January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 1 Undulator BLM PDR Review Heinz-Dieter Nuhn, SLAC / LCLS.

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  • Slide 1
  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 1 Undulator BLM PDR Review Heinz-Dieter Nuhn, SLAC / LCLS January 24, 2008 Available Damage Data Requirements [System Overview] Charge to the Committee Available Damage Data Requirements [System Overview] Charge to the Committee
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 2 Beam Loss Monitors (BLMs) Radiation protection of the permanent magnet blocks is very important. Funds are limited and efforts need to be focused to minimize costs. A Physics Requirement Document, PRD 1.4-005 has been completed, defining the minimum requirements for the Beam Loss Monitors. The damage estimates are based on published measurement results and a in-house simulations. Radiation protection of the permanent magnet blocks is very important. Funds are limited and efforts need to be focused to minimize costs. A Physics Requirement Document, PRD 1.4-005 has been completed, defining the minimum requirements for the Beam Loss Monitors. The damage estimates are based on published measurement results and a in-house simulations.
  • Slide 3
  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 3 Estimated Radiation-Based Magnet Damage The loss of magnetization caused by a given amount of deposited radiation has been estimated by Alderman et al. [i] in 2000. [i] Their results imply that a 0.01% loss in magnetization occurs after absorption of a total fast-neutron fluence of 10 11 n/cm 2 has been absorbed. A more recent report by Sasaki et al. [ii] challenges fast neutron fluence as damaging factor and, instead, proposes photons and electrons but does not provide a relation between integrated dose and damage.[ii] [i][i] J. Alderman, et. A., Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001) [ii][ii] S. Sasaki, et al, Radiation Damage to Advanced Photon Source Undulators, Proceedings PAC2005. The loss of magnetization caused by a given amount of deposited radiation has been estimated by Alderman et al. [i] in 2000. [i] Their results imply that a 0.01% loss in magnetization occurs after absorption of a total fast-neutron fluence of 10 11 n/cm 2 has been absorbed. A more recent report by Sasaki et al. [ii] challenges fast neutron fluence as damaging factor and, instead, proposes photons and electrons but does not provide a relation between integrated dose and damage.[ii] [i][i] J. Alderman, et. A., Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001) [ii][ii] S. Sasaki, et al, Radiation Damage to Advanced Photon Source Undulators, Proceedings PAC2005.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 4 Estimate of Neutron Fluences from LCLS e - Beam The radiation deposited in the permanent magnets blocks of the LCLS undulator, when a single electron (e - ) strikes a 100-m carbon foil upstream of the first undulator, has been simulated by A. Fasso [iii].[iii] The results are a peak total dose of 1.010 -9 rad/e - including a neutron (n) fluence of 1.810 -4 n/cm 2 /e -, which translates into 1.810 5 n/cm 2 for each rad of absorbed energy. These numbers are based on peak damage results and should therefore be considered as worst case estimates. [iii][iii] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 m Diamond Profile Monitor, RP-05-05, May 2005. The radiation deposited in the permanent magnets blocks of the LCLS undulator, when a single electron (e - ) strikes a 100-m carbon foil upstream of the first undulator, has been simulated by A. Fasso [iii].[iii] The results are a peak total dose of 1.010 -9 rad/e - including a neutron (n) fluence of 1.810 -4 n/cm 2 /e -, which translates into 1.810 5 n/cm 2 for each rad of absorbed energy. These numbers are based on peak damage results and should therefore be considered as worst case estimates. [iii][iii] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 m Diamond Profile Monitor, RP-05-05, May 2005.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 5 Simulated Neutron Fluences for LCLS e - Beam on C Foil Simulated neutron fluences in the LCLS undulator magnets (upper jaw) from a single electron hitting a 100-m-thick carbon foil upstream of the first undulator. Maximum Level is 1.810 -4 n/cm 2 /e - Simulated neutron fluences in the LCLS undulator magnets (upper jaw) from a single electron hitting a 100-m-thick carbon foil upstream of the first undulator. Maximum Level is 1.810 -4 n/cm 2 /e -
