycle due due toto the the induced induced persistent persistent currents. currents. The The reproducibility reproducibility ofof the the injection injection trajectory, trajectory, the the precision precision ofofthe thebeam beamposition positionmonitors monitors (BPMs) (BPMs) of of about about0.5 0.5mm mm(resolution (resolution0.1 0.1mm) mm)and andthe the kicker kicker ripple ripple of of about about11%%results resultsinto intoa atotal totalinjection injection trajectory trajectory error error ofofabout about11mm. mm. This Thisisisachieved achievedafter after pilot injection of a few proton bunches which pilot injection of a few proton bunches whichare areused used to to adjust adjust the the trajectory trajectory ofof the the injected injected beam beam toto the the closed closed orbit. orbit. The The maximum maximum beta-function beta-function atat the the FIGURE 1. Photograph of of the the HERA HERA tunnel. tunnel. The The superconducting magnets of the proton ring ring are are installed installed above the (normal conducting) magnets of of the the electron/ electron/ positron ring. SOURCES OF EMITTANCE EMITTANCE DILUTION DILUTION An emittance dilution is caused by filamentation filamentation of of a coherent oscillation. Possible sources a coherent oscillation. Possible sources are are an an injection injection CP642, High Intensity and High Brightness Hadron Beams: 20th ICFA Advanced Beam Dynamics Workshop on High Intensity and High Brightness Hadron Beams, edited by W. Chou, Y. Mori, D. Neuffer, and J.-F. Ostiguy © 2002 American Institute of Physics 0-7354-0097-0/02/$ 19.00 65 injection amounts to about 10 % - 15 % (Ref [2]). LONGITUDINAL LONGITUDINALEMITTANCE EMITTANCE LONGITUDINAL EMITTANCE DILUTION DILUTION DILUTION 2.6 2.6 _u_u 29.03.2000 100 mA 29.03.2000100mA 29.03.2000 10091 mA 01.03.2000 mA 01.03.200091 mA 01.03.2000 91 93 mAmA 28.03.2000 28.03.2000 93 mA 28.03.2000 93 mA average of bunch length average of bunch (FWHM) in ns length (FWHM) in ns 2.4 2.4 factor of 6 during the ramp, which is shown in Fig. 3. 400 400 400 300 300 200 200 Two Tworf-systems rf-systems with with frequencies frequencies ofof 5252 MHz MHz Two rf-systems frequencies of 52 (harmonic number h h= =1100) and (h(h==MHz 4400) (harmonic numberwith 1100) and208 208MHz MHz 4400) (harmonic number hHERA-p =HERA-p 1100) ring. and 208 MHz (h =bunch 4400)isis are ininthethe The proton areinstalled installed ring. The proton bunch are installed in the HERA-p ring. The proton bunch isrfessentially essentiallyinjected injectedinto intoa abucket bucketofofthe the5252MHz MHzrfessentially injected into a bucket of the 52 MHz rfsystems systems(total (totalvoltage voltage140 140kV) kV)with with anan additional additional systems (totaldeformation voltage 140from kV) towith additional small 208 MHz smallbucket bucket deformation from tothe thean 208 MHzrfrfsmall bucket deformation from tototo the 208 MHz rfsystem (about 1010kV) increase Landau system (about kV)included included increase Landau system (about 10the kV) included to40GeV increase Landau damping. During from damping. During theramp ramp from40 GeVtoto920 920GeV GeV damping. During the ramp from 40 GeV to 920 GeV thethe voltage (to voltageofofthe the208 208MHz MHzrf-systems rf-systemsisisincreased increased (to the voltage of the 208 MHz rf-systems islongitudinally. increased (to about compress the about600 600kV) kV)toto compress thebunch bunch longitudinally. aboutbunch 600 kV) to compress the bunch longitudinally. The The bunchlength lengthand andthe theenergy energyofofa aproton protonbunch bunch The bunch length and the energy of a proton bunch during duringthetheramp rampofofthe theHERA-p HERA-pring ringisisshown shownininFig. Fig. during the ramp of the HERA-p ring is shown in Fig. 2.2. 2. . . The Thebunch bunchlength lengthisisobserved observed to to decreased decreased from from about about 2.4 ns to 1.6 ns (FWHM). These measurements The is observed decreased from aboutare 2.4bunch ns tolength 1.6 ns (FWHM).toThese measurements are based on signals from gap One 2.4 ns to ns (FWHM). These measurements based on1.6 signals from aa resistive resistive gap monitor. monitor.are One would even smaller length ifif the based onexpect signalsan from a resistive gap monitor. would expect an even smaller bunch bunch lengthOne the longitudinal emittance would be not diluted during would expect an even smaller bunch length if thethe longitudinal emittance would be not diluted during the ramp. longitudinal emittance isis increased by longitudinal would be not diluted during the ramp. The Theemittance longitudinal emittance increased by aa factor of 6 during the ramp, which is shown in Fig. ramp. emittance by a3. factorThe of 6longitudinal during the