1 / 8

Longitudinal impedance identification

Longitudinal impedance identification. T. Argyropoulos, T. Bohl, J. E. Muller, H. Timko, E. Shaposhnikova Thanks to H. Damerau for preparing the beam LIU-SPS BD WG 30/08/2012. Motivation. The increase of the average bunch length of the batches along the flat bottom

jackson-daniel
Download Presentation

Longitudinal impedance identification

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Longitudinal impedance identification T. Argyropoulos, T. Bohl, J. E. Muller, H. Timko, E. Shaposhnikova Thanks to H. Damerau for preparing the beam LIU-SPS BD WG 30/08/2012

  2. Motivation • The increase of the average bunch length of the batches along the flat • bottom • Observations of high frequency pattern on the nominal SPS bunches at flat • bottom during the single bunch measurements for threshold instabilities

  3. Measurements • Same method used in the past (Measuring the Resonance Structure of Accelerator Impedance with Single Bunches, T. Bohl, T. Linnecar, and E. Shaposhnikova, PRL, 1998) • Experimental conditions: • Long single proton bunches (εL(90%) ~ (0.23 – 0.26) eVs – τinj~ (25-30) ns) • Small momentum spread (to be more unstable and debunch slowly) • Intensity scan from 0.5x1011 to 2.0x1011 p • SPS RF off • Method: • Acquisitions of beam profiles for a period of ~90 ms after injection each 10 turns. • followed by a Fourier analysis  The presence of resonant impedances with high R/Q and low Q leads to line density modulation at the resonant frequencies Example with Np=1.58x1011 and τinj(4σ) = 28.5 ns 1.4 GHz Video of bunch profile

  4. Example at average (90 ms) Np= 8x1010 Contour plot Mountain range Projection Mode Amplitude vs Time

  5. Comparison with old measurements Contour plot Projection T. Bohl, 2007 Np = 8x1010 ? 2012

  6. Simulations • SPS long. impedance model: • TWC 200 • TWC 200 HOM (629 MHz) • TWC 800 • all kickers + resistive impedance (C. Zannini) • Initial particle distribution: • Saved at PS (tomoscope – for low intensity  smaller bunch length) • Simulated (with ESME) until extraction (Helga) • Simulations here have been done with my code (in Matlab): • (Helga is currently working with HEADTAIL)

  7. Comparison with Simulations (preliminary) Simulations with SPS long. impedance model + fr = 1.4 GHz – R/Q = 58 kOhms – Q = 7 for Np = 1x1011 Good agreement but more fine tuning is needed

  8. Summary Mode amplitude ratio of 1.4/0.2 versus Intensity Simulations were done with the SPS impedance model + fr = 1.4 GHz – R/Q = 35 kOhm – Q = 20 • Strong peak at 1.4 GHz observed in the beam • spectrum • Threshold around Np~8x1010 p: observed also • in old measurements (2001 and 2007)  this • impedance was always there! • Impedance evaluation through simulations  • Using low Q and high R/Q  more fine tuning is • necessary Any ideas about the possible impedance source would be very welcome!

More Related