CARE/JRA3: First Quarterly Report /04/2008

Transcription

1 CARE/JRA3: First Quarterly Report /04/2008 Title: High Intensity Pulsed Proton Injectors (HIPPI) Coordinator: M. Vretenar (CERN), Deputy: A. Lombardi Participating Laboratories and Institutes: Institute (participant number) Acronym Country Coordinator Scientific Contact Associated to CCLRC Rutherford Appleton Laboratory (20) CCLRC UK P. Norton C. Prior Commissariat à l Energie Atomique (1) CEA F R. Aleksan A. Mosnier CERN (17) CERN CH G. Guignard M. Vretenar Forschungszentrum Jülich (7) FZJ D R. Tölle R. Tölle Gesellschaft für Schwerionenforschung, Darmstadt (4) GSI D N. Angert L. Groening Institut für Angewandte Physik - Frankfurt University (5) IAP-FU D U. Ratzinger U. Ratzinger INFN-Milano (10) INFN-Mi I S. Guiducci C. Pagani INFN CNRS Institut de Physique Nucléaire d Orsay (3) CNRS-IN2P3- Orsay F T. Garvey G. Olry CNRS CNRS Laboratoire de Physique Subatomique et de CNRS-LPSC Cosmologie (3) F T. Garvey J.M. De Conto CNRS INFN-Naples INFN-Na I S. Guiducci V.G. Vaccaro INFN Main Objectives: Research and Development of the technology for high intensity pulsed proton linear accelerators up to an energy of 200 MeV. Cost: Total Expected Budget 12 M (FC) M (AC) Total 14.7 M EU Funding 3.6 M 1

2 1 Management Activity Meetings External Scientific Advisory Committee... Erreur! Signet non défini. 2 Dissemination Activity List of talks List of papers Additional staff hiring Status of the Work Work Package 1 : Management and Communication Work Package 2: Normal Conducting Accelerating Structures Work Package 3: Superconducting Accelerating Structures Work Package 4: Beam Chopping Work Package 5: Beam Dynamics Appendix 1: Gantt chart at end of April

3 1 MANAGEMENT ACTIVITY 1.1 Meetings List of meetings All meetings to be organized by HIPPI in the year 2008 have been planned (Work Package meetings and general meeting). Only WP3 (Superconducting structures) has decided to have, instead of a general WP Meeting, a series of dedicated meetings with limited participants, specifically aimed at the preparation of the common deliverables foreseen in The planned WP events will take place between May and June, and will be followed by a General Meeting moved this year to end of October, far from the important LINAC08 Conference and closer to the end of the Activity. The year 2008 will see two large Accelerator Conferences and few specialized Workshops, and preparation of the HIPPI participation is already going on. The events concerning HIPPI during the year 2008 are shown in Table 1.1.1a. A review of the Linac4 project (one of the projects supported by HIPPI) has been already taken place at CERN in January, and several presentations concerned the progress with HIPPI prototypes and studies General meeting The HIPPI general meeting for 2007 will be held at Geneva (Switzerland), in the premises of CERN (AB Auditorium Meyrin), from October 29 th to 31 st. Being the last in the series of HIPPI Meetings, its structure will be partly different from previous meetings. More space will be devoted to the common assessment (and related deliverables) that are one of the main goals of the Activity and to the presentation of the Linac designs that have benefited from HIPPI. The assessment from the ESAC will cover the full duration of the Activity. 1.2 External Scientific Advisory Committee contacts with the members of the ESAC have continued after the HIPPI Meeting in Orsay (September 2007) and some measures have been taken following the ESAC recommendations, in particular: o o Preparation for bench testing of the chopper line elements at CERN. Simulations of PIMS field stability during transient and under beam loading have been performed and presented at the Linac4 Review at CERN ( 3

4 Table 1.1.1a: Overview of meeting, workshop and event (co)organized by the Activity or with Activity contributions Jan Feb March Apr May Jun Jul Aug Sep Oct Nov Dec CARE & HIPPI CSC Meeting WP2 Meeting 9 Paris Grenoble (tbd) WP3 Meeting WP4 Meeting WP5 Meeting HIPPI Annual Meeting CARE Meeting Collaboration meetings LINAC4 Review ISTC CCDTL Meeting Conferences, workshops EPAC 2008 HB2008 LINAC CERN C ERN 19 GSI 20 CERN Genoa (I) Nashville (TN, USA) 28-3 Victoria (BC, Canada) CERN 2-5 CERN 4

5 Table 1.1.1b: List of meeting, workshop and event (co)organized by the Activity Number of Date Title/subject Location Main organizer Comments and Web site participants January Linac4 Machine Review Geneva (CH) CERN ~