ramp, whichisisincreased shown in Fig. 3. average of bunch emittance (FWHM) in meVs average of bunch emittance (FWHM) in meVs injection injectionenergy energyofof4040GeV GeVisisabout about9090m, m,while whilethe the emittance of the injected proton beam is 0.12 jim. The injection energy 40 GeVproton is about 90ism,0.12 while emittance of theofinjected beam µm.the The emittance due injection errors isisabout emittance ofdilution the injected beam is 0.12 µm. 8The emittancedilution duetotoproton injection errors about 8%. %. emittance dilution due to injection dilution errors is about 8 %. Other sources of emittance are of less Other sources of emittance dilution are of less significance. The dilution due a amismatch Other sources of emittance dilution are of less significance. Theemittance emittance dilution duetoto mismatch of the beta function is about 3 % assuming significance. The emittance dilution due to a amismatch of the beta function is about 3 % assuming abeta-beat beta-beat of A/?//? dilution due ofofthe beta isThe about 3 % assuming a beta-beat Theemittance emittance dilution dueaadisdis∆β / β=function =1010%.%. ofpersion The emittance dilution due a dis∆β / mismatch, βmismatch, = 10 %.coupling persion in the transfer line and coupling in the transfer line and nonlinear fields isisnot than persion mismatch, coupling in line the line and nonlinear fieldsininthe thetransfer transfer linetransfer notlarger larger than about %.%. The total emittance nonlinear in transfer line is dilution not largerduring than about 1 1 fields Thethe total emittance dilution during injection about 1010%%-15 about 1 amounts %. Thetotototal dilution during injection amounts aboutemittance - 15% %(Ref (Ref[2]). [2]). 29.03.2000100mA 29.03.2000 100 mA 01.03.2000 01.03.2000 91mA mA 29.03.2000 100 91 mA 28.03.2000 93 28.03.2000 93mA mA 01.03.2000 91 mA 28.03.2000 93 mA 100 100 0 0 0 0 20 20 10 10 20 30 30 30 40 time timeininmin min 40 40 50 50 60 60 time in min FIGURE FIGURE 3.3. Longitudinal Longitudinal emittance emittance of of aa proton proton bunch bunch FIGURE 3.ramp Longitudinal emittance of a proton bunch during ofofthe ring from duringthe the ramp theHERAp HERAp ring(Adapted (Adapted from [4].) [4].) during the ramp of the HERAp ring (Adapted from [4].) An Ananalysis analysisofofmulti-bunch multi-bunchphase phase oscillation oscillation of of the the An analysis of (see multi-bunch phase oscillation of the proton protonbunches bunches (seeRef. Ref. [4]) [4]) indicates indicates that that aa possible possible proton bunches (see Ref. [4]) indicates that a possible cause cause ofof the the emittance emittance dilution dilution isis aa coupled coupled bunch bunch cause of the emittance dilution is a coupled bunch instability. instability.The Themodal modalspectrum spectrum of of multi-bunch multi-bunch phase phase instability. The modal spectrum of multi-bunch phase oscillationsisisshown shownininFig. Fig.44 ..The Themodes modes 1=1, l=1, which which oscillations oscillations is shown in Fig. 4 . The modes l=1, which has aaphase phase shift shift ofof 2n 2π along along the the bunch bunch train, train, and and has has a phase shift of 2π along the bunch train, and l=163(phase (phaseshift shiftabout about3;c/4) 3π/4)are arethe thedominant dominantmodes modes 1=163 l=163 (phase shift about 3π/4) are the dominant modes inthe thespectrum. spectrum. ininthe spectrum. 2.2 2.2 2.0 2.0 1.8 1.8 1.6 1.6 1.4 1.4 1.4 0 0 10 10 2020 20 3030 30 4040 40 5050 50 6060 60 time in min time min time inin min energy in GeV energy in GeV 1000 1000 800 800 800- > ? ? o> —h?T—¥-\— /r i /—— 600 600 600 400 400 400 ~ 200 200 2000 -0 0 / ! ! V INTRA-BEAM SCATTERING INTRA-BEAM SCATTERING INTRA-BEAM SCATTERING ——|——[__..... 1 00 ! FIGURE Modal spectrum of the multi-bunch phase FIGURE 4.4.4.Modal spectrum of of thethe multi-bunch phase FIGURE Modal spectrum multi-bunch phase oscillations (Adapted from [4].) oscillations (Adapted from [4].) oscillations (Adapted from [4].) 0 1 10 10 10 l 20 20 20 I ' 30 40 40 30 30 40 50 50 50 60 60 60 time in min time time inin min min FIGURE2. Bunchlength lengthand andenergy energy aproton proton bunch FIGURE 2.2. Bunch Bunch of aa proton bunch FIGURE length and energy ofof bunch during the ramp of the HERA-p ring (Adapted from [4].) during the ramp of the HERA-p ring (Adapted from [4].) . during the ramp of the HERA-p ring (Adapted from [4].). . 66 Intra-beam scattering scattering was was first first analyzed analyzed Intra-beam Intra-beam scattering was first analyzed theoreticallyinininRef. Ref.