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Influence of proton bunch and plasma parameters on the AWAKE experiment

Explore how using antiprotons as wakefield drivers affects energy imbalance and nonlinearity in the AWAKE experiment data.

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Influence of proton bunch and plasma parameters on the AWAKE experiment

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  1. Influence of proton bunch and plasma parameters on the AWAKE experiment Mariana Moreira Advisor: Jorge Vieira GoLP / Instituto de Plasmas e Fusão Nuclear Instituto Superior Técnico, Lisbon, Portugal epp.tecnico.ulisboa.pt || golp.tecnico.ulisboa.pt

  2. The PIC method Conclusion Question 1:Robustness in the AWAKE experiment Question 2:Beyond the linear theory of the SMI Question 3:Antiprotons as wakefield drivers Contents Mariana Moreira | AWAKE group meeting | February 19, 2018 2

  3. Antiprotons as wakefield drivers Asymmetry between opposite charges • most PWFA experiments have used electrons as drivers • positrons seem to be less efficient as drivers • linear wakefield theory is perfectly symmetrical for opposite charges * Third question How would the hypothetical substitution of the driver protons by antiprotons change the AWAKE experiment? * S. Lee et al. Phys. Rev. E 64 045501 (2001) Mariana Moreira | MSc Thesis Defense | November 13, 2017

  4. More driver charge available An antiproton driver brings several benefits 2.8x more driver charge at 10.33 m 1.5x higher average |Ez| at 10.33 m Mariana Moreira | MSc Thesis Defense | November 13, 2017 27

  5. Field configuration recaptures off-axis charge Why is so much antiproton charge retained? Mariana Moreira | MSc Thesis Defense | November 13, 2017

  6. Antiprotons have more energy available for focusing larger energy imbalance for antiprotons 3.8x more energy in focusing fields Energy contained in Er offers important clues Why is so much antiproton charge retained? Mariana Moreira | MSc Thesis Defense | November 13, 2017

  7. Antiprotons have more energy available for focusing larger energy imbalance for antiprotons 3.8x more energy in focusing fields Energy contained in Er offers important clues Why is so much antiproton charge retained? The antiproton-driven wakefield is more nonlinear • 2D Fourier transform of Ez • purely linear wake: Mariana Moreira | MSc Thesis Defense | November 13, 2017 28

  8. Charge density in longitudinal and transverse force plane Bunch-plasma energy transfer provides no answer Why is the amplitude of the antiproton wakefield lower than expected? • normalized, unsigned forces: • each increment of charge is deposited in Wr/Wz plane according to the fields acting on it Mariana Moreira | MSc Thesis Defense | November 13, 2017

  9. Bunch-plasma energy transfer provides no answer Why is the amplitude of the antiproton wakefield lower than expected? Charge density in longitudinal and transverse force plane • normalized, unsigned forces: • each increment of charge is deposited in Wr/Wz plane according to the fields acting on it A lower portion of the remaining antiprotons gives up energy • integrate charge density on Wr/Wz plane for Wz > 0 and Wz < 0 55% of antiprotons left difference is not large enough to explain the underwhelming amplitude of Ez 61% of protons left Mariana Moreira | MSc Thesis Defense | November 13, 2017

  10. Witness charge Benefits are also reflected on witness electrons A witness electron bunch is introduced in the simulation 4.6x Max. electron energy 1.7x Mariana Moreira | MSc Thesis Defense | November 13, 2017 29

  11. The PIC method Conclusion Question 1:Robustness in the AWAKE experiment Question 2:Beyond the linear theory of the SMI Question 3:Antiprotons as wakefield drivers Contents Mariana Moreira | AWAKE group meeting | February 19, 2018 2

  12. Antiprotons are more efficient as wakefield drivers The wakefield driven by antiprotons is more nonlinear than the one driven by protons More antiproton charge is preserved due to stronger fields The temporal decline of the wakefield amplitude is due to charge loss The spatial decline is due to incoherent interference between individual wake contributions A parallel program was developed to study the nonlinear phase of the SMI Conclusions Deterministic injection of electrons is possible for AWAKE The outputs from the experiment are robust against shot-to-shot fluctuations Mariana Moreira | MSc Thesis Defense | November 13, 2017 31

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