6 2 DISSEMINATION ACTIVITY 2.1 List of talks During the LINAC4 External Review Committee (CERN, January 29-30) several talks included work developed in HIPPI. The talks containing specific HIPPI-supported work are listed in Table 2.1. They are all linked from Table 2.1: List of talks presented by the JRA Alessandra Lombardi (CERN) Mauro Paoluzzi (CERN) Suitbert Ramberger (CERN) Matteo Pasini (CERN) Frank Gerigk (CERN) Alessandra Lombardi (CERN) Carlo Rossi (CERN) Chopper line design and components Chopper structure and driver Drift Tube Linac Cell-coupled Drift Tube Linac Pi-mode structure Linac Beam Dynamics, PMQs Linac4 Test Stand 2.2 List of papers Two CARE note have been issued during the first quarter of Three CARE report have been issued in support of HIPPI deliverable number 32,33 and 39 for The publications are listed in Table 2.2. Table 2.2: List of document issued by the NA or JRA # CARE document type and number CARE-Note HIPPI CARE-Note HIPPI CARE-Report HIPPI CARE-Report HIPPI.. CARE-Report HIPPI Title Authors and Labs Date Beam diagnostics based on Photo Detachment for the Front End Test Stand FETS Using the Chopper as emittance exchanger Design and Manufacturing of a DTL prototype power coupler On-Line Transmission Control Set-Up at the GSI UNILAC Development of Side Coupled Cavities C. Gabor, J.K. Pozimski, A. Letchford, C. Prior STFC/ RAL/ ASTeC, JB. Lallement, F. Caspers, T. Kroyer CERN. S. Ramberger 1, P.-E. Bernaudin 2, J.-M. De Conto 3, D. Marchand 3, E. Vernay 3, M. Vretenar 1 1) CERN, 2) CEA, 3) LPSC P. Forck, H. Reeg, N. Schneider, M. Witthaus, GSI J.-M. De Conto, J.-M. Carretta, Y Gomez- Martinez, R Micoud,LPSC 01/ / / / /2008 6

7 2.3 Web site The HIPPI web site ( contains the most recent information on the JRA activity. 7

8 3 ADDITIONAL STAFF HIRING No additional hiring during the first quarter of Table 3: Temporary staff hiring # Lab Job Type Duration Work subject Status 8

9 4 STATUS OF THE WORK 4.1 Work Package 1 : Management and Communication The main Management activities in the 1 st Quarter 2008 have been: - the follow-up of implementing the recommendations from the ESAC reviewers, - the preparation of the Work Package meetings and of the HIPPI Annual meeting, - the follow-up of the HIPPI milestones and deliverables: contacting the responsible persons for the different deliverables, keep track of the delays, and when the deliverable is achieved be sure that the proper supporting document is prepared and submitted. The follow-up of ESAC recommendations lead to an important result for the PIMS accelerating structure (WP2). At the HIPPI Meeting of September 2007, the ESAC expressed some concerns for the field stability in the 5-cell PIMS in presence of loading from the particle beam, and for its influence on longitudinal beam dynamics. After the meeting and following the suggestion of the Coordinator, work was oriented in this direction coming to a set of satisfactory calculations that were presented already at a meeting in January and generally accepted as solving the issue. For the Deliverables, apart from the still important work of following up the correct preparation and filing up of the deliverables, more effort went into the preparation of the final common assessments (on Normal Conducting structures, Superconducting structures and on choppers) that are the most important outcomes of the HIPPI work. For these very peculiar deliverables, it was decided that the compilation of the common assessments should be given to young researchers within the HIPPI team, persons with more time available and less preopinions than the team leaders. These assessments will be an excellent way for them to become familiar with all the possible structures foreseen for linacs and their features. As for the beam tests of the chopper line at CERN, it is now clear that the IPHI RFQ will never be ready before mid 2009 at the earliest. On the other hand, the HIPPI ESAC discouraged looking for alternative beam lines to perform the chopper tests, and the consequence is that the chopper line will go only through a bench test, with all components operating together, to put in evidence possible interferences or other problems, but will not undergo beam tests within the time frame of HIPPI. 9

10 4.2 Work Package 2: Normal Conducting Accelerating Structures Drift Tube Linac Activities at CERN (WBS 2.1.1) The last few months have seen good progress towards the construction of a new DTL prototype financed outside HIPPI but fully profiting of the design developed within HIPPI; the components have been received at CERN in March. This prototype development was started in November 2006 as consequence of the recommendations of the HIPPI ESAC committee. Following the delivery of the drift tube pieces, the drift tube cores have been dimensionally checked and have been found acceptable with respect to the required tolerances. The tank elements arrived in early March and are currently being dimensionally checked at the CERN metrology laboratory. Figure 4.2.1: DTL prototype cavity and drift tube core after machining. In parallel to the production of the prototype structure, a pre-prototype structure of 320 mm length consisting of a tank segment, a short girder for 2 drift tubes and pieces for two simplified test drift tubes have been machined. The purpose of this pre-prototype structure is to verify the drift tube E-beam welding procedure, the drift tube to girder assembly procedure, and their compliance with tolerances. As soon as the pre-prototype is completed, it will serve as a test structure for alignment procedures until the prototype structure will be completed. All pieces of the pre-prototype have been dimensionally checked. Results show minor deviations which are acceptable with respect to the purpose of procedure verification. The assembly of the drift tube cores with the drift tube stems by e-beam welding was tested and the two drift tubes show excellent results in two dimensions. The third dimension (longitudinal with respect to the beam direction) however shows deviations of up to 0.22 mm. This deviation is at the very limit of what was found to be acceptable with respect to longitudinal random static errors. The aim is to halve this error in order that a reliable assembly procedure can be defined and to avoid any complicated correction procedures. 10

