HEPL is Stanford's first and oldest independent research laboratory. It supports interdisciplinary research programs in fundamental science and engineering and provides unique research and educational opportunities for undergraduate, graduate and postdoctoral students.
A Brief History of HEPL
The W.W. Hansen Experimental Physics Laboratory (HEPL) began as the High Energy Physics Laboratory (also HEPL) in 1951 (it was renamed in 1990), after the Stanford Microwave Laboratory was split into two divisions, HEPL and the Microwave Laboratory (subsequently renamed Ginzton Laboratory). Before 1990, the two laboratories were collectively known as the W.W. Hansen Laboratories of Physics.
The predecessor Microwave Laboratory began as a division of the Physics Department in 1945. It was there that the world's first high power klystrons were developed by Edward L. Ginzton and Marvin Chodorow, and there, under the leadership of William Webster Hansen, that the world's first electron linear accelerator was built.
The microwave research began in the Physics Department by Hansen with Russell H. Varian, and Sigurd F. Varian before World War II had a dual impact on physics and engineering evident throughout HEPL's history. As Ginzton modestly put it: "Not only did the microwave art promise new application, but as a new tool, it promised to be helpful in physics research as well." New lines of research originated at HEPL continue to "promise new application" and "promise to be helpful in physics research."
For its first decade, HEPL's operations centered on accelerator research, though following two distinct lines: high-resolution electron scattering under Robert Hofstadter and meson physics under Wolfgang K.H. Panofsky. Hofstadter was awarded the 1961 Nobel Prize for his work on nuclear form factors. Panofsky developed the immensely successful two-mile-long accelerator at the Stanford Linear Accelerator Center (SLAC), the successor to HEPL accelerators.
Expanding the Scope of HEPL in the 1960s
Starting around 1963, many new research programs were based in HEPL.
In accelerator physics, the dominating new activity of the Laboratory from 1964 through 1981 was the development of the superconducting accelerator (SCA). The idea of the SCA was simple. It operated an accelerator structure at superfluid helium temperatures with resonant cavities made of superconducting niobium instead of copper. Between 1979 and 1981, the SCA demonstrated its capability for doing nuclear physics in several experiments, and even more important, that it had two deeply significant technological offshoots: it provided the way for making the free electron laser (FEL) a success, and it gave HEPL an internationally unique capability in the application of large scale cryogenic technology.
The FEL, invented by John M.J. Madey, is a device that generates intense coherent radiation by the motion of free electrons through a resonant structure. The Stanford FEL, operating at wavelengths between 1.6 and 10 micrometers, began operation in 1976, involving the collaboration of Electrical Engineering, Physics, Applied Physics, SLAC and Medical School faculty. Since its initial development at Stanford, FEL research has become a major international activity.
Gravity Probe B (GP-B)
Gravity Probe B (GP-B) is a NASA physics mission to experimentally investigate Albert Einstein's 1916 general theory of relativity—his theory of gravity. GB-B used four spherical gyroscopes and a telescope, housed in a satellite orbiting 642 km (400 mi) above the Earth, to measure in a new way, and with unprecedented accuracy, two extraordinary effects predicted by the general theory of relativity (the second effect having never before been directly measured):
- The geodetic effect—the amount by which the Earth warps the local spacetime in which it resides.
- The frame-dragging effect—the amount by which the rotating Earth drags its local spacetime around with it.
The GP-B experiment tests these two effects by precisely measuring the displacement angles of the spin axes of the four gyros over the course of a year and comparing these experimental results with predictions from Einstein's theory.
GP-B is the second dedicated NASA physics experiment to test aspects of general relativity. The first, Gravity Probe A, was led in 1976 by Dr. Robert Vessot of the Smithsonian Astrophysical Observatory. Gravity Probe A compared elapsed time in three identical hydrogen maser clocks—two on the ground and the third traveling for two hours in a rocket and confirmed the Einstein redshift prediction to 1.4 parts in 104.
After 31 years of research and development, ten years of flight preparation, a 1.5-year flight mission and five years of data analysis, our GP-B team has arrived at the final experimental results for this landmark test of Einstein's 1916 general theory of relativity. Here is the abstract from our PRL paper summarizing the experimental results. Data collection started on 28 August 2004 and ended on 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of -6,601.8±18.3 mas/yr and a frame-dragging drift rate of -37:2±7.2 mas/yr, to be compared with the GR predictions of -6,606.1 mas/yr and -39.2 mas/yr, respectively ('mas' is milliarcsecond; 1 mas= 4.848 X10-9 radians or 2.778 X10-7 degrees).
In addition to a group of programs clustered around a broad theme of space physics and astrophysics, which involve collaborations with the Aero-Astro, Electrical Engineering, Applied Physics and Mechanical Engineering, HEPL is home to programs in the field of biomedical physics in general and electro-neural interfaces in particular. In the past decade, methods adapted from experimental physics have transformed our understanding of the nervous system in areas ranging from optical imaging to large-scale electrical recordings. These methods enable the precision, bandwidth, and quantitative analysis required for deeper exploration of massively parallel neural networks in the brain.