Revised Proposal for the Superconducting Accelerator Project (SCA) in the Stanford High-Energy Physics Laboratory No. −229 (67) Accomplishments relating to the superconducting accelerator (SCA) In work sponsored by the Office of Naval Research we have made substantial progress in the development of the first superconducting accelerator. A number of essential experiments relating to the microwave properties of superconductors have been completed; a small test accelerator has been successfully operated; a ten foot long prototype of a large accelerator is near completion; experiments on the transport of heat by superfluid helium are in progress. We have ordered a refrigerator from the Arthur D. Little Co. which is to be delivered in September 1967. The refrigerator is designed to remove 300 watts at 1.85° K, and a prototype has already been built by this company. This is the first refrigerator to operate below the λ point in helium (2.18°K), and represents a major advance in refrigerator design. We have obtained reproductible Q's of 5 x 10o in superconducting lead cavities operating in the TE11 mode. This represents an improvement of a factor 100 over the highest Q's obtained before this research began, and is 105 times that obtained with room temperature copper which is used in conventional linear accelerators. We have demonstrated that this Q is independent of magnetic field strength up to the DC critical magnetic field, which for lead is about 700 gauss. Electric fields up 4.5 x 10 volts per foot have been obtained before the Q showed any drop due to field emission from whiskers. Preliminary experiments indicate that this RF critical electric field can be considerably increased by burning off the whiskers with a gas discharge, and that the above value is not the ultimate limitation. A superconducting accelerator plated with lead would make possible unity duty cycle operation at energy gradients comparable to those used in conventional linacs. Within the last week we have tested some niobium samples made by the Linde Division of Union Carbide, and also by Varian Associates, which gave a higher Q than lead although the experiments are still preliminary. The theoretical magnetic breakdown for niobium is about 1500 gauss which corresponds for the accelerater cavity to 25 x 106 volts per foot. In order to demonstrate the feasibility of accelerating electrons in a superconducting cavity we constructed a small test accelerator 4 inches in length. Electrons injected into this superconducting cavity were accelerated to 500 kilovolts; this indicates peak electric fields in the excited part of the cavity in excess of 4 x 106 volts per foot. At the present time construction of a 10 foot prototype accelerator is near completion. This system will consist of two 5 foot accelerator sections and is designed to stimulate the conditions encountered in large superconducting accelerators. Many of the design problems for large superconducting accelerators are being worked out in this system. With the cooperation of the accelerator group at Los Alamos detailed calculations have been performed relating to the choice of accelerator mode and to the optimum geometry of the accelerator structure. We have selected the biperiodic π/2 mode and a frequency of 952 megacycles as most appropriate for a SCA. Experiments at helium temperatures have shown that multipacting does not occur in this structure. Calculations of the starting current for beam blowup in our high Q accelerator structure have been carried out by Dr. Helm at SLAC; they show that for the parameters we expect to use beam blowup will not occur. Prospects for full-scale SCA Detailed considerations demonstrate that a SCA can be built and operated at an expense comparable to that for conventional electron linacs of the same energy. The SCA, however, would be vastly superior to its conventional counterpart. First, in the SCA continuous (CW) operation will be possible. This is of great importance and repersents an improvement by a factor of 1000 in duty cycle compared to conventional electron linacs. Further, because of the continuous mode of operation, the amplitude of the electric field in the structure can be kept very nearly constant. Thus intense electron beams that are very homogenous in energy (perhaps to one part in 104, which is a factor of 100 improvement over conventional electron linacs) can be produced. Temperature stability is a problem common to both a superconducting accelerator and a conventional room temperature accelerator. Because of the unique thermal properties of liquid helium below 2.18°K it is possible to obtain far greater dimensional stability against tempreature changes in a superconducting accelerator than in a room temperature accelerator. Below 2.18°K liquid helium behaves as a "superconductor" of heat. This is important in achieving very high energy resolution. We have conducted experiments which indicate that superfluid helium at 1.85°K in a pipe of roughly 1 foot diameter will maintain a temperature equilibrium