11 Figure 4.2.2: Completed sample drift tube of the pre-prototype structure. The drift tube tests in the ISTC project 2888 have been completed by end of November The design is promising and passed practically all non-destructive tests. When destructing the drift tube for weld tests however, it became clear that the laser weld penetration of 0.15 μm-0.2 μm is not sufficient to guarantee long-term leak tightness and sufficient durability in assembly operations. An improvement of the laser welds as prove of technology was requested on an additional drift tube sample. Concerning the CERN prototype the findings are not as critical as the assembly procedure of the stem to core connection foresees e-beam welding. E-beam welding guarantees a full penetration of the weld area and would be compatible with an assembly procedure executed on CERN manufacturing equipment including the insertion of a permanent magnet quadrupole Activities at Rutherford Laboratory (RAL) (WBS 2.1.4) At Rutherford Appleton Laboratory, activities were concentrated mainly on the design of the normal conducting part of a future 800 MeV linac. The proposed linac is being considered as a possible replacement for the aging current 70 MeV ISIS injector (MW upgrade plans), and the same linac has also been included in designs for the proton driver for a possible UK Neutrino Factory. The first two DTL tanks of the new linac have been modelled using Superfish and Microwave Studio and will accelerate a 40 ma H- beam up to 35 MeV. Beam dynamics studies are being made using Trace3D, Parmila and TraceWin and efforts are put into matching the beam from the three existing FETS front end designs. In order to optimize the choice of accelerating structures for the new linac, a comprehensive comparison is being performed at RAL and the HIPPI normal conducting structures are being analyzed in collaboration with our HIPPI colleagues. The structures considered in this work are the DTL, S-DTL, CCDTL, SCL, the H-mode DTL and the PI-mode structure. We expect to have a full report ready for the HIPPI yearly meeting. 11

12 4.2.2 H-mode DTL (IAP Frankfurt) RF cold model design & construction (WBS 2.2.2) Structure development: The fabrication of the 1:2 scaled model of the second resonator of the GSI P-Injector has been completed and the model in now under experimental investigation. Preliminary results indicate a good agreement between the simulations and the experimental results in terms of frequency and field distribution. Figure 4.2.3: Top: internal view of the scaled model of the second resonator of the FAIR proton injector. Bottom: the cavity of the test bench built at IAP. Fig.4.2.4: An example of field distribution At the moment the main activities point to investigate the effect of mobile tuners on the field distribution and on the coupling strength and to verify the effective shunt impedance. Following those results preparation of technical drawings for the production of the full scale prototype will start as soon as possible. 12

13 4.2.3 Side Coupled Linac (LPSC and CERN) (WBS and 2.3.2) PI Mode Structure (PIMS) at CERN Thermal calculations for the PIMS were performed to investigate the possibility of using copper plated stainless steel to reduce material cost. Unfortunately, the heat conductivity of stainless steel is about 20 times poorer than the one of copper, leading to a temperature increase of more than 130 degrees on critical parts of the structure. Therefore, the PIMS needs to be constructed out of copper. The PIMS has numerous advantages compared to the SCL, for instance an operating frequency of MHz as in the DTL and the CCDTL, less coupled cells (7 compared to 117) and easier manufacturing and tuning procedures. On the other hand, pi/2-mode structures are widely used in comparable proton accelerators (SNS, JPARC) as they are electrically very stable against individual cell errors and beam loading effects. The electrical stability of the PIMS has already been studied in detail. The number of coupled cells and the coupling between cells has been chosen such that the statistical gap voltage error is below ±2.5%. Can transients during the filling process or beam loading introduce errors that might spoil the performance of the PIMS? A detailed study has been performed using the equivalent circuit model. Pi-mode structures are electrically not as stable as pi/2-mode structures. During the filling process, many modes are excited in the PIMS that transport the electromagnetic energy from the powered cell to its neighbours and backward. As the power increases, the relative difference in energy between cells gets smaller and the power in the pi-mode compared to the power in all other modes increases. In our case, the loaded Q-value is about The filling of the cavity takes roughly RF cycles. Already after 5000 cycles, the relative max-min difference of all 7 gap voltages is less than 1 (compare Figures 1 and 2). Above that, the sum voltage over all 7 cell raises almost identically with the voltage in an equivalent 1 cell cavity. Although the beam is brutally chopped in case of Linac4 (133 out of 355 bunches), the voltage difference under beam loading between cells is less than 2.5 (compare Figure 3). For this simulation, no feed forward to compensate for the voltage drop due to the beam loading was applied. In reality when feed forward is used, the drop (here 4kV) will be far smaller and consequently also the voltage difference between cells will decrease proportionally to the drop. 13

14 Figure 4.2.5: The filling process of a 7 cell PIMS cavity for the first cycles. In the 1st plot, the individual gap voltages of all 7 cells are drawn in amplitude. The phases are given in the graphic at the bottom. The normalised difference of all voltages is shown in the 2nd plot. Figure 4.2.6: The filling process of a 7 cell PIMS cavity. The individual gap voltages of all 7 cells are drawn in amplitude (1st plot) and phase (3rd plot). The normalised difference of all voltages is shown in the 2nd graph. 14

