Comment by Fred Mills (Feb 21, 2008):
"In 1976 at Fermilab we began investigating cooling for p-pbar colliders. Shortly thereafter Milton White of Princeton, who was a member of the URA Board, told me about a need to reduce the emittance of a beam from a van de Graaff for injection into the Princeton Pennsylvania Accelerator. This was discussed at a faculty lunch and Lyman Spitzer (a well-known plasma physicist) suggested a moving electron plasma, i.e., electron beam, with which to equilibrate the proton beam. Gerry O'Neill, or a student, did some calculations which showed that the process was too slow to help.
I don't recall whether both Gerry and Gersh Budker were at the 1959 CERN conference or if so they discussed it there, but the next chance would have been in 1963 at the Dubna Conference and at Novosibirsk afterwards. Gerry, Arnold Schoch, about ten others and I visited the INP (now BINP) after the conference. On the flight back to Moscow, I was accompanied by Igor Meshkov who built the first electron cooling system for NAP. Igor had built an electron gun-collector system but had discovered that space charge caused the effective beam temperature to increase too rapidly. Three years ago Igor reminded me that I had suggested immersing the beam in a magnetic field to control it. (I had extensively studied electron beam formation and propagation when I designed and built the injector for the 50 MeV FFAG at MURA.) Thus electron cooling was already under way experimentally and theoretically (Sagdeev et al.) at INP in 1963. Budker then gave his paper at the Orsay Conference in 1966.
Since they are both deceased, we cannot ask them who came first. My own view is that while the Princeton bunch fiddled with an idea and dropped it, INP under Budker, with Meskov and Dikansky, built and tested the system which proved the method. In fact, Budker built his whole laboratory to accommodate 25 GeV p-pbar collisions, which doesn't work without cooling. He deserves to be called the inventor."
8/66, Design Study for a Muon and Antiproton Facility at SLAC, F. Lobkowicz, D. Green and S. Serio, UR-875-161 (Aug. 10, 1966). A continuation of the paper by Tinlot and Green. It is stated on p. 25 that there is no transverse damping mechanism for the stored muon beam. That is, ionization cooling was not considered here.
5/65, On the Oscillation Decrements in Accelerators in the Presence of Arbitrary Energy Losses, A.A. Kolomenskii, Sov. Atomic Energy 19, 1511 (1965). The first Russian analysis of ionization cooling.
3/65, A Storage Ring for 10 BeV/c Muons, J. Tinlot and D. Green, UR-875-76 (March 10, 1965). The ring is also called a `trap`. Its purpose is to perform muon-nucleus scattering experiment off internal targets at SLAC. John Tinlot died in Sept. 1965.
60, An unpublished note, A.C. Melissinos (1960). Perhaps the first written discussion of a muon storage ring. The purpose of the ring was to produce a pure, extracted muon beam (no pions), that would be used as a source of neutrinos for the famous BNL 2-neutrino experiment.
7/56, Modification of Liouville's Theorem Required by the Presence of Dissipative Forces, D.B. Lichtenberg, P. Stehle and K.R. Symon, MURA-126, July 12, 1956. This paper expands on O'Neill's idea of ionization cooling (and does not mention wedge cooling). The paper concludes, however, that multiple scattering would mask any cooling effect.
4/56, Storage-Ring Synchrotron: Device for High-Energy Physics Research, G.K. O'Neill, Phys. Rev. 102, 1418 (1956). First published discussion of wedge cooling. When E. Wigner heard about this from O'Neill at tea one day (1955-56), he immediately commented that this process violates Liouville's theorem. F.C. Shoemaker believes that Wigner's remark was the first mention of the relevance of Liouville's theorem to accelerator physics. [See also MURA88, and footnote 3 of Kerst et al, Phys. Rev. 102, 590 (1956).] O'Neill then worked out that the primary effect of the wedge is a phase space exchange. But, the paper contains a line that indicates that O'Neill understood that an effect of ionization is that `the area in phase space available to a particle can be made to decrease with time.' This appears to be the genesis of ionization cooling. This paper is also O'Neill's first statement of the advantage of colliding beams over fixed-target in reaching high center of mass energies.
papers below are not concerned with either muons or cooling,
but are the earliest records of the thoughts of Kerst and his immediate
colleagues on the concept of colliding beams.
