Jørgen S. NielsenInstitute for Storage Ring Facilities, Aarhus,

University of AarhusDenmark

What is ISA?• ISA operates and develops the storage ring ASTRID

and related facilities

• ISA staff assist internal and external users in their experiments

• ASTRID operated 5+5 weeks for ions and

18+15 weeks for SR in 2004

• ISA is used by ~150 users/per year from

from Århus (1/4), DK (1/4) and abroad (1/2)

History of ISA

• 1983 First ideas about storage ring in Århus• 1990 First operation with ions• 1991 SX-700 monochromator installed at BESSY• 1993 Inauguration synchrotron-radiation source• 1994 SX-700 installed at ASTRID• 1996-1999 national laboratory contract

undulator + 4 additional beamlines• 1997 Additional laboratory space• 2001 EC contract

– Access to research infrastructure

ASTRID as a Synchrotron Radiation Source

• Energy 100-580 MeV• Injector: microtron 3 GHz, 10 mA, 1 s, 0.2-10 Hz

• Critical energy, wavelength c=360eV, c=35Å

• Current 150-200 mA• Emittance 140 7nm• Lifetime 40-50 hours• RF 105 MHz, 14 bunches, 70 kV• One undulator 30 periods of 55 mm,

min. gap 22 mm, first harmonic 11-59 eV• 7 beamlines

ISA/ASTRID laboratory

S G M 1

m icro tron

1 0 m

A R U P S

S X -7 0 0lab .

R IN G -W O R K S H O P

T O IL E T

S X 7 00

x -ray m icrosco p e

test

M iyak e

S G M 2 undu la to r

e -coo le r

kicker

R Fsep tum

A S T R ID

S G M 3U V -1

F S -L A S E R(P B )

S E P II(L H A )

P U L S E DL A S E R S

D F

X -raym icro sco p e

P O S IT R O N S

E B IS

S E P A R A T O Rn eu tra lb eamd etek tio n

TE S LA F E L te s t

UV1 33 de g re eTE S LA 40 de g re e

M1M2

E nS

E xS

M5

M4

M3

G

E L IS A

Typical current and lifetimeElectron Run 2003/2

BeamCurrent_slow _2 BeamCurrent_tau10_2

25-10-200323-10-200321-10-200319-10-200317-10-200315-10-200313-10-200311-10-2003

Cu

rre

nt

[mA

]

220

200

180

160

140

120

100

80

60

40

20

0

Life

time

[ho

ur]

100

90

80

70

60

50

40

30

20

10

0

The ASTRID RF system

• 105 MHz system• One cavity

– Copper-plated Coaxial TEM cavity

• 20 kW tube based (tetrode) FM transmitter• The bandwidth has been increased resulting in a lower maximum

output (~8 kW)

• Standard amplitude loop• Standard cavity tuning loop

• Fast feedback loop• Which we are very dependent on

The ASTRID RF system

PreAmp+40 dB, 10 W

FM transmitter+36 dB, 10 kW

Splitter

Rohde&Schwartz SMY01

104.95 MHz + phase modulation

CombinerPhase shifter

Atten-nuator

-5 – -55 dB

-150° –+40°Amplitude

detectorManual or closed loop

Phasecomparison

Amplitude loop

Cavity Tuning loop

Fast feedback loop

RF power at Injection

• Want low RF voltage at injection– Inject (pulsed) DC beam from microtron

• Induce strong synchrotron oscillations => poor capture efficiency

– Improved lifetime• Too high RF power => shorter bunch =>

increased Touschek scattering

• Need enough RF power to overcome beamloading

• Increase power as current increase

• Finding the balance !

Beam Current Plunger1 RF pow er Plunger2

13:1013:0513:0012:5512:50

Bea

m C

urre

nt [m

A]

200

195

190

185

180

175

170

165

160

155

150

145

140

135

130

125

120

115

110

105

100

95

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

Plunger / R

Fpow

er

72

70

68

66

64

62

60

58

56

54

52

50

48

46

44

42

40

38

36

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Plunger and RF power during a fill

Fighting the beamloading

• Fast Feedback Loop– Pickup the cavity voltage and feed it back to the

cavity in opposite phase.– This way any beam induced voltage is counteracted

• Problem: – Can only achieve perfect in opposition for one

frequency– Needs to have a small group delay to have a large

bandwidth

Fast Feedback Loop Principle

Reference: A. Gamp, “Servo Control of RF Cavities under Beam Loading” CERN 92-03, 1992F. Perez et.al., “Fast Feedback Loop for Beam Loading Compensation in the ANKA Booster”