15 Figure 4.2.7: The PIMS cavity under beam loading for the beam chopping structure of Linac4. No feed forward was applied to compensate beam loading effects. A 7 cell prototype for a high power test is being designed. The first PIMS module (Ekin=104 MeV) has been chosen. The cell gap was optimised to give high shunt impedance while limiting the peak electric field to 1.8 Kilpatrick for the nominal power of 807 kw. A coupling of k=5.5% between adjacent cells guarantees a gap voltage error of less than ±2% for cell frequency errors of df 25 khz. Predicting the resonant frequency in simulations as precise as 25 khz / 352 MHz is not easy. Therefore, we have decided to use a tuning ring for a pre-tuning of each cell. Tolerances are defined to limit machining errors to ±200 khz in frequency. Tuners will be used in all 7 cells. 5 of them will be fixed and 2 will be movable (in cell 2 and 6, respectively). The tuning range is 0 to +1.0 MHz. Simulations have been performed to compare tuners with and without RFfingers. Without RF-fingers, currents flow around the tuners and produce additional losses (in our case up to 1%). The end cells will have a groove in form of a ring to lower the resonant frequency by 4.75 MHz. This is necessary to make the electric field of the π-mode flat in all 7 cells. Choosing appropriate dimensions of the groove (inner radius, outer radius and depth) provides the desired frequency shift and keeps the shunt impedance equal to the one of a centre cell. The tolerances for the coupling slots were calculated by equivalent circuit simulations. An error of ±1 of the coupling factor (k=5.5%) leads to a gap voltage error of ±0.5% over all cells. This error in coupling is quite small, but as the coupling slot is large (L=86mm) a tolerance of dl= ±50 μm is required only. A waveguide coupler is being designed. Simulations for placing cooling channels in the discs are being performed. We have good hopes that the heat conductance between cylinders and discs is sufficient to avoid additional cooling rings on the outside of cylinders. The frequency shift due to deformations is less than 300 khz and the maximum temperature increase is less than 40 degrees on all parts (cooling water temperature is 20 degrees on the inlet). Mechanical stresses are analysed. Optimisations are in progress. A scaled cold model at 704 MHz was build. Measurements have just started. 15

16 Figure 4.2.7: A 7 cell cold model of the PIMS SCL at LPSC Due to some lack of technical people because of sick leaves, the SCL activity has been reduced during the first months of A report has been written (CARE report ) which summarizes the work done on this part up to now. The tuning procedure study is now restarted and is done on a reduced set of cells (4 accelerating cells, 3 coupling cells), where a careful characterization of the cavity parameters is under way. After a preliminary step, where the theoretical simulations (obtained from measured parameters) were far from the reality, a more accurate analysis has show a better concordance and understanding of the cavity behaviour Cell Coupled DTL (CERN) (WBS to 2.4.3) CCDTL final note was released last year in the CARE-Report HIPPI, and this task is now completed. The revision of the design after the high-power tests of the two prototypes took place during a meeting at CERN (March 10-13) between the CERN experts and the Russian experts who have contributed to the second ( ISTC ) prototype. In preparation for the finale decision on the mechanical solutions to be adopted, different tests were made in Russia and reported at the meeting. 16

17 Test with various surface conditions of the flanges were made in Snezhinsk. The flange surfaces were rectified and achieved a roughness of 0.28 < Ra < 0.32, which is finer than specified for the use with Helicoflex gaskets. Tests with HN and HNV type gaskets showed no vacuum leaks. After copper plating the surface, there was no leak with an HNV gasket, but a subsequent test with a HN gasket produced a leak. Looking at the gasket it seems that a small surface area was ripped from the aluminum gasket. It was not clear if this leak was a consequence of the previous test with the sharp edged HNV gasket. After a 2nd copper plating the flange was leak tight with an HN gasket. It was concluded that the flange surfaces must be rectified. 17

18 Table 4.2a : Status of the Sub tasks in WP2 which are supposed to have started according to the MS project breakdown in Annex 1 WBS Original begin date Original end date Estimated Title # (Annex 3) (Annex 3) Status Revised end date 2.1 Drift Tube linac DTL Design July 2004 June % June DTL Coupler prototype construction July 2005 June % End DTL beam dynamics design January 2004 June % 2.2 H mode DTL RF cold model design & construction January 2004 January % April RF model construction December 2004 June % December CH prototype construction and test December 2004 Decembre % October Side Coupled Linac RF model mechanical design July 2004 December % June RF model construction January 2005 December % November RF model testing January 2006 June % September SCL module design January 2006 June % June Cell Coupled DTL Pre-prototype high power RF tests July 2004 March % July Prototype mechanical design January 2005 December % Revision of design October 2005 October % March Prototype high-power RF tests August 2006 June % December Testing of ISTC prototype January 2008 June % June2008 Table 4.2b: Status with respect to the interim reports and deliverables due in 2008 according to the MS project breakdown WBS Due date in Title # Annex 1 Status Revised delivery date DTL design March 2007 Delayed June H mode prototype construction December2007 Delayed Octobre CCDTL design June 08 On time 18

