A Brief History of High Power Pulsed Magnetic Fields and Electromagnetic Forming ("magneforming")
Russian Nobel Prize winning physicist Pyotr L. Kapitza was the first researcher to generate and study the effects of pulsed ultra-strong magnetic fields. Kapitza began his magnetic field research in 1924, initially using specially designed lead-acid storage batteries as high-current power sources. He combined these with a custom high-current switch and fuse arrangement to briefly apply huge currents (10,000+ Amperes) into robust wire coils (called solenoids). Using this arrangement, Kapitza was able to briefly generate magnetic fields of up to 500,000 Gauss (50 Tesla) for 3 milliseconds. In later work, he employed specially designed combinations of flywheels and dynamos and, ultimately, banks of high voltage capacitors to develop even higher fields for even shorter intervals. In earlier experiments, huge currents were briefly forced into solenoids from a powerful source of electrical energy which was then disconnected before the coil could overheat and melt. However, his attempts to achieve fields greater than 300 kilogauss always resulted in violent explosions of the solenoids due to extreme magnetic forces acting on the wire turns of the solenoid ("magnetic pressure" and Lorentz force). At 500 kilogauss, the energy density of the magnetic field inside the coil becomes comparable to that of a high explosive, and forces on the coil exceed the tensile strength of even the strongest metals or alloys.

The first laboratory application that used a capacitor discharge to reshape metal pieces (electromagnetic forming) is credited to T. F. Wall in 1926. Wall was able to create fields exceeding 450 kilogauss by using heavily-built work coils that subsequently exploded (after the forming action had completed). In the mid 1950's, Harold Furth and Ralph Waniek at the Harvard Cyclotron Laboratory developed special coil construction techniques which permitted electromagnets to survive the intense forces associated with pulsed ultra-strong magnetic fields. In the late 1950’s these techniques were first applied on an experimental basis in industry. US Patent #2,976,907, issued to G. F. Harvey and D. F. Brower (General Dynamics Corp.), covers the basic process, which is sometimes called Magnetic Pulse Forming or “Magneforming”.  A. P. Langlois reported on electromagnetic forming using expendable wire coils to expand or reduce ("swage") tubular parts in 1960. Gulf General Atomic introduced the first commercially available magnetic metal forming equipment in 1962. This machine had a capacity of 4,500 foot-pounds ( about  6,100 joules per shot), and could cycle at 10 shots/minute. A number of other aerospace and capacitor manufacturers further evolved the technology, increasing the power levels during the 1970’s and 80’s. These included McDonnell Douglas, Boeing, LTV Aerospace, Advanced Kinetics, Inc., Republic Aviation, and General Dynamics, and capacitor manufacturers Maxwell, Cornell Dubilier, and Aerovox. Energy levels were eventually boosted to over 230,000 Joules/shot in the largest capacitor discharge machines.

Most of the above activities were pretty much hidden from the general public. However, one notable exception was a special, custom-made "vending machine" that resided within the Smithsonian during the early 1970's. This machine was actually designed and built by a group of scientists at Los Alamos National Laboratories. It was used to demonstrate the principles of the magnetic "Pinch Effect" to squeeze plasma for controlled thermonuclear fusion experiments. A hollow aluminum tube was substituted for plasma since the basic principles are the same. When a visitor dropped a quarter into the machine, a mechanism would drop a 1" diameter aluminum tube inside a pair of heavy-duty work coils. The coils were then briefly pulsed by a high voltage capacitor discharge. The resulting pulsed magnetic field instantly necked down the sections of tubing that were directly inside the coils, causing these sections to assume hourglass shapes. All of the operations could be safely observed through the clear front and sides of the machine. After collapsing the tube, the machine then delivered the (still warm!) tube to the visitor as a souvenir.      

