Beam manipulation by self-wakefield at ATF

Sergey Antipov

Euclid Techlabs

ATF Program Advisory Committee and the ATF Users' Meetings, April 26 - 27, 2012

Outline

1. Enhanced Transformer Ratio demonstration (wakefield mapping with the shaped beam)

2. Tunable beam energy chirp compensator

3. Conversion of self-wake energy modulation into a THz bunchtrain

1. HIGH TRANSFORMER RATIO

High Transformer Ratio

• Wake mapping at higher frequency > 1 λ covered, if you can pass the beam through. Rule of thumb: aperture ≥ 6∙σr

• TR = lower gradient for witness beam long structure;

• Structure-to-beam alignment is the name of the game; virtually 100% transmission is required

• 5D positioning stage, similar to what UCLA/SLAC designed for Kraken chamber at FACET.

– Can be used for many other experiments

– Can carry different structures simultaneously

Kraken chamber “insides” O. Williams, S. Barber (UCLA) M. Dunning, D. McCormick (SLAC)

2. TUNABLE ENERGY CHIRP COMPENSATION

2m

m

200um

L

• Structure – to – beam alignment • Changing chirp – adjusting structure for chirp compensation • Spectrometer resolution: adding slits and performing slice – scan • It can be a part of other experiment (energy modulation –

bunchtrain conversion)

Plans: tunable E-chirp compensation

Proposed Experiment: Tunable Energy Compensation

• Adjustable geometry WF structure

• Tunable energy compensation is required in a real device

• Experiment is similar to the previous E - chirp compensation measurement

• Change beam E-chirp adjust chirp compensation system

• Spectrometer resolution

spectrometer image of a beam that passed through the structure

Energy, MeV57 57.05 57.1 57.15 57.2 57.25 57.3

spectrometer image of unperturbed beam

Energy, MeV57 57.05 57.1 57.15 57.2 57.25 57.3

beam image after the mask, triangle length is 247 micron

200 250 300 350

70

80

90

100

110

3. ENERGY MODULATION CONVERSION TO A BUNCHTRAIN FOR THZ SOURCE

Table top beam-based THz source

Energy modulation via self-wakefield

Chicane energy modulation conversion to bunch train

THz radiation wakefield structure

THz

Flexible: each step has a tuning range

BNL, ATF: S. Antipov, C. Jing et. al. Phys. Rev. Lett. 108, 144801 (2012)

BNL, ATF: G. Andonian et. al. Appl. Phys. Lett. 98, 202901 (2011)

SLAC, NLCTA: D. Xiang et. al. Phys. Rev. Lett. 108, 024802 (2012)

Measured beam spectrum

Energy chirped rectangular beam

Measured beam spectrum

Energy modulated rectangular beam Bunch train frequency content

Tunable 10% source: Range: 0.3-1.5 THz

Pulse bandwidth: 1% Energy in pulse: ~ mJ

DWA structure

Beam @ the entrance

THz Radiation @ the exit

0.3mm / 0.4mm Quartz 3cm long

(ATF beam) 2.4mm, 0.8nC rectangular

6 MW peak, 0.7THz, 161ps pulse, 0.9%BW, 1.4mJ per pulse

1mm / 1.2mm Quartz 10cm long

(AWA beam) 6.3mm, 10nC rectangular

0.5 GW peak, 0.3THz, 320ps pulse, 1%BW, 155mJ per pulse

Couple Scenarios

ATF example. Stage I: self-wake

-0.2 0 0.2 0.4 0.6-40

-20

0

20

40

z, cm

wa

ke

, M

V/m

wake from ginput beam, 0.24 cm long, with 0.8 nC charge

0 0.05 0.1 0.15 0.260

60.5

61

61.5

62

z,cm

En

erg

y,

Me

V

no structure

with structure

ID = 300um; OD = 400um; Quartz 0.7 THz, vgr = 0.395c, rsh/Q = 210kOhm/m

800 pC, 2.4 mm long flattop rectangular 2MeV energy chirp ≤ 1 cm structure is required

ATF example, stage II: chicane

-6 -4 -2 0 2 4112

113

114

115

116

117energy - position along the bunch, ATF case

t, ps

o

f th

e b

ea

m

chicane input

chicane output

0 2 4 6 80

50

100

150

200

250

300beam current profile, ATF case

t, ps

be

am

cu

rre

nt

chicane input

chicane output

0 1 2 3 4 50

0.2

0.4

0.6

0.8

1beam frequency content, ATF case

Frequency (THz)

Bu

nch

ing

fa

cto

r

bunched up beam

original beam• R56 = 0.03m • Particles between the bands are

bunched! • Bunched frequency content is higher

then the self-wake bunching frequency (can be almost 2 times higher)

• Tunability

Adjustment by chicane

-1.5 -1 -0.5 0 0.5 1 1.5 2111.5

112

112.5

113

113.5

114

114.5energy - position along the bunch; based on ATF experimental data

t, ps

o

f th

e b

ea

m

chicane input

chicane output, case 1

chicane output, case 2

Proposed Experiment: Bunching with Chicane

• Demonstrate Stage I + Stage II; Energy modulation followed by the chicane

• We are designing a chicane to fit after the “IP” chamber (R56~=0.03m; 0.5m long design with PM); spectrometer will have to move a little bit

• Use CTR interferometry to measure bunching

• Observe tunability by a) adjusting the chicane, b) using tunable wakefield structure

Summary

1. Enhanced Transformer Ratio demonstration

2. Tunable beam energy chirp compensator

3. Conversion of self-wake energy modulation into a THz bunchtrain

• designed on previous experience

• inter-related, share hardware, structures

• part of a big picture:

– FEL applications

– table top high power, narrow band, tunable THz source

• Hardware

– Positioning stage

– Spectrometer resolution

– Chicane