LCLS Magnet Damage Management HeinzDieter Nuhn SLAC LCLS

LCLS Magnet Damage Management Heinz-Dieter Nuhn, SLAC / LCLS June 19, 2008 · · Present Strategies for LCLS Beam Loss Monitoring Review of the Individual Magnet Irradiation Test T-493 Results of Damage Measurements Plans for follow-up Mini-Undulator Irradiation Test June 19, 2008 LCLS Magnet Damage Management 1 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

LCLS Beam Loss Monitors (BLMs) Strategies Radiation protection of the permanent magnet blocks is very important. Funds have been limited and efforts needed to be focused to minimize costs. A Physics Requirement Document, PRD 1. 4 -005 exists, defining the minimum requirements for the Beam Loss Monitors. The damage estimates are based on published measurement results and a in-house simulations. June 19, 2008 LCLS Magnet Damage Management 2 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

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. Their results imply that a 0. 01% loss in magnetization occurs after exposure to a fast-neutron fluence of 1011 n/cm 2. 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. [i] J. Alderman, et. A. , Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001) [ii] S. Sasaki, et al, Radiation Damage to Advanced Photon Source Undulators, Proceedings PAC 2005. June 19, 2008 LCLS Magnet Damage Management 3 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

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 -µm carbon foil upstream of the first undulator, has been simulated by A. Fasso [iii]. The simulations predict a peak total dose of 1. 0× 10 -9 rad/eincluding a neutron (n) fluence of 1. 8× 10 -4 n/cm 2/e-, which translates into 1. 8× 105 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] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 µm Diamond Profile Monitor, RP-05 -05, May 2005. June 19, 2008 LCLS Magnet Damage Management 4 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

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 -µm-thick carbon foil upstream of the first undulator. Maximum Level is 1. 8× 10 -4 n/cm 2/e- June 19, 2008 LCLS Magnet Damage Management 5 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Total Dose from LCLS e- Beam on C Foil Corresponding maximum deposited dose. Maximum Level is 1. 0× 10 -9 rad/e- June 19, 2008 LCLS Magnet Damage Management 6 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Radiation Limit Estimates Neutron Fluence for 0. 01 % magnet damage from Alderman et al. 1011 n/cm 2 Maximum neutron fluence in LCLS magnets from hit on 100 micron C foil from Fasso 1. 8× 10 -4 n/cm 2/e- Maximum total dose in LCLS magnets from hit on 100 micron C foil from Fasso 1. 0× 10 -9 rad/e- Ratio of neutron fluence per total dose 1. 8× 105 n/cm 2/rad Maximum total dose in LCLS magnets for 0. 01 % damage 5. 5× 105 rad Nominal LCLS lifetime 20 Number of seconds in 20 years 6. 3× 108 Maximum average permissible energy deposit per magnet Corresponding per pulse dose limit during 120 Hz operation 0. 88 7. 3 years s mrad/s µrad/pulse ~0. 01 mrad/pulse @ 120 Hz; ~1 mrad/s June 19, 2008 LCLS Magnet Damage Management 7 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Undulator Roll-Away and K Adjustment Function Pole Center Line Neutral; First; K=3. 5000; K=3. 4881; Dx=-4. 0 Dx= 0. 0 mm Vacuum Chamber Neutral; K=3. 4881; Dx= 0. 0 mm Roll-Out; Neutral; K=3. 4881; K=0. 0000; Dx=+80. 0 mmmm Horizontal Slide June 19, 2008 LCLS Magnet Damage Management 8 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Undulators on DS Girders Rolled-Out (1/100) All Undulators Rolled-In Maximum Estimated Radiation Dose from BFW Operation Maximum neutron fluence in magnets of the last undulator due to BFW hit; based on Fasso simulations; scaled to Total Charge: 1 n. C; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm; Corresponding radiation dose 1. 5× 105 1 Ratio of peak BFW dose to maximum average dose limit 100 Maximum number of full BFW scans to reach 20 % a maximum dose budget 103 Maximum neutron fluence in magnets of an undulator on same girder due to BFW hit; based on Fasso simulations; scaled to Total Charge: 1 n. C; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm; Ratio of peak BFW dose to maximum average dose limit Radiation dose received by last undulator by 33 full x and y scans Maximum number of full BFW scans to reach 20 % a maximum dose budget June 19, 2008 LCLS Magnet Damage Management rad/pulse 105 Radiation dose received by last undulator by 33 full x and y scans Corresponding radiation dose n/cm 2/pulse rad 1. 5× 103 n/cm 2/pulse 10 mrad/pulse 103 1 rad 105 The small amount of scans expected, can be ignored for Nuhn, SLAC / LCLS but might require MPS exception. 9 damage purposes; Heinz-Dieter Nuhn@slac. stanford. edu

