What is CASPAR?

The Compact Accelerator System for Performing Astrophysical Research (CASPAR), is a National Science Foundation (NSF) funded underground accelerator laboratory housed in the Sanford Underground Research Facitily (SURF), located in the Black Hills of South Dakota. CASPAR resides 4850 ft underground and is dedicated to the study of nuclear reactions fuelling stellar environments and elemental production. CASPAR is the only deep underground accelerator laboratory in the U.S. A strong focus of the laboratory is the education and training of the next generation of nuclear physicists through strong graduate and undergraduate student involvement.



Play the video for a trip underground with CASPAR physicists.



What is CASPAR looking for?

At the intersection of observational astronomy, astrophysics and nuclear physics, there stands the field of experimental low-energy nuclear astrophysics. Through the understanding of stellar burning processes, their energetics and mechanisms, we strive to build a picture of the chemical evolution of our Universe. The driving force of CASPAR is to push this understanding down into the stellar burning regime of astrophysical interest where nuclear reactions take place at low energy.

At low energy, reaction probabilities are extremely low and studying them requires a high sensitivity level difficult to achieve in high background environments. The solution adopted by CASPAR to suppress the overwhelming cosmic-ray induced background is to move underground. Located 4850 ft below the surface, at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, CASPAR is a complete accelerator laboratory focused on low-energy nuclear physics. The collaboration between the University of Notre Dame (ND), South Dakota School of Mines and Technology (SDSMT) and Colorado School of Mines (CSM), is a joining of three institutions. The first accelerated ion beam was achieved in 2017 with commissioning and calibration tests.

Where is CASPAR?

CASPAR is located on the 4850 ft level of the Sanford Underground Research Facility, in Lead, South Dakota, at the former site of the Homestake Gold Mine. The largest and deepest gold mine in North America until its closure in 2002. The site has over 370 miles of shafts, drifts and ramps previously carved out for gold mining purposes. Currently operations are supported by the Department of Energy and concentrated on 12 miles for science activities.

The mine was the site of the ground breaking work of Ray Davis and John Bahcall in the mid-1960s, often referred to as the "Homestake Experiment". Their work on the solar neutrino problem would later earn Davis a Nobel Prize in 2002, shared with Masatoshi Koshiba and Riccardo Giacconi.





The Ross Headframe as seen from the main administration building

What does CASPAR look like?

The CASPAR underground laboratory is a low-energy accelerator laboratory primarily focused on the study of reactions important for elemental production in stellar environments. The driver of this research is the 1 MV JN model Van de Graaff accelerator, previously operational at the Nuclear Science Lab at Notre Dame. This is the 4th incarnation of the JN over its near 60-year lifetime, a detailed account of which can be found here "The Four Lives of a Nuclear Accelerator".


The CASPAR beamline overview

Begining from the 1 MV JN accelerator, the CASPAR system is ~ 16 meters long, with a 25 degree deflection for momentum selection at the midpoint and a modular target station equipped for either gas or solid-target experiments.

Positive ions are created in the terminal of the accelerator via a gas-fed RF ion source, equipped to produce both proton and alpha beams. All ion optic elements on the beamline (quadrupoles, steerers etc) are magnetic and external to the beamline.

JN Accelerator Electrostatic accelerator, voltage range 150 kV-1.1 MV
RF Ion Source Proton Beam ~250 μA, Alpha Beam ~220 μA
Analyzing Magnet 25-degree dipole, 0-degree and "mass 2" lines
Target Station Extended, recirculating, windowless gas target
0-degree and 55-degree solid target system
Vacuum System Turbomolecular pumping, conflat system beamlines


Research & Experiments

Background Suppression

In the low energy regime associated with nuclear reactions in stars, the tendency is for the reaction probability (cross-sections) to drop off exponentially, making the detection of such events an extremely rare occurrence. The ever present abundance of cosmic-ray induced background inhibits such measurements by traditional means, swamping out the rarer events of interest sometimes by orders of magnitude. The goal is to measure reactions of interest in the stellar burning regime utilizing the 4300 m.w.e shielding provided by the deep underground environment.

