Investigation of Relationships Among Beam Tuning Magnets MB0, MB1, XCB2-6 by D.A. Hutcheon & Anthony Olivieri June 13th, 2003 Introduction A requirement of DRAGON experiments is to get a beam of particles to hit a target at the right position and at the right angle. The beam particles react with the target, producing new particles, ?recoils,? that travel in the same average direction as the impinging beam, but cover a much broader range of angles. These recoils are detected when they hit a silicon detector some distance from the target. It is necessary to have the beam of particles interact with the target at the right position and angle to maximize the number of recoils detected. To ensure maximum detection, magnetic fields in the High Energy Beam Transport line (HEBT2) are used to tune the beam, that is adjusting the path of the beam to ensure proper position and angle at the DRAGON target. An inherent problem is that there is no established method to tuning; it is a fancy way of fumbling with knobs until the operator gives the experimenter what he wants. By investigating the relationship among 5 critical magnets we hoped an easier, reproducible method to tuning the beam may be found, thereby decreasing time lost in the experiment, and making life easier for the operators. Background & Origin of Data The magnets of interest were MB0 and MB1, the main magnets that direct the beam into the DRAGON apparatus, as well as XCB2, 4, and 6, small steering magnets for the beam in the DRAGON beam line. MB0 and MB1 direct the beam from the High Energy Beam Transport line to the HEBT2 line and the DRAGON apparatus. XCB2 is a small, fine steering magnet that is located after MB1, near the beginning of the HEBT2 beam line. XCB4 is located near the middle and XCB6 near the end of HEBT2. Dragon snap files, containing hourly and daily data relevant to the DRAGON beam line, were gathered from April 5th, 2003 to May 22nd, 2003. Due to lack of information 31 files were omitted and the new range of data spread from April 6th, 2003 to May 6th, 2003. The data of interest were the square root of the (requested) beam energy per run, the current values in XCB2-6, the sum of the currents in MB0 and MB1, and the asymmetry (MB0 and MB1 current difference divided by the current sum). Analysis & Results A combination of graphs were plotted that would identify relationships among 2 or 3 of the 5 magnets of interest at a time. One such graph was the plot of the asymmetry in the MB0 and MB1 magnets, a ratio of the current differences over the current sum, against the current in the XCB2 steerer magnet. These 3 magnets are the first group of magnets responsible for the beam position and direction as observed by the rotating profile monitor, RPM4, located downstream after XCB2 and before XCB4. It was expected that any asymmetry would be correlated with a similar fluctuation in the XCB2 current. If the MB0 and MB1 pair over-bend the beam, then XCB2 would correct it by the time the beam reaches RPM4. A general trend was expected and a general linear trend was found, but with substantial deviations from the trend line. # The corrected asymmetry (Asymmetry-0.011XCB2-0.0101) was then plotted against XCB6 current values. This corrected asymmetry is a variable that should affect mainly the direction of the beam at the rotating profile monitor; it groups MB0, MB1, and XCB2 into one effective variable whose current values could be correlated with those of XCB6. A general trend was expected, as with the asymmetry against XCB2, but none that were clear were found. # The XCB2-6 steerer magnets help to tune the beam as far as direction and position on the target are considered. It is expected that any steering done by one magnet is likely to require steering by one or both of the remaining magnets. Hence, plots of XCB2 vs. XCB6 and XCB4 vs. XCB6 were expected to have some visible correlation. XCB2 showed no visible correlation with XCB6. XCB4 showed some correlation, but was too vague to be of use. # # The final attempt to establish a correlation of some sort was the plot of the MB0 and MB1 current sum divided by the square root of the (requested) beam energy for each experiment run against the XCB2 steerer current. The current sum over root energy should affect the angle and position of the beam at the rotating profile monitor; the beam deflection should be a product of the current settings of MB0, MB1, and XCB2. The amount of current in MB0 and MB1 should be related to how much current there is in XCB2 as, for each experiment run, there is a total current value from MB0, MB1, and XCB2 that will result in the desired beam angle. No useful correlation was found between the variables. # Conclusion After analyzing the data, it is reasonable to conclude that there is no simple correlation among the 5 magnets examined. The HEBT2 beam line has a number of quadrupoles that all bend the beam and affect its position and direction at the target. A relationship might be seen more easily when these magnets are taken into account. Note that by doing so, things get very complicated very quickly leading into an analysis that is bound to cause (more than) a few headaches. We can conclude that there is no easy, cookbook solution to beam tuning that can make life easier for the operators based on the data presented here. To improve tuning either more devices are needed in the HEBT2 and/or DRAGON target, or a systematic study of HEBT2 (e.g. looking for quad steering) should be undertaken.