John McDowell “Mac” Walsh
November 06, 1923 — March 09, 2009
From Physics Today
Submitted by John K. Dienes, Los Alamos, NM
John McDowell (Mac) Walsh, noted for work in shock wave physics, died March 9, 2009 at his home in Santa Fe, NM. He was awarded, with M. Rice and R. McQueen, the first George E. Duvall Shock Compression Science Award "In recognition of pioneering contributions in the use of intense shock waves to determine high-pressure equations of state for condensed matter."
Mac enlisted in the Naval V-12 program soon after Pearl Harbor and eventually served as a deck officer on a destroyer in the Pacific theater. After the war, he entered graduate school at the University of Texas in Austin, majoring in physics with a minor in mathematics. His dissertation, Wave Mechanics of Hydrogen Cystems, concerned molecular orbital theory. On completion of his PhD in 1950 he joined Group GMX-6 at Los Alamos, which he served as group leader in the period 1956–1960. During those ten years Mac, with numerous collaborators, published research that extended the science of shock wave physics and its role in determining material equations of state at extreme pressures. Novel experimental techniques, as well as refined theoretical methods, were developed while at Los Alamos. Much of this work is summarized in the 1958 review article in Seitz and Turnbull's Solid State Physics, Vol. 6. The Topical Group for Shock Compression of Condensed Matter of the APS, established in 1981, gave him its first Shock Wave Science Award in 1987 along with Melvin Rice and Robert McQueen.
Mac was invited to join Project Orion at General Atomic in 1960 to address the many issues in high-pressure physics. Orion was to be an enormous spaceship propelled by nuclear explosion pulses and designed to navigate the solar system. Concern about shock wave damage in the pusher plate led him to develop a criterion for shockless acceleration. Orion was eventually terminated because of the Test Ban Treaty, but many scientists and engineers considered the project a high point in their lives. All this was documented in Project Orion, an excellent book by George Dyson, Freeman's son, who drew heavily on his father's experiences and contributions.
While at General Atomic, Mac was awarded a long-term contract to investigate hypervelocity impact. This led to a revolutionary approach known as Late Stage Equivalence. The concept states that it is neither the energy nor the momentum of a projectile that controls the late-stage behavior following hypervelocity impact, but an intermediate quantity mvβ, with m the projectile mass and v its velocity. It was shown with computer simulations that all impacts with the same mvβ converge toward the same late-stage behavior for β =1.74, slightly less than the value of 2 for energy equivalence. Thus, the effects of impacts far above the experimental range could be inferred. This was important because it was being argued by some that momentum governed, implying β equal to 1. At Mac's suggestion, Dienes addressed this issue analytically and showed that, in one dimension, β is an eigenvalue of the (nonlinear) flow equations supplemented by shock wave behavior at one boundary of the flow and zero pressure at the other. Approximate analytic solutions to the multi-dimensional problem were later found by W. Rae. This result accounts for momentum multiplication in the target as a result of the backward ejecta. Walsh joked privately that the record for momentum multiplication was held by the photoelectric effect. Walsh and Dienes went on to show that strength effects, including crater size, could be accounted for with a special plastic-flow model, as reported in High Velocity Impact Phenomena, R. Kinslow, Ed.. While the first calculations were performed with a one-material Eulerian code, subsequent studies were performed with a multi-material code known as HELP, developed with L. Hageman and now used throughout the world in various incarnations.
Mac was instrumental in starting Systems, Science, and Software, a California corporation specializing in weapons effects. When it was acquired by another company, he was invited to return to Los Alamos as Associate Division Leader for M Division. Subsequently, he led group M4 until his retirement. While back at LANL, he initiated a variety of applied programs involving high explosives. He also investigated the interaction of oblique detonation waves with metals, the topic of his paper opening the 1987 Shock Wave Physics Meeting. In those years he also taught a variety of hydrodynamics courses both at LANL and externally.
He was widely admired for his deep insights into thermodynamics and hydrodynamics, his leadership abilities, subtle sense of humor, and humility.
