Update on TMCI measurements March 5, 2008 G. Arduini, R. Jones, E. Métral, G. Papotti, G. Rumolo, B. Salvant, R Tomas, R. Steinhagen Many thanks to the OP teams, A. Bland, H. Burkhardt, T. Bohl, E. Chaposhnikova, E. Genuardi

Agenda Where we are Issues –Longitudinal aspects –Fitting the slope of the tune shift with intensity What to do next

MD on November 4th, 2007 Observing all the modes 2 intensity scans LOD = - 4 (Q-Qy)/Qs Bunch population (10 10 p/b)

MD on November 4th, 2007 Observing the main mode 2 intensity scans LOD = - 4 (Qmax-Qy)/Qs Bunch population (10 10 p/b)

HeadTail Simulations Fitting the measured tuneshift slope with intensity with headtail simulations (flat chamber, non linear bucket, wake field recalculated at every turn): Headtail parameters : ZyBB = M  / m QBB=1 fresBB=1.3 GHz Rms bunch length = m norm. mom. spread= Voltage = 1 MV long emittance = 0.2 eVs

Where we are Fitting the measured tuneshift slope with intensity with headtail simulations: 4 nov measurements HeadTail simulations 3 main issues  fitted BB impedance with HeadTail = M  /m (instead of 23/1.234)  values for the longitudinal parameters in the simulation?  similar behaviour but at about twice the bunch population

Where we are Fitting the measured tuneshift slope with intensity with headtail simulations: Headtail parameters : ZyBB = M  / m QBB=1 fresBB=1.3 GHz Rms bunch length = m norm. mom. spread= Voltage = 1 MV emittance = 0.2 eVs

Issues for simulating the SPS bunch with Headtail What longitudinal parameters should we put in the headtail simulations? –PS Beam is not matched to the SPS bucket (we could not find a satisfactory matching voltage, and filamentation is clearly visible on the HeadTail monitor on some traces) –Tomoscope before rotation in the PS gives 0.15 eVs –Bsm before rotation gives 0.26 eVs –The rms bunch length in the SPS measured with the HeadTail monitor is 0.21 m (0.7 ns rms at injection) HeadTail monitor 

Analysis of the MD from November 4 Longitudinal emittance as measured in the PS BSM 

Analysis of the MD from November 4 Longitudinal emittance as measured in the PS Tomoscope 

Issues for simulating the SPS bunch with Headtail For a longitudinal emittance of 0.21 m (value given by the HeadTail monitor), the bucket is rather full… Therefore we are in the non linear bucket regime, and it is more tricky to find the matching parameters Rms bunch length = 0.05 m Rms bunch length = 0.21 m

Issues for simulating the SPS bunch with Headtail Let’s check the headtail non linear bucket model with the linear bucket at small rms bunch length (0.05 m). Intensity Scan at low intensity ( to p/b) to prevent modes from shifting non linearly Linear bucket, non linear bucket, frozen and not frozen simulation results are superimposed on the following graph Round pipe Flat pipe

Issues for simulating the SPS bunch with Headtail Effective impedance deduced from the tuneshift (mode m=0) slope with intensity. (Sacherer formula) Round pipeFlat pipeFlat/round Headtail input 17.8 M  /m Expected from theory Z Z *  ²/ Headtail output Sacherer Parabolic 16.1 M  /m20 M  /m Headtail output Sacherer Gaussian 14.3 M  /m17.7 M  /m Parabolic : Gaussian : (from Elias) (from Helmut and Giovanni)

What to do next ? On the MD data 2007 –Choose the right longitudinal parameters for the headtail simulations (matched with 0.15 eVs, despite the measured bunch length? 0.15 eVs with 0.21 m not matched? None of the above?) –Perform HeadTail simulations with the chosen parameters, and include space charge. –Assess the starting distribution (bunch rotation in headtail?) –Can we crosscheck the HeadTail monitor bunch length with the scope in the Faraday cage? –Compare sussix algorithm to NAF algorithm (from Yannis), and understand the low phase difference value given by sussix for the phase advance between BPM1 and BPM2. MD in 2008? –As Gianluigi found out, BPM1 and BPM2 are not at 90° phase advance but 45°  possibility to improve the efficiency of the frequency analysis by using BPM3? –Can we monitor the longitudinal emittance in the SPS? –Is there a way to avoid the mismatch at injection?