Short bunches in SPEAR J. Safranek for the SPEAR3 accelerator group November 2, 20101J. Safranek CLS THz Workshop

Outline Low alpha in SPEAR (X. Huang, J. Safranek) – Lattice – Bunch length measurements (J. Corbett et al.) Prospect of THz beamline (X. Huang) – Edge radiation and synchrotron radiation – Vacuum chamber shielding – Bunch profile, CSR enhancement November 2, 20102J. Safranek CLS THz Workshop

November 2, 20103J. Safranek CLS THz Workshop

November 2, 2010J. Safranek CLS THz Workshop4 Long lifetime Good injection Can run with alpha = 4e-6 or smaller

November 2, 20105J. Safranek CLS THz Workshop

November 2, 20106J. Safranek CLS THz Workshop  = 4e-6

November 2, 20107J. Safranek CLS THz Workshop

Cross-correlation bunch length measurement Corbett et al. Starved for photons Average over many turns ~1 minute or longer Would like to try with THz., single pass. November 2, 2010J. Safranek CLS THz Workshop8

November 2, 20109J. Safranek CLS THz Workshop

SPEAR3 vacuum chamber November 2, J. Safranek CLS THz Workshop

Dipole geometry November 2, entranceTop of arc Mirror centerSource point The source point is at ¼ of the bending angle, or 0.38 m into the bend. The mirror center to trajectory exit is 78 mm. The full aperture at the mirror center is 58 mm. lens J. Safranek CLS THz Workshop

Dipole entrance Dipole midpoint Dipole exit Solid black is existing dipole chamber Dotted black is proposed chamber in THz dipole Red dot is beam position Dipole magnet pole face is red and blue. mirror November 2, J. Safranek CLS THz Workshop

Flux calculation, = 1 mm November 2, = 1 mm Mirror is 0.5 meter from the dipole exit in SRW calculation. Total flux on the mirror is 0.80E13 ph/s/0.1%bw Total flux at the focused spot is 0.75E13 ph/s/0.1%bw Focused with a lens f=0.82 m, half of the distance to the source point (1:1 imaging) Aperture 100 (H) x 46 (V) mrad 2 Apparent SR source size Bend radiation J. Safranek CLS THz Workshop

Flux calculation, = 0.5 mm November 2, = 0.5 mm = 0.1 mm Total flux on the mirror is 1.17E13 ph/s/0.1%bw Bend radiationEdge radiation J. Safranek CLS THz Workshop

Flux vs. wavelength November 2, H-polarized V-polarized The flux is comparable to the chicane option. J. Safranek CLS THz Workshop

November 2, Shielding of ER and SR For near field ER For far field ERwhen (1)Wavelengths that are shielded by the far-field condition are shielded at the formation length, i.e., they won’t make out to the far-field zone at all! (2)Shielding occurs when the wall cut into the central cone of radiation. For SR, condition for shielding (far field) is ER SR Graph taken from R. A. Bosch, NIMA 482 (2002); reflection from two parallel plates was assumed. h is full vacuum chamber height. J. Safranek CLS THz Workshop

Vacuum chamber shielding November 2, Edge radiation Synchrotron radiation Assume full aperture Most of ER with wavelength longer than 2 mm will be suppressed. Most of SR will pass through, up to wavelength of 4 mm. J. Safranek CLS THz Workshop

November 2, Edge radiation from an enlarged ID port Parameters ER results  =8.15 m,  =5871, h=48 mm, d=10 cm (magnet edge length to bend angle of 1/  ), R 0 =1.5 m (aperture to edge), L=5.29 m (straight section length) The limiting aperture for ER is 48 mm (full) at 1.5 m downstream from the entrance edge of a SPEAR dipole. Edge radiation present for photon energy below it. In near-field regime for photon energy below it. Direct flux of ER through aperture for photon energy above it. No flux of ER through aperture for photon energy below it. J. Safranek CLS THz Workshop

THz Power November 2, ps rms, 5.0  A/bunch 1.7 ps rms, 17.3  A/bunch Integrated for wavelength 5 mm or shorter J. Safranek CLS THz Workshop

THz power (<2mm wavelength) November 2, ps rms, 5.0  A/bunch1.7 ps rms, 17.3  A/bunch 372 bunches assumed Wavelength>2 mm ignored in power calculation J. Safranek CLS THz Workshop

Conclusion, THz beamline It is viable to extract dipole radiation for the THz beamline, with performance comparable to the chicane option. Assuming 48 mm full aperture, SR of wavelength of 1 mm or shorter fully passes through; between 1 and 4 mm will partially passes through; longer than 5 mm will be suppressed by shielding. ER of wavelength longer than 2 mm will be suppressed by shielding. The port extracts mainly SR. Integrated power is 120 mW for the 1 ps rms bunch length mode, with 372 bunches, 5.0  A/bunch. November 2, 2010J. Safranek CLS THz Workshop21

Reasons to build THz beamline Characterize short X-Ray pulses (through spectroscopy of x-correlation/electro-optics) AP CSR studies THz for photon experiments November 2, 2010J. Safranek CLS THz Workshop22 Questions How much stable CSR (mW) has been measured? How to calculate realistic performance? Are linac-based sources better compared to bursting mode in storage rings? How to optimize source? (Energy, dipole field & gap, chamber)