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UCLA Experiments with short single e-bunch using preformed and beam ionized plasma Retain ability to run short single bunch with pre-ionized plasma Ken.

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Presentation on theme: "UCLA Experiments with short single e-bunch using preformed and beam ionized plasma Retain ability to run short single bunch with pre-ionized plasma Ken."— Presentation transcript:

1 UCLA Experiments with short single e-bunch using preformed and beam ionized plasma Retain ability to run short single bunch with pre-ionized plasma Ken Marsh, Navid Vafaei, Chan Joshi

2 UCLA Optimized density W. Lu

3 UCLA Why is this important? In theory, we should be able to reach transformer ratio > 2 Experiments so far TR < 2. What limits TR? – Head erosion? – Trapped particles? Can we maximize energy gain?

4 UCLA Facet Proposal for High Energy Gain Test Head erosion is likely the most important factor limiting energy gain. Does pre-ionized plasma solve the HE problem? Experimental study: using single electron bunch in the 35 cm lithium oven Example: For 2x10 17 cm -3 E z = 110 GeV/m, total gain 40 GeV in 35 cm E loss = 45GeV/m, total loss 16 GeV in 35 cm

5 UCLA Experimental Requirements n b > n p Lithium plasma n p =2x10 17 cm um bunch length, um bunch radius matched radius = 2 to 4 um Charge 1.8x10 10

6 UCLA How does pre-ionization affect our most basic diagnostics? Diagnostics Energy spectrometer – Can FACET spectrometer measure 60 GeV? – Can we see drive beam energy go down to 4 GeV. Energy gain has only a weak dependence on emittance Participating charge? Should strongly increase. X-ray level should increase because more participating charge and longer propagation distance.

7 UCLA Concluding Remarks We will need – High density 30x30x30 electron beam – Pre-ionized and beam ionized lithium plasma – 200 mj to preionize

8 HIGH TR EXPERIMENT WITH LITHIUM OVEN USING MIXED GAS BUFFER

9 UCLA Example of High TR Simulation with “Ionization Trapping” Generation of fully loaded transformer ratio wakes of 3 using the FACET II beam. Drive Beam Parameters: Q = 4 nC, σ r = 5 μm, σ z = 20 μm, ε N = 5 mm mrad, E = 10.0 GeV. Trailing Beam Parameters: Q = nC, σ r = 2 μm, σ z = 2 μm, ε N = 1.0 mm mrad, E = 100 MeV. Distance between two beams: 93.5 μm. Plasma Density n p = 2.0 x cm -3 (the beam propagates in a pre-ionized plasma). (Courtesy Weiming An)

10 UCLA Localized Self-Trapping Experiment No Trapping with lithium oven using helium buffer gas Add argon impurity to create a large number of self trapped electrons in a controlled way What bounds the Ar impurity ratio is reduction of TR due to beam loading This experiment needs – High density electron beam to ionize Lithium – Argon or Neon impurity mixing

11 UCLA Mixed Gas Results in LWFA 4mm injector cell gas cell is compared to 8 mm two stage cell. – Two stage: Electron density of 3x10 18 cm -3, coupled laser power of 40 TW – Injector only: 3.4x10 18 cm -3, coupled laser power of 50 TW – 0.5% N2 mixed in He in both cases


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