of better than 0.03°K over a distance of 500 feet with a heat input of several hundred watts. This is sufficient for a beam stability of better than 1 part in 104. To obtain this equilibrium with high conductivity copper would require a bussbar 100 feet in diameter. A superfluid heat transport system together with a refrigerator removing heat at 1.85° represents a major new concept in large scale low temperature refrigeration. The refrigerator which has been ordered promises reliable 24 hour per day operation at a cost of $50,000 per year. Such a refrigeration system opens up the possibility of large scale refrigeration at helium temperatures aboard a ship or submarine, or in other military installations. Large distances could be covered without need for mechanical pumps. Because of the tremendous promise of the SCA for future accelerator design, and because of its impact on large scale technology at low temperatures, we believe that the full capabilities of such an accelerator and refrigeration system should be tested as quickly and as thoroughly as possible with respect to capability, reliability, and cost of operation. In addition we believe that such an accelerator promises to open up a whole new area of nuclear and high energy research at Sanford, an area complementary to but not duplicated by SLAC. Proposed program modifications In view of the above prospects, and because of the initial success of the SCA research program, we propose to modify our five year program so that a larger fraction of the effort and funds will be concentrated on the development, completion, and test of the superconducting 2 BEV accelerator, which is one of the ultimate goals of the SCA program. Important modifications in the operations of the High Energy Physics Laboratory have been agreed upon by all senior personnel of the laboratory. These make possible a program in which the full 500 foot, 2 BEV superconducting accelerator, with end station, spectrometer, and shielding facilities can be obtained by the end of 1970. The budget, which includes laboratory operations, is slightly reduced from the original 4.4 million dollars per year. The necessary economies have been effected by eliminating the proposed 400 Mev superconducting acelerator and microtron bending magnets: by reducing research expenditures of the laboratory by about 10 percent: by phasing out research on the existing Mark III accelerator some time in 1968 in order to get full efort on the completion of the first 1 Bev section of the superconducting accelerator and its subsequent operation; by assuming that we will be able to live within the architects' estimates of the cost of the nonseverable items and the estimated cost of the spectrometer, without the use of a 10 percent contingency built into the previous budget; and by making full use of forward funding. We propose to start by building the underground tunnel, counting room and refrigerator room and placing the accelerator in the tunnel, section by section, starting with the injector end. Each 20 feet of the superconducting accelerator would be tested in the tunnel before the next section is completed and desirable improvements incorporated in subsequent sections. When the first 250 feet of the SCA is completed, hopefully by the end of 1968, bending magnets placed before the beam switchyard of end station number one would permit the beam of the SCA to be bent upward, turned horizontally, and passed through the two present end stations. The present Mark III accelerator would then be turned off, and the first part of the superconducting accelerator would substitute for it. The research efforts of the laboratory could thus be utilized to test the first half of the superconducting accelerator, but only at the reduced beam currents which could be tolerated with the inadequate shielding available in the present end stations. At the same time, construction of additional accelerator sections would proceed in the tunnel during the day time when the accelerator is not running. The shielded underground end station would also be built at this time and the 2 BEV spectrometer would be installed in the end station, so that the full capabilities of the SCA could be tested a 2 BEV or higher energies by the end of 1970. It is important to note that the research applications of the combination of accelerator, end station, and spectrometer offer such exciting new possibilities in nuclear and high energy physics that the enthusiastic cooperation and help of the entire laboratory will be available full time for developing and testing the accelerator. Future low-temperature developments The proposal makes provision for a single 300 watt, 1.85° K refrigerator capable of operating a lead coated accelerator at an estimated 20 percent duty cycle. We anticipate that a design and engineering effort in cooperation with industry will produce in the future the possibility of building a larger refrigerator using a turbine pump to compress the helium at 1.85° K, thus eliminating the necessity of larger room