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Exchange of Transverse and Longitudinal Emittance at the A0 Photoinjector Tim Koeth (this talk was initially prepared for TK’s committee meeting of March 11, 2008) Updated March 14th, 2008 Outline • Brief Photoinjector introduction • Motivation & Theory of Emittance Exchange • Exchange Apparatus at the A0 Photoinjector • Results to date… • Next Steps • Acknowledgements The A0 Photoinjector Next, Artur will talk about the low level RF systems that keep the laser, two 1.3 GHz and one 3.9 GHz systems in sync. • Laser energy 16 mJ/pulse @ 263nm • <5nC/bunch (have had >12 nC in the past) • Typically 10 bunches/RF pulse. 1 Hz rep rate • 4 MeV gun output energy • 16 MeV total energy • Dp/p ≈ 0.3%@ 16MeV (1nC) • Bunch length ≈ 2 mm (1nC) • gez ≈ 120 mm-mrad (RMS @ 1nC) • gex,gey≈4 mm-mrad (RMS @ 1nC) The Idea: Emittance Exchange (EEX) • In 2002 M. Cornacchia and P. Emma proposed using a TM110 deflecting mode cavity in the center of a chicane to exchange a smaller longitudinal emittance with a larger transverse emittance for a FEL. • Kim & Sessler in 2005 proposed using a flat beam (ex<<ey) combined with a deflecting mode cavity between 2 doglegs to produce a beam with very small transverse emittances and large longitudinal emittance to drive an FEL. • We are doing a proof of principle emittance exchange at A0 using the double dogleg approach with a round beam (ex=ey) . – We’ll be exchanging a larger longitudinal emittance with a smaller transverse emittance. – Keep in mind that emittance is the area beam phase space, e x 2 x'2 xx' 2 • Why ? • Basic and unique beam dynamics manipulation – proof of principle • FEL’s - low transverse emittance, large brightness • This phase space manipulation could have application in a linear collider TM110 (Deflecting) Mode Cavity a (from Figure 1 of C&E) Electric field at synchronous phase. Magnetic field a quarter period later. k • No longitudinal electric field on axis. eV0 • Electric field imparts an energy kick proportional to distance off axis. – Plan to use this to change the kx aE x' kz momentum deviation in presence of dispersion! k is the integrated • Electro-magnetic field provides longitudinal energy gain deflection as a function of arrival time. at a reference offset a • This is the type of cavity used as a crab cavity or for bunch length normalized to the beam measurement. energy E. Concept of Emittance Exchange A typical non-dispersive transport matrix: x A11 A12 0 0 x x' A21 A22 0 0 x' z 0 0 D11 D12 z 0 D22 in out 0 D21 What we want to develop is a matrix like: x 0 0 B11 B12 x x' 0 0 B21 B22 x' z C C12 0 0 z 11 C 0 in out 21 C22 0 EEX: Linear Optics Model Initial e- bunch D1 3.9 GHz TM110 D2 D3 final e- bunch D4 First, break the EEX-line into three sections: ex > ez Magnetic dogleg before cavity: Mbc TM110 cavity (thin lens): Mcav Magnetic dogleg after cavity: Mac 1 L 0 D 1 0 0 0 0 1 0 0 0 1 k 0 M bc M ac and M cav 0 D 1 D 0 0 1 0 0 0 0 1 k 0 0 1 1 L 0 D 1 0 0 0 1 L 0 D To get: 0 1 0 0 0 1 k 0 0 1 0 0 R M ac M cav M bc 0 D 1 D 0 0 1 0 0 D 1 D 0 0 0 1 k 0 0 1 0 0 0 1 EEX: Linear Optics Model 1 Dk L Dk (1 Dk ) L kL D D(1 Dk ) DkL 0 1 Dk k Dk R Dk D D(1 Dk ) aDkL 1 Dk D D 2 k ad (1 Dk ) k 1 Dk kL 0 Now if we take the trivial case of k =0 we get: 1 2L 0 2D 0 1 0 0 R 0 2D 1 2D 0 0 1 0 However, if we take the special case of k = -1/D = ko we get: L 0 0 D L D 1 R 0 0 D D aL 0 0 1 L 0 0 D D All of the X-X and Z-Z coupling elements are zero ! EEX: Linear Optics Model L 0 0 D L With our k=ko D 1 R 0 0 