19 4.2 Work Package 3: Superconducting Accelerating Structures All the institutes involved in this Workpackage are now close to the end of the fabrication phase. All the cavity prototypes as well as the different equipments and components needed for the RF tests are almost available. This last year of program is mainly dedicated to the preparation and accomplishment of RF tests of the prototypes designed and fabricated. The last deliverable of the WP3 is a final report aiming to assess the different cavity types. In the Workpackage meetings held these last years, we already fixed the main chapters and comparison criteria. In order to prepare efficiently this final report, it has been decided to organize several dedicated meetings (or video-conferences), each with only few number of participants. INFN-Milano Cavity assembly with tuner (subtask ) All the components needed for the future test of 5 cells cavity (cavity A) in CryHoLab are available, but the magnetic shielding. This last component should be delivered in the next months and will be integrated to the cavity before the final welds of the Titanium Helium tank. CEA-Saclay Construction of cavity B (subtask 3.1.6) The cavity B has been equipped with its Helium tank, stiffening wings are welded, as well as the threaded rods needed for the cold tuning system and for connection to the support and handling tools. After delivery at Saclay, the measurement of the field flatness showed that no degradation occurred during the transportation (field flatness = 89%). A new chemical polishing has been performed (15 microns) and the preparation process is going on (High pressure Rinsing and assembly in clean room). The goal is to test the cavity in vertical cryostat before end of April Figure 4.3.1: Chemical treatment of the Cavity B 19

20 Figure 4.3.2: Cavity B inside Clean room after the HP Rinsing Power coupler design and engineering (subtask 3.1.7) All the pieces of the couplers are in fabrication. Many technical problems were encountered during the fabrication phase (precise machining of the coupler cold parts, deformation of pieces after welding, etc.). For this reason, the coupler fabrication is delayed. However, the 704 MHz RF windows with antennas, which are critical pieces, are already at Saclay. Once all the parts are received, we will proceed with assembly of couplers on the coupling box in Saclay clean room. Then, couplers will be installed on the test stand and conditioning will start (May 2008). RF source testing (subtask ) All the equipments of the 704 MHz-1MW test stand have been installed last year. The power tests at nominal duty cycle of all the components are finished. In order to operate the test stand efficiently, we are optimizing the control system and interlock thresholds. FZ-Juelich Integration of coupler and tuning options (subtask ) Work is in progress. Manufacturing of 352 MHz Multi-gap Resonator (subtask ) All parts of the cavity are fabricated now. The cavity preparation should start end of May with the chemical etching. The Ecole des Mines, Evry, Paris (C2P) could successfully coat the outer surface of the end cup using copper plasma spraying. The layer had a maximum thickness of about 19 mm and took about 8 days of effective spraying work. In the central part of the end cup the visual inspection showed a circular crack in the copper. 20

21 Ultra-sonic inspections in Jülich indicated a uniform copper layer all over the end cup. The circular crack turned out not to change during 10 cycles of cooling down by immersing in LN 2 and subsequently warming up to room temperature. No changes of the copper coating could be detected by ultra-sonic inspection. Figure 4.3.3: End cup as received from plasma spraying Figure 4.3.4: End cup immersed in LN 2 for cycle tests. No changes of copper layer could be detected. However, it turned out that the available spraying robot would need major modifications to allow proper handling of the complete cavity (120 kg on the turning table, process optimization for long spraying times, and twice about a week up-time). This upgrade would have caused a delay of the project beyond its planned end date and would have exhausted the financial frame of the project. Thus a different approach for cavity stiffening was used. 21

22 Figure 4.3.5: 352 MHz cavity with all spokes welded into the cavity body. Figure 4.3.6: Niobium end cup on the precision measurement machine The spokes are now welded to the cavity body. Prior to welding the end cups to the cavity a last dimensional control has to be done. Cavity is to be closed within the next few weeks. Remaining activity is laser welding the outer stiffening ribs to the cavity body. The following BCP is scheduled for May 2008 at CEA Saclay. High pressure rinsing will be done at IPN Orsay on the same day. RF measurements in Jülich which will follow immediately are being prepared right now. IPN-Orsay Evaluation of 352 MHz 2-gap prototypes (subtask 3.2.3) We are preparing a new test of the beta 0.15 Spoke cavity inside the CM0 cryomodule. Some modifications have been done to better thermalize the cold tuning system and the helium buffer vessel. The goal is to reduce the losses down to 5 Watts (instead of 10 Watts in the first configuration). 22

23 The first test of the piezo-actuators used for the fast tuning is also planned during this cool-down. The test is foreseen for mid of May. Construction of Coupler Prototype (subtask 3.2.5) Antennas have been welded on the windows (see Figure A - left). The couplers have been connected to the coupling cavity (see Figure A - right). Unfortunately, the frequency of the coupling cavity is far from the target (i.e. 347 MHz measured for 352 MHz targeted). A coarse tuning (total range of 1.5 MHz) was foreseen by mean of 4 tuning plungers located on the cavity s equator but the frequency shift which was measured is too large. In that configuration, the couplers could not be conditioned (mainly due to the narrow bandwidth of the 10-kW amplifier). So, a new coupling cavity has been ordered and should be delivered by end of May. Figure 4.3.7: RF coupler with its antenna (left), test bench with the pair of couplers RF design of 352 MHz multi-gap resonator (subtask 3.2.6) The stiffening systems were defined in order to reduce the Lorentz forces detuning. What about the influence of these systems on the structure s eigenmodes? A complementary simulation has been realized and some remarks have been observed. Four possibilities to stiffen the 4 mm triple Spoke cavity are shown in the figure B. On the left side, only eight niobium ribs (4 cm x 2.5 cm) are welded on the end-cups. This option has an alternative: the copper coating with a variable thickness (maximum 20 mm). On the right side, additional rings (1 cm x 2.5 cm) are placed on the cavity's cylindrical body. Figure 4.3.8: Cavity stiffening scheme (8 ribs; Cu coating; ribs + rings; Cu coating+ rings) 23

