Production of a thin diamond target by laser for HESR at FAIR

At a Glance

Metadata	Details
Publication Date	2016-04-01
Journal	Journal of Physics Conference Series
Authors	F. Balestra, Sergio Ferrero, R. Introzzi, Candido Fabrizio Pirri, Luciano Scaltrito
Institutions	Istituto Nazionale di Fisica Nucleare, Sezione di Torino, COMSATS University Islamabad
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Purity Thin Diamond Targets for HESR/PANDA

This document analyzes the requirements for producing ultra-thin, high-purity diamond targets for high-energy physics applications (HESR/FAIR PANDA experiment) and outlines how 6CCVD’s advanced MPCVD capabilities provide superior material solutions.

Executive Summary

The research successfully demonstrated the production of ultra-thin, wire-shaped ¹²C diamond targets suitable for the PANDA experiment at FAIR, leveraging MPCVD diamond for its exceptional thermal and mechanical properties.

Critical Material: High-purity Single Crystal Diamond (SCD) films were required to minimize beam depletion and detector background noise in the High Energy Storage Ring (HESR).
Dimensional Achievement: Prototypes achieved a critical thickness of 3 µm (± 0.5 µm) and widths of 100 µm to 145 µm, mounted on a Silicon support ring.
Purity Validation: Back Scattering (BS) tests confirmed outstanding ¹²C purity (99.9%), meeting stringent experimental requirements for minimizing light element impurities (H, O).
Radiation Hardness: Irradiation tests using 1.5 MeV protons showed no structural variation or charge pile-up, confirming the material’s stability under high-flux conditions.
Processing Technique: The final wire shape was achieved via femtosecond laser cutting, which induced localized graphitization (nc-G phase) at the wire edges, providing a beneficial conductive path for charge dissipation.
6CCVD Value Proposition: 6CCVD specializes in delivering the high-purity, ultra-thin SCD precursor wafers (0.1 µm to 500 µm thickness) with custom dimensions and superior surface quality (Ra < 1 nm) necessary to replicate and advance this research.

Technical Specifications

The following hard data points were extracted from the analysis of the diamond target prototypes and testing procedures:

Parameter	Value	Unit	Context
Target Material	¹²C Diamond	N/A	Primary target for antiproton annihilation
Target Thickness (Achieved)	3 ± 0.5	µm	CVD Diamond Wire
Target Width (Prototype 1)	100	µm	Wire shape achieved via laser cutting
Target Width (Prototype 2)	≈ 145	µm	Wire shape achieved via laser cutting
¹²C Purity (CVD)	99.9	%	Measured via Back Scattering (BS)
Impurity Content (Amorphous Attempt)	7% ¹⁶O, 39% H	%	Rejected material due to low hyperon efficiency
Areal Density (CVD)	50 * 10¹⁸	atom/cm²	Required density for target efficiency
Proton Irradiation Energy	1.5	MeV	Used for radiation hardness and BS control
Femto Laser Power (P1)	3	W	Used for first prototype cutting
Femto Laser Wavelength (P2)	343	nm	Used for second prototype cutting (PHAROS)
Raman Diamond Peak (D band)	1332	cm^-1	Pure diamond structure (Wire center)
Raman Graphite Peak (G band)	1585	cm^-1	Graphitized structure (Wire border)

Key Methodologies

The production of the thin diamond wire target involved a two-step process focusing on high-quality CVD growth followed by precision micromachining and rigorous characterization.

CVD Diamond Growth: Disk-shaped diamond films were manufactured via Chemical Vapor Deposition (CVD) onto a Silicon plate (15 mm diameter, 500 ± 100 µm thickness).
Substrate Preparation: An internal disk (11 mm diameter) was etched away from the Si support, resulting in a freestanding diamond plate mounted on the Silicon ring.
Precision Laser Micromachining (P1): A “Femto Edge” type laser (3 W power, 1064 nm wavelength, 100 fs pulse duration) was used to cut two rectangles from the disk, forming the 100 µm wide wire shape.
Precision Laser Micromachining (P2): A PHAROS femtosecond laser (1.5 W power, 343 nm wavelength, 220 fs pulse duration) was used to cut the second, wider (≈ 145 µm) prototype.
Purity and Density Characterization: Back Scattering (BS) technique, utilizing a 1.5 MeV proton beam at a 165° scattering angle, was employed to measure ¹²C purity and areal density.
Structural Analysis: Micro-Raman spectroscopy was performed across the wire width (center, periphery, border) to scan for carbon phase modifications (Diamond D band vs. Graphite G band) induced by the laser cutting process.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational MPCVD diamond material required for high-energy physics targets, ensuring the purity, thickness control, and mechanical stability demanded by the HESR/PANDA experiment.