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 by PCMUON collimator. Beam Halo Expected to be sufficiently suppressed through upstream collimation system. May require halo detection system. June 19, 2008 LCLS Magnet Damage Management 10 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

D General E LIZ A Requirements. LY RE UL F T NO 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 µrad/pulse [0. 1 µGy/pulse] and up to the maximum expected level of 10 mrad/pulse [100 µGy/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. June 19, 2008 LCLS Magnet Damage Management 11 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Monitor Requirements D IZE L EA Each BLM device will be able Rto measure the total LY L amount of absorbed dose. Fcovering the full area in U OT N front of the undulator magnets. 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. June 19, 2008 LCLS Magnet Damage Management 12 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

D Beam Loss Monitor Area 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: T NO E LIZ EA R Coverage Y LL U F (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. June 19, 2008 LCLS Magnet Damage Management 13 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

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 106) and much more sophisticated diagnostics hard and software. June 19, 2008 LCLS Magnet Damage Management 14 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

ANL Beam Loss Monitor Design BLM Mounted on BFW in Front of Undulator Segment m Bea A total of 5 BLM devices will be installed. Rendering of Detector June 19, 2008 LCLS Magnet Damage Management 15 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of W. Berg, ANL Nuhn@slac. stanford. edu

Plan View of Short Drift Undulators Segments Beam Dire ction BFW Beam Loss Monitor BPM Quadrupole June 19, 2008 LCLS Magnet Damage Management 16 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

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. June 19, 2008 LCLS Magnet Damage Management 17 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

LCLS Undulator Irradiation Experiment (T-493) The LCLS electron beam is stopped in a copper dump, and 9 samples of magnet material are positioned at different distances from the dump. The layout to achieve a range of doses is calculated using FLUKA. The radiation absorbed will be measured by dosimeters. Magnetization will be measured before and after exposure. The integrated beam current will be needed to be recorded to 10%. June 19, 2008 LCLS Magnet Damage Management 18 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Linac Coherent Light Source SLAC LINAC Injector T-493 Endstation A Undulator Tunnel Near Hall Far Hall June 19, 2008 LCLS Magnet Damage Management 19 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

T-493 Components installed ESA Beamline with copper cylinder and magnet blocks. Copper target for 13. 7 Ge. V e- Beam. Diameter: 4 inches Length: 10 inches BEAM Dosimeters positioned at in the vicinity of each block. [See presentation by Johannes Bauer] June 19, 2008 LCLS Magnet Damage Management 20 Heinz-Dieter Nuhn, SLAC / LCLS Photo courtesy of J. Bauer Nuhn@slac. stanford. edu

Magnet Block Assembly Straight-ahead mounting fixture on work bench with four magnet blocks (viewed in the direction of the beam. ) June 19, 2008 LCLS Magnet Damage Management 21 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Mounted Magnet Block Next to Heat Shield Mounting Magnet block fixture mounted with magnet next to heat for first shield. forward position with heat shield. June 19, 2008 LCLS Magnet Damage Management 22 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

ANL Delivery of 12 LCLS Undulator Magnet Blocks Material: Block Thickness: Block Height: Block Width: Material Density: Block Volume: Block Mass: Curie Point: Ne 2 Fe 14 B 9 mm 56. 5 mm 66 mm 7. 4 g/cm 3 33. 6 cm 3 248. 4 g 310 °C June 19, 2008 LCLS Magnet Damage Management 23 Heinz-Dieter Nuhn, SLAC / LCLS Photo courtesy of S. Anderson Nuhn@slac. stanford. edu

