hzb, berlin (germany)

G. Wüstefeld et al., BESSYVSR, ICFA Workshop FLS, March 5-9, 2012, Jefferson Lab

HZB, Berlin (Germany)

Vision for the Future: BESSYVSR

A Variable Pulse Length Storage Ring*

A. Föhlisch, A. Jankowiak, J.Knobloch, P. KuskeA. Neumann, M. Ries and G. Wüstefeld

ICFA Workshop on Future Light Sources, March 5-9, 2012Thomas Jefferson National Accelerator Facility, Newport News, VA (USA)

* G. Wüstefeld et al., IPAC 2011


Outline

- MotivationBESSYVSR

2

- Expected results

- Long. bunch focusing by sc-cavities

- Current limit of short bunches: measurements & scaling laws


why short e- bunches:- time resolved, picoseconds X-ray experiments- CSR for THz experiments

present situation at BESSY:- dedicated low- shifts, =3ps 4 blocks of 3 days per year, two operation modes: 40 mA (bursting) and 15 mA (stable)

Motivation

future goal: - simultaneously 15 ps & 1.5 ps bunch mode up to 100x more current in short bunches ( 10 000x more THz power)

3


BESSY II synchrotron radiation source

number of cellsbeam currentnat. emittancenat. moment. spread

2x8<300 mA6 nm rad0.7x10-3

storage ring parameters

4 rf-cavities0.5 GHz , 1.5 MV

BESSY II ring1.7 GeV

240/ m

nat. bunch length0 = 13 ps (rms)

4


Low- optics

- BESSY THz-optics short bunch, low current operation 15 ps 3 ps (rms) 700 fs are proven and analyzed- MLS – ring of PTB advanced, successful low- optics

definition of V'σ0

relation 0 , and V’ (=dV/dt=2frfV0):

coherent THz radiationshort bunch studiesdouble-beam

5

a tool to produce and study short bunches

0pΔp 1LL 0


0.1

Bunch length – current relation for the BESSY II ring

streak cameraFourier transform spectrometerTHz bursting threshold

Stupakov & HeifetsPRSTAB 5, 054402 (2002)

Are short bunches limited to low currents ??

good agreement between measurement and prediction single bunch current Ib/ mA

100.11E-21E-31E-4 1

bunc

h le

ngth

/

ps (

rms)

1

10

threshold fromcoasting beam

THzoptics

user optics

Ib3/7

measurements theory

- beyond bursting threshold bunches blow up in energy spread

8 nC

fixed rf voltage amplitude of 1.35 MV

- rule of thumb: (, Ib) (2, 5Ib)

6

P. K

uske

et a

l., P

AC 2

003


Are short bunches limited to low currents ??

increasing the rf-gradient V’ x 100 can be increased x 100 I can be increased x 100

scaling law between and I predicted by:- Vlasov-Fokker-Planck simulation- bunched beam theory (Sacherer)- and coasting beam (Landau Damping)

/eEpΔpF |/nZ|I 0

0

||0

2)( I~

7

bunch length V'σ

I~V’for fixed

‘Keil-Schnell’:

recent papers:K.L.F. Bane, Y. Cai, and G. Stupakov, Phys. Rev. STAB 13, 104402 (2010)andY. Cai, talk, IPAC 2011


CSR bursting measurements BESSY IIcomparison with theory, good agreement

8

threshold of instability forCSR of parallel metal plates

zero current bunch length caculated fromVoltage, and long. tuneVoltage range: 0.6MV – 1.8 MV

Scaling of CSR bursting threshold

Y. Cai, talk, IPAC 2011

scaled bunch length

scal

ed b

unch

cur

rent

BCS: =0.5+0.34+dip

scaled single bunch current A / MV

Nov. 2011

Jan. 2012

before 2003

BCS: =0.5+0.34+dip

rms b

unch

leng

th /

ps

coasting beamtheory

1086

4

2

1 1 10 100 1000


BESSY II & sc-cavities

bunch length – current relationsc-cavities for bunch shortening

sc-cavities (scheme)100x enhanced rf-gradient

straight~ 5 m

cavity V1,f1 cavity V2,f2

9

->J. Feikes et al, EPAC 2006


Simultaneously long & short bunches

- flexible fill pattern, I<300 mA- 15 ps & 1.5 ps pulses simultaneous at all beam ports- all IDs available

rel. long. phase position / ns

Volta

ge /

MV

0.5 GHz, 1.5 MV V’=Vxfrf= 0.75 MVGHz

long bunch

present nc-cavity (power)

