research activities of the Laboratory of Advanced

We studied the possibility of the high brightness operation of the NewSUBARU electron storage ring without lattice modification. By turning-off the RF shaker that is used to enlarge the vertical size and the lifetime of stored electron beams, the brightness can be improved 2.7 times assuming that the stored current is the same. As the lifetime decreases, the top-up current is also reduced due to the limitation for the total charge that can be injected to the ring. Using a top-up simulator, we found that the brightness improvement factor could be 1.6 including the stored current decrease effect. Introduction Beam lifetime of the NewSUBARU electron storage ring is dominated mainly by the Touschek effect at 1.0 GeV operation. The industrial users in our radiation facility such as EUVL lithography and LIGA have been performed irradiation experiments and prefer the beam operation with a long beam lifetime and an high top-up current more than that with an high brightness. To improve the lifetime the ring has been operated with intentionally enlarged vertical beam size using RF shaker, where amplified white-noise signal is added to four strip-line electrodes to vertically shake electron beams, and now we achieved the lifetime of 7.4 hrs at the top-up operation of 220mA. Recently, increasing number of industrial analysis users in our facility want the high resolution of synchrotron radiation and the high brightness operation. Generally speaking, the high brightness operation of storage rings needs re-design of ring lattice and re-arrangement of magnets and vacuum chambers and so on. However, in case of NewSUBARU, there is room for making the brightness higher by an easy way, that is, the operation without RF shaker. Laws and regulations on radiation safety restrict the total charge that can be injected from a linac to our ring per eight hours (one shift). This fact means that the reduced beam lifetime causes the reduction of the top-up current that should be kept constant for eight hours. It is important to evaluate how much the brightness is improved and how much top-up current is reduced by turning-off RF shaker. Measurement of Lifetime and Beam Size The total beam lifetime  is determined by the Touschek lifetime Tous and the gas scattering lifetime gas; 1/ =1/Tous+ 1/ gas. We measured the dependence of the lifetime on RF shaker power as shown in Fig. 1. The inverse lifetime increases according to the inverse square root of the RF shaker power. Turning-off RF shaker, the lifetime was reduced to 2.1 hrs. The vertical size of electron beams was also measured using a visibility monitor [1]. As shown in Fig. 2, the vertical beam size increases according to the square root of shaker power, that is, kick strength. From these data, we found that 1/ =0.664 / W + 1/ gas, and  gas is about 470 hrs at 1.0Gev, 220 mA. Fig.1. Lifetime vs. RF shaker power Fig.2. Vertical beam size vs. RF shaker power Improved Brightness Estimated by Calculation The brightness of synchrotron radiation is given by