THE SURVEYING AND ALIGNMENT FOR THE PROSCAN PROJECT. Jean-Luc Pochon Paul Scherrer Institute, 5232 Villigen PSI

Transcription

1 THE SURVEYING AND ALIGNMENT FOR THE PROSCAN PROJECT Jean-Luc Pochon Paul Scherrer Institute, 5232 Villigen PSI October 2002

2 Content 1 The PROSCAN Project The Survey Task The Network Summary Conceptual Aspects Instrumentation / Software Results of the First Part The Alignment Concept for Beamline Components Design of the girders The building of the Beamline (Girders) Conclusion Appendix...9 iwaa02_text_jlp_word00.doc :15 Seite 1

3 1 The PROSCAN Project PROSCAN is a new facility for medical research now being realised at PSI. The goal of this project is to build a dedicated prototype cancer therapy centre, which will consist of an accelerator (designed and built by ACCEL GmbH our industry partner), a beam line and a gantry with spot scan technique. The design will allow installation in hospitals. Since the facility will be independent of the rest of PSI, it can be run 365 days a year, which is essential for the treatment of patients and system development. Because PSI builds this facility in an existing hall and because there is an operating gantry, which will later be connected to the new accelerator, some specific problems occur. Since the therapy program with the existing Fig. 1 COMET (Compact Medical Therapy Cyclotron) gantry will continue during the installation of the new facility, we are obliged to perform many important tasks during the annual shutdown of the existing PSI accelerator facility. In order to complete our work within this limited time, we need extremely well thought out concepts. Gantry 1 (existing) ~10m / ~30f Existing beamline for Gantry 1 Gantry 2 (new ) Accelerator Shielding Beamlines Fig. 2 PROSCAN Layout in the NA-Hall at PSI iwaa02_text_jlp_word00.doc :15 Seite 2

4 2 The Survey Task 2.1 The Network Summary Our task is to build a network, which will allow adjustment of neighbouring components with an accuracy of one tenth of a millimetre in all directions (relative accuracy). For several reasons we have to divide the build up of the network into three parts. The first part has been measured this summer Conceptual Aspects I. Our aim is to build the network with a minimum of points. This means that the points have to be placed at good locations, which of course are related to the layout of the whole machine complex. Furthermore it was necessary to define them in a general layout, so that other occupational groups (like cooling, electricity, construction) working on this project could easily recognise them. This avoided other installations being planned at this places and no points had to be omitted. Especially the shielding (built of standardised concrete blocks at PSI) caused some problems, because it changed with every new design of the beamline and the network points changed with it. The definite location of the points we had to measure had been fixed only a few days before we started with the network measurement. The last changes were small, so we could get a general idea of how the network would look like a few weeks before. II. The network is built in 3 steps. This is necessary because: - not all the beamlines are built in one step 1. accelerator and first part of the beamline 2. second part of the beamline and connection of Gantry 2 (new) 3. further parts of the beamline and connection of Gantry 1 (existing) - we had to save our existing points, which will be destroyed during the construction work - the binding to the existing gantry is, from the point of view of the surveying group, more complicated because it is now separated from the rest of the hall and from the rest of the network (concrete shielding), but has to be linked with it. The first step was completed this summer, before construction work begun. The goal of this step was to save our existing points and to ensure that there are enough points left for the next steps. Of course these new points have been placed where they can be used later. In the beamline area, where no shielding is planned. The next step involves the network in the accelerator bunker and in the gantry 2 area. There have to be enough points to do all alignment necessary to adjust these huge components. The last step involves the network in the beamline area for gantry 1. III. The shielding is movable and because of this all points are on the floor of the hall. The one exception is the accelerator bunker, where the shielding is built of normal concrete iwaa02_text_jlp_word00.doc :15 Seite 3

5 walls. There we will install points at various heights planned up to 2m. They are necessary for the installation and alignment of the accelerator itself. IV. Since the machine and the beamlines will be built oriented to gravity, the network has to follow. The Laser Tracker does not normally work oriented to gravity and therefore the measured and calculated network has to be oriented afterwards. To do so we levelled all points and transformed them. This proceeding is show in figure below. Position (2D: X and Y) In the existing hallcoordinate-system Height (1D: Z) Measured and calculated (relative to the existing hallcoordinate-system) Combined File With 3D information for every point 3D coordinates measured with the Laser Tracker and the Totalstation Transformed coordinates X, Y and Z: Points are in the hallcoordinate-system the network is oriented to gravity Fig. 3 Flow diagram for 3D coordinates oriented to gravity out of a 2D plus 1D initial system Remarks: We had to start with this 2D+1D-coordinate-system because, due to the shielding, the height was the only dimension that could and, because the height changes the most, that had to be checked in the old network, during the period of 10 years the hall was used for other projects and experiments. This procedure assumes that the X and Y positions of the existing points have not changed. If this is not the case the newly defined highly accurate levelled heights of the points become less accurate because the errors in X and Y have an affect on the heights ( 3D transformation). V. One of the most important prerequisites of working with the laser tracker is that there are no other actions taking place in the hall during measurements. Even a draught can make it impossible to reach the required accuracy. If the time schedule is tight it is not easy to convince those responsible that these environment conditions are necessary in order to avoid prolongation of the measurement time due to the consequent repetitions. iwaa02_text_jlp_word00.doc :15 Seite 4