temperature vacuum pumps which would become prohibitive in size for a much larger refrigerator. Furthermore, if shipboard application is ever considered, an additional refrigeration capability should be added to eliminate completely the necessity of liquid nitrogen in the dewars and the refrigerator so that only electric power would be required as an input. We would hope to be able to participate in the development of a larger turbine refrigerator under Navy support and to add such a refrigeration capability to the accelerator in future years. This would make it possible to run the 500 foot accelerator at 2 BEV with CW operation. We plan to study the feasibility of making use of low temperatures throughout the entire High Energy Physics Laboratory; for example, superconducting magnets will be used for quadruple focusing magnets, for bending magnets, and for spectrometers when considered feasible. We are also developing a method of reading the beam current with a superconducting magnetometer. We anticipate that the High Energy Physics Laboratory with the superfluid helium refrigerator and heat transport system which delivers the refrigeration throughout the entire laboratory offers an ideal experimental setup to test many different kinds of low temperature applications on a practical scale. The high Q cavities which we have developed for the accelerator represent the highest Q macroscopic structures available in nature and offer interesting possibilities for new kinds of very stable oscilators and frequency systems which might have use in Navy communications and guidance. We will continue to test the properties of such cavities. The SCA represents a reliability test under high power continuous operation. As a parallel effort under separate support we are developing a superconducting magnetometer which is more sensitive than any in existence. It appears capable of detecting 10-10 gauss. We are also developing a truly zero magnetic field region using superconducting shields and the principle of quantized flux. In such a magnetic field free region it is possible in principle to construct a free precession nuclear He3 gyro with a drift rate orders of magnetude less than existing gyros. We are constructing an experimental model of such a gyro. University contribution to the project The University has made major contributions already to the project in terms of land and the normal 5 percent prorata charges for relocating facilities, professors' salaries during the academic year and the appointment of Dr. H. Alan Schwettman as a new tenure associate professor. In addition the University has already contributed over two hundred thousand dollars in reduced indirect cost rate by agreeing not to increase it retroactively for the past two years from the present 46 percent. The University is also willing to continue the 43 percent rate rather than the government approved 55 percent for at least two more years, and possibly for the full four years, a tangible indication of its willingness to keep the agreement reached with the Navy on this five year program; this could reduce the cost of the program by as much as half a million dollars. It has been realized from the beginning by both the Stanford Linear Accelerator Center (SLAC) and the Physics Department that the development of a superconducting accelerator at the High Energy Physics Laboratory would provide an ideal test and demonstration of the possible practicality of ultimately converting SLAC to superconducting operation. In the recent 6 year projected program submitted by SLAC to the AEC, a study of the feasibility of converting SLAC to SCA was included to begin in 1971 when the HEPL superconducting accelerator should be completed. Mr. JOHN S. FOSTER, Jr., Director of Defense Research and Engineering, MAY 23, 1967. DEAR JOHNNY: Thank you for your letter of May 8, 1967 concerning developments at Stanford University in regard to the Mark III electron linear accelerator program. We recognize that the work performed by the Stanford group using the Mark III accelerator has been and continues to be of the highest quality. Furthermore, this group has successfully pioneered the development of superconducting linear accelerators. The recent successful operation of a test section of a superconducting linear accelerator is a most significant accomplishment. The proposed program for fabricating a 2 Bev superconducting linear accelerator represents a major and important step forward in accelerator technology. We agree with your confidence in the ability of the Stanford group to carry out this project and certainly feel that this project is worthy of support. The Office of Naval Research (ONR) has very capably supported the Stanford linear accelerator program to date. We do not consider that the proposed 2 Bev program and the SLAC program will be in competition but rather that the programs will complement each other, particularly since the 2 Bev accelerator will provide a facility for electron research with beams of very high duty cycle and