W.S. Graves 2002 Berlin CSR workshop 1 Microbunching and CSR experiments at BNL’s Source Development Lab William S. Graves ICFA CSR Workshop Berlin, Jan., 2002

W.S. Graves 2002 Berlin CSR workshop 2 SDL Facility 1.6 cell gun with copper cathode 75 MeV Bend 50 m 5 MeV Bend Dump IR interferometer Time domain measurements UndulatorsLinac tanks 200 MeV Bunch compressor 30 mJ, 100 fs Ti:Sapphire laser Goal is to reach deep UV wavelength using High Gain Harmonic Generation (HGHG) process seeded by conventional laser for full longitudinal coherence. Currently commissioning undulator with SASE at 400 nm.

W.S. Graves 2002 Berlin CSR workshop 3 Tank 1Tank 2 Tank 4 Tank 3 Chicane Kly AKly CKly B 1.6 cell gun with copper cathode Pop 14 YAG DUVFEL Accelerator 45 MW Thompson Klystrons 197 MeV137 MeV77 MeV40 MeV Bend 3m S-band tanks 25 m 30 mJ, 100 fs Ti:Sapphire laser 5 MeV Coherent IR detector OTR screen can intercept dipole radiation and not beam Slice quad scan Matching triplet

W.S. Graves 2002 Berlin CSR workshop 4 Technical Data Gun energy: 5.37 MeV Gradient: 114 MV/m. E-beam parameters at chicane entrance: Emitnx = 1.08 um, Alphax = -0.78, Betax = 3.1 m, Emitny = 1.30 um, Alphay = -1.78, Betay = 3.1 m Initial phase: leading edge of beam at 30 degrees from phase of zero crossing. RMS laser size on cathode: mm hor, mm ver. Charge: 50 pC Pop14: pixel size: 28.8 um (all electron beam profiles are from pop14), image size: 640 X 480, dispersion: 1.1 m Cathode pix.el size: um Linac gradient approx MV/m. Final max energy: 76.7 MeV Chicane angle at 50 A, 75 MeV:.2097 rad SDL data from 1/8/ Hor. Position (mm) Intensity (A.U.) File: lasera, Hor. RMS width = mm Ver. Position (mm) Intensity (A.U.) File: lasera, Ver. RMS width = 0.64 mm UV laser virtual cathode image Horizontal projection Vertical projection Time (ps) Detector (mV) File: CC010822, RMS length = 1.26 ps UV laser time profile Time (ps) Current (A) File: rfplus01, RMS length = ps Ebeam time profile

W.S. Graves 2002 Berlin CSR workshop 5 Energy spectrum measurement L1L2L3L4 L3 off Chicane varies from 0 cm < R56 < 10.5 cm L2 phase varies, amplitude constant L1 phase = 0, amplitude constant L4 off L1L2L3L4 L1L2L3L4 RF zero-phase time profile L3 phase = +90, amplitude varies (removes chirp from L2) L4 phase = -90, amplitude varies (adds known chirp) L2 phase varies, amplitude constant L1 phase = 0, amplitude constant T. Smith method time profile Chicane varies from 0 cm < R56 < 10.5 cm Chicane set for R56 ~ 9 cm L3 off L4 phase = -90, amplitude ~ 1/R56 L1 phase = 0, amplitude constant L2 phase varies, amplitude constant

W.S. Graves 2002 Berlin CSR workshop Energy (MeV) RMS width = 151 keV Energy (MeV) RMS width = 90.1 keV Energy (MeV) RMS width = 16.6 keV Energy (MeV) RMS width = 74.6 keV Energy (MeV) RMS width = 188 keV Energy spectrum measurement with chicane off. L1L2L3L4 L3 off R56 = 0 cm L2 phase varies, amplitude constant L1 phase = 0, amplitude constant L4 off Pop 14 YAG Images from Pop 14 at varying L2 phase and and chicane off. Energy spectrum is modified by CSR in chicane. L2 = -16 deg.L2 = -8 deg.L2 = 0 deg.L2 = +16 deg.L2 = +28 deg.