6 2.1.3 Instrumentation / Software The following Instrumentation is used for the measurements: Name Leica Laser Tracker LTD500 Leica Totalstation TDA5005 Zeiss Digital Level Dini11T Accuracy (* = Value determined by us, not by manufacturer) Angle 0.013mgon (horizontal vertical) and 0.013mgon (horizontal vertical) and Distance Laser Interferometer less than 0.05mm. ( Accuracy depending on how well the environmental conditions [temperature, pressure] can be measured) 0.2mm * Height Difference at ~15m 0.01mm to 0.02mm * Picture Remark + accuracy subject to environment conditions / used for most measurements / very fast / data storage on PC. easy handling / used to make the network stiff (measurements across the hall) / data storage on PC. easy handling / works with bar code staff / fast measuring / data storage with PC-Card. The LTD500 and the TDA5005 both work with Axyz. Axyz is a group of Programs that is used for measurements (data storage) and calculations like network orientation, bundle adjustment or transformations Results of the First Part The full lists are in the following appendix. A: The layout of the machine with the measured points. B: The coordinates measured with the Laser Tracker and the Totalstation. C: Comparison between the heights measured with the Laser Tracker and the levelled heights. D: The transformed coordinates. (Transformation described in chapter point IV.) E: Comparison between the transformed heights and the levelled heights. iwaa02_text_jlp_word00.doc :15 Seite 5

7 2.2 The Alignment Concept for Beamline Components At PSI most beamlines have the same structure concept: several beamline components are mounted on a girder. The components are adjustable to each other in all directions. The girders stand on the floor in the hall. They although are adjustable. Only the dipolmagnets are standalone. This makes sense since they are much havier then the rest of the components and like this only the supports for the dipols have to be dimensioned to carry their weight. Fig. 4 shows this very systematically: Quadrupol tripplet Diagnostic Box Dipol Coordinates of yellow points are known. Adjustable feet of components Adjustable feet of girders Fig. 4 Structure Concept for Beamlines at PSI The biggest advantage of this system is, that the most alignment jobs can be done outside a beamline area. Inside, where radiation forces you to do a job within a given space of time you only have to check three points per work piece: the girder. It although helps for deformation measurements: much less points have to be measured and you know the positions of each single component Design of the girders There is only one major difference in the concept of the beamline for the PROSCAN-Project to other beamlines at PSI. We have foreseen a plate between the grider an the components. Like this the drill holes for the lower part of the adjust devices are not in the girder itself. If the position of any component change only the plate has to modifield or has to be replaced. This is easier because the work piece is smaller and therefore faster and cheaper. All Quadurpols look in the same direction. So the cooling system and the power supply always are on the right respectively on the left side. Like this the Quadrupols can be exchanged. This although helps the surveying team, because like this it is always the same situation we have to get grips with. Most survey jobs will be done from the left side (in beamdirection). The power supply normally is the lesser of the two evils to reach the points used for the alignment. iwaa02_text_jlp_word00.doc :15 Seite 6

8 2.2.2 The building of the Beamline (Girders) coordinates known 3 points on each girder 6 points on each QP adjust device Fig. 5 Girder with quarupol triplet The following procedure is chosen for the built of the beamline and the alignment of the components: 1. Mark the Beamline and the positions of the feet of the girders on the floor 2. Girders are placed in the hall and attched to the floor 3. Girders will be adjusted in height and in position with an accuracy of ±1mm and will be leveled. This part will be done by the surveying team 4. A packet (a quadrupol tripplet for example) is placed on a girder. This packets will be built outside the beamline area but will not be adjusted there 5. Each single beamline component will be adjusted in height an in position. Quadrupols with an accuracy of ± 0.1mm, diagnostic elements with an accuracy of ± 0.5mm 6. The three points on the girder as well as the points on the beamline components will be measured (control measurement). iwaa02_text_jlp_word00.doc :15 Seite 7

9 3 Conclusion The main challenge is not the surveying or alignment itself since this is easy and fast with modern instrumentation. The problems must be resolved in the planning and concept phase of the project when the space in the narrow bunkers is allocated. There is not much room for the entire infrastructure (water, helium, electricity, etc.) and it is seldom possible to preserve visible measuring lines. That is why the construction group draws the beamline in 3D. Especially in the cyklotron bunker this is inevitable. Each single position of the Laser Tracker and what point of the network can be measured for the orientation of the Laser Tracker is defined. It is extremely difficult to define a network in the concept phase, because nothing is fixed or can be fixed. This leads to an iterative process, leaving only a short time between finalising the network concept and its realisation. iwaa02_text_jlp_word00.doc :15 Seite 8

10 4 Appendix A The layout of the machine with the measured points Legend: New points Existing points Construction work areas (loss of points) Scale: Temporary shielding ~10m iwaa02_text_jlp_word00.doc :15 Seite 9

11 B Coordinates measured with the Laser Tacker and the Totalstation Point number X Y Z NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA iwaa02_text_jlp_word00.doc :15 Seite 10

12 C Comparison between the heights measured with the Laser Tracker and the levelled heights Z Z Point number Difference (levelled) (Laser Tracker) NA NA matched NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA iwaa02_text_jlp_word00.doc :15 Seite 11

13 D Transformed coordinates Point number X Y Z NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA iwaa02_text_jlp_word00.doc :15 Seite 12

14 E Comparison between the transformed heights and the levelled heights Point number Z (levelled) Z (Laser Tracker / transformed) Difference NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA iwaa02_text_jlp_word00.doc :15 Seite 13