high intensity and will operate in an energy range below which SLAC would normally operate. Continued ONR support for the linear accelerator program at Stanford, including the proposed 2 Bev superconducting accelerator, appears to be in accord with the spirit of the 1965 interagency study. We feel that it most appropriate for ONR to support the full program associated with the development as well as operation and research utilization of the proposed 2 Bev superconducting accelerator and would like to encourage you to agree. In conclusion, I would like to reaffirm our opinion that development of the 2 Bev superconducting accelerator facility should be pursued and strongly urge that the Department of Defense make every effort to provide full support for this activity. Cordially, GLENN T. SEABORG, Chairman. OFFICE OF THE DIRECTOR OF DEFENSE RESEARCH AND ENGINEERING, Hon. GLENN. T. SEABORG, DEAR GLENN: Before leaving the country for an overseas trip, Dr. Foster asked me to reply to your letter of 23 May about the proposed Stanford accelerator. The 1965 interagency study group was convened because of a DoD decision to withdraw support from furher expensive undertakings in high-energy physics accelerators. At that time DoD agreed only to supply funds for modernizing the Mark III machine, and for the superconducting technology then being developed at Stanford. The proposal for support of construction of a superconducting machine was specifically disapproved by the interagency group. We are increasingly interested in Stanford's excellent low-temperature work, which has advanced significantly during the last two years. But we are even less interested now in supporting high-energy physics since this area has not shown much relevance to defense problems. No longer can we assign limited research funds to high-energy physics while much more relevant and promising fields are competing for our support. Specifically, we have decided not to provide the funds for constructing the proposed superconducting machine at Stanford. If this machine is really important to the future of our national high-energy physics program, then it should be supported by an agency that has the responsibility for, and a vigorous interest in, that future. We are prepared to share the funding during a transition period, and intend to do so. I hope very much that you will re-examine this matter in light of our strong, clear view that DoD cannot continue its support for the high-energy physics program at Stanford. Sincerely yours, FINN J. LARSEN. SEPTEMBER 15, 1967. Mr. JOHN S. FOSTER, Jr., Director of Defense Research and Engineering, DEAR JOHNNY: I am writing again concerning the status of plans for the superconducting accelerator proposed by Stanford University. Mr. Finn Larsen's letter of June 9, 1967, (copy attached) indicated that you had decided not to provide funds for constructing the proposed superconducting accelerator at Stanford University. On August 18, 1967, Mr. Fred Schuldt (BOB) requested a meeting with representatives of those agencies involved in supporting high energy physics research to discuss the situation at Stanford. At that meeting, Mr. Nichols of your staff disclosed that approximately $5.5 million was being provided to Stanford University to construct an end station for the modernization of Mark III and a tunnel for the cryogenic test facilities. Recent discussions between members of my staff and yours indicate that you have now authorized approximately $5.5 million for this work. In view of these developments, a further statement from you placing into perspective recent decisions affecting the proposed superconducting accelerator and restating your position regarding the Stanford proposal, would be of value to us in considering this matter further. Information as to how the DOD decision regarding the Stanford project will affect your overall program in nuclear physics in FY 1968, FY 1969 and future years would also be useful to us at this time. Cordially, Hon. CHARLES L. SCHULTZE, Director, Bureau of the Budget. Chairman, OCTOBER 3, 1967. DEAR CHARLIE: "In accordance with the provisions of the Budget and Accounting Act of 1921, as amended, and the budgetary and fiscal policies set forth in your letter of August 9, 1967, we are submitting budget estimates for the Atomic Energy Commission for fiscal year 1969 . . "Finally, on several occasions in the past, we have discussed AEC's role as executive agent for the country's high energy physics program. You will recall we have exchanged correspondence on this subject. It is important to note that the Commission cannot discharge this responsibility in a responsive manner under the budget policies controlling the preparation of the budget this year and in the past few years, and also meet its program obligations in the other areas of the Commission's operations. For the Commission to function adequately as executive agent for this country's high energy physics program, the following additions would have to be provided in the Commission's budget: |