4/56, Properties of an Intersecting-Beam Accelerating System, D.W. Kerst, MURA-111 (April 26, 1956).
4/56, Intersecting Beam Accelerator with Storage Ring, D.B. Lichtenberg, R.G. Newton and M.H. Ross, MURA-110 (April 26, 1956).
1/56, Attainment of Very High Energy by Means of Intersecting Beams of Particles, D.W. Kerst et al., Phys. Rev. 102, 590 (1956).
12/55, Some Estimates of Properties of Intersecting Beam Accelerators, D.W. Kerst, MURA-88, DWK/13 (Dec. 3, 1955). Credits Wigner with having pointed out the importance of phase space to accelerator theory.
8/55, The Possibility of High Intensities from FFAG Accelerators Providing a Means of Increasing the Energy, D.W. Kerst, MURA-81, DWK/12 (Aug. 26, 1955). May be the first mention in writing of accelerators with colliding beams. Credits Symon and Sessler with having worked on these ideas in the preceding months.
6/54, On the Application of Very High Energy Machines, R.G. Sachs, MURA-38, RGS-1 (June 19, 1954).
9/53, A Study of the Feasibility of a Multi-BeV Circular Electron Accelerator, L.W. Jones and J. Laslett, MURA-6, LWJ-LJL/MAC-5 (Sep. 26, 1953). This and MURA-38 by Sachs lament the inefficiency of fixed-target accelerators in producing large center-of-mass energies, but do not appear to suggest colliding beams as an improvement.
9/98, Comments by Fred Mills: I first heard about "ionization cooling" in 1956 when I went to MURA. The "Piccione lip" on the extraction target, or foil, was well understood. It reduced the emittance of the beam (while increasing the momentum spread) in a process we now call "phase space exchange". Gerry O'Neill of Princeton proposed using this process to increase the luminosity (a term which had not yet been coined) of Storage Ring Colliders, (also not yet coined) which he invented at the same time as Don Lichtenberg and Roger Newton (we called them "Newton's Rings").
There was a disagreement, settled in a MURA Report 126 by Lichtenberg, Stehle and Symon, in which they showed the relationship between energy loss (of any type) and phase space reduction. I suppose this constitutes the "invention" of ionization cooling. Since the cooling required many strong interaction mean free paths, that ended that for hadrons. We of course knew it might work with muons, but that seemed a bit far off, if not far-fetched. At that time ANY collider seemed far-fetched to the HEP community, particularly one using particles from a secondary beam.
I might comment that Lichtenberg et al. missed the phase space exchange simply because they didn't include a change in the coordinate as well as the momentum in the generalized forces, nor did they consider individual projected phase spaces. This is shown in my 1963 NIM paper on radiation damping of electrons.
Just before Milt White died he cornered me (I was beginning to work on electron and stochastic cooling at Fermilab, he was president of URA) and told me about the origin of the electron cooling idea. At a faculty meeting Milt and Gerry were talking about how to reduce the emittance of the van der Graaff beam which was to be injected into the PPA. Lyman Spitzer suggested that they could do it by passing the proton beam along with an electron beam of the same velocity, but he pointed out that it was impractical because it would take too long a path. Gerry got a student working on it but never pursued it much further. I heard about this work at MURA in the 50's also. In Budker's first paper (Saclay, 1966) he states "this is an idea told to me by Gerry O'Neill". Of course Budker saw to the development of the theory and practice of electron cooling and deserves to be called its inventor. By the same standard, there is as yet no inventor of ionization cooling.
In 1956, after a Postdoc helping to make one of R.R. Wilson's machines work, I went to MURA where in one year I learned at least ten times as much as I had at Cornell. One year later, we effortlessly turned on the world's first spiral sector accelerator. I suggested to Don Kerst that we should send a letter to Phys. Rev. Don smiled and said that it would not be accepted. After I persisted, he agreed. The letter was turned down. I had to confront the fact that the field I was in had no legitimate means of publishing its work. Only in 1965 with the advent of the PAC (I was asked to be on its first committees, but sent someone else) was there any means of publication, even in a non-refereed form. NIM and RSI would take review articles occasionally...
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