Caltech EN Tandem Van de Graaf Accelerator

Dec 8, 1998

After 38 years of service to the Nuclear Astrophysics and Material Science communities, Caltech's EN Tandem Accelerator facility has closed. Sorry to see the old machines fade away. This one had been very good to us.

Not putting it too delicately; the machine was cut up and sold for scrap.

The Collapse

Since the machine was not to be reused, we felt it unnecessary to gently roll back the columns during the disassembly. The column was to be broken in place. Our first attempts at this were quite humbling.

The EN tandem columns meet in the middle of the machine with no central support mechanism beyond the tension exerted from the ends. This tension is maintained by a large spring . We fully expected the column to collapse when the spring tension was removed. No such luck; we released the spring and nothing happened. Next we put ropes around the central region and pulled it sideways trying to sproing the silly thing into collapse. The amount of terminal motion induced was truly frightening; but no cigar.

Those of us who worked inside the Tandem tank, lo these many years, had always treated the cantilevered column with fear and respect. This last exercise demonstrated how incredibly strong the structure actually was.

There was great gnashing of teeth and ringing of hands. How to break the column? The answer came during a late night phone call about possibly softening the glue joints with heat. Why not freeze the little buggers instead? "Fire and Ice" has always been one of my favorite poems. By extending a long piece of copper tubing through the manhole we could direct a flow of liquid nitrogen onto particular glass blocks near the column ends

Once again the strength of the structure amazed us. At the ends of the machine there are essentially just four glued contact joints between the column and the baseplate. Starting with the high energy end, freezing the first block yielded only a few tinkling sounds. The second block on the same side rewarded us with some serious crackling and clunking but the column did not measurably sag. Upon fracturing the third block (a bottom one) the column groaned and lurched, but did not fall! It was only when the fourth and final block was frozen that we heard the column crash to the floor of the tank. When all was quiet we peered inside only to discover the entire low energy section still intact!! There it was; standing straight out from the LE baseplate with no supplemental support at all. I'll spare you the drama, but we actually had to break THREE of its remaining contact points before the low energy section fell.

It took the salvage contractors less than 4 days to carry the entire machine, piece by piece, through a double wide door into the hallway. The first cuts on the tank were made topside; the roof pieces falling inward on top of the crashed column debris. After a few hours of this, one was reminded of a banana split sundae with the tank bottom acting as the dish filled with tempting scrap metal delights.
High Energy Column has collapsed.Photo of EN pressure vessel being cut open from top (Steve Stryker)EN Tank has been completely removed.  (Alan Rice)

My thanks to all of you who offered advice during our closing months. It was hard to let go, but nothing will erase the many satisfying years of work we did on this wonderful machine.

On a more personal note, I've moved on to an administrative position at the Institute; pushing paper instead of protons. After 13 years of hiding underground in an accelerator vault I have, get this, an office with a WINDOW! Take care everyone.