short bunches in spear

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)