10

1.75 GHz, 21.4 MVV’ = Vxfrf= 75 MVGHz

short & long bunches

sc-cavity # 1 & 2 (focusing)

sum voltage

short bunch

1.5 GHz, 25 MVV’=Vxfrf= 37.5 MVGHz

sc-cavity # 1 (focusing)


MAD tracking

single particle tracking, BESSY II user optics & two sc-cavities

-300 -200 -100 0 100 200 300

-20 -10 0 10 20

rel. long. position / ps

rel. long. position / ps rel. long. position / ps

rel. long. position / psrel.

mom

entu

m /

0.00

1

40

20

0

-20

-40

40

20

0

-20

-40

rel.

mom

entu

m /

0.00

1

2

1

0

-1

-2

2

1

0

-1

-2

rel.

mom

entu

m /

0.00

1

rel.

mom

entu

m /

0.00

1

short & long bunchmomentumacceptance > +/- 4%

short & long bunchquantum excitation & damping10 damping times

4% 4%

0.7ps (rms)

short long

11

p/p acceptance

quantum limit

-20 -10 0 10 20

-300 -200 -100 0 100 200 300


More advanced scheme: double beam

- double beam scheme combined with two sc-rf cavities

long and short bunches longitudinally and transversely separated

2 sc-rf cavities & low optics

long puls

short puls

2020 )pΔp()pΔp(1LL 00

chromatic orbit length:00pΔp 0

orbits of equal length L=L0: 2 solutions if =0, 1=0

double beam scheme

beam port

I) II)

12

20F0 /Δp/p

>0 <0

alternatively:short bunches are kicked on separate orbits, like the quasi-SB operationG. Portmann, et al., Proc. 2008 BIW, Tahoe City, CA (2008).


photon beam image (beam port exit)

6cm

double beam can be easily produced at the MLS (low- optics)

good life time, high currents

transverse separation of photon beams

13

More advanced scheme: double beam

beam current: 170 mAlifetime: 10 h

e- beam, beam profile image

horizontal displacement

verti

cal d

ispla

cem

ent

measurements at MLS


HZB expertise

BESSYVSRBERLinPro

14

BERLinPro and BESSYVSR: cavity design for BESSYVSR is similar to BERLinPro,1.3 GHz structures to be scaled to 1.5 GHz and 1.75 GHz

high current beam interaction with sc cavities to be studied at BERLinPro

-

-


Summary

- 175 long bunches, 15 ps < 300 mA - 175 short bunches, 1.5 ps (rms) - at all beam ports available - all IDs available - present transverse user optics applied

bunch length (rms) / ps

current (sb) / mA

current (mb) / mA <300

present 350 bunch

fillingTHz optics

BESSYVSR

175 bunch filling

user optics

BESSYVSR

175 bunch filling

THz optics

3

0.04 (0.03 nC)

14

1.5

0.8

(140)

0.7 0.3

0.14 0.02

24 3.5

beamparameter

expected results:

long & short bunches simultaneously :

15

G. Wüstefeld et al., BESSYVSR, ICFA Workshop FLS, March 5-9, 2012, Jefferson Lab 17


MLS measurements


Measurements from SPEAR3

J. Corbett et al.


Measurements from DIAMOND

priv. comm. Ian Martin, DIAMOND


- 870 fs, 140 nA- 700 fs, 300 nA- 1.2 ps, 140 nA

- Gaussian fit

105 20wave number / cm

10

10

10

10

3

6

5

4

Pcoh

/ Pi

ncoh

-1

BESSY: sub-ps bunch diagnostics at low currents

applied currents below bunch lengthening /deforming effects


power spectrum analysis

10 gain7 10 gain7

power spectra

BESSY II user optics, single bunch 15 mA

dete

ctor

sig

nal /

a.u

.

Pcoh

eren

t / P

inco

here

nt

eN form factor

power spectra by Fourier transform

spectroscopy

wave number cm5 10 15 20 25

-1 wave number cm 5 10 15 20 25 -1

N = 10e11CSR in frequency domain

hzb, berlin (germany)

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