Transcript Overview and Charge to the Committee

Undulator BLM PDR Review
Heinz-Dieter Nuhn, SLAC / LCLS
January 24, 2008
Available Damage Data
Requirements
[System Overview]
Charge to the Committee
January 24, 2008
Undulator BLM PDR Review
1
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 absorption of a total fast-neutron fluence of
1011 n/cm2 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.
[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
PAC2005.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 results are a peak total dose of 1.0×10-9 rad/eincluding a neutron (n) fluence of 1.8×10-4 n/cm2/e-, which
translates into 1.8×105 n/cm2 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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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/cm2/e-
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Total Dose from LCLS e- Beam on C Foil
Corresponding maximum
deposited dose.
Maximum Level is
1.0×10-9 rad/e-
January 24, 2008
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Radiation Limit Estimates
1011
Neutron Fluence for 0.01 % magnet damage from Alderman et al.
n/cm2
Maximum neutron fluence in LCLS magnets from hit on 100 micron C foil from Fasso
1.8×10-4
n/cm2/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/cm2/rad
Maximum total dose in LCLS magnets for 0.01 % damage
5.5×105
rad
Nominal LCLS lifetime
20
6.3×108
Number of seconds in 20 years
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
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 last undulator due to BFW hit;
based on Fasso simulations; scaled to
Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm;
Corresponding radiation dose
1.5×105
1
Radiation dose received by last undulator by 33 full x and y scans
100
Maximum number of full BFW scans to reach 20 % a maximum dose budget
103
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 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
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Undulator BLM PDR Review
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rad/pulse
105
Ratio of peak BFW dose to maximum average dose limit
Corresponding radiation dose
n/cm2/pulse
rad
1.5×103
n/cm2/pulse
10
mrad/pulse
103
1
rad
105
Small amount of scans expected can be ignored for
Heinz-Dieter
Nuhn,MPS
SLAC
/ LCLS
damage purposes;
but might require
exception.
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 145×145 mm2 ([2×72.8]×[108.25+34.25] mm2), 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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
End of Presentation
January 24, 2008
Undulator BLM PDR Review
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]