Pre-Irradiation Magnetic Moment Measurements The table shows the results of the measurement of magnetic moments for one of the magnet blocks (Serial No. 00659) as an example. The Magnetic Moments are measured with a Helmholtz-Coil. All magnetic measurements have been carried out by Scott Anderson. June 19, 2008 LCLS Magnet Damage Management 24 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Magnet Block Assembly (Top View) Top View M 9 Magnet Blocks M 8 4 Magnet blocks in forward direction 5 Magnet blocks in transverse direction 3 Magnet blocks kept for reference M 7 Copper Cylinder Heat Shield M 6 r z Beam Direction M 5 June 19, 2008 LCLS Magnet Damage Management M 1 M 2 M 3 25 M 4 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Magnet Block Assembly (View in Beam Directions) Copper Cylinder View in Beam Direction M 9 M 8 M 7 M 1 -M 4 M 6 M 5 y r Heat Shield Magnet Blocks June 19, 2008 LCLS Magnet Damage Management 26 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Experiment T-493 Shift Records Magnet Irradiation Experiment T-493 ran for 38 shifts from 7/27 -8/09/2007 June 19, 2008 LCLS Magnet Damage Management 27 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Delivered Power Delivered power levels alternated between about 125 W during Day and Swing Shifts and 185 W during Owl Shifts. During Day and Swing Shifts the experiment ran parasitically with LCLS commissioning. June 19, 2008 LCLS Magnet Damage Management 28 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Tunnel Temperature Profile The temperature in the ESA tunnel stayed between 23 -24. 6°C during the entire 12 -day data collection period. The plot shows diurnal cycle fluctuations. June 19, 2008 LCLS Magnet Damage Management 29 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Magnetic Moment Evaluations: Results Summary Shown are parameters for the 9 irradiated magnets and the Cu target the estimated neutron fluence and dose levels peak power levels temperature estimates The last two columns contain the results of the magnets’ demagnetization measurements. June 19, 2008 LCLS Magnet Damage Management 30 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Detailed FLUKA model of the experiment 13. 7 Ge. V electron beam impinging on the copper dump Computation of total dose, electromagnetic dose, neutron energy spectra Quantity scored using a binning identical to the one used for the mapping of the magnetization loss M 4 M 9 M 8 M 3 M 7 M 2 M 1 M 6 June 19, 2008 LCLS Magnet Damage Management Beam M 5 31 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of J. Nuhn@slac. stanford. edu Vollaire, SLAC

Damage Gradients FLUKA Simulations by J. Vollaire, SLAC M 1 M 2 M 4 M 3 Threshold Estimates for 0. 01 % Damage Source Deposited Energy Dose Neutron Fluence T-493 0. 17 k. J 0. 70 k. Gy 0. 070 MRad 0. 64× 1011 n/cm 2 0. 5 k. Gy 0. 05 MRad 5. 5 k. Gy 0. 55 MRad TTF-2 (Lars Fröhlich) Previous Estimate 1. 4 k. J June 19, 2008 LCLS Magnet Damage Management 32 1× 1011 n/cm 2 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Additional Evaluation: Field Map Measurements Grid Size: 26 x 31 Points = 806 Points; Point Spacing: 2 mm; Method: Hall Probe Reference Magnet SN 16673 June 19, 2008 LCLS Magnet Damage Management 33 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Field Map Measurements for M 1 Absolute Magnetic Field Amplitudes [T] June 19, 2008 LCLS Magnet Damage Management Reference Magnet Fields subtracted [T] 34 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Field Map Measurements for M 2 Absolute Magnetic Field Amplitudes [T] June 19, 2008 LCLS Magnet Damage Management Reference Magnet Fields subtracted [T] 35 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Field Map Measurements for M 3 Absolute Magnetic Field Amplitudes [T] June 19, 2008 LCLS Magnet Damage Management Reference Magnet Fields subtracted [T] 36 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Field Map Measurements for M 5 Absolute Magnetic Field Amplitudes [T] June 19, 2008 LCLS Magnet Damage Management Reference Magnet Fields subtracted [T] 37 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Example of Dose Mapping for the Four Downstream Samples Fluence [cm-2] June 19, 2008 LCLS Magnet Damage Management Total Dose [J cm-3] 38 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of J. Nuhn@slac. stanford. edu Vollaire, SLAC