A B D D aL 0 0 C D 1 L 0 0 D D We can transports the initial uncoupled beam (sigma) matrix through the EEX line e x0 x e x0 x 0 0 And remember det x e x 0 e x0 x ex g x 0 0 2 o x 0 0 z 0 0 e z z 0 e z0 z 0 0 ez z e z0 g z 0 via R o RT : A xo AT B zo BT A xo C T B zo DT C x AT D z BT T o o C xo C D zo D T We know from above that A = D = 0, so this reduced to: B zo B T 0 T 0 C xo C Then take the determinate of σx, σz and we get: det x e z2 det z e x 2 a complete swap of the emittances is seen. ex ez EEX Beam Line at the Photoinjector Vertical bend avoids residual dispersion of X- plane Diagnostics: = Beam Position Monitor (BPM) = Diagnostic cross: viewing screen(s) & digital camera - Transverse beam position - Measuring transverse beam size = Slit/Screen pair for transverse emittances. = MagneticSpectrometer – P & ∆P Not shown: Streak camera & Interferometer – e- bunch length, Phase Mon – e- TOF EEX Beam Line at the Photoinjector Vertical Spectrometer Dipoles TM110 Cavity Beam direction EEX Beam Line at the Photoinjector (Cav off) 25 Beamline Layout 1.2 1 20 betax 0.8 betay 0.6 etax 15 0.4 beta (m) eta (m) etay 0.2 10 0 -0.2 5 -0.4 -0.6 0 -0.8 5 6 7 8 9 10 11 12 s(m) Deflecting Mode Cavity TM110 Cavity Details Construction: 5 cells (of CKM design) Punched OFHC Copper Vacuum brazed Radio Frequency: 3.9 GHz (3x 1.3GHz) Q300K=14,900 Q80K=35,600 Coupling (β) = 0.7 Req’d RF power @ full gradient: 50kW Cavity Polarizaton and Field Flatness Red: theory 0 Black: fit cell 2 355 5 345 350 10 15 Blue: fit cell 3 340 20 335 25 Green: fit cell 4 330 30 325 35 320 40 315 45 310 50 305 55 300 60 295 65 290 70 6 285 75 280 Vertical 80 4 275 85 270 90 265 95 2 260 100 255 105 250 110 0 245 115 0 50 100 150 200 250 300 350 400 450 240 120 235 125 230 130 -2 225 135 220 140 215 145 210 150 205 155 -4 200 160 195 190 165 185 175 170 180 -6 • Longitudinal electric field vs angle in -8 cells 2-4 determined by bead pull. -10 • Cavity polarization is set by input coupler • Bead pull results of cavity field flatness tuning. TM110 Cavity: 1st Deflection Operating phase for exchange The induced kick is about 70% of what was expected for the input power, however, sufficient contingency was built into the cavity to accommodate this. BPM26 Early Vertical Spectrometer Images • Preliminary investigations showed encouraging results. For instance, as we increased the TM110 cavity ~ 550keV strength we saw a reduction in momentum spread… Spectrometer Screen Cavity 100% Cavity 70% Cavity80% Cavity40% Cavity: OFF 50% 60% 10% 20% 30% Measuring the EEX Line Matrix There is exciting evidence that the cavity was indeed modifying the momentum spread, so we have begun to systematically measure the EEX beam line matrix. Again, describing the beam line with linear optics we have: x R11 R12 R13 R14 R15 R16 x x' R21 R22 R23 R24 R25 R26 x' y R R32 R33 R34 R35 R36 y 31 y' R41 R42 R43 R44 R45 R46 y ' z R R52 R53 R54 R55 R56 z 51 R66 in out R61 R62 R63 R64 R65 Adjusting one input parameter at a time and measuring all output parameters we can map out the transport matrix. For example, introducing a momentum offset yields the 6th column: Dx R11 R12 R13 R14 R15 R16 0 Dx' R21 R22 R23 R24 R25 R26 0 Dy R R32 R33 R34 R35 R36 0 31 Dy ' R41 R42 R43 R44 R45 R46 0 Dz R R52 R53 R54 R55 R56 0 51 D R66 D in out R61 R62 R63 R64 R65 Do this with the TM110 cavity off, partially on, 100% on, and greater EEX Beamline: Vertical Spectrometer BPM For a given TM110 strength, k, changed beam central momentum by ± 2.15 % in 0.70% increments by varying 9-Cell