JOHN MCDOWELL WALSH
From Los Alamos Monitor
By The Staff
Tuesday, March 17, 2009 at 10:00 pm
John McDowell Walsh, was born November 6, 1923, and died March 9, 2009.
Mac was a physicist, husband, tennis player, father and a Democrat. He was born in 1923 in Wichita Falls, Texas, to Charles Kyran and Edna MacDowell Walsh. He was the third of four children and the only boy. His father, Charles, was an attorney. Mac recently lost his dear sister, Lucy Ann Phillips, and was also preceded in death by his son, Mark Jay Walsh, and his first wife, Bernice Weinheimer Walsh.
By his first marriage, he is survived by his daughter, Rachel Ann Walsh; by his son, John McDowell Walsh; and by his daughter-in-law Marie-Christine Walsh. He is also survived by his wife of 22 years, M’Lea Walsh and her two sons, David Wray and Kevin Wray and his wife Jami.
Mac served as a deck officer on a Navy destroyer in the Pacific theater. He trained to spot Japanese Zeroes on Oahu and patrolled the Aleutians. Helped by the GI Bill, Mac attended the University of Texas in Austin, majoring in physics with a minor in mathematics. His dissertation research subject was molecular orbital theory.
He completed his PhD in 1950 and joined Group GMX-6 of the Los Alamos Scientific Laboratory where he served as group leader until 1960. During this initial 10 years at Los Alamos, he published research that originated the field of shock wave physics specifically for determining material equations of state at extreme pressures. In these efforts, he collaborated with Robert McQueen, Melvin Rice, and others.
In 1981, the American Physical Society established The Topical Group for Shock Compression of Condensed Matter. The first biennial meeting of this group was in 1983, and its first Shock Wave Science Award was given to Mac Walsh, the father of the field, in 1987. He loved to teach and explain science and taught short courses and was thesis advisor to several students.
Mac was asked to join project Orion at General Atomic in 1959 to address the many problems in high-pressure physics. Orion was to be an enormous spaceship propelled by nuclear explosion pulses and designed to navigate the solar system. The project was terminated following the Test Ban Treaty. While at General Atomic, he was awarded a long-term contract to investigate hypervelocity impact. This led to a revolutionary approach known as Late Stage Equivalence. The theoretical work was complemented by his development of HELP, a computer program to model high-pressure hydrodynamics that has been widely used throughout the world.
He was instrumental in starting System, Science and Software, an important California corporation specializing in weapons effects. When it was acquired by another company, he was invited to return to LANL as Associate Division Leader for MDO. Subsequently he was Group Leader for M4 from 1977 until 1980. While back at LANL he initiated a variety of major programs involving applications of high explosives. He retired in 1988 but served as a Lab Associate until 1993.
Mac was admired for his deep insights into thermodynamics, hydrodynamics, his wonderful sense of humor, and his humility. Mac greatly admired the numerous contributors to the field of physics, but his personal hero was FDR. He worked in fairly congenial environments and regularly enjoyed playing tennis with coworkers. He mixed up the world’s best Old Fashioned. In the 50’s and 60’s he enjoyed a regular game of poker. Later, he did well in stock market and real estate investing. He enjoyed vacationing and traveling with his family.
Mac and M’Lea retired in the early 1990s and designed and built a home in Santa Fe which he loved. Mac lost his memory to dementia, but always retained a sweet, easy-going personality. Despite being confused, Mac always retained a certain level of composure, and was always a true gentleman. All who knew Mac will remember him as a caring, genuine and loving man.
A memorial service will be held for Mac at the Fuller Lodge at 2132 Central Ave in Los Alamos, New Mexico on March 23, 2009 at 2:00 pm. Their phone number is 505-662-8405.
In lieu of flowers, the family requests that memorial donations be made in Mac’s name to Habitat for Humanity (www.habitat.org).
Arrangements are under the direction of Berardinelli Family Funeral Service, 1399 Luisa St., Santa Fe, NM 87505 (505) 984-8600.
John McDowell “Mac” Walsh Photo Album