The History of "Quarter Shrinking"
It's not exactly clear just when electromagnetic forming was first applied to “shrink” coins.  I first learned about "quarter shrinking" via a posting by Richard Hull (Tesla Coil Builders of Richmond, VA or TCBOR) on the Tesla Coil Builders Mailing List in 1996. Richard described a videotape of coin crushing made by Dr. James Goss at Central Alabama College, where James was a professor of Electrical and Electronics Engineering. On the tape, Dr. Goss performed various coin crushing experiments in a system that used a bank of four 15 uF utility Power Factor Correction (PFC) capacitors. He constructed a special high voltage switch from a pair of massive graphite anodes (removed from special purpose electron tubes called ignitrons). A small cannon ball  was rolled down a PVC pipe to in order to bridge the connection between the graphite electrodes, discharging the capacitor bank into the work coil!  Although his experiments were temporarily stalled when one of the capacitors failed, splitting its case, the remaining three capacitors are still in use in his coin shrinker today. Unfortunately, most high voltage capacitors are simply not designed to handle the huge magnetic forces and mechanical shocks associated with the high discharge currents used in magneforming. Poorly-designed capacitors can progressively tear themselves apart during each discharge. Voltage reversals can also cause the insulating oil and dielectric material inside the capacitor to break down, liberating gases which begin bulging the metal case. Continued use (abuse?) can cause the case to rupture or a high voltage insulator to be blown out of the case. And, when one of the capacitors abruptly shorts out, it may explode when the other capacitors in the bank suddenly dump all their stored energy into the failing capacitor.

About a year later (1997), I was fortunate to acquire a batch of 54 uF 15 kV GE pulse capacitors on the surplus market. These were metal-cased beauties with big "Frankenstein's lab" insulators. Each capacitor weighed about 150 pounds - a veritable mad scientist treasure! I cobbled three of these in parallel, along with a HV power supply and a triggered spark gap (made by fellow Tesla coiler Rob Stephens from near Ontario, Canada), to build a combination can and quarter shrinker in early 1998. It worked!! However, unbeknownst to me, the high voltage capacitors suffered from progressive flexing and weakening of the internal capacitor buses from magnetic forces during each shot. This quickly lead to catastrophic capacitor failures after only a few dozen shots. One particularly destructive failure at 8500 Joules ruptured the steel case of one of the capacitors, allowing it to disgorge a few of gallons of foul-smelling, blackened oil and tinsel-like aluminum foil fragments which proceeded to dribble onto the indoor-outdoor carpeting in the lab! Needless to say, the wife was NOT amused by these events! Upon autopsy, I was able to determine that these "pulse caps" were internally constructed as Power Factor Correction (PFC) capacitors. It became obvious that they could not withstand the high-currents and electromagnetic forces involved with quarter shrinking.  

After a long search, I was finally able to locate a batch of reasonably-priced and very robust Maxwell 70 uF 12,000 volt energy discharge capacitors through eBay. Dr. John Gudenas (another local high voltage experimenter) and I drove to central Ohio to pick up eleven of these monsters - 1700 pounds of mad scientist heaven! Each capacitor is rated for 100,000 Amperes per shot for 300,000 shots(!). They have since proven to be the Timex's of pulse capacitors - they take a lickin' and just keep on tickin'. A pair of these caps has successfully completed over 7,500 shots with nary a whimper. 

In 1998, another local high voltage researcher mentioned an article written by Gary Hawkins ("Electromagnetic Z-Pinch: Exploring the Nature of Electromagnetism in High-Energy Capacitor Discharges") that appeared in a 1993 issue of "Extraordinary Science" magazine. In the article, Gary described using a high voltage x-ray power supply and a 60 kV capacitor bank to launch rings and plates, and later on, to crush coins. The article also contained a picture of a series of coins he'd shrunk using coils with different numbers of turns at varying power levels. Until 2001, this was all that I knew of the brief history of coin crushing. However, a subsequent conversation with science experimenter Bill Beaty revealed that Quarter Shrinking was apparently discovered in 1991...

Bill Beaty’s fascinating account of what is believed to be the first "Quarter Shrinker"
"Dale Travous is a sculptor who once had a big studio space in downtown Seattle, and was making Tesla coils (and later a big Tesla Magnifier.)  He traded some equipment for some big caps around 1990 or so.  I think they were 150 kV, maybe 10 uF, six of them.  He was charging them up and using them to destroy pieces of wire, and I told him about an article I'd seen in the 1970s about an "optical shutter" made from a coil of copper rod wound around a soup can with the ends removed.  When a big laser energy storage capacitor was discharged through the coil, the soup can would instantly neck down to close the aperture." [NOTE: A Sandia scientist has recently forwarded a picture of the device, invented by Art Van Hook and Gene Neau, and pictured in the Aug 2, 1974 issue of Sandia's "Lab News". The Sandia article indicates that they used beer cans, not soup cans, and the researchers DO look a bit mellow in the image.].

