# Opportunities for Bright Beam Generation at the Argonne Wakefield Accelerator (AWA)

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## Abstract

**:**

## 1. Introduction

## 2. The AWA Upgraded Photoinjector

## 3. Beam Brightness Optimization

#### 3.1. Methods

#### 3.2. Results

#### 3.3. Impact of 3D Fields

#### 3.4. Opportunity for Peak Current Enhancement via Magnetic Bunch Compression

## 4. Discussion

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Diagram of the AWA photo-injector (

**a**) and available Gaussian (

**b**) and flat-top (

**c**) temporal laser pulse distributions (the horizontal scale is in ps). In (

**a**), the labels LB, LF, LM, and LSi represent solenoids, and Ci represents the accelerating cavities. The red chevron symbols indicate the direction of the RF input couplers.

**Figure 2.**Pareto fronts of transverse normalized emittance and bunch duration for different MTEs using a Gaussian laser pulse (

**a**) and a flat-top laser pulse (

**b**). The optimization considers a 100 pC bunch charge.

**Figure 3.**Emittance evolution along the AWA beamline for an MTE value of 250 (

**a**), 60 (

**b**), and 5 meV (

**c**). The solid and dash traces correspond, respectively, to the case of a Gaussian and flat-top temporal shape for the photocathode laser pulse.

**Figure 4.**Example of bunch length (${\sigma}_{z}$) and transverse size (${\sigma}_{\perp}$) evolution (

**a**–

**c**) with the corresponding final transverse (

**d**–

**f**) and longitudinal (

**g**–

**i**) phase spaces simulated using a flat-top laser pulse for an MTE of 250 (

**a**,

**d**,

**g**), 60 (

**b**,

**e**,

**h**), and 5 meV (

**c**,

**f**,

**i**). Only the horizontal phase space $(x,{p}_{x})$ is shown, given that the beam is cylindrical-symmetric. The colormap in the density plots (

**d**–

**i**) represents the particle density with blue (resp. orange) corresponding to a higher (resp. lower) charge density.

**Figure 5.**Change in transverse momentum, ${p}_{\perp}$, as a particle with the initial co-ordinates $({x}_{0},{y}_{0})$ passes through an accelerating cavity, as described using the 1D model (

**a**) and the 3D field maps associated with a single (

**b**), and dual RF-input coupler (

**c**). Contours (

**d**) and (

**e**) represent the difference map between, respectively, (

**b**) and (

**a**) and between (

**c**) and (

**a**). The color map for contour (

**e**) is scaled by $\times 10$ so that the maximum value is about $\delta {p}_{\perp}\simeq 0.3$ keV/c.

**Figure 6.**Horizontal (

**a**) and vertical (

**b**) emittance evolution along the beamline for the 1D (blue) and 3D (orange) field map model and the associated transverse phase-space (

**c**–

**e**) and spatiotemporal (

**f**–

**h**) distributions. The density plots (

**c**,

**f**) give the phase space associated with the 1D model (cylindrical symmetry), whereas the plots (

**d**,

**g**) and (

**e**,

**h**) give the distributions along the horizontal and vertical direction, respectively, for the 3D map model. The colormap used in the density plots (

**c**–

**h**) is the same as employed in Figure 4.

**Figure 7.**Initial (blue curve) and final (orange curve) peak current (

**a**), along with the final longitudinal phase-space distribution (

**b**), after magnetic bunch compression. The colormap used in the density plot (

**b**) is the same as employed in Figure 4.

Parameter | Range |
---|---|

Laser rms spot size | 0.02–5 mm |

Laser launch phase | −40–40${}^{\circ}$ |

Peak field on photocathode | 40–80 MV/m |

Linac C1 and C2 phase | −50–50${}^{\circ}$ |

Linac C1 and C2 amplitude | 10–20 MV/m |

Solenoid LB peak magnetic field | 0–0.4 T |

Solenoid LF peak magnetic field | −0.4–0 T |

Solenoid LM peak magnetic field | −0.4–0 T |

Solenoid LS1 peak magnetic field | 0–0.5 T |

**Table 2.**Values of optimized parameters “Beamline Settings” for the optimized flat-top cases for each photocathode MTE along with the resulting final beam parameters “Beam Parameters”.

Photocathode MTE (meV) | 250 | 60 | 5 |
---|---|---|---|

Beamline Settings | |||

Laser rms spot size ${\sigma}_{\perp ,c}$ (mm) | 0.146 | 0.239 | 0.255 |

Laser launch phase (${}^{\circ}$) | −2.88 | 5.30 | −3.08 |

Peak field on photocathode (MV/m) | 75.12 | 64.62 | 72.37 |

Cavity C1 phase (${}^{\circ}$) | −49.82 | −43.17 | −49.52 |

Cavity C1 amplitude (MV/m) | 19.96 | 17.73 | 19.97 |

Cavity C2 phase (${}^{\circ}$) | −49.96 | −48.25 | 11.21 |

Cavity C2 amplitude (MV/m) | 10.18 | 11.01 | 13.53 |

LB peak magnetic field (T) | 0.34 | 0.25 | 0.32 |

LF peak magnetic field (T) | −0.34 | −0.26 | −0.32 |

LM peak magnetic field (T) | −0.25 | −0.25 | −0.24 |

LS1 peak magnetic field (T) | 0.02 | 0.04 | 0.08 |

Beam parameters | |||

Kinetic energy K (MeV) | 37.53 | 36.71 | 39.96 |

Transverse emittance ${\epsilon}_{\perp}$ (µm) | 0.190 | 0.170 | 0.112 |

Bunch length ${\sigma}_{z}$ (mm) | 0.674 | 0.596 | 0.570 |

Peak current $\widehat{I}$ (A) | 16.85 | 17.43 | 16.95 |

Brightness ${\mathcal{B}}_{5d}$ (TA·m${}^{-2}$) | 466.63 | 603.16 | 1350.93 |

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## Share and Cite

**MDPI and ACS Style**

Frame, E.; Al Marzouk, A.; Chubenko, O.; Doran, S.; Piot, P.; Power, J.; Wisniewski, E.
Opportunities for Bright Beam Generation at the Argonne Wakefield Accelerator (AWA). *Instruments* **2023**, *7*, 48.
https://doi.org/10.3390/instruments7040048

**AMA Style**

Frame E, Al Marzouk A, Chubenko O, Doran S, Piot P, Power J, Wisniewski E.
Opportunities for Bright Beam Generation at the Argonne Wakefield Accelerator (AWA). *Instruments*. 2023; 7(4):48.
https://doi.org/10.3390/instruments7040048

**Chicago/Turabian Style**

Frame, Emily, Afnan Al Marzouk, Oksana Chubenko, Scott Doran, Philippe Piot, John Power, and Eric Wisniewski.
2023. "Opportunities for Bright Beam Generation at the Argonne Wakefield Accelerator (AWA)" *Instruments* 7, no. 4: 48.
https://doi.org/10.3390/instruments7040048