W.S. Graves 2002 Berlin CSR workshop 7 L2 = -32 deg.L2 = -28 deg.L2 = -24 deg.L2 = -20 deg.L2 = -16 deg. L2 = -12 deg.L2 = -8 deg.L2 = -4 deg.L2 = 0 deg.L2 = +4 deg. L2 = +8 deg.L2 = +16 deg.L2 = +24 deg.L2 = +28 deg. Energy profiles at many L2 phases L2 phase varying. Chicane, L3, and L4 off.

W.S. Graves 2002 Berlin CSR workshop 8 Energy spectrum measurement with chicane on. L1L2L3L4 L3 off 0 cm < R56 < 10.5 cm L2 phase = -28, amplitude constant L1 phase = 0, amplitude constant L4 off R56 = 0 cm, L2 = -28 deg. R56 = 1.8 cm, L2 = -28 deg. R56 = 3.3 cm, L2 = -28 deg. R56 = 5.2 cm, L2 = -28 deg. Pop 14 YAG Images from Pop 14 at fixed L2 phase and increasing chicane strength. Energy spectrum is modified by CSR in chicane.

W.S. Graves 2002 Berlin CSR workshop 9 0 deg.-8 deg.-16 deg.-24 deg.-28 deg. R56 L2 phase ~1.6 cm ~6.8 cm ~2.9 cm ~4.6 cm 0 cm Two parameter scan: Energy profiles as function of upstream chirp and chicane strength. Scan of L2 phase and chicane strength

W.S. Graves 2002 Berlin CSR workshop Energy (MeV) RMS width = 139 keV Energy (MeV) RMS width = 120 keV Energy (MeV) RMS width = 87.9 keV Energy (MeV) RMS width = 68.3 keV Energy (MeV) RMS width = 151 keV Bend Angle (deg.) RMS dE (keV) Energy spectrum measurement vs chicane strength Bunch is compressing with increasing chicane strength. Energy spectrum can only be modified by CSR and wakes. Charge = 50 pC. L2 phase = -16 degrees. L3, L4 are off. R56 = 0 cmR56 = 1.5 cmR56 = 2.7 cmR56 = 4.3 cmR56 = 6.3 cm

W.S. Graves 2002 Berlin CSR workshop 11 L1L2L3L4 RF zero-phase time profile L3 phase = +90, amplitude varies (removes chirp from L2) L4 phase = +/-90, amplitude varies (adds known chirp) L2 phase varies, amplitude constant L1 phase = 0, amplitude constant Chicane varies from 0 cm < R56 < 10.5 cm L4 phase = -90 degreesL4 phase = +90 degrees L3 corrects residual chirp, L4 is off

W.S. Graves 2002 Berlin CSR workshop Time (ps) Current (A) File: rfplus01, RMS length = ps Time (ps) Current (A) File: rfminus01, RMS length = ps Time (ps) File: rfzero01, RMS length = ps Time (ps) Detector (mV) File: CC010822, RMS length = 1.26 ps UV laser profile from scanning cross- correlation with laser IR pulse. Resolution ~200 fs. RF zero-phase time profiles L4 phase = -90 degreesL4 phase = +90 degreesL4 is off

W.S. Graves 2002 Berlin CSR workshop Current (A) Time (ps) Current (A) Time (ps) Current (A) Time (ps) RF zero phasing measurement of electron beam time profile. No compression Mild compression Strong compression Mild compression case shows ~7 periods in ~1 ps = 45 um wavelength. Strong compression case shows ~5 periods in 0.8 ps = 60 um wavelength. IR Spectrum from scanning interferometer courtesy of L. Carr (10 minutes/scan). Data from March, Charge = 250 pC.

W.S. Graves 2002 Berlin CSR workshop Time (ps) Current (A) File: c5007t4, RMS length = ps Phi2 = Time (ps) Current (A) File: c5006t4, RMS length = ps Phi2 = Time (ps) Current (A) File: c5003t4, RMS length = ps Phi2 = Time (ps) Current (A) File: c5005t4, RMS length = ps Phi2 = Time (ps) Current (A) File: c5004t4, RMS length = ps Phi2 = Time (ps) Current (A) File: c5001t4, RMS length = ps Phi2 = 0, chicane on Time (ps) Current (A) File: c5002t4, RMS length = ps Phi2 = Time (ps) Current (A) File: rfplus03, RMS length = ps Phi2 =0, chicane off RF zero-phase time profiles vs chirp Chicane = 50 A, 4.1 cm < R56 < 5.2 cm, -28 deg. < L2 phi < 0 deg.