"He tried this on copper pipe and was making hourglass effects (even shredding very thick 0.75" pipe when the necked-down part would *bounce*.)  Then he found that he could distort a penny with a very thick coil from a 500-amp circuit breaker.  Then he found that he could smoothly shrink pennies to less that 50% of their original diameter, but the coil would be destroyed after a few shots.  Then he started using coils made from #10 solid copper  wire.  Eventually he tried lots of other coins, and settled on using quarters (they were a bit more impressive than pennies or $.50 coins for some reason.)  I'm pretty sure this was all in 1991. "

"We found more big caps at Boeing Surplus.  Boeing uses them as dent-pullers.  I saw what was probably the dent-puller power supply at auction, a huge thing the size of several refrigerators with a bunch of big energy storage caps in parallel within.  We learned that many manufacturers also use capacitor discharges to crimp the metal fittings onto the ends of rubber hoses."

"Gary Hawkins was a co-renter of the lab space, and he sent an article to the International Tesla Society about the "Quarter Shrinker" cap bank. They published it in their magazine,  see EXTRAORDINARY SCIENCE, Volume 5 No.3, summer 1993, p10. This magazine was a publication of the International Tesla Society, Colorado Springs, CO - the group is now defunct.  Email the author at ghawk@eskimo.com, or http://www.eskimo.com/~ghawk   Others who built later Quarter Shrinkers probably saw this article, or heard about it second-hand."

"Around 1994 or 1995 Dale Travous had some pieces in an art exhibit at Seattle COCA gallery.  One was a series of about twenty progressively shrunken quarters mounted in a row on a piece of white Plexiglas.  At the same time he stopped shrinking coins and instead was using the cap bank attached to a steel "watergun", a short stubby cannon which could explode a cubic centimeter of water and drive a plastic slug through a 12" block of clay.  Big fun.  Later he entered the cap bank in the "science fair" put on by THE STRANGER adult newspaper.  It was a room-freshener.  He was vaporizing cherries, strawberries, etc. An immense blast like a shotgun going off, and then the room smells nice."

"Around the same time we got some 100 uF 30 kV Maxwell capacitors free after a government auction, and built a second quarter shrinker.  Lots of people in the Seattle area have coins which were crushed by this version. Around 1995 I downloaded Mozilla and found eskimo.com, and posted the article on my beastie that mentioned the quarter shrinker,  http://amasci.com/amateur/capexpt.html.  Much later I added photos of the original capacitor bank. The photos is still there near the top of the article - go see! All the lab space is long gone, and the cap banks have been in storage since 1996 or so…”

“A smell of burning fills the startled air - the electrician is no longer there!” - Hilaire Belloc 1870-1953

If you are aware of any earlier history, please let me know!

References:

• Frank W. Wilson, “High Velocity Forming of Metals”, ASTME, Prentice-Hall, 1964
• E. J. Bruno, editor, “High Velocity Forming of Metals” Revised Edition, ASTME, 1968
• T. F. Wall, "Generation of Intense Magnetic Fields", Journal of Institution of Electrical Engineers, 64, 1926, pp 745-757
• H. P. Furth, R. W. Waniek, "Production and Use of High Transient Magnetic Fields, Part 1 of 2", Review of Scientific Instruments, Volume 27, Issue 5, pp. 195 - 203, April, 1956
• H. P. Furth, M. A. Levine, R. W. Waniek, "Production and Use of High Transient Magnetic Fields, Part 2 of 2", Review of Scientific Instruments, Volume 28, Issue 11, pp. 949 - 958, November, 1957
• Noland, M. C., Gadberry, H. M., et al, "High-Velocity Metalworking, a Survey", NASA, 1967
  
• A. P. Langlois, "Metal Forming with Electromagnetics", ASTME Creative Manufacturing Seminars, Paper SP60-170, 1960
• D. ter Haar, editor, “Collected Papers of P. L. Kapitza”, Volume 1, 1916-1934", Macmillan Co., 1964
• Hawkins, Gary, "Electromagnetic Z-Pinch: Exploring the Nature of Electromagnetism in High-Energy Capacitor Discharges", Extraordinary Science Magazine, Jul-Sept 1993, Volume 5, Number 3.
• William J. Beaty, Usenet and private email correspondence, 12/19/01

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