24 mode Without stiffener 8 ribs Cu coating Ribs + rings Cu coating + rings Table 1: triple Spoke cavity fixed on four supports arranged axis-symmetrically; frequency of first mechanical vibration modes (Hz). The simulations results concerning the structure s vibration modes are presented in table 1. The first observation is that the ribs and rings added to the cavity s cylindrical body allow a rise of the first mode of vibration. The copper coating is limited in thickness (maximum 20 mm no uniform) compared to the rings (25 mm). The second observation is that in any case the first vibration mode is sufficiently high: more than 200 Hz. This result comes from the axis-symmetrical fixation, if the cavity is fixed by the beam pipe, the lower modes concerning the cavity s rotation appears, the first frequency is 45 Hz for the cavity stiffened by ribs and rings and 53 Hz for the cavity stiffened by copper coating and rings. So it s highly important to fix the cavity axis-symmetrically IAP-Frankfurt University Measurements of tuning system (subtask 3.3.3) The horizontal cryostat has now been prepared to include the piezo elements. Therefore we had to separate the axial beam pipe to insert the piezo tuner, which has been welded to the parts. It will be located between the inner cold mass containing the helium and the outer room temperature vacuum vessel. The slow mechanical tuner is also in progress and will soon be equipped with a stepping motor together with an appropriate digital control unit for driving the mechanism with a computer. Additional mechanical preparations for a first cold test without the CH-structure are under way. They concern mainly the liquid air cooling system, the µ-metal shielding which has to be machined to match the dimensions of the CH-Structure and the vacuum system. 24

25 Figure 4.3.9: Scheme of the cryostat with tuner positioning. Three piezo elements will be used for the fine tuning 25

26 WBS Title Participants Original begin date Original end date Estimated Status Revised end date 3.1 Elliptical cavities Tuner design INFN 07 / / % Integration of piezo design INFN 07 / / % Tuner construction INFN 01 / / % Construction cavity B CEA 11 / / % Power coupler design & engineering CEA 01 / / % RF coupler construction CEA 05 / / % 04/ RF source order and preparation CEA 07 / / % Modulator preparation for test stand CEA 01 / / % RF source testing CEA 01 / / % High power pulsed tests CEA 05/ / % 12/ Cavity A assembly with tuner INFN 06/ / % 05/ Vert. test & final welding of cavity B CEA 07/ / % 03/ Spoke cavities Evaluation of 700 MHz prototype FZJ 09 / / % Design of coupler prototype IPNO 01 / / % Construction of coupler prototype IPNO 01 / / % Final design of 352 MHz multigap res. FZJ-IPNO 07 / / % Test of coupler prototype FZJ-IPNO 07/ / % 07/ Manufacturing of 352 MHz multigap res FZJ-IPNO 04/ / % 05/ CH resonators Design of tuning system IAP-FU 01 / / % Construction of tuning system IAP-FU 01/ / % Measurements of tuning system IAP-FU 01/ / % 10/2008 Table 4.3a : Status of the Sub tasks in WP3 which are supposed to have started according to the MS project breakdown in Annex 1 26

27 Table 4.3b: Status with respect to the interim reports and deliverables due in 2006 according to the MS project breakdown WBS Due date in Title # Annex 1 Status Revised delivery date Cavity A ready (milestone) March 2007 Delayed June Spoke prototype ready October 2007 Delayed May