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 6 Total Dose from LCLS e - Beam on C Foil Corresponding maximum deposited dose. Maximum Level is 1.010 -9 rad/e - Corresponding maximum deposited dose. Maximum Level is 1.010 -9 rad/e -
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 7 Radiation Limit Estimates Neutron Fluence for 0.01 % magnet damage from Alderman et al.10 11 n/cm 2 Maximum neutron fluence in LCLS magnets from hit on 100 micron C foil from Fasso1.810 -4 n/cm 2 /e - Maximum total dose in LCLS magnets from hit on 100 micron C foil from Fasso1.010 -9 rad/e - Ratio of neutron fluence per total dose1.810 5 n/cm 2 /rad Maximum total dose in LCLS magnets for 0.01 % damage5.510 5 rad Nominal LCLS lifetime20years Number of seconds in 20 years6.310 8 s Maximum average permissible energy deposit per magnet0.88mrad/s Corresponding per pulse dose limit during 120 Hz operation7.3rad/pulse ~0.01 mrad/pulse @ 120 Hz; ~1 mrad/s
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 8 Maximum Estimated Radiation Dose from BFW Operation Maximum neutron fluence in magnets of last undulator due to BFW hit; based on Fasso simulations; scaled to Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 m; RMS Beam radius 37 m; 1.510 5 n/cm 2 /pulse Corresponding radiation dose1rad/pulse Ratio of peak BFW dose to maximum average dose limit10 5 Radiation dose received by last undulator by 33 full x and y scans100rad Maximum number of full BFW scans to reach 20 % a maximum dose budget10 3 All Undulators Rolled-In Maximum neutron fluence in magnets of undulator on same girder due to BFW hit; based on Fasso simulations; scaled to Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 m; RMS Beam radius 37 m; 1.510 3 n/cm 2 /pulse Corresponding radiation dose10mrad/pulse Ratio of peak BFW dose to maximum average dose limit10 3 Radiation dose received by last undulator by 33 full x and y scans1rad Maximum number of full BFW scans to reach 20 % a maximum dose budget10 5 Undulators on DS Girders Rolled-Out (1/100) Small amount of scans expected can be ignored for damage purposes; but might require MPS exception.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 9 Radiation Sources Possible reasons for generating elevated levels of radiation are Electron Beam Steering Errors Will be caught and will lead to beam abort. Unintentional Insertion of Material into Beam Path Will be caught and will lead to beam abort. Intentional Insertion of Material into Beam Path BFW operation Is expected to produce the highest levels. May only be allowable when all down-stream undulators are rolled-out and beam charge is reduced to minimum. Screen insertion May only be allowable when all undulators are rolled-out and beam charge is reduced to minimum. Background Radiation from Upstream Sources including Tune-Up Dump Expected to be sufficiently suppressed through PCMUON collimator. Beam Halo Expected to be sufficiently suppressed through upstream collimation system. May require halo detection system.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 10 General Requirements One BLM device will be mounted upstream of each Undulator Segment The BLM will provide a digital value proportional to the amount of energy deposited in the device for each electron bunch. The monitor shall be able to detect and measure (with a precision of better than 25%) radiation levels corresponding to magnet dose levels as low as 10 rad/pulse [0.1 Gy/pulse] and up to the maximum expected level of 10 mrad/pulse [100 Gy/pulse]. The monitor needs to be designed to withstand the highest expected radiation levels of 1 rad/pulse without damage. The radiation level received from each individual electron bunch needs to be reported after the passage of that bunch to allow the MPS to trip the beam before the next bunch at 120 Hz.