[5]. [5]. The transverse emittance theoretically The transverse emittance theoretically Ref. [5]. The transverse emittance growth caused a decrease decrease of thespecific specific luminosity growth caused a adecrease of of thethe luminosity growth caused specific luminosity during a long (say 10 h) run. Data from the HERA during a long (say 10 h) run. Data from the HERA during a long (say 10 h) run. Data from the HERA to the the HERA HERA lattice lattice predicted predicted an an initial initial growth growth of ofthe the to to the length HERA of lattice predicted an initial growth of of thethe bunch 1.8 %. An alternative analysis bunch %. An An alternative alternativeanalysis analysis ofthethe bunch length length of of 1.8 1.8which %. bunch length data, is based based on on rf-noise, rf-noise,ofcan can be bunch length data, which is bunch length data, which is based on rf-noise, can bebe found in Ref. Ref. [8]. [8]. found in archive archive are are shown shown in in Fig. Fig. 6. 6. The The average average specific specific archivedecrease are shown in Fig. 6. The average specific luminosity during that run was about 10 %. luminosity decrease during that run was about 10 luminosity decrease during that run was about 10%.%. The archive data show also the influence of orbit drifts The archive datadata show alsoalso thethe influence of of orbit drifts The archive show influence orbit drifts on specific luminosity, which could be on the the luminosity, which could beberemedied remedied on specific the specific luminosity, which could remedied by of in interaction region. by resteering resteering of the the beam in the the interaction region. by resteering of beam the beam in the interaction region. During the same luminosity run the bunch length During the same luminosity runrun thethe bunch ofof During the same luminosity bunchlength lengthof proton bunch number 144 was recorded. The increase proton bunch number The increase proton bunch number 144 was recorded. The increase of width half maximum of the the full full width halfhalf maximum of full the width maximum(FWHM) (FWHM)ofofthe the longitudinal proton bunch profile from longitudinal proton bunch profile frominitially initiallyofof longitudinal proton bunch profile from about 2.25 ns 2.5 ns thethe runrun is is show to about ns during showinin aboutabout 2.252.25 ns to tonsabout about 2.5 2.5 ns during 5 also (see A to fit recorded to recorded data shows Fig. (see Ref. [6]).[6]). A data Fig. 55Fig. (see alsoalso Ref.Ref. A fit fit shows that the initial increase in bunch length is 2 % per that the initial increase in bunch length is 2 % per that the initial increase in bunch in agreementwith withintra-beam intra-beam hour. This in agreement hour.hour. ThisThis in good goodgood scattering theory of Ref. applicationofofthe the scattering theory of [7].[7]. AnAn application scattering theory of Ref. Ref. formula: formula: formula: 1 τs 1 = A σh σp found in Ref. [8]. initiaHncrease: 2 % / h (fit to data) time/h f (a, b, q) =τ s A σσ hp f (a, b, q) FIGURE 5. Bunch length (FWHM) of bunch number 144 FIGURE 5. Bunch Bunch length length (FWHM) ofbunch bunchnumber number144 144 FIGURE of during the5.luminosity run on(FWHM) July 27, 2000. during the the luminosity luminosity run run on on July July 27, 27, 2000. 2000. during ( the function f and the parameters a, b and q are ( the function function /f and and the the parameters and qq are (the parameters a, a,bband are defined in Ref. [7]) defined in in Ref. Ref. [7]) [7]) defined FIGURE 6. The proton current (93 mA, black line), the positon current (initially 50 mA, red line), the luminosity (initially 1.8 ili 1030 cm-2s-1mA-2, blue line) are shown versus time during a 10 cm s , brown line) and the specific luminosity (aboutlll0.8 FIGURE 6. The The proton current (93 mA, black line), the positon current (initially 50 luminosity run at July 27, 2000. FIGURE 6. proton current (93 mA, black line), the positon current (initially 50 mA, mA, red redline), line),the theluminosity luminosity(initially (initially1.8 1.8 31 -2 -1 30 -2 -1 -2 3103:00:21 -2 -1 2000 Ju 127 1031 cm'Y cm s1,, brown brown line) line) and and the the specific specific luminosity s mA 2,, blue 10 luminosity (about (about 0.8 0.8 10 1030 cm cm'Y^A" blue line) line) are areshown shown versus versustime timeduring duringaa 3. HERA-B Target Group, Ehret, K. et al., Nucl. Instrum. luminosity run at July 27, 2000. luminosity run at July 27, 2000. Meth. A 456 , 206-216 (2001). 3. HERA-B Target Group, K. Nucl. Instrum. 3. HERA-B Group, Ehret, Ehret, K.etetal., al.,for Nucl. Instrum. ACKNOWLEDGMENTS 4. Vogel, E.,Target Fast Longitudinal Diagnostics the HERA Meth. A 456 , ,206-216 (2001). Mem. A 456 206-216 (2001). Proton Ring, Thesis, University of Hamburg, Hamburg, I would like to thank G. Hoffstaetter, E. Vogel and F. 2002, DESY-THESIS-2002-010. ACKNOWLEDGMENTS 4. 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