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Short bunches in SPEAR. J. Safranek for the SPEAR3 accelerator group. 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 - PowerPoint PPT Presentation
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J. Safranek CLS THz Workshop 1
Short bunches in SPEAR
J. Safranek for the SPEAR3 accelerator group
November 2, 2010
J. Safranek CLS THz Workshop 2
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, 2010
J. Safranek CLS THz Workshop 3November 2, 2010
J. Safranek CLS THz Workshop 4November 2, 2010
• Long lifetime• Good injection• Can run with alpha = 4e-6 or smaller
J. Safranek CLS THz Workshop 5November 2, 2010
J. Safranek CLS THz Workshop 6November 2, 2010
a = 4e-6
J. Safranek CLS THz Workshop 7November 2, 2010
J. Safranek CLS THz Workshop 8
Cross-correlation bunch length measurementCorbett et al.
• Starved for photons• Average over many turns
~1 minute or longer• Would like to try with
THz., single pass.
November 2, 2010
J. Safranek CLS THz Workshop 9November 2, 2010
J. Safranek CLS THz Workshop 10
SPEAR3 vacuum chamber
November 2, 2010
J. Safranek CLS THz Workshop 11
Dipole geometry
November 2, 2010
-80 -60 -40 -20 0 20 40 60 80 1000
5
10
15
20
25
30
35
X (mm)
Y (m
m)
pole profile definition
entranceTop of arc
Mirror center Source 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 12
Dipole entrance
Dipole midpoint
Dipole exit
Solid black is existing dipole chamberDotted black is proposed chamber in THz dipoleRed dot is beam positionDipole magnet pole face is red and blue.
mirror
November 2, 2010
J. Safranek CLS THz Workshop 13
Flux calculation, = 1 mm
November 2, 2010
= 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) mrad2
mm 4.924
)046.005.0(15.8 2
22
Apparent SR source size
Bend radiation
J. Safranek CLS THz Workshop 14
Flux calculation, = 0.5 mm
November 2, 2010
= 0.5 mm
= 0.1 mm
Total flux on the mirror is 1.17E13 ph/s/0.1%bwBend radiationEdge radiation
J. Safranek CLS THz Workshop 15
Flux vs. wavelength
November 2, 2010
H-polarized
V-polarized
The flux is comparable to the chicane option.
J. Safranek CLS THz Workshop 16November 2, 2010
Shielding of ER and SR
3/13/22/1 ),(/ Rh
For near field ER
For far field ER /1),(2/1 R when 2R
RR /),(2/1 Rh
fRh
(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 17
Vacuum chamber shielding
November 2, 2010
mLRRLReff 17.12906.55048.12906.55058.1)/(
Edge radiation
m15.8
Synchrotron radiation
mmh 48Assume 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 18November 2, 2010
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/ ), R0=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.
m 2.1)( 0
0
LRLRReff
eV) (0.004 mm 30.0/1
14 00
2
ap
LRR
h
eV) (0.00065 mm 9.12
shielding effRh
eV) (427 nm 9.22edgemin,
d
eV) (35.4 nm 352fieldnear
effREdge 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 19
THz Power
November 2, 2010
1 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 20
THz power (<2mm wavelength)
November 2, 2010
1 ps rms, 5.0 A/bunch 1.7 ps rms, 17.3 A/bunch
372 bunches assumedWavelength>2 mm ignored in power calculation
J. Safranek CLS THz Workshop 21
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, 2010
J. Safranek CLS THz Workshop 22
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, 2010
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)