The new GTS-LHC ECR ion source was installed in 2005. An oxygen 4+ beam was delivered to LEIR both for injection line (June 2005) and for the ring commissioning (September to December 2005). During these runs, studies were made of the beam transport in the Linac and towards LEIR. Some of the most significant results concerning the Linac are presented in this report. From 2006 the ECR source and the Linac3 delivered a lead beam for the LEIR commissioning, leaving some questions open for the oxygen beam transport. This report serves as a summary of the status of the investigations on the oxygen beam

Dumas, L

Küchler, D

Scrivens, R

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH  CERN  ⎯  AB DEPARTMENT  AB-Note-2007-005 ABP      Preliminary Characterization of the O4+ Beam in Linac 3   L. Dumas, D. Küchler, R. Scrivens   Abstract   The new GTS-LHC ECR ion source was installed in 2005. An oxygen 4+ beam was delivered to LEIR both for injection line (June 2005) and for the ring commissioning (September to December 2005). During these runs, studies were made of the beam transport in the Linac and towards LEIR. Some of the most significant results concerning the Linac are presented in this report. From 2006 the ECR source and the Linac3 delivered a lead beam for the LEIR commissioning, leaving some questions open for the oxygen beam transport. This report serves as a summary of the status of the investigations on the oxygen beam.                      Geneva, Switzerland January, 2007       Preliminary Characterization of the O4+ Beam in Linac 3  L. Dumas, D. Küchler, R. Scrivens  Introduction The new GTS-LHC ECR ion source was installed in 2005. An oxygen 4+ beam was delivered to LEIR both for injection line (June 2005) and for the ring commissioning (September to December 2005). During these runs, studies were made of the beam transport in the Linac and towards LEIR. Some of the most significant results concerning the Linac are presented in this report. From 2006 the ECR source and the Linac3 delivered a lead beam for the LEIR commissioning, leaving some questions open for the oxygen beam transport. This report serves as a summary of the status of the investigations on the oxygen beam.  Source – ITL Measurements of the O4+ beam after extraction were made on 6 June 2005. The solenoid scan, guillotine and spectrometer method was used (1D method). The calculation of the emittance relies on the following assumptions: • No growth of the emittance in the solenoid of the subsequent drift. • The beam is well centred. • The beam is symmetric in the horizontal and vertical planes, • There is no coupling between x & y planes.  The main configuration parameters for the measurement were the following (see Table 1):  Guillotine step: 0.5mm Current measurements per point: 6* Number of solenoid settings: 7 Energy: 2.563 keV/u Bρ (10.25kV O4+): 0.02914 Tm Table 1: Settings for the solenoid scan (*Typical value)  The ITL.SOL01 was scanned, and the magnet AQN values were converted with the calibration factor of 29.1 Gauss/Ampere. The resulting beam profiles are given in Figure 1. 00.0250.050.0750.10.1250.150.1750 5 10 15 20 25Position (mm) - non-centredIntensity (arb units with an offset k*0.025)sol1=68.5sol1=67.5sol1=69.5sol1=70.5sol1=71.5sol1=72.5sol1=73.5 Figure 1. Measurement of the beam width at ITL.SLV01 The beam current in ITL.MFC02 could be maintained at approximately 260µA for all the settings.  The Twiss parameter results (see Table 2)  - 2 -    are very sensitive to the calibration of the solenoid strength (i.e. the magnet current, calibration factor and the beam energy). However, the emittance does not change by more than 10% for reasonable assumptions about these values.   