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Linear Variation of BPM Pickup Voltages with Bunch Charge in EMMA Injection Line

This report presents the results of measurements taken from the EMMA Injection Line BPM-02 on April 25, 2012, during the final shift of the commissioning run. The primary objectives were to demonstrate the linear relation between the summed values of four pickup voltages and bunch charge, as well as to analyze beam position adjustments in relation to charge variations. Key findings include the threshold attenuation level required for detecting non-zero bunch charge, along with systematic variations in beam position based on different attenuation levels. Detailed data analysis is included, highlighting significant trends observed during the study.

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Linear Variation of BPM Pickup Voltages with Bunch Charge in EMMA Injection Line

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  1. Results from EMMA Injection Line BPM-02 measurements on 25-04-12 May 6th 2012 Ian Kirkman, James Jones IK/JJ May 6th 2012 Slide 0

  2. Measurements Data taken quickly at end of the final shift of the April 2012 commissioning run (25th / 26th) Initial aims: to demonstrate that the summed value of the 4 pickup voltages from a cylindrical BPM varies linearly with bunch charge; to examine beam position vs bunch charge. Method: • ALICE in SB mode at 5 Hz • Switch off DIP-02, monitoring charge in Faraday cup DUMP-01 • Set ALICE attenuation level (proportional to laser power?) • View FC response on ‘scope, and save digitised data to file • Issue multiple EPICS ‘caget’ commands at each attenuation level to read BPM-02, and save data to file IK/JJ May 6th 2012 Slide 1

  3. Measurements Oscilloscope screens for attenuation level at the 2 extreme values, 1.0 (left) and 0.3 (right) • For each attenuation value: • 10000 points in each saved data file • Determine background level from mean and σ of points 500-2500 • Determine background subtracted peak height, and apply ± σ • Note that below attenuation ~ 0.3, the pulse becomes hard to distinguish IK/JJ May 6th 2012 Slide 2

  4. Variation of Bunch Charge from FC with Attenuation level • The ‘threshold’ attenuation level required for non-zero bunch charge in EMMA is ~ 0.1 IK/JJ May 6th 2012 Slide 3

  5. Details of data analysis at attenuation value = 0.3 • Pedestal values v4 and v8 are nicely constant, with ~ 1mV jitter • Apparent jitters on horizontal (Xm) and vertical (Ym) beam positions • Apparent systematic variation of mean Xm and Ym with attenuation level (slides 6, 7, 8) IK/JJ May 6th 012 Slide 4

  6. Variation of 4 Summed Pickups with Attenuation Level • Nicely linear with reasonable statistics • Threshold attenuation level again ~ 0.1 IK/JJ May 6th 2012 Slide 5

  7. Horizontal bunch movement with bunch charge (IL-BPM02) • Systematic narrowing of the horizontal spread of positions with increasing bunch charge • Systematic mean movement outwards with increasing bunch charge IK/JJ May 6th 2012 Slide 6

  8. Vertical bunch movement with bunch charge (IL-BPM02) • Indication of downwards beam movement with increasing bunch charge (to Att. ~ 0.7) • Some indication of vertical narrowing (again to Att. ~ 0.7) IK/JJ May 6th 2012 Slide 7

  9. Beam positions at IL BPM-02 with bunch charge • Summarises plots in slides 6 and 7 IK/JJ May 6th 2012 Slide 8

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