Density characterization of discharged gas-filled capillaries through common-path two-color spectral-domain interferometry

Tilborg, J. van; Gonsalves, A. J.; Esarey, E.; Schroeder, C. B.; Leemans, Wim

doi:10.1364/ol.43.002776

Cited by 14 publications

(17 citation statements)

References 27 publications

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“…Further, for many of the applications identified above it will be necessary to operate at pulse repetition rates, f rep , several orders of magnitude above the few hertz typical of today's GeV-scale LWFAs.To date, the workhorse waveguide for LWFAs has been the capillary discharge waveguide [18,19]. Capillary discharge waveguides have generated plasma channels up to 150 mm long [20], with on-axis densities as low as approximately 3 × 10 17 cm −3 . Electrical operation at f rep = 1 kHz has been reported [21], but high-intensity guiding at such high repetition rates has yet to be demonstrated.…”

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confidence: 99%

Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens

Shalloo

Arran

Picksley

et al. 2019

Phys. Rev. Accel. Beams

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We demonstrate optical guiding of high-intensity laser pulses in long, low density hydrodynamic optical-field-ionized (HOFI) plasma channels. An axicon lens is used to generate HOFI plasma channels with on-axis electron densities as low as ne(0) = 1.5 × 10 17 cm −3 and matched spot sizes in the range 20 µm WM 40 µm. Control of these channel parameters via adjustment of the initial cell pressure and the delay after the arrival of the channel-forming pulse is demonstrated. For laser pulses with a peak axial intensity of 4 × 10 17 W cm −2 , highly reproducible, high-quality guiding over more than 14 Rayleigh ranges is achieved at a pulse repetition rate of 5 Hz, limited by the available channel-forming laser and vacuum pumping system. Plasma channels of this type would seem to be well suited to multi-GeV laser wakefield accelerators operating in the quasi-linear regime.Many applications of high-intensity laser-plasma interactions require the propagation of high-intensity laser pulses through plasmas which are orders of magnitude longer than the Rayleigh range. One example of particular current interest is the laser wakefield accelerator (LWFA) [1], in which a laser pulse with an intensity of order 10 18 W cm −2 propagates though a plasma, driving a trailing density wave. The electric fields generated within this plasma wave are of the order of the wave-breaking field E 0 = m e ω p c/e, where ω p = (n e e 2 /m e ǫ 0 ) 1/2 and n e is the electron density [2,3]. For plasma densities in the range n e = 10 17 −10 18 cm −3 , E 0 ≈ 30 − 100 GV m −1 , which is several orders of magnitude higher than the fields generated in radio-frequency machines.Plasma accelerators can drive compact sources of femtosecond-duration [4-6] radiation via betatron emission [7,8], undulator radiation [9, 10], and Thomson scattering [11][12][13], with many potential applications in ultrafast science. In the longer term they could provide a building block for future high-energy particle colliders [14].For LWFAs operating in the quasilinear regime [2], the energy gain per stage varies as W ∝ E 0 L acc ∝ 1/n e , and the required length of the stage varies as L acc ∝ 1/n 3/2 e . Hence reaching higher energy gains requires the drive laser to propagate over longer lengths of lower density plasma.To date, the highest reported electron energy generated in a LWFA is 7.8 GeV, which was achieved by guiding intense laser pulses through a 200-mm-long plasma channel with an axial electron density of 2.7 × 10 17 cm 3 [15].Laser-plasma accelerators providing 10 GeV energy gain per stage will require laser guiding through 100s of millimetres of plasma of electron density n e ≈ 10 17 cm −3 [16,17]. Further, for many of the applications identified above it will be necessary to operate at pulse repetition rates, f rep , several orders of magnitude above the few hertz typical of today's GeV-scale LWFAs.To date, the workhorse waveguide for LWFAs has been the capillary discharge waveguide [18,19]. Capillary discharge waveguides have generated plasma channels up to 150...

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mentioning

confidence: 99%

Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens

Shalloo

Arran

Picksley

et al. 2019

Phys. Rev. Accel. Beams

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“…To date, SHIs have mostly been developed and applied to monitor the free-electron density in magnetically confined large plasma machines [43, 44] . Recently, due to their versatility and robustness, SHIs have been successfully applied also for the characterization and monitoring of gas targets for LWFA (namely discharged gas-filled capillaries [45, 46] and gas cells [21, 47] ).…”

Section: Interferometric Methodsmentioning

confidence: 99%

“…Specifically, spectral-domain (SD) second-harmonic interferometry [48] has been adopted instead of spectral-domain TAI to monitor the density inside a discharged gas-filled capillary, due to the much easier implementation and much higher stability of the common-path configuration compared to the two-arm design [45] . In an SD SHI, the spectral interference takes place between the second-harmonic pulse generated before the sample and the time-delayed second-harmonic pulse generated after the fundamental pulse has propagated through the sample.…”

Section: Interferometric Methodsmentioning

confidence: 99%

“…The time delay is estimated by measuring the modulation period in the frequency spectrum of the two interfering pulses ( ). For laser pulses propagating in a discharged gas-filled capillary with a near-match guided configuration typical for LPA, the relation between the time delay and the average on-axis plasma density can be approximated very well by assuming free propagation in a plasma with an average density [45] , resulting in the same phase shift as a function of the electron density (see Table 1). When applying SD interferometry, also the spectral phase of the modulated frequency spectrum can be measured.…”

Section: Interferometric Methodsmentioning

confidence: 99%

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Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators

Brandi

Gizzi

2019

High Pow Laser Sci Eng

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Implementation of laser-plasma-based acceleration stages in user-oriented facilities requires the definition and deployment of appropriate diagnostic methodologies to monitor and control the acceleration process. An overview is given here of optical diagnostics for density measurement in laser-plasma acceleration stages, with emphasis on well-established and easily implemented approaches. Diagnostics for both neutral gas and free-electron number density are considered, highlighting real-time measurement capabilities. Optical interferometry, in its various configurations, from standard two-arm to more advanced common-path designs, is discussed, along with spectroscopic techniques such as Stark broadening and Raman scattering. A critical analysis of the diagnostics presented is given concerning their implementation in laser-plasma acceleration stages for the production of high-quality GeV electron bunches.

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“…It is therefore necessary to suitably tailor and measure the plasma-density profiles at the exit of the cell in order to optimise the witness beam release from plasma. At FLASHForward's diagnostics laboratory -situated directly above the electron beamline tunnel, hosting a laser path with identical path lengths and optics to that of the laser transport to the interaction point in the tunnel -the plasma profiles in these windowless cells (capable of plasma generation via an ionisation laser or electric discharge) are characterised using a range of techniques including spectroscopy [28] and group dispersion velocity [29], with the results then benchmarked against magnetohydrodynamic codes. • Active plasma lens development.…”

Section: (C) Ancillary Experimentsmentioning

confidence: 99%

FLASHForward: plasma wakefield accelerator science for high-average-power applications

D’Arcy

Aschikhin

Bohlen

et al. 2019

Phil. Trans. R. Soc. A.

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The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.

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Density characterization of discharged gas-filled capillaries through common-path two-color spectral-domain interferometry

Cited by 14 publications

References 27 publications

Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens

Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens

Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators

FLASHForward: plasma wakefield accelerator science for high-average-power applications

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