Results of the first BBA testsat FERMI@Elettra, Trieste

A. Latina for the CERN BBA Team

Thanks to Simone Di Mitri, Eduardo Ferrari, Giulio Gaio (Elettra)

CLIC Beam Physics Meeting – May 28, 2014

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Plan of the Elettra Laboratory

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FERMI electron beamlines

Linac energy: from 100 MeV to ~1.2 GeVBunch charge: 800 pCBunch length: from 1.5 mm to 60 micron 10 Hz bunch repetition rateEmittance at gun: ~1.2 mm mrad

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FERMI linacs

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The Fermi control room

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BBA parameters• 27 X correctors• 27 Y correctors• 30 BPMs

• 1.5 betatron oscillations• Effective bpm resolution = 5 - 10 micron• 10 Hz repetition rate• SysID time required:

– About 3 minutes to measure 1 response matrix (can be reduced to 30 seconds, with deeper integration in their control system)

Measured horizontal orbit response matrix

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Orbit correction – 1:1

• First test of orbit correction:– Excited an oscillation – BBA algorithm is able to cancel it

Used 18 singular values in each axis (out of 27)

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Emittance before BBAat the end of L4

HV

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1:1 + DFS

The dispersion was measured reducing the amplitude of klystron 2 to 98% of its nominal value

This operation occurs in 1 cycle @ 10 Hz

Weight for DFS = 7 (tuned for ~10 micron BPM resolution)

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11Vertical dispersion reduced by a factor ~40 ! Horizontal dispersion by factor ˜4 (!)

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Emittance measurement after DFS

Horizontal emittance from 4.21 mm mrad to 3.30 mm mrad. Vertical emittance wasn’t very good though : we had many klystron failures / the machine was drifting away

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1:1 + WFS

The wakefields were measured by changing the bunch charge to 650 pC(tests with 900 pC were foreseen, but there was not time for performing them)

Changing the charge takes about 10 seconds (time for charge feedback to converge)

Weight for WFS = 7-20 (tuned for ~10 micron BPM resolution)

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Horizontal and vertical beam sizes during WFS

WFS !

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Horizontal and vertical beam sizes during WFS

WFS !

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1:1 + DFS + WFS

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Emittance measurement after1:1 + DFS + WFS

HV

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Conclusions

• Looks like an ideal machine for tests– Very fast control system– Excellent diagnostics

• Debug – debug – debug. Only three hours of effective beam-time

• Everything worked really well. Emittance (H; V):– Before correction: 4.31 mm mrad; 3.21 mm mrad– After DFS: 3.30 mm mrad; -– After DFS+WFS: 2.75 mm mrad; 2.57 mm mrad

• Future– Fully explore the the space of parameters: e.g.

• 1 axis at time | both axes decoupled | both axes coupled• DFS weight scan• WFS weight scan• Dependence of the result on the number of singular values

– Tests of on-line parasitic DFS / WFS ?