One-Body Capillary Plasma Source for Plasma Accelerator Research at e-LABs

At a Glance

Metadata	Details
Publication Date	2023-02-16
Journal	Applied Sciences
Authors	Sihyeon Lee, Seong‐Hoon Kwon, Inhyuk Nam, Myung Hoon Cho, Dogeun Jang
Institutions	Pohang University of Science and Technology, Gwangju Institute of Science and Technology
Citations	2
Analysis	Full AI Review Included

Technical Analysis and Documentation: MPCVD Diamond for Plasma Accelerator Research

Executive Summary

This documentation analyzes the development of a one-body sapphire capillary plasma source for Laser Wakefield Acceleration (LWFA) and Active Plasma Lens (APL) applications. The findings validate the use of diamond machining techniques and highlight the critical need for materials with superior durability and thermal properties—a requirement perfectly addressed by 6CCVD’s MPCVD diamond solutions.

Novel Design: Successful development of a compact, leak-free, one-body capillary gas cell manufactured from sapphire using diamond machining, eliminating gas leakage risks associated with traditional two-plate assemblies.
LWFA Validation: The capillary source demonstrated stable and reproducible operation in LWFA experiments, generating electron beams with energies of 200 ± 25 MeV.
APL Performance: Investigated the potential as an Active Plasma Lens (APL), achieving a peak discharge current of 140 A at 10 kV, resulting in a high focusing gradient of 97 T/m.
Material Limitation Identified: The research implicitly calls for materials harder and more durable than sapphire for high-repetition-rate, high-intensity laser systems, positioning MPCVD diamond as the ideal next-generation solution.
Manufacturing Synergy: The core manufacturing technique—precision diamond drilling and machining—is a primary capability of 6CCVD, allowing for direct replication and enhancement using superior diamond substrates.
Engineering Advantage: 6CCVD offers custom SCD and PCD substrates, providing unmatched thermal conductivity and robustness necessary for next-generation plasma accelerator components.

Technical Specifications

The following hard data points were extracted from the research paper detailing the performance and dimensions of the capillary plasma source:

Parameter	Value	Unit	Context / Application
Capillary Material	Sapphire (One-Body)	N/A	Manufactured via diamond machining
Capillary Length (LWFA)	7	mm	Electron acceleration experiments
Capillary Length (APL)	15	mm	Active Plasma Lens investigation
Capillary Diameter	1	mm	Used for both LWFA and APL tests
Electron Beam Energy (LWFA)	200 ± 25	MeV	Stable and reproducible output
Laser System Power	150	TW	Used for LWFA experiments
Laser Pulse Duration	25	fs (FWHM)	Used for LWFA experiments
Helium Gas Pressure (LWFA)	150	mbar	Used for LWFA
Estimated Plasma Density	7.2 x 10¹⁸	cm^-3	Full ionization of Helium
Peak Discharge Current (APL)	140	A	Achieved at 10 kV applied voltage
Focusing Gradient (APL)	97	T/m	Calculated for 140 A discharge current
RMS Beam Size (Input APL)	179	µm	Input beam from photocathode gun (e-LABs)

Key Methodologies

The experiment relied on precision manufacturing and advanced characterization techniques to validate the capillary source:

One-Body Capillary Fabrication: A single block of sapphire was machined using electroplated diamond drill bits. This process created the longitudinal capillary hole (up to 15 mm length, 1 mm diameter) and internal threads for gas delivery, ensuring a compact, leak-free structure.
Electrode Integration: Oxygen-free electrolytic copper electrodes were installed at both ends of the capillary, secured and insulated using PEEK material to prevent unintended discharges.
Gas Density Characterization: Mach-Zehnder interferometry, utilizing a continuous wave He-Ne laser (632 nm wavelength), was employed in a vacuum chamber (1.2 x 10^-4 Torr) to measure the phase shift and determine gas pressure distribution.
Computational Fluid Dynamics (CFD): 3D CFD simulations (ANSYS FLUENT) were used to model the gas density distribution, confirming that maximum gas density was reached and stabilized within 50 ms of gas injection.
LWFA Experiment Setup: A 150 TW Ti:sapphire laser system was focused into the 7 mm capillary filled with 150 mbar Helium. The resulting electron beams were diagnosed using a 1 T dipole magnet and LANEX phosphor screens.
APL Discharge System: A pulsed, high-voltage (10 kV) discharge system, triggered by a thyratron switch, was applied to the 15 mm capillary (300 mbar He) to generate the plasma lens, with current monitored by a current transformer.

