An ion source of the magnetron type,''2 which produces a 50-mA negative hydrogen-ion beam of good quality for accelerator injection, has been developed."4 This source has been in use for over a year and has become the principal ion source for all modes of accelerator operation at Fermilab. Details of the design and operation of this source along with information regarding beam quality and reliability are presented.

In the spring of 1975, the decision was made to start preparations for negative hydrogen-ion injection into the Fermilab booster. The key to the success of this endeavor was the development of a reliable H source of adequate intensity. Direct extraction sources giving H beams over 100 mA had been produced by this time in Russia and reproduced in the U.S.A. at Brookhaven. Furthermore, the success of the multiturninjection technique with use of thin stripping foils had been demonstrated at Argonne.' A surface-plasma source has been adopted for accelerator application at Fermilab and is described in a companion paper.2 The goal of 50 mA at 750 keV with a pulse length of 60 pisec was achieved.The usual motivation for H injection into synchrotrons is to increase the intensity of the circulating proton beam by multiturn injection without increasing the phase-space area of the beam. In the Fermilab application, the high-intensity proton beam from the linac (up to 300 mA for single-turn booster injection) was already approaching the existing space charge limit of the booster. Although H injection could not be expected to yield a dramatic increase in booster beam current immediately, other significant advantages were anticipated in H operation. The lower beam current (-30 mA) would mean easier operation of the linac whose rf systems were not designed to accelerate beam current in the 200-300-mA range. The quality of the lower-current beam was expected to be better, with somewhat lower emittance and momentum spread. In addition, the different requirements of integrated beam intensity from the various linac beam users would be more readily satisfied with a programmed beam chopper. Another advantage became apparent in the lower loss of beam during capture in the booster, whose performance is discussed in another conference paper.A second preaccelerator and beam transport line were installed to facilitate switching between H and H+ operation. Installation was completed and H beam first accelerated through the linac in October of 1977. The new injection girder for the booster was ready in February, 1978 and H-injection has been the primary operating mode since that time. THE 750-keV TRANSPORT LINE Preparation for H operation was carried out without interference with the ongoing high-energy physics program by excavating a second pit adjacent to the pit housing the operating Cockcroft-Walton accelerator. A second accelerator was installed in this pit with its H -beam direction at 450 to the H+-beam direction as shown in Figure 1. An H_ transport line was designed and installed to bring the H-beam through 450 and 900 bends into conjunction with the H+ beam line just upstream of the last two triplets. These triplets, without field reversal, and the buncher are used in common for the positive and negative beams. The old H+ line was lengthened by 16 inches to accommodate the 900 bend magnet.

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Sixty-Mev electrons from a pulsed betatron passed through lead foils of thicknesses 0.001, 0.005, and 0.015 inch placed in a magnetic cloud chamber. Measurements of approximately 1100 large energy losses gave the differential bremsstrahlung cross section as a function of x-ray energy for the high energy portion of the x-ray spectrum. Corrections were applied for instrumental discrimination and for multiple radiation and ionization energy losses in the foils. While the shape of the top 30 percent of the x-ray spectrum agreed with the theory within experimental uncertainty, the magnitude of the cross section was about 7 percent lower than theory.

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