W.S. Graves 2002 Berlin CSR workshop Time (ps) Current (A) 3.0 mm spot, FWHM=3.0 ps 2.5 mm spot, FWHM=3.9 ps 2.0 mm spot, FWHM=4.6 ps 1.5 mm spot, FWHM=5.8 ps Time profiles vs cathode diameter RF zero-phasing data from March, 2001 before gun upgrade and laser cross- correlation measurements. Gradient ~95 MV/m, charge = 200 pC, chicane off. Structure is due to laser. At high charge density structure smears (and pulse lengthens) due to space charge near cathode. Speculate that structure is shifted from time to energy.

W.S. Graves 2002 Berlin CSR workshop Time (ps) Current (A) File: comp02, RMS length = ps Single pulse beam break-up at full compression of 300 pC Interesting observations Single-frequency perturbation

W.S. Graves 2002 Berlin CSR workshop Time (ps) Detector (mV) File: uv010315, RMS length = 1.98 ps Energy (MeV) Current (A) File: q50pc02 blm, RMS length = 165 keV Time (ps) Current (A) File: q50pc02 blm, RMS length = ps Two-pulse studies UV laser time profile from cross- correlation measurement. Fourier-plane mask produces two closely spaced pulses. Energy distribution using T. Smith method. R56 = 9.5 cm, upstream chirp near zero (~no compression). Peak spacing ~64 um. HeadTail

W.S. Graves 2002 Berlin CSR workshop 18 L1L2L3L4 Chicane set for R56 ~ 9 cm L3 off L4 phase = -90, amplitude ~ 1/R56 L1 phase = 0, amplitude constant L2 phase varies, amplitude constant Time (ps) Current (A) File: onepulse minus, RMS length = ps Time (ps) Current (A) File: onepulse plus, RMS length = ps T. Smith method time profile measurement

W.S. Graves 2002 Berlin CSR workshop Time (ps) BBO ang. = -35 mr Time (ps) BBO ang. = -27 mr Time (ps) BBO ang. = -19 mr Time (ps) BBO ang. = -11 mr Time (ps) BBO ang. = -3.4 mr Time (ps) BBO ang. = 4.5 mr Time (ps) BBO ang. = 13 mr Time (ps) BBO ang. = 18 mr Laser time profiles Time profiles measured by scanning cross-correlation (difference frequency generation) of few ps UV cathode pulse with 100 fs IR oscillator pulse. Time resolution is 200 fs FWHM. Data from B. Sheehy and H. Loos. ~5 minutes/scan. Different plots are for different matching angles in BBO harmonic generation crystal. 130 uJ 120 uJ 280 uJ700 uJ1000 uJ 880 uJ80 uJ420 uJ

W.S. Graves 2002 Berlin CSR workshop 20 Image of electron beam on pop14. Horizontal axis is time. Laser BBO crystal deliberately detuned to produce structure. Bunch time profile from YAG image. Structure is due to laser…chicane off. Streak camera measurement of UV light. Hamamatsu FESCA 500 streak camera with reflective input optics, sub-ps synch, and wide-response cathode. Measured FWHM time resolution is 760 fs repetitive mode, 1.0 ps single-shot at 800 nm, and 2.4 ps single-shot at 266 nm Time (ps) Current (A) File: p14f.bmp Time (ps) RF zero-phase compared to ‘sub-ps’ streak camera

W.S. Graves 2002 Berlin CSR workshop 21 Next steps… Tomography: Use existing RF and chicane to measure complete 2D longitudinal distribution upstream of chicane. Currently under test. IR spectrum: Installing new interferometer to measure CSR spectrum. RF Deflector: Would provide unambiguous single-shot 2D longitudinal distribution upstream and downstream of chicane. Simulation: Continue to build detailed comparison with experiment. Benchmark different codes against experiment.