28 4.4 Work Package 4: Beam Chopping Web-site: The annual (last) working package meeting has been scheduled for June 20 th at CERN. It will give the participants the occasion to provide and discuss the material for the final report. As the measurements with beam are not possible before the end of HIPPI the comparison of the chopper structures will be done on the basis of electrical measurements and beam dynamics considerations. The work towards producing these data is practically completed in both laboratories. CERN: 1. Chopper structure (subtask 4.1.4): Both assemblies are ready since the end of Chopper driver (subtask 4.1.3): Tests on the first amplifier with positive output have been completed with a long term run (2 weeks, 24 hours per day). The amplifier generated bursts of 1000 pulses, 300 ns length with a repetition frequency of 1 MHz. The burst repetition frequency was 50 Hz. The amplifier behaved reliably during the whole test giving positive indications about the reliability of the Fast Ionization Dynistors. The second pulse amplifier produced by FID technology was delivered to CERN in the second half of October and was the object of a partial measurement campaign. Measurements were stopped by a device failure that required returning it to the manufacturer for repair. As compared to the first amplifier some important improvements have been achieved even if the specifications are not fulfilled yet. The rise time and the pulse distortion are now stable, practically independent from the pulse position within the burst and the specifications can be considered as achieved at least up to the working frequency of 10 MHz. The minimum pulse length is now the sum of a rising and a falling front thus well below the specified 8 ns. The propagation delay time can now be considered as stable for working frequencies up to 1 MHz while at 10 MHz it does not meet the specifications. The fall time is similar for this generator version as for the previous one. The values are 2.6 ns for the 90%-10% transitions and 3 ns for the 90%-3% and cannot be accepted for the chopper operation. Also unacceptable is the presence of an oscillation after the falling edge. Its amplitude reaching about 10% of the full signal would perturb some bunches after each transition. Operation at 1 MHz and 10 MHz with 1 ms burst and 50 Hz burst repetition frequency was tested during about 1 hour. When the driving signal was set to 20 MHz, 10 ns pulse length, 1 ms burst and 50 Hz burst repetition frequency, the generator broke-down after few seconds. A third amplifier, replacing the first positive output unit, was delivered in March It is supposed to implement all the improvements achieved in the negative output unit. Unfortunately a breakdown in the power stage happened shortly after the beginning of tests while switching off the device. For both failures, discussions with the manufacturer suggest that the triggering procedure used at Cern is not correct as it can drive the pulse amplifiers in unsafe situations. If this true the internal pulse amplifier drivers and interlocks have to be improved to achieve reliable operation. 28

29 The low level timing electronics activity also continued with the design and manufacture of a fast synchronization circuit. The core of the system is composed of a synchronism detector, a fast adjustable delay and some digital circuitry that locks the rising front of a pulse returning from the pulse amplifier, to that of a reference pulse and compensates possible slow delay variations as shown in Fig Delay [ps] Delay compensation loop of 10 MHz, 30 ns pulses Servo ON Servo OFF Pulse # Fig : Delay compensation loop of 10 MHz 30 ns pulses The use of the chopper as a longitudinal-transverse emittance exchanger has been numerically verified under different beam conditions. Such a concept, which is outside the HIPPI scope, can be another application of the meander line chopper structure. The outcome of this calculation has been summarized in a CARE note (CARE-Note HIPPI) RAL: Important aspects of the RAL HIPPI WP4 activity for this quarter are as follows: 1.0 Hybrid quadrupole design 1.1 Ciprian Plostinar continues development of design options for a 180 MeV H- Linac for next generation proton drivers, and for hybrid quadrupoles. 2.0 Fast chopper electrodes - slow-wave structures 2.1 Preliminary engineering designs for the planar and helical electrodes have been refined. The detailed design of three test assemblies is in progress. The engineering drawings for test assembly 01 are now complete and arrangements have been made to manufacture the assembly on-site, in RAL s Millimetre - Wave Technology (MMT) development facility (c/o J. Spencer, M. Beardsley). The three initial precision assemblies will serve as test 29

30 beds for the materials and design concepts to be employed in the subsequent quarter scale planar and helical electrode designs. 2.2 Considerable effort has been expended during this reporting period on the selection and sourcing of suitable materials (e.g. copper and aluminium alloys, and machine-able ceramics), and of specialised RF components (e.g. large diameter semi-rigid coaxial cable from Microstock Inc, USA, and miniature L-C trimming elements from Temex Ceramics, France). In addition, effort was expended on the identification of specialist services (e.g. precision machining and metallisation of ceramics, precision bending and terminating of large diameter semi-rigid coaxial cable, electro-plating, and electro-polishing). 1.3 The slow-wave electrode design activity is continuing. The latest slow wave structure is shown in Fig Fig : Slow wave structure A survey on the most suitable coaxial and strip-line dielectric support material has identified two materials as candidate for the RAL chopper. The properties of all the material considered are listed in Table

31 Table Selection of coaxial and strip-line dielectric support material 3.0 RAL fast pulse generator (FPG) 3.1 No activity in this quarter. 4.0 RAL slow pulse generator (SPG) 4.1 This activity has been given a low priority in this quarter. A number of 2 4 KVDC, oil filled capacitors have been purchased, with the intention of reducing the exponential pulse amplitude decrease seen during the burst duration. A scheme to provide active stabilisation of the high voltage power supply is being considered. Initial estimates indicate that fast active voltage stabilisation should reduce burst pulse amplitude droop by an order of magnitude. 5.0 Care Preparation and presentation of the following talk on: Beam chopper development for next generation high power proton drivers, 4 th CARE annual meeting, Meyrin, CERN, Geneva, Switzerland, 29 th - 31 st October, Preparation and presentation of the following: Fast - Slow chopper animation, 4 th CARE annual meeting, Meyrin, CERN, Geneva, Switzerland, 29 th - 31 st October, EPAC 08 31

32 6.1 Preparation and submission of the following: The Development of a Fast Beam Chopper for Next Generation High Power Proton Drivers, Michael A. Clarke-Gayther (STFC/RAL/ISIS), 6.2 Contribution to the following: Hybrid Quadrupole Designs for the RAL Front End Test Stand (FETS), Dan Ciprian Plostinar (STFC/RAL/ASTeC), Michael A. Clarke-Gayther (STFC/RAL/ISIS), 32

