Skip to main content

HPEPL employs a wide range of plasma probe diagnostics and facility measurement techniques. HPEPL also employs a rigorous probe calibration and check-out procedure to accurately define the uncertainty of each measurement.

Laser Thomson Scattering

Laser Thomson scattering (LTS) is a technique that uses the number density and spectral distribution of photons scattered by free electrons to measure the electron temperature and electron number density of a plasma.

More information (web page)


Terahertz time-domain spectroscopy (THz-TDS) is a method by which material or plasma properties are determined through measurement of attenuation and refraction of broadband pulsed THz radiation in media.

More information (web page)

Quartz Crystal Microbalance (QCM)

Quartz crystal microbalances (QCMs) are devices used to measure the rate of mass deposition per unit area by correlating changes in the measured frequency of an exposed quartz crystal resonator to a corresponding change in crystal mass.

More information (web page)

Inverted Pendulum Thrust Stand

A null-type stand differs from other inverted pendulum thrust stands in that it actively holds the thrust stand in a nearly stationary position at all thrust levels. This eliminates changes in the elevation angle of the thrust vector and reduces error in the thrust measurement.

More Information (article)

Thrust Stand for Pulsed-mode Devices

This thrust stand makes accurate measurements of thrust for devices operating in a pulsed mode.  Many high-power thruster concepts such as magnetoplasmadynamic thrusters and pulsed inductive thrusters operate in short pulses. 

More Information (article)

Langmuir Probe

The Langmuir Probe is used to measure electron number density and electron temperature. 

More information (article)

RF-compensated Langmuir Probe

This Langmuir probe employs both a floating electrode immediately adjacent to the probe tip and multiple RF chokes to facilitate measurements of electron number density and electron temperature in RF plasmas.  Example RF plasmas include capacitively-coupled, inductively-coupled, and helicon discharges. 

More information (article)

Faraday Probe – JPL

Faraday probes provide a measurement of ion current density. The measurement is often performed in angular sweeps across the thruster plume to quantify the divergence angle of the thruster plume. The probe pictured is modeled on the JPL nude Faraday probe design.

More information (article)

Emissive Probe

True to its name, the emissive probe obtains its measurement (plasma potential) by emitting electrons to neutralize the Debye sheath surrounding the probe. 

More Information (article)

High-Speed Axial Reciprocating Probe

The high-speed axial reciprocating probe (HARP) rapidly translates probes to enable measurements in high-energy plasma environments.

HARP in use in VTF2 (Video)

HARP Test 4 m/s (Video)

More information (article)

Retarding Potential Analyzer – HPEPL

A Retarding Potential Analyzer directly measures ion energy distribution by quantifying their ability to migrate across a biased grid. Three other grids provide shielding from the plasma and repulsion/suppression of electrons.

More information (article)

Retarding Potential Analyzer – AFRL

The Retarding Potential Analyzer makes a direct measurement of the ion energy distribution.

More information (article)

Hiden EQP 300

The EQP is a high-sensitivity energy analyzer and mass analyzer combined, enabling accurate measurements of ionization and energy distribution of arbitrary species.

More information (external web page)

ExB Probe

The E x B probe measures the charge state of ions.

More information (article)

Anode Flame Test Stand

HPEPL has developed a novel method for propellant flow characterization employing a premixed flame stabilized on the exit plane of the propellant distributor. This technique yields immediate visual feedback on the flow through the propellant distributor by making spatial nonuniformities in mass flow rate visible. A quantitative measure of the uniformity can be obtained by examination of the flame luminosity and its variability in circumferential and radial directions.

Testing of a Single-Inlet Propellant Distributor (Video)

Testing of T-140 Propellant Distributor (Video)