LEIR Transverse Dampers Alfred Blas LIU-ION LEIR Internal Review 20.08.2014 1 Associated colleagues:...

LEIR Transverse Dampers

Alfred Blas LIU-ION LEIR Internal Review 20.08.2014 1

Associated colleagues:

Michel CHANELAlan FINDLAYWolfgang HOFLEReinier LOUVERSE

Increasing the beam intensity in LEIR

Possible challenges for the transverse feedback

Present situation: multi(70)-turn injection with 22μA-Pb54+ up to 7 times every 200 ms under electron cooling. 6E10 charges ejected on h2 with a 200 ns bunch length (4 sigma).

Foreseen: multi(70)-turn injection with 22μA-Pb54+ up to 13 times every 100 ms under electron cooling. 8.6E10 charges ejected on h2 with a 200 ns bunch length (4 sigma).

http://upload.wikimedia.org/wikipedia/sh/4/42/CERN_logo_400x400.gif



Executive summary:

In case of an increase of the beam intensity in LEIR,

the present bandwidth (100 MHz) of the transverse feedback system might be insufficient to preserve the beam stability.

The other parameters are compatible.




2 stripline PUsUDHV 41 and 42almost 90 Betatron deg apart (whatever the tune)

Signal processing in 3 racks in the middle of the ring

1 stripline kicker KDHV21receives the processed Betatron transverse error, synchronous with the beam and with the apropriate 90 deg Betratron phase shift.




PU bandwidth = 280 MHzPU length = 0.47 m




Model PU de-skew BufferPS/AAC 0020/2

Bandwidth (+/5o phase error)

[1 kHz ; 100 MHz]

Bandwidth of the setup with pick-up(31.4 pF pick-up, 50 pF coaxial interconnect)

[19.5 kHz ; 100 MHz]

Input impedance 100 kΩGain (50 Ω load) 0 dBDrive 3 VP-P into 50 Ω (3VP-P on the input)Noise Factor ≤ 30 dB (50 Ohm source impedance)Noise level 740 nV/√Hz with OPA 656 (op-amp)Gain 28 dB

PU head amplifier




Estimation of the possible saturation of the PU head amplifiers with the increased beam intensity:

Voltage developed on the PU head amplifier input for a 200 ns long bunch with sinusoidal shape and 4.3E10 charges?

In the worst case (beam really off-center close to a single PU-plate)VPU = -1.31 V to +2.31 V

The PU head amplifier can accept +/- 3 V

=> No saturation expected on the PU amplifier




Power amplifiers

Output Power 100 W

In/Out impedance 50 Ohm

Gain 50 dB

Frequency range 100 kHz – 100 MHz

Phase ripple +/- 5 deg

Power is required:

• To improve the damping time with injection trajectory errors (no estimation yet of the requirements with the multi-turn injection and cooling)

• To compensate the imperfect rejection of the PU closed orbit related signal within the BOSS (not measured yet)

• To absorb the beam signal as picked-up by the kicker (< 0.2 W = negligible)




Required BandwidthLandau damping is achieved when the Betatron frequency spread is greater than the tune shift.

Tune spread :

LEIR: η ≈1 and ξ≈0

Stability Criteria:




References concerning bandwidth requirements

http://cds.cern.ch/record/316202/files/ps-96-009.pdf

http://cds.cern.ch/record/280706/files/p177.pdf




coasting

Bunchedh = 2

injection

Bunchedh = 2

extractionh v h v h v

T[MeV/n) 4,2 4,2 4,2 4,2 72 72

beta 0,0946419 0,094642 0,094642 0,094642 0,371954 0,371954

gamma 1,00450886 1,004509 1,004509 1,004509 1,077295 1,077295Qh,v 1,82 2,72 1,82 2,72 1,82 2,72

Half chamber[m] 0,06 0,03 0,06 0,03 0,06 0,03N Z 5,00E+10 5,00E+10 5,00E+10 5,00E+10 5,00E+10 5,00E+10Bf 1 1 0,38 0,38 0,38 0,38

DQ coherent 0,0021 0,0056 0,0055 0,0146 0,0003 0,0008eh,norm 0,5 0,5 0,8 0,8 0,8 0,8ev,norm 0,3 0,3 0,5 0,5 0,5 0,5

DQ incoh(0,0) 0,0372 0,0480 0,0606 0,0766 0,0134 0,0170eta 0,87 0,87 0,87 0,87 0,74 0,74

Dp/p(2s) 4,00E-04 4,00E-04 3,00E-03 3,00E-03 1,00E-03 1,00E-03n threshold for

Instability 318 385 67 75 56 69Frev(Hz) 3,62E+05 3,62E+05 3,62E+05 3,62E+05 1,42E+06 1,42E+06

Lower stability limit [MHz] 115 139 24 27 79 98

Table created by Michel Chanel for 4.8 E10 charges. The tune shifts, and thus the frequency limits, should scale linearly with the intensity. ( => multiply by 1.8 for 8.6E10 charges)




Conclusion:

With the increased intensity in LEIR, the transverse Landau damping is theoretically only obtained above 207 MHz in the worst case (value to be confirmed)

Below this limit an active damping is required.

Open questions:Do we need to need to “actively” cover this entire range to remain stable? Would the available 100 MHz be sufficient?… else can we relax some beam parameters? Δp/p?, transverse emittances?




Some references:

http://betacool.jinr.ru/COOL/COOL%2703/137.pdf

http://cas.web.cern.ch/cas/BRUNNEN/Presentations/PDF/Albert-II.pdf


LEIR Transverse Dampers Alfred Blas LIU-ION LEIR Internal Review 20.08.2014 1 Associated colleagues:...

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