33 Table 4.4a: Status of the Sub tasks in WP4 which are supposed to have started according to the MS project breakdown in Annex 1 WBS # Title 4.1 Chopper structure A (CERN) Original begin date (Annex 1) Original end date (annex1) Estimated Status Revised end date Prototype testing w/o beam January 2006 December 2007 finished 4.2 Chopper Line Beam line assembling June 2005 December 2007 Finished Full assembly not possible 4.3 Chopper structure B (RAL) Prototype construction January 2006 June % May Prototype testing November 2007 June2008 0% December 2008 Table 4.4b: Status with respect to the interim reports and deliverables due in 2007 according to the MS project breakdown WBS # Title Due date in Annex 1 Status Revised delivery date Chopper A beam line assembling and meas. December % December Chopper B Prototype ready June % June

34 4.5 Work Package 5: Beam Dynamics Collaborative work on code benchmarking Evaluations of UNILAC data on high intensity Ar 10+ beam have been continued to understand discrepancies with the data of emittance measurements. Three codes have been used for the recent comparison campaign with institutional support: Dynamion (GSI), PARTRAN (CEA) and PARMILA (SNS). The code results on rms emittance growth as function of transverse phase advance were found in sufficiently good agreement. As the simulated emittance growth was generally found to be about 50% smaller than the measurements efforts have been made to understand the discrepancy. Partly better agreement could be achieved by improving matching for the experimental beam. On the simulation side it was found using DYNAMION that the original approach of using a truncated Gaussian distribution wasn't necessarily a good choice to match best with measured distribution. In particular distributions with more pronounced tails have been found to be a promising modification. Quantitative results and comparison with the particle-in-cell programs PARTRAN and DYNAMION are still in development. Work at RAL on non-destructive ion beam diagnostics at the Front End Test Stand For diagnostic non-destructive measurement devices provide minimum influence on the ion beam. In addition, for applications like High Power Proton Accelerators (HPPA) very often problems arise due to the power deposition on wires, pinhole or slit plates as used for different types of beam diagnostics. Therefore diagnostic devices without any mechanical part inside the ion beam would be a large improvement. The work has been concentrating on building up a small laser lab to achieve the possibility of testing different ways of laser beam guiding. Sufficient spatial resolution means high demands particular with regard to laser beam alignment, i.e. a constant perpendicular angle between photons and H- ions over the whole scanning range. Varying the angle with the position leads to a lot of error handling afterwards or is impossible. Beside the alignment the transverse photon density distribution is important which makes it necessary to use a well-collimated, Gaussian shaped laser beam with TEM 00 mode. But unlike misalignment it is possible to consider the density distribution easier during emittance computation or simpler the collimation is good enough to neglect fringe effects. Therefore all the laser equipment will be tested with the new laser lab during the next time with the aim to proof various aspects of spatial resolution. 34

35 Table 4.5a : Status of the Sub tasks in WP5 which are supposed to have started according to the MS project breakdown in Annex 1 WBS # Title Original begin date (Annex 3) Original end date (Annex 3) Estimated Status Revised end date 5.1 Code development Preparation, Dev. of 3D space charge routines, Testing January 2004 June % December Neutralization and ECR source model. January 2004 December % December Codes preparation for SC linacs January 2004 December % June Code comparison and benchmarking January 2005 September % 5.2.2,3 Measurement campaigns June and Oct % July Diagnostics and collimation Non-interceptive bunch measurement construction (GSI) January 2005 December % April Halo monitor tests and improvement (CERN) January 2004 June % March Beam profile monitor design (FZJ) January 2005 June % On-line transmission control (GSI) October 2005 September % February

36 Table 4.5b: Status with respect to the interim reports and deliverables due in 2007 according to the MS project breakdown WBS # Title Due date in Annex 1 Status Revised delivery date RAL 3D code development December Profile measurement by fluorescence final report July 2006 delivered February Simulations and experiment at UNILAC final report December 2006 Task finished July Non-interceptive bunch measurement final report December 2006 Task finished April Online Transmission Control October 2007 delivered Beam profile monitor for high Intensity (FZJ) June 2007 delivered 36

37 Appendix 1: Gantt chart at end of April 2008 ID Task Name 1 WP2: NORMAL CONDUCTING STRUCTURES Drift Tube Linac DTL beam dynamics design H-mode Drift Tube Linac CH-prototype construction, tests CH-DTL beam dynamics study Side Coupled Linac RF model testing Cell Coupled Drift Tube Linac Testing of ISTC prototype 11 WP3: SUPERCONDUCTING STRUCTURES ELLIPTICAL CAVITIES High pow er pulsed tests SPOKE CAVITIES Manufacturing of 352MHz multi-gap prototype Evaluation of 352MHz multi-gap prototype CH RESONATOR Measurement of tuning system 19 WP4: CHOPPING CHOPPER STRUCTURE A Prototype testing CHOPPER LINE Beam line assembling CHOPPER STRUCTURE B Prototype testing 26 WP5: BEAM DYNAMICS Code development Neutralization and ECR source modelization study Code benchmarking w ith experiment Diagnostics and collimation Beam profile monitor design RAL'CERN FZJ LPSC'CERN CEA CERN FZJ IAP-FU CERN RAL CEA'INFN-MI FZJ'IN2P3-Orsay 37