Editing Calutron (section)

== Design ==
Much of the great progress on the electromagnetic process can be attributed to Lawrence's leadership style. His audacity, optimism and enthusiasm were contagious. His staff put in long hours, and University of California administrators sliced through red tape despite not knowing what the project was about. Government officials began to view the development of atomic bombs in time to affect the outcome of the war as a genuine possibility. [[Vannevar Bush]], the director of the OSRD, which was overseeing the project, visited Berkeley in February 1942, and found the atmosphere there "stimulating" and "refreshing".{{sfn|Hewlett|Anderson|1962|p=60}} On 9 March 1942, he reported to the president, [[Franklin D. Roosevelt]], that it might be possible to produce enough material for a bomb by mid-1943, based on new estimates from Robert Oppenheimer that the critical mass of a sphere of pure uranium-235 was between 2.0 and 2.5 kilograms.{{sfn|Hewlett|Anderson|1962|p=61}}{{sfn|Jones|1985|p=125}}

[[File:Calutron operators.jpg|thumb|alt=Two rows of control panels with dials and switches. Operators sit at them on four-legged stools.|Control panels and operators for calutrons at the Oak Ridge [[Y-12 National Security Complex|Y-12]] Plant. The operators, mostly women, worked in shifts covering 24 hours a day.]]
The experiments with the 184-inch magnet led to the construction of a prototype calutron called the XA. It contained a rectangular, three-coil magnet with a horizontal field in which the calutron tanks could stand side by side, with four vacuum tanks, each with a double source.<ref name="Lawrence">{{cite web |url=http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1981/81fepi2.html |title=Lawrence and his Laboratory: The Calutron |archive-url=https://web.archive.org/web/20150208134741/http://www2.lbl.gov/Science-Articles/Research-Review/Magazine/1981/81fepi2.html |archive-date=8 February 2015 |access-date=4 September 2015}}</ref> At the 25 June 1942 meeting of the S-1 Executive Committee, which had superseded the S-1 Uranium Committee on 19 June, there was a proposal to build the electromagnetic plant at Oak Ridge, where the other [[Manhattan Project]] uranium separation facilities would be located, for reasons of economy and security. Lawrence lodged an objection due to his desire to have the electromagnetic separation plant located much nearer to Berkeley.{{sfn|Jones|1985|pp=46–47}} The [[Shasta Dam]] area in California remained under consideration for the electromagnetic plant until September 1942, by which time Lawrence had dropped his objection.{{sfn|Jones|1985|p=70}} The 25 June meeting also designated [[Stone & Webster]] as the primary contractor for the design and engineering.{{sfn|Jones|1985|pp=126–127}}

The Army assumed responsibility for the Manhattan Project on 17 September 1942, with [[Brigadier General (United States)|Brigadier General]] [[Leslie R. Groves, Jr.]], as director,{{sfn|Hewlett|Anderson|1962|p=82}} although the Army did not formally take over the contracts with the University of California from the OSRD until 1 May 1943.{{sfn|Jones|1985|p=120}} Major Thomas T. Crenshaw, Jr., became California Area Engineer in August 1942, with Captain [[Harold A. Fidler]], who soon replaced him, as his assistant. Crenshaw established his office in the Donner Laboratory at the University of California.{{sfn|Jones|1985|pp=118–122}}<ref>{{cite news |newspaper=Princeton Alumni Weekly |url=https://paw.princeton.edu/memorial/thomas-t-crenshaw-jr-%E2%80%9931 |title=Thomas T. Crenshaw Jr. '31 |date=13 October 1993 |access-date=5 September 2015 }}</ref> In September 1942, the S-1 Executive Committee recommended that a five-tank pilot plant be built along with a 200-tank section of a production plant.{{sfn|Hewlett|Anderson|1962|p=82}}

Between October 1942 and November 1943, Groves paid monthly visits to the Radiation Laboratory in Berkeley.{{sfn|Jones|1985|p=125}} Reports indicated that compared to the alternatives of a gaseous diffusion plant or a [[plutonium]]-producing [[nuclear reactor]], an electromagnetic plant would take longer and require more scarce materials to build, and need more manpower and more electricity to operate. The cost of a kilogram of fissile material would therefore be much greater. On the other hand, while the alternative processes still faced considerable technical obstacles, the electromagnetic process was proven to work, and could be built in stages that would immediately start producing fissile material.{{sfn|Jones|1985|pp=117–118}} Groves cancelled the pilot plant on 14 November, in favor of proceeding immediately with the production plant.{{sfn|Hewlett|Anderson|1962|p=108}}

The Radiation Laboratory forwarded the preliminary designs for a production plant to Stone & Webster before the end of the year, but one important issue remained unsettled. Oppenheimer contended that [[weapons-grade]] uranium would have to be 90% pure uranium-235. [[Edward Lofgren]] and [[Martin Kamen]] thought that this could not be achieved without a second stage of enrichment.<ref name="Lawrence and his Laboratory" /> The two stages became known as Alpha and Beta.{{sfn|Yergey|Yergey|1997|p=947}} In March 1943, Groves approved the construction of five Alpha and two Beta racetracks. In September, he authorized four more Alpha racetracks, which became known as Alpha II, along with two more Beta racetracks to process their product.<ref name="Lawrence and his Laboratory" />{{sfn|Jones|1985|pp=128–129}}