Applicable Materials

To replicate or extend this research, the highest quality SCD material is mandatory due to the stringent requirements for thermal conductivity, mechanical strength, and purity.

Optical Grade Single Crystal Diamond (SCD): Recommended material. 6CCVD provides SCD wafers with extremely low nitrogen content and high crystalline quality, ensuring the necessary thermal management and radiation hardness observed in the study.
Ultra-Thin SCD Films: 6CCVD specializes in growing SCD films precisely tailored to the required thickness, ranging from 0.1 µm up to 500 µm. We can guarantee the 3 µm (± 0.5 µm) thickness used in the prototypes with high uniformity across the wafer.
Isotopic Control: While the paper used natural ¹²C, 6CCVD offers capabilities for high-purity material growth, critical for minimizing light element contamination (H, O) that severely reduces hyperon production efficiency.

Customization Potential

The success of the PANDA target relies heavily on precision shaping and mounting, areas where 6CCVD provides comprehensive engineering support.

Requirement from Paper	6CCVD Capability	Benefit to Customer
Ultra-Thin Film (3 µm)	SCD thickness control from 0.1 µm	Guaranteed thickness uniformity and high mechanical strength.
Custom Wire Shape (100-145 µm width)	Custom laser cutting and micromachining services.	We deliver the precursor diamond disk ready for final shaping, or perform the complex C-shaped cutting in-house.
Si Ring Support	Custom Substrate and Mounting Solutions.	We can grow the SCD directly on customer-supplied substrates or provide the freestanding film mounted on standard or custom Si frames (up to 10mm thick).
Surface Quality	SCD Polishing (Ra < 1 nm).	Minimizes surface defects that could lead to stress concentration or brittleness during the critical laser cutting phase.
Large Area Potential	PCD plates up to 125 mm diameter.	While SCD was used here, 6CCVD can provide large-area PCD targets for less demanding applications or future scaling needs.

Engineering Support

6CCVD’s in-house PhD team offers expert consultation for complex target fabrication projects. We can assist researchers in optimizing material selection to manage the trade-offs between thermal stress, radiation damage, and charge dissipation observed in this study.

Graphitization Management: We can advise on precursor material properties (e.g., strain, crystal orientation) to influence the resulting graphitization layer during femtosecond laser processing, potentially enhancing the beneficial conductive channel for electrostatic charge mitigation.
Material Certification: All SCD materials are supplied with detailed characterization reports, including Raman spectroscopy data, ensuring the material meets the required purity and structural integrity before costly micromachining begins.

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

View Original Abstract

In the future hadron facility FAIR, the HESR ring will supply antiprotons in the momentum range 1.5-15 GeV/c as projectiles to study charm, strangeness and a wide range of other Physics topics. For all these reactions it will be necessary to use internal targets and in particular, for the production of systems with double strangeness, a solid 12C target will be used. Inserting a solid target inside an antiproton ring creates two main problems: a large background on the detectors due to the overwhelming amount of annihilations and a strong depletion of the beam due to all the hadronic and Coulomb interactions of the antiprotons with the 12C nuclei. The width of the target plays a crucial role in minimizing these unwanted effects. Two wire-shaped prototypes have been already realized, starting from a thin diamond disk. The wire shape has been obtained by using a femto-edge laser. One prototype has been submitted to irradiation by protons of 1.5 MeV and to simultaneous Back-Scattering control to test the impurity level, the 12C density, the radiation hardness and possible phase modifications during irradiation. Both the prototypes have been submitted to Micro-Raman spectroscopy in order to scan the carbon phases along the width. The results show performances which satisfy the experimental requirements.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1742-6596/713/1/012003