X & Y – GTS-LHC O4+ X & Y – ECR4 Pb27+αx -1.1 -0.9 βx 0.22 0.04 γx 9.5 45 εx (4rms geom) mm.mrad 200 100 εx (1rms norm) mm.mrad 0.12 0.058 Width 4rms (mm) 13.27 4.0 Table 2. Twiss parameters and emittances calculated 44.5cm upstream of the ITL.SOL01 magnet.  The beam can then be transported through the ITL line, the resulting TRACE output is shown in Figure 2. The beam is transported without losses, and stays well within the vacuum chamber. The large emittance growth in the calculation is caused by the non circular beam at the entrance of the last solenoid.                            Figure 2. Beam transport through the ITL line to the RFQ, based on the input conditions calculated with a solenoid scan  However, beam measurements further downstream do not confirm these results. Measurements of the beam emittance using the quadrupole scan technique in the ITL line after the spectrometer, have not been successful. Due to the very large beam, it is not possible to scan quadrupoles without large beam losses. In this case stable emittance values cannot be calculated.   - 3 -    Possible errors in the understanding of the line optics could not be investigated with oxygen due to lack of time.  Further measurements have been completed with a lead beam [2].  ITF Measurements on the O4+ beam in the ITF line were performed on 2 June 2005. A quadrupole scan from ITF.QDN02 to ITF.MSG02 was performed in both horizontal and vertical planes. The beam parameters at the IH structure exit are given in Table 3.   X Y αx -2.5 -0.09 βx m/rad 2.5 1.75 γx rad/m 2.9 0.403 εx (4rms geom.) mm.mrad 5.2 8.0 εx (1rms norm.) mm.mrad 0.12 0.19 Table 3. Beam parameters at the exit of the IH structure, beginning of the ITF line.  ITH ? Measurements ramping cavity OFF (06/07/2005)  The emittance was measured at the input of the ITH line, using the quadrupole and SEMGrid scan technique. Table 4 shows the results of the scan done on 6 July 2005 with the first quadrupoles of ITH line and ITH.MSG11, and Table 5 gives the parameters at the entrance of the ITH line.   X Y αx 0 -2.9 βx m/rad 9.0 46 γx rad/m 0.11 0.205 εx (4rms geom) mm.mrad 6.4 7.2 εx (1rms norm) mm.mrad 0.15 0.17 Table 4. Emittance and Twiss values at the entrance of ITH.QDN08.   X Y αx 0.543 -1.9 βx m/rad 11.65 22.5 γx rad/m 0.111 0.205 εx (4rms geom) mm.mrad 6.4 7.2 εx (1rms norm) mm.mrad 0.15 0.17 Table 5. Emittance and Twiss values at the entrance of ITH (0.0646 m upstream of the wall), back calculated from ITH.QDN08.   Measurements of the dispersion in the ITF and ITH lines[3] are compared with the model in Figure 3. Two data sets of measurements are shown to suggest the continued ambiguity of the polarity of the profile monitors. There is a reasonable agreement, except between the third and  - 4 -    forth bending magnets (B3 and B4), where the wrong sign of the dispersion is found. However, an inversion of the polarity of the profile monitor is not confirmed by other beam measurements. The difference may be explained by additional focussing from the bending magnets, and more measurements will be required with the Pb beam.  Figure 3: Evolution of the dispersion along the ITF-ITH lines. The green curve is calculated from TRACE3D and the points come from LEIR team’s dispersion measurements.  Those values were measured on July 8th 2005 after re-steering the beam in the filter line. 2 1 -1 -2 0 Dispersion (m) B3 B4 B2 B1 ? Measurement ramping cavity fixed phase (21/09/2005)  In September, the Linac returned to the O4+ beam after a test with lead. In this case the source operation mode was pulsed with an afterglow and a pulsed biased disk, and the low energy line settings had been re-optimized. In addition, the ramping cavity was working at a fixed phase. Measurements with two different quadrupole scans in the ITH line yield the following results (Table 6). All elements after the RFQ had the same setting as used for the previous section, and listed in Table 4. There is good agreement in the horizontal and vertical planes with measurements.  