cavity gradient. Repeated for several TM110 k: TM110 cavity strength, ko 90% 73% OFF 105% 100% Intro p from 9-Cell Vary k Dx R11 R12 R13 R14 R15 R16 0 Dx' R21 R22 R23 R24 R25 R26 0 record vertical BPM reading R Dy R32 R33 R34 R35 R36 0 31 Dy ' R41 R42 R43 R44 R45 R46 0 Dz R R52 R53 R54 R55 R56 0 51 D R66 D in out R61 R62 R63 R64 R65 EEX: Beam Line Horizontal Dispersion measurement with TM11O cavity off Lines: ideal Dots : Horizontal D1 D2 TM110 D3 D4 SPECT. BPM measured difference data δP = ± 1.05 % in 0.35 % increments +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05% EEX: Beam Line with TM110 Cavity On, Ideal: Lines: ideal D1 D2 TM110 D3 D4 SPECT. 100% 80% 60% 120%20% OFF 40% δP = ± 1.05 % in 0.35 % increments +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05% EEX: Beam Line with TM110 Cavity on Measured: Cavity D1 D2 TM110 D3 D4 SPECT. strength, ko 100% 44% 85% 67% OFF +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05% Streak Camera TOF measurements Introduce p from 9-Cell Streak camera ~ 1pSec resolution 6 y = 18.214x - 260.38 5 R² = 0.9968 Dx R11 R12 R13 R14 R15 R16 0 Dx' R21 R22 R23 R24 R25 R26 0 4 TM110 k=75%ko Dy R R32 R33 R34 R35 R36 0 31 Dy ' R41 R42 R43 R44 R45 R46 0 delta-z [mm] 3 TM110 off Dz R R52 R53 R54 R55 R56 0 51 D R66 D in y = 8.0444x - 115.04 out R61 R62 R63 R64 R65 2 R² = 1 1 0 14.25 14.3 14.35 14.4 14.45 14.5 14.55 14.6 -1 Beam energy [MeV] Similar for 2nd Column: vary ∆xin’ Impart Dx’ by adjusting a horizontal corrector magnet Dx R11 R12 R13 R14 R15 R16 0 k=62%ko Dx' R21 R22 R23 R24 R25 R26 Dx' Dy R R32 R33 R34 R35 R36 0 31 Dy ' R41 R42 R43 R44 R45 R46 0 Dz R R52 R53 R54 R55 R56 0 51 D R66 0 in out R61 R62 R63 R64 R65 … And Dx, Dy, Dy’… The Dz can be achieved by adjusting the TM110 cavity phase Dx’in data from today Today’s BPM8/30 Dispersion Measurements BPM8 & 30 Special 4-inch housing Ray’s cald XS4 Vert Disp : 865mm Tim’s measuremnt 855+/-5mm Ray’s calc of XS3 Horz Disp: 225mm Tim’s measurement 226mm Finally nice agreement ! Note non-lin > 8 mm Summary of Today & yesterday data collection (March 13 thru 14) TM110 5-Cell off 25% ko 50% ko 75% ko ~90% ko ∆x X X X X X ∆x’ X X X X X ∆y X X X X X ∆y’ X X X X X ∆z(ф) - X X X X δ X X X X X δ energy incriments calibration against BPM8 Now, off to analyze… x R11 R12 R13 R14 R15 R16 x x' R21 R22 R23 R24 R25 R26 x' y R R32 R33 R34 R35 R36 y 31 y' R41 R42 R43 R44 R45 R46 y ' z R R52 R53 R54 R55 R56 z 51 R66 in out R61 R62 R63 R64 R65 EEX: Next Steps • Continue to populate the matrix • Measure input and output emittances • Graduate ! Many thanks go to: • Helen Edwards - Advisor • Don Edwards - Voice of reason • Leo Bellantoni – [tor]Mentor & CKM • Ray Fliller – A0 Post Doc • Jinhao Ruan – Laser, All things optical • Jamie Santucci – fireman • Alex Lumpkin – streak camera • Uros Mavric – Ph.D. Student • Artur Paytan – Yerevan U. Ph.D. Student • Mike Davidsaver – UIUC staff, controls guru • Grigory Kazakevich – Guest Scientist, OTRI • Manfred Wendt & Co – Instrumentation, BPMs • Elvin Harms – kindly sharing a klystron • Randy Thurman-Keup – Instrumentation, Interferometer • Vic Scarpine – Instrumentation, OTR and cameras • Ron Rechenmacher – CD, controls • Lucciano Piccoli – CD, controls • Brian Chase, Julien Branlard, & Co – Low Level RF • Gustavo Cancelo – CD, Low Level RF • Wade Muranyi & Co – Mechanical Support • Bruce Popper – drafter & artist • Chris Olsen - assistant

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posted: | 3/24/2012 |

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