  • Slide 11
  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 11 Monitor Requirements Each BLM device will be able to measure the total amount of absorbed dose covering the full area in front of the undulator magnets. The magnet cross section seen by the beam is 56.5 mm wide by 66 mm high. In their home position, the magnets are located between 6.8 mm and (6.8+66) mm= 72.8 mm both, above and below the beam axis. Their horizontal extend is 28.25 mm. They are expected to be moved during operations by 80 mm in positive x-direction and by 6 mm in the opposite direction, which sets the limits horizontal coverage range to +108.25 mm to -34.25 mm. The detector material thus needs to cover an area of about 145145 mm 2 ([272.8][108.25+34.25] mm 2 ), but is allowed a horizontal cut-out of 7 mm so that it can be mounted without the need for breaking vacuum. Each BLM device will be calibrated based on the radiation generated by the interaction of a well known beam with the BFW devices. The calibration geometry will be simulated using FLUKA and MARS to obtain the calibration factors, i.e., the ratio between the maximum estimated damage in a magnet and the voltage produced by each BLM device.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 12 Beam Loss Monitor Area Coverage Main purpose of BLM is the protection of undulator magnet blocks. Less damage expected when segments are rolled-out. One BLM will be positioned in front of each segment. Its active area will be able to cover the full horizontal width of the magnet blocks Two options for BLM x positions will be implemented to be activated by a local hardware switch: (a) The BLM will be moved with the segment to keep the active BLM area at a fixed relation to the magnet blocks. (b) The BLM will stay centered on the beam axis to allow radiation level estimates in roll-out position. Main purpose of BLM is the protection of undulator magnet blocks. Less damage expected when segments are rolled-out. One BLM will be positioned in front of each segment. Its active area will be able to cover the full horizontal width of the magnet blocks Two options for BLM x positions will be implemented to be activated by a local hardware switch: (a) The BLM will be moved with the segment to keep the active BLM area at a fixed relation to the magnet blocks. (b) The BLM will stay centered on the beam axis to allow radiation level estimates in roll-out position.
  • Slide 13
  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 13 BLM Purpose The BLM will be used for two purposes A: Inhibit bunches following an above-threshold radiation event. B: Keep track of the accumulated exposure of the magnets in each undulator. Purpose A is of highest priority. It will be integrated into the Machine Protection System (MPS) and requires only limited dynamic range from the detectors. Purpose B is desirable for understanding long-term magnet damage in combination with the undulator exchange program but requires a large dynamic range for the radiation detectors (order 10 6 ) and much more sophisticated diagnostics hard and software. The BLM will be used for two purposes A: Inhibit bunches following an above-threshold radiation event. B: Keep track of the accumulated exposure of the magnets in each undulator. Purpose A is of highest priority. It will be integrated into the Machine Protection System (MPS) and requires only limited dynamic range from the detectors. Purpose B is desirable for understanding long-term magnet damage in combination with the undulator exchange program but requires a large dynamic range for the radiation detectors (order 10 6 ) and much more sophisticated diagnostics hard and software.
  • Slide 14
  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 14 Additional Loss Monitors Other Radiation Monitoring Devices Dosimeters Located at each undulator. Routinely replaced and evaluated. Segmented Long Ion Chambers Investigated (Quartz)-Fibers Investigated Non-Radiative Loss Detectors Pair of Charge Monitors (Toroids) One upstream and one downstream of the undulator line Used in comparator arrangement to detect losses of a few percent Electron Beam Position Monitors (BPMs) Continuously calculate trajectory and detect out-of-range situations Quadrupole Positions and Corrector Power Supply Readbacks Use deviation from setpoints Estimate accumulated kicks to backup calculations based on BPMs.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 15 Other Considerations Vacuum System The BLM will not be part of the LCLS Undulator vacuum system. Alignment The active volume of each BLM needs only rough alignment to cover the downstream magnet blocks in all roll-in/out locations.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 16 Other Radiation Monitoring Devices In addition to the BLMs, the use of TLD monitor segmented Long Ion Chambers (segmented LIONs), and Fibers shall be investigated.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 17 Charge to the Committee The LCLS ANL and SLAC BLM support groups have developed a Beam Loss Monitor System to support purpose A, i.e., protect the undulator magnets from above-threshold radiation events. The committee is charged with determining that the Beam Loss Monitor System is ready to enter the final design stage. The committee is asked to evaluate the following: 1.Is the Beam Loss Monitor System sufficient for the operational needs of the Undulator System? 2.Have safety hazards been appropriately identified and mitigated? 3.Is the interface to the rest of the Undulator system understood and controlled? Are interfaces to other neighboring systems understood and controlled? 4.Is there a plan in place for assembly, checkout, startup, commissioning, and maintenance? 5.Are the budget and schedule for fabrication, installation and commissioning of the BLM complete and adequate? The committee is asked to report on its findings in a written report within a reasonable time following the review. All suggestions and comments are welcome.
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  • January 24, 2008 Heinz-Dieter Nuhn, SLAC / LCLS Undulator BLM PDR Review Nuhn@slac.stanford.edu 18 End of Presentation

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