6CCVD Solutions & Capabilities

The successful implementation of diamond machining on sapphire validates the core fabrication technique, but the inherent limitations of sapphire (especially under high thermal load and high repetition rates) necessitate a material upgrade. 6CCVD’s MPCVD diamond is the definitive solution for replicating and extending this research into industrial-grade, high-power plasma accelerator systems.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials, offering superior performance compared to sapphire:

Optical Grade Single Crystal Diamond (SCD): Ideal for the capillary body where maximum thermal conductivity (up to 2200 W/mK) and optical transparency are required. SCD ensures minimal thermal distortion and superior robustness against high-intensity laser pulses and high-current plasma discharge.
High-Durability Polycrystalline Diamond (PCD): Recommended for larger-scale or multi-capillary arrays. PCD offers exceptional mechanical strength and can be grown in large formats (up to 125mm diameter), facilitating the development of complex, integrated plasma accelerator modules.
Boron-Doped Diamond (BDD): For applications requiring integrated electrodes or sensors within the capillary structure, BDD provides a conductive diamond material with high chemical and thermal stability.

Customization Potential

6CCVD’s in-house capabilities directly address the complex manufacturing requirements demonstrated in this paper:

Research Requirement	6CCVD Customization Capability	Technical Advantage
Precision Capillary Drilling (1 mm diameter, 7-15 mm length)	Custom Diamond Machining: We utilize advanced diamond tools and laser cutting to drill precise, high-aspect-ratio holes and complex internal geometries (e.g., tapered profiles) directly into SCD or PCD substrates.	Ensures leak-free, one-body construction in the most durable material available.
Electrode Interface (Holey Copper Electrodes)	In-House Metalization: 6CCVD provides custom metal deposition services, including Au, Pt, Pd, Ti, W, and Cu. We can deposit robust, multi-layer metal stacks directly onto the diamond surface for superior, low-resistance electrical contacts required for the 140 A APL discharge.	Eliminates the need for external copper electrodes and PEEK holders, simplifying assembly and improving thermal management.
Large-Scale Integration	Large Format Substrates: We supply PCD plates up to 125mm in diameter and SCD substrates up to 500µm thick, enabling the fabrication of multi-capillary arrays or longer acceleration columns (up to 30 mm or more, as suggested by the authors).	Supports scaling of LWFA and APL systems for higher energy and repetition rates.
Surface Finish (Critical for gas flow and optics)	Ultra-Precision Polishing: Our standard SCD polishing achieves surface roughness Ra < 1nm, minimizing laser scattering and optimizing gas flow dynamics within the capillary channel.	Essential for maintaining beam quality and stability in high-power systems.

Engineering Support

6CCVD maintains an in-house team of PhD-level material scientists and engineers specializing in MPCVD diamond applications. We offer comprehensive consultation services to assist researchers in transitioning from sapphire to diamond substrates for Laser Wakefield Acceleration (LWFA) and Active Plasma Lens (APL) projects. Our expertise ensures optimal material selection, custom design implementation, and reliable integration into high-vacuum and high-voltage discharge systems.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We report on the development of a compact, gas-filled capillary plasma source for plasma accelerator applications. The one-body sapphire capillary was created through a diamond machining technique, which enabled a straightforward and efficient manufacturing process. The effectiveness of the capillary as a plasma acceleration source was investigated through laser wakefield acceleration experiments with a helium-filled gas cell, resulting in the production of stable electron beams of 200 MeV. Discharge capillary plasma was generated using a pulsed, high-voltage system for potential use as an active plasma lens. A peak current of 140 A, corresponding to a focusing gradient of 97 T/m, was observed at a voltage of 10 kV. These results demonstrate the potential utility of the developed capillary plasma source in plasma accelerator research using electron beams from a photocathode gun.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app13042564

References

2004 - High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding [Crossref]
2004 - A laser-plasma accelerator producing monoenergetic electron beams [Crossref]
2006 - GeV electron beams from a centimetre-scale accelerator
2007 - A compact synchrotron radiation source driven by a laser-plasma wakefield accelerator [Crossref]
2008 - Generation of stable, low-divergence electron beams by laser-wakefield acceleration in a steady-state-flow gas cell [Crossref]
2011 - Gamma-rays from harmonically resonant betatron oscillations in a plasma wake [Crossref]
2021 - Free-electron lasing at 27 nanometres based on a laser wakefield accelerator [Crossref]
2013 - The role of the gas/plasma plume and self-focusing in a gas-filled capillary discharge waveguide for high-power laser-plasma applications [Crossref]
2003 - Gas-filled capillary discharge waveguides [Crossref]
2011 - Discharge characteristics of a gas-filled capillary plasma for laser wakefield acceleration [Crossref]