Dose Profile versus Magnetization Loss Profile June 19, 2008 LCLS Magnet Damage Management 39 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Nuhn@slac. stanford. edu J. Vollaire, SLAC

Next Experiments T-493 was a measurement of the demagnetization of stand-alone magnets with no significant demagnetizing fields present. Inside an undulator, the magnet blocks will be tightly packaged next to one another and magnet blocks might experience the magnetic fields of the neighboring magnets. This scenario will be covered by the “Mini – Undulator Irradiation Test”. Ben Poling, SLAC, has designed and built a Mini-Undulator from spare LCLS Undulator magnet and pole pieces. A second Mini-Undulator (for reference) will be built before the first irradiation run. The magnetization of individual magnet pieces as well as the on-axis magnetic field of the assembled Mini-Undulators will be measured before and after the irradiation processes. Irradiation will be done similar to T-493: A radiation field will be generated by the LCLS electron beam hitting a copper target in ESA. This time, irradiation will be done in phases. June 19, 2008 LCLS Magnet Damage Management 40 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Mini-Undulator Design by Ben Poling June 19, 2008 LCLS Magnet Damage Management 41 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of B. Poling, SLAC Nuhn@slac. stanford. edu

Mini-Undulator Design by Ben Poling Made from spare LCLS undulator magnet blocks (2 x 3) and pole pieces (2 x 5). Total number of periods: 3. Gap height and period length identical to LCLS undulator. June 19, 2008 LCLS Magnet Damage Management 42 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of B. Poling, SLAC Nuhn@slac. stanford. edu

Schedule for Test Sequence Friday, May 16, 2008 20: 00 - Monday, May 19, 2008 07: 00 First irradiation run. Thursday, June 19, 2008 Irradiation Collaboration Meeting Friday, June 27, 2008 20: 00 - Monday, June 30, 2008 07: 00 Second irradiation run. Friday, July 11, 2008 20: 00 - Monday, July 14, 2008 07: 00 Third irradiation run. Friday, August 1, 2008 20: 00 - Monday, August 4, 2008 07: 00 Fourth irradiation run. MINI-UND RUN 1 MINI-UND RUN 3 MINI-UND RUN 2 MINI-UND RUN 4 D E L E CANC June 19, 2008 LCLS Magnet Damage Management 43 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

Summary The plan for monitoring and protecting the LCLS undulators from radiation was presented. Irradiation test at SLAC have been carried out in August 2007: Nine of the spare Nd 2 Fe 14 B permanent magnet pieces for the LCLS undulators have been exposed to radiation fields of various intensities under conditions that can be precisely calculated by FLUKA simulations. The total exposure time was 12. 5 days during which a copper target was hit by the 13. 7 Ge. V LCLS electron beam. The total energy of the 36. 8 x 1015 electrons that hit the target was 80 MJ. After a cool-down period, the magnetization levels of the magnets have been measured and compared with the pre-irradiation values. The difference is being compared to the (FLUKA) estimated radiation levels received. In addition, Mini-Undulators (3 periods, each) have been prepared for testing. The magnetic moments of each of the magnets as well as the on-axis magnetic fields after assembly will be measured and recorded. The plan is to irradiate one of them in up to four periods. The present plan to do the irradiation before the August shutdown will probably not work out. June 19, 2008 LCLS Magnet Damage Management 44 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu

End of Presentation June 19, 2008 LCLS Magnet Damage Management 45 Heinz-Dieter Nuhn, SLAC / LCLS Nuhn@slac. stanford. edu