Jørgen S. Nielsen Institute for Storage Ring Facilities, Aarhus, University of Aarhus Denmark

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1 Jørgen S. Nielsen Institute for Storage Ring Facilities, Aarhus, University of Aarhus Denmark

2 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 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)

3 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 national laboratory contract undulator + 4 additional beamlines 1997 Additional laboratory space 2001 EC contract Access to research infrastructure

4 ASTRID as a Synchrotron Radiation Source Energy MeV Injector: microtron 3 GHz, 10 ma, 1 µs, Hz Critical energy, wavelength ε c =360eV, λ c =35Å Current ma Emittance 140 7nm Lifetime hours RF 105 MHz, 14 bunches, 70 kv One undulator 30 periods of 55 mm, min. gap 22 mm, first harmonic ev 7 beamlines

5 ISA/ASTRID laboratory ELISA M5 M4 ExS TESLA FEL test TOILET M3 G EnS M2 M1 PULSED LASERS FS-LASER (PB) ARUPS SX-700 lab. DF X-ray microscope SGM3 Miyake SGM2 test x-ray microscope kicker RF UV-1 undulator ASTRID e-cooler septum UV1 33 degree TESLA 40 degree neutral beam detektion SEPARATOR EBIS SEP II (LHA) RING- WORKSHOP SX700 SGM1 10 m POSITRONS microtron

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7 Typical current and lifetime Electron Run 2003/ Current [ma] Lifetime [hour] BeamCurrent_slow _2 BeamCurrent_tau10_2

8 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

9 The ASTRID RF system Rohde&Schwartz SMY MHz + phase modulation Amplitude loop Fast feedback loop Attennuator Phase shifter Combiner PreAmp +40 db, 10 W FM transmitter +36 db, 10 kw Amplitude detector Manual or closed loop db Cavity Tuning loop Splitter Phase comparison

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11 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! Plunger and RF power during a fill Beam Current [ma] Beam Current Plunger1 RF pow er Plunger :50 12:55 13:00 13:05 13:10 Plunger / RFpower

12 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

13 Fast Feedback Loop Principle From amplitude loop Attennuator Phase shifter Combiner +40 db, 10 W +36 db, 10 kw db Splitter To amplitude loop Reference: A. Gamp, Servo Control of RF Cavities under Beam Loading CERN 92-03, 1992 F. Perez et.al., Fast Feedback Loop for Beam Loading Compensation in the ANKA Booster Proc. EPAC 2000, Vienna, Austria, p 1996

14 Benefits Fast Feedback Loop Very effective to fit beamloading Cheap: Phase Shifter, Variable gain amplifier/attenuator, more low power Problem: Can only achieve perfect in opposition for one frequency Needs to have a small group delay to have a large bandwidth

15 Cavity Voltage with Fast Loop Fast Feedback Loop OFF Fast Feedback Loop ON

16 Accumulation 180 Accumulation Limit Vs. Fast Loop Gain fixed RF voltage (2.4 'kw') 160 Accumulation Limit [ma] d:\users\jsn\accphys\e-beammeas\rfmeas\fastloop\accumlimitvsffg_ gffldbm :15:34 Fast Feedback Gain [dbm]

17 Beam drop-out CRE31FPW CRE31RPW CRE31DPW50 CRE31DET CRE31PLP1 CRE31PLP2 Power [dbm] :18 10:19 10:20 10:21 10:22 10:23 10:24 10:25 10: Plunger Pos [%], Cavity Detector [*10]

18 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? Power [dbm] :28 10:29 CRE31FPW CRE31RPW CRE31DPW50 CRE31DET CRE31PLP1 CRE31PLP2 10:30 10:31 10:32 10:33 10:34 10: Plunger Pos [%], Cavity Detector [*10]

19 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 period gets longer with more current We only see it with the Fast Feedback Loop on Partly induced by the kicker Could be due to a small modulation of the cavity voltage (induced by the beam), which is strongly amplified by the Fast Loop Voltage Accumulation, I=72 ma 0.00 Cav.Mon. Forward Pickup d:\users\jsn\accphys\e-beammeas\rfmeas\ rfmonmeas\cavmonmeas_ glt :56:59 Time [µs] Data from

20 Modulation of Forward Power Accumulation, I=72 ma Cav.Mon. Forward Pickup Voltage d:\users\jsn\accphys\e-beammeas\rfmeas\ rfmonmeas\cavmonmeas_ glt :56:59 Time [µs] Data from

21 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 Power [dbm] Forward and Reflected Power vs. Cav. Freqeuncy for OPEN amplitude loop, Fast Feedback Loop OFF No Beam Forward Power [dbm] Return Power [dbm] Cav. Detector [a.u.] Cav. Detector [a.u.] d:\users\jsn\accphys\e-beammeas\rfmeas\fpw,rpw,detectorvscavfreq_ gfflcableoff :56:38 Cavity Frequency [khz]

22 60 Forward and Reflected Power vs. Cav. Freqeuncy for OPEN amplitude loop, Fast Feedback Loop OFF No Beam Power [dbm] Forward Power [dbm] Return Power [dbm] Cav. Detector [a.u.] Cav. Detector [a.u.] d:\users\jsn\accphys\e-beammeas\rfmeas\fpw,rpw,detectorvscavfreq_ gfflcableoff :32:56 Cavity Frequency [khz]

23 The future of ISA? M4 M5 ExS ASTRID 2000 TESLA FEL test ELISA TOILET M3 G EnS microtron M2 M1 PULSED LASERS FS-LASER (PB) ARUPS SX-700 lab. DF X-ray microscope SGM3 Miyake SGM2 test x-ray microscope kicker RF UV-1 undulator ASTRID e-cooler septum UV1 33 degree TESLA 40 degree neutral beam detektion SEPARATOR EBIS SEP II (LHA) RING- WORKSHOP SX700 SGM1 10 m POSITRONS microtron

24 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

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26 Minimum Fast Loop Gain for stable Beam Vs. Beamcurrent Fast Loop Gain [dbm] Beamcurrent [ma] d:\users\jsn\accphys\e-beammeas\rfmeas\fastloop\accumlimitvsffg_ glosslimit :59:13