Otherwise scans use standard LEIR settings. At the time of the measurements ITM.MFC03= 110 µA, ITF.TRA15=50µA, ITF.TRA25=50µA, ITH.TRA41~46µA, indicating good transmission in this region.   H-Q09-MSG11 (103,scan,off)* H-Q10-MSG15 (103,184,scan,off,off)* V-Q08-MSG15 (scan, off,off,off,off)* V-Q10-MSG15 (103,184,scan,off,off)* αx,y 0.5 0.7 -4.7 -5.5 βx,y m/rad 7.0 6.0 60 75 γx,y rad/m 0.18 0.25 0.39 0.417 εx,y (4rms geom) mm.mrad 3.1 2.8 6.4 8.0 εx,y (1rms norm) mm.mrad 0.08 0.07 0.16 0.2 Table 6. Results of quadrupole scan emittance measurements in the ITH line on 21/09/2005, with O4+ beam. All values are given at the entrance of ITH.QDN08.  * Currents (Amps) in quadrupoles ITH.Q08, Q09, Q10, Q11S, Q12  ? Measurements ramping cavity active (15/12/2005)  Measurements were performed with O4+ beam and dynamic momentum ramping (Phase ramp: 214° to 41°, Amplitude: 6030). Integration time of the SEMGrids = 400µs, hence the measurement includes the whole ramped beam pulse.  - 5 -      H-Q9-MSG11 (56,scan,off) V-Q08-MSG15 (scan,off,off,off,off) Scan Q10 Vert – SEM 15 (103,184,scan,off,off) α 0.6 -7.8 -8.1 β m/rad 9 104 100 γx,y rad/m 0.151 0.595 0.666 εx,y (4rms geom) mm.mrad 8.4 5.2 5.2 Table 7: Twiss parameters just before ITH.QDN08 from quad scans done 15/12/05  The ramping effect might explain such an emittance growth. That could modify the beam position or its Twiss parameters. In these scans, the dispersion was not taken in account.    LBS Spectrometer – beam energy To centre the beam in the LBS line, it requires ~229Amps on the magnet LBS.BVT10 (Figure 4), compared to 222Amps for Pb53+.   However, comparison of the required B Field on the magnet gives the following: Pb53+ I=222A B=0.9399 T O4+ I=229A B=0.9684 T  BBO4+ / BPb53+ = 1.0303    but: (A/q)O4+ / (A/q)Pb53+ = 1.0191  Hence the magnetic field reading suggests the velocity of O4+ is 1.1% higher than Pb53+. The momentum loss in the stripper foil for lead ions is ~0.66% (which is not the case for O4+ ions). A calibration of the NMR probe showed no drift, measured with an accuracy of 10-6. Comparing high LBS.BVT10 magnet currents of 2002 to 2005, shows a variation in the magnetic field reading against magnet current of between 0.2% and 0.5% higher in 2005 than 2002 (see Figure 5). Some of this difference may also be explained by a drift in the power supply control and acquisition circuits, however, the Linac 2 proton beam is “centred” in the LBS measurement for the same BVT10 current (196.5A) in April 2002 and July 2005. The remaining difference should be explained by the RF tank setting which can change the energy of 1%.   From Figure 4 the beam momentum spread is 0.72‰.  The magnet LBS.BVT10 cannot be continuously run at 230Amps. 1. The power converter provides 230A at 105V (cold) giving 24.2kW. 2. The power converter trips when the voltage reaches 120V, a 14% increase. The resistivity coefficient for copper is 4.27x10-3, suggesting a 33oC temperature rise. 3. Water cooling with a temperature rise of 33oC can extract 2.3kW (liter/minute)-1. So 10.5l/min cooling rate is the minimum required. (This is only to keep the power supply below the voltage limit because that resistance follows the temperature increase). Evaluating the flow rate required to keep the converter voltage below 120V gives: Pb54+ - 218Amps - 8l/min. Measurements on 4 October 2005 measured a water flow of 9 l/min with the return pressure removed, resulting in 7.5 l/min for the normal operation (entrance 14.5 bar to 2.5 bar at output).  - 6 -    The LBS.BVT10 supply can (at the end of 2005) provide the 230A current for up to 10 minutes (on the first switch on). Operation for longer periods will therefore be possible for Pb54+.   