Proc. EPAC 2000, Vienna, Austria, p 1996

+40 dB, 10 W +36 dB, 10 kWCombinerPhase shifter

Atten-nuator

-5 – -55 dB

-150° –+40°

Splitter

To amplitude loop

From amplitude loop

Cavity Voltage with Fast Loop

Fast Feedback Loop OFF

Fast Feedback Loop ON

Accumulation

-25 -20 -15 -10 -5 0 5 10 15 20 25

0

20

40

60

80

100

120

140

160

180

Accumulation Limit Vs. Fast Loop Gainfixed RF voltage (2.4 'kW')

d:\users\jsn\accphys\E-beamMeas\RFmeas\FastLoop\AccumLimitVsFFG_040920 gFFLdBm 21-09-2004 14:15:34

Acc

um

ula

tion

Lim

it [m

A]

Fast Feedback Gain [dBm]

Beam drop-outCRE31FPW CRE31RPW CRE31DPW50 CRE31DET CRE31PLP1 CRE31PLP2

10:2610:2510:2410:2310:2210:2110:2010:1910:18

Pow

er [d

Bm

]

74

72

70

68

66

64

62

60

58

56

54

52

50

48

46

44

42

40

38

36

34

32

30

28

26

24

22

20

18

16

Plunger P

os [%], C

avity Detector [*10]

62

60

58

56

54

52

50

48

46

44

42

40

38

36

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

-2

-4

Why is the Beam dropping out?• Good question, which we would very much like to know the answer to.

– Is it because the Fast Loop is ringing, or is the ringing just because the detuning is so large when the beam drops out?

• At lower Fast Feedback Gain, we see the beam drop-out without the fast loop ringing.

– Why the large variation in forward and reverse power?• Is it a signature of the fast loop

working, or is it a problem?

– Could we get some warning?CRE31FPW CRE31RPW CRE31DPW50 CRE31DET CRE31PLP1 CRE31PLP2

10:3510:3410:3310:3210:3110:3010:2910:28

Pow

er [d

Bm

]

74

72

70

68

66

64

62

60

58

56

54

52

50

48

46

44

42

40

38

36

34

32

30

28

26

24

22

20

18

16

Plunger P

os [%], C

avity Detector [*10]

46

44

42

40

38

36

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

-2

-4

Modulation of Forward Power• Just after a pulse from the microtron, we see a strong

modulation on the forward (and reverse) power– We believe that the modulation is at

the synchrotron frequency

– The modulation periodgets longer with more current

– We only see it with theFast Feedback Loop on

– Partly induced by the kicker

– Could be due to a small modulationof the cavity voltage (induced by thebeam), which is strongly amplifiedby the Fast Loop

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 200 400-0.02

0.00

d:\users\jsn\accphys\E-beamMeas\RFmeas\040902-RFmonMeas\CavMonMeas_040906 gLT027 22-09-2004 10:56:59

Volta

ge

Time [µs]

Cav.Mon.

Data from 040906

Accumulation, I=72 mA

Forward Pickup

Forward Power Variation• With Amplitude Loop off, we see a change in Forward

Power when scanning the RF frequency across the cavity resonance

• True or not? (crosstalk in the directional couplers?)

• Properly due to back reflection from the transmitter due to lack of circulator

• Problem or not?

– Maybe increases the fast loop off resonance power

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-250 -200 -150 -100 -50 0 50 100 150 200 25030

35

40

45

50

55

60

d:\users\jsn\accphys\E-beamMeas\RFmeas\FPW,RPW,DetectorVsCavFreq_040927 gFFLcableOff 27-09-2004 15:56:38

Pow

er [d

Bm

]

Cavity Frequency [kHz]

Forward Power [dBm] Return Power [dBm]

Cav. Detector [a.u.]

Cav

. Det

ecto

r [a

.u.]

Forward and Reflected Power vs. Cav. Freqeuncyfor OPEN amplitude loop, Fast Feedback Loop OFF

No Beam

ASTRID2000

S G M 1

m icro tron

1 0 m

A R U P S

S X -700lab .

R IN G -W O R K S H O P

T O IL E T

S X 700

x-ray m icroscope

test

M iyake

S G M 2 un du la to r

e -co o le r

kicker

R Fsep tum

A S T R ID

S G M 3U V -1

F S -L A S E R(P B )

S E P II(L H A )

P U L S E DL A S E R S

D F

X -raym icro sco p e

P O S IT R O N S

E B IS

S E P A R A T O Rn eu tra lb eamd etek tio n

TE S LA F E L te s t

UV1 33 de g re eTE S LA 40 de g re e

M1M2

E nS

E xS

M5

M4

M3

G

E L IS A

The future of ISA?

Conclusions

• Shown you ASTRID and its RF system

• Shown you our Fast Feedback Loop

• Shown you some issues, which we believe are part of the limitations to the attainable current

0 20 40 60 80 100 120 140 160-25

-20

-15

-10

-5

0

5

10

15

20

25

d:\users\jsn\accphys\E-beamMeas\RFmeas\FastLoop\AccumLimitVsFFG_040920 gLossLimit 27-09-2004 16:59:13

Fa

st L

oo

p G

ain

[dB

m]

Beamcurrent [mA]

Minimum Fast Loop Gain for stable Beam Vs. Beamcurrent