Research Focus

Initial reactions of interest are focused on, but are not restricted to, the production of seed neutrons for the s-process, specifically 13C(α,n) and 22Ne(α,n) The combination of the low-background environment and a high-efficiency neutron counting system (3He tube array) enables low-energy measurements with low count rates.

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Experimental Products



News & Featured Research

Feb. 2018

First stage commisioning experiments have recently wrapped up at CASPAR after a two week experimental campaign. The intial measurements focused on the 27Al(p,γ)28Si and 15N(p,γ)16O reactions for accelerator energy calibration. This was followed by the initial stages of a PhD thesis work associated with the astrophysically important CNO cycle reaction 14N(p,γ)15O.

Jul. 2019

CASPAR members from SDSM&T took part in the annual SURF Neutrino Day. This year nearly 1,700 guests took part in the event, with over 250 volunteers. The amazing outreach event enables community interaction and a chance to learn the wide range of scientific and engineering programs supported at the facility. Photo thanks to Matt Kapust.

Aug. 2019

A team of faculty from the Nuclear Science Laboratory, Anna Simon, Joachim Goerres, Manoel Couder, Daniel Robertson, led by Michael Wiescher received 4-year support from the NSF to continue measurements at the underground accelerator facility investigating reactions important for the stellar nucleosynthesis processes.



CASPAR Creation & Future in DIANA

The DIANA project (Dual Ion Accelerators for Nuclear Astrophysics) was the founding idea for a deep-underground accelerator laboratory in the US. The working collaboration between the University of Notre Dame, University of North Carolina, Western Michigan University and Lawrence Berkely National Laboratory, conceived and designed the accelerator laboratory as part of the DUSEL proposal (Deep Undergrund Science and Engineering Laboratory). The design consists of two high-current accelerators, a 30 to 400 kV variable, high-voltage platform, and a vertical accelerator with a higher voltage range of 350 kV to 3 MV, delivering available beam densities on target of up to 100 mA on the low energy accelerator and several mA on the high energy accelerator.

As a demonstration of obtainable scientific goals, CASPAR has emerged as the first stage of a possible DIANA system. Future expansion will hopefully merge the current and proposed systems, further driving the world class research of hte underground facility.



Collaboration & Members

The CASPAR collaboration has three founding member institutions, the University of Notre Dame (ND), South Dakota School of Mines and Technology (SDSMT) and Colorado School of Mines (CSM).

Dr. Frank Strieder
CASPAR P.I. (SDSMT)

Dr. Daniel Robertson
Co-P.I. & Technical Director (ND)

Dr. Michael Wiescher
Co-P.I. (ND)

Dr. Uwe Greife
Co-P.I. (CSM)

Dr. Manoel Couder
Experimenter (ND)

Dr. Joachim Görres
Experimenter (ND)

Dr. Anna Simon
Experimenter (ND)

Dr. Edward Stech
Experimenter (ND)

Bryce Frentz
Graduate Student (ND)

Mark Hanhardt
Graduate Student (SDSMT)

Thomas Kadlecek
Graduate Student (SDSMT)

Rebecca Kelmar
Graduate Student (UND)

Orlando Gomez
Graduate Student (UND)

August Gula
Graduate Student (UND)

Shahina Shahina
Graduate Student (UND)

Core Institutions

University of Notre Dame South Dakota School of Mines and Technology Colorado School of Mines

Collaborating Institutions

Oak Ridge National Lab
JINA-CEE
Ohio University





Contact Us

For any query about CASPAR, please contact

Daniel Robertson
Nuclear Science Laboratory
University of Notre Dame
Notre Dame, INDIANA, 46556 USA
Email: drobert4@nd.edu
Phone: (574) 631-7716

Frank Strieder
South Dakota School of Mines and Technology
Department of Physics
Rapid City, SOUTH DAKOTA, 57701 USA
Email: frank.strieder@sdsmt.edu
Phone: (605) 394-1227