Top-up operation experience at APS. Page: 1 of 5
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TOP-UP OPERATION EXPERIENCE AT APS *
L. Emery, M. Borland, ANL, Argonne, IL S p e
Abstract We found that if the dipole magnets a Q supplies
The Advanced Photon Source (APS) is a 7-GeV, third- are operating normally, no configuration error magnet
generation synchrotron radiation source. To provide more fault can produce an accident. Simulations gave a stronger
stable beam for users, in September 1998 we began com- conclusion, that even with a shorted dipole and other er-
missioning a new operating mode called "top-up:' In this rors, one cannot have stored beam while extracting injected
mode, the beam current does not decay but is maintained beam down a photon beamline. Thus, we ensure the top-up
at a high level using frequent injection, while photon shut- safety with an interlock that inhibits injection with shutters
ters are open and photon beams are delivered to users. The open if there is no stored beam.
hardware, software, and safety requirements for top-up will The simulations used a series of lattices and conserva-
be reported. Safety issues related to injection with open tive (i.e., accident-enhancing) choices of magnet faults. All
photon shutters are covered in companion papers in this scenarios involved a shorted dipole of variable strength.
conference. Present operational experience includes test- Other faults considered simultaneously were hypothetical
ing aspects of top-up injection and delivering beam to X- mis-set quadrupoles, worst-case dipole steering from mal-
ray users for a few hours with fractional current stability of functioning nearby multipoles, and injected beam energy
10-3. We expect to run several top-up operation shifts in error. To limit the possible steering from multipoles, we
Spring 1999. Issues of importance are orbit and emittance ran the simulations for 6 GeV; a hardware interlock on the
transients during the injection and scheduling of injection dipole power supply enforced this minimum energy.
pulses for the convenience of users. Because of the importance of aperture location and di-
mensions in limiting the possible trajectories of the injected
I INTRODUCTION beam, we require controlled drawings and documents list-
ing the relevant apertures (those used in the tracking simu-
Top-up injection refers to injecting with photon shutters lations). Tolerances for the placement of apertures (deter-
open to deliver a near-constant stored beam current. This mined from tracking) are also documented. Routine checks
will improve X-ray beam stability through a constant heat of the placement of apertures are required. Since apertures
load on X-ray optics and eliminate current-dependent sys- in the SR vacuum chambers and photon beamline are not
tematics of storage ring (SR) beam diagnostics. visible from the outside, this is done indirectly using survey
A relative current stability of 10-4 is our long-term goal. measurements of the magnets and photon beamline safety
We have acheived this for a few hours of running during shutter, and using measurement gauges to verify the posi-
machine studies (shutters not necessarily open). A lower tion of vacuum chambers in magnets.
stability of 10-3 was achieved routinely, and has been de-
livered to users for several hours on a trial basis. 3 OTHER OPERATIONAL CONCERNS
An equally important beam quality aspect of top-up in-
jection is the beam disturbance that may be caused by the The injector produces a single bunch at 2 Hz, with a nom-
injection process. Though any closed orbit or emittance inal charge of 1 nC and design maximum of 20 nC. For
disturbance is damped out after several tens of millisec- 10-4 current stability, the injected charge is about 0.04 nC,
onds through synchrotron radiation damping or the decay at the bottom range of the beam transport line diagnostics
of pulsed magnet fields, these disturbances affect most X- sensitivity. Beam diagnostics with higher sensitivity are
ray experiments. We will report on steps taken to reduce the planned. In the meantime, scrapers in the transport line can
impact of these injection transients on X-ray experiments. be used to scrape down to the required low charge.
Permanent magnets in insertion devices (IDs) can be de-
2 RADIATION SAFETY magnetized by a large radiation dose. Injected beam losses
are highest at the ID vacuum chambers (VCs). In top-up
Photon shutters are normally closed during injection to operation the IDs are closed, almost touching the VCs.
block any injected beam particles from escaping the SR en- Shielding cannot reduce the dose at the downstream end
closure and entering the experiment hall, where they would of the ID since a radiation shower travels inside the beam
constitute a radiation hazard. (This might occur, say, due to pipe and through the thin (1 mm) Al chamber. Injection
a short in a dipole magnet with a photon port.) Prevention losses will have to be closely monitored. We plan to install
of such an accident is the main safety issue in top-up and radiation monitors on the ID VC to serve as diagnostics.
was the subject of extensive studies [1, 21. SR injection uses a four-magnet kicker bump lasting less
Work supported by U.S. Department of Energy, Office of Basic En- than one turn, as well as two septa at the end of the transfer
ergy Sciences, under Contract No. w-31-109-ENG-38. line. Poor injection efficiency is typically due to variation
The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38
with the U.S. Department of Energy. The U.S. Government retains for itself. and others acting on its behalf, a paid-up, nonexclusive. irrevocable worldwide license in said
article to reproduce, prepare derivative works. distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
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Emery, L. Top-up operation experience at APS., article, March 31, 1999; Illinois. (digital.library.unt.edu/ark:/67531/metadc620418/m1/1/: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.