Observing Transverse Modes shifting and Coupling in the SPS : MDs in the SPS G. Arduini, R. Calaga, E. Metral, G. Papotti, G. Rumolo, B. Salvant, R. Tomas PhD on improving the model of the SPS impedance. Acknowledments: T. Bohl, E. Chapochnikova, R. Jones, R. Steinhagen, OP team LIS meeting - Oct. 15 2007

Agenda Context MD settings MD results What we do next?

Context Headtail Simulations and MOSES calculations predict a transverse mode coupling instability for the SPS beam at low longitudinal emittance Objectives: Can we see modes shifting in the machine? TMCI threshold for 2007?

Agenda Context MD settings MD results What we do next?

Issues for the measurements Need of high number of turns before decoherence  correct non linear chromaticity and amplitude detuning with octupoles (also reduces Landau damping…) Need of both position and momentum signals  find 2 pickups in the same region (ideally, phase=90° between them)

MD settings Parallel MD on August 2nd Quick MD on August 27th Beam current [1 1010  1.3 1011] p/b Low chromaticity in the vertical plane (-0.2-0.25), high chromaticity in the horizontal plane RF Voltage very high at injection (3 MV instead of 700 kV in 2006), as in transverse impedance MD. Observation of the beam behaviour mainly with SPS Qmeter and Faraday Cage Transverse BPM after kicking in the vertical plane, about 900 ms after injection (both in section 3) As a consequence, no bunch length measurement… Quick MD on August 27th Beam current [3 1010  1.3 1011] p/b Chromaticity at 0.05 (H)/0.05 (V) find the threshold instability

Agenda Context MD settings MD results What we do next? August 2nd, 2007 August 27th, 2007 What we do next?

MD on August, 2nd 2007 Conclusions Measurements Very long decoherence time (more than 4000 turns) …However… Large longitudinal oscillations due to longitudinal bunch mismatch TMCI threshold measurement should be performed right at injection

Aug 2nd : Comparison with July 27 MD SPS Transverse Impedance measurement on July 27, 2007 TMCI MD on August 2, 2007 Slope = - 0.002614 H. Burkhardt et al (APC 17/08/2007) Slope consistent with transverse impedance measurement on July 27, 2007

Aug 2nd : Comparison with simulations Headtail simulations (Z=10 MOhm/m) Measurements (Zmeasured=20MOhm/m) x y Round Chamber x y Flat Chamber

Agenda Context MD settings MD results What we do next? August 2nd, 2007 August 27th, 2007 What we do next?

MD on August, 27th 2007 BCT BPM V BPM H Vertical BPM signal affected by saturation?

MD on August, 27th 2007 (6/3) Measurements in 2007 (Sussix frequency analysis BPM H)

MD on August, 27th 2007 Measurements in 2007 (horizontal)

MD on August, 27th 2007 Faraday cage sum signal Headtail monitor sum signal Ralph confirmed that there is a 1.35 GHz reflexion present on the headtail monitor signal

Agenda Context Issues for the measurement MD results What to do next?

What to do next? Conditions were not ideal in both MDs in August In case of another MD: Possibility to use both BBQ pickups in the same plane (270° apart)  Rhodri and Ralph Check vertical Qmeter pickup Make sure that the bunch is matched to the bucket (bunch length measurements in the Faraday Cage) First find the TMCI threshold Then observe the effect of correcting non linear chromaticity on the transverse modes