Figure 4. Beam energy measurement in the LBS line. With debuncher on and ramping cavity off.    205 210 215 220 225 2300.880.900.920.940.960.98 Measured Probe and Current 29/04/2002 Measured Probe and Current 09/06/2005Magnetic Probe (T)LBS.BVT10 Current (A)             Figure 5. Comparison of the magnetic field measurement verses magnet current in April 2002 and June 2005.  LBE Emittance measurement Measurements of the emittance in the LBE line have been made with all the ITH and LTB settings scaled to O4+ (see Figure 6). The parameters of the LBE line were not scaled for O4+, and hence there is some influence on the value of the emittance, which is probably less that 5% of the recorded values.  - 7 -    The emittance values are significantly larger than the values measured in the ITF line, and the Twiss parameters are very different from the indium beam measured in 2003. The beam length was only 40µs, which is sufficient for measurements.   Figure 6. Emittance measurements in the LBE line. Scaled PSB transport settings were used on the ITH and LTB lines (not LEIR transport settings).  The emittance measurements do show signs of saturation in the profile (in particular in the horizontal plane) which will increase the measured emittance. It should not be forgotten that the 63% emittance quoted corresponds to √2σ. A summary of the mean results (and the width of the measurement distribution) is given in Table 8.  So far it has not been possible to make a reliable measurement of the beam with the LEIR settings of ITH.Q08 to ITH.Q13. This is still under investigation.    εx αx βx εy αy βy Mean 11.2 0.4 8.2 8.0 0.0 4.5  - 8 -    St. Dev. 0.7 0.3 1.9 0.2 0.1 0.6 Table 8. Mean and measurement distribution widths of the measurements of the beam emittance and Twiss parameters in the LBE line (using the original PSB transport settings, not those for LEIR). β in mm/mrad, ε 2RMS in mm.mrad (calculated with threshold).  Transmissions Table 1Table 9 gives the transmissions found through the Linac for the 3 beam types delivered from Linac 3 either to the PSB or LEIR. Similar poor transmission was found for He+ beams from the ECR4 source[1]. Table 10 gives snap shot measurements of the O4+ beam intensity in the Linac.    O4+ O4+ Pb27+ Pb27+ In21+ In21+ He1+ He1+  µA  µA  µA  µA  ITL.MFC02 300  100    500  ITM.MFC01 120 40% 80 80% 80 - 270 54% ITF.TRA15 70 58% 140 89% 115 82% 160 59% ITF.TRA25 70 100% 25 18% 20 17%   ITH.TRA41 70 100% 25 100%     ‡ ‡ Table 9: Transmissions of 3 different  elements. ‡ Change in charge state – transmission given for particle numbers  O4+ for GTS-LHC in June 2005; others for ECR4 source    FC2 TRA05 FC3 TRA15 TRA25 TRA41 01/06/2005 200  95 59 46  02/06/2005 180  103 55 43  06/06/2005   115 65 50  07/06/2005 260  105 60 63  18/09/2005  180 106 61 54  22/09/2005  170  59 54 48 18/09/2005 223 180 111 55 44 40 27/10/2005  190  62 60 50 03/11/2005    81 74 62 Table 10: Examples of transmission of the O4+ beam FC2: After ITL spectrometer; TRA05: In front of RFQ; FC3 After RFQ; TRA15: After ramping cavity in ITF; TRA25: In selection spectrometer; TRA41: In ITH line. The last 5 measurements correspond to ion production with pulsed microwave power.   References [1] CE Hill, D Kuchler, R Scrivens, F Wenander, “Studies on ECR4 for the CERN Ion Programme”, Rev. Sci. Instrum. 73 (2), 564 (2002). [2] L. Dumas, R. Scrivens, “Characterization of the Lead beam of Linac3” EDMS: 704788  [3] LEIR Injection Line Studies, F.Roncarolo, G. Arduini, C.Carli, I-LHC meeting, 19 July 2005, http://cern.ch/project-i-lhc/ILHCandLEIR/Meeting_05_07_19/roncarolo_ILHC.pdf   - 9 -

Preliminary Characterization of the O4+ Beam in Linac 3

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