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NSLS-II Storage Ring Parameters

Photo of NSLS-II wigglers

General Description

National Synchrotron Light Source II is a medium energy (3.0 GeV) electron storage ring designed to deliver photons with high average spectral brightness exceeding 1021 ph/s in the 2 – 10 keV energy range and a flux density exceeding 1015 ph/s in all spectral ranges. This performance requires the storage ring to support a very high-current electron beam (I = 500 mA) with a very small horizontal (down to 0.5 nm-rad) and vertical (8 pm-rad) emittance. The electron beam will be stable in its position (<10% of its size), angle (<10% of its divergence), dimensions (<10%), and intensity (±0.5% variation).

Radiation Sources

Continuing the tradition established by the NSLS, the NSLS-II radiation sources span a very wide spectral range, from the far infrared (down to 0.1 eV) to the very hard x-ray region (>300 keV). This is achieved by a combination of bending magnets, three-pole wigglers, and insertion device (ID) sources. The basic parameters characterizing the NSLS-II IDs and bending magnet sources are listed in Table 2. Here, SCU stands for superconducting undulator, CPMU for cryogenic permanent magnet undulator, EPU for elliptically polarized undulator, PMW for permanent magnet wiggler, SCW for superconducting wiggler, and 3PW for three pole wiggler.  All of the source properties described in Tables 1 and 2 assume a fully-damped horizontal emittance of 0.55 nm-rad. This is the performance goal for the NSLS-II storage ring when operating with a full complement of insertion devices, including damping wigglers. The initial horizontal emittance of 0.9 nm-rad will be somewhat larger than this, due to the fact that only a limited number of insertion devices, including three 7 m damping wigglers, will be installed at the start of operations.

Storage Ring Lattice

The NSLS-II storage ring lattice consists of 30 double-bend achromat (DBA) cells that will accommodate at least 58 beamlines for user experiments, distributed by type of source as follows:

  • 15 low-beta ID straights for undulators or superconducting wigglers
  • 12 high-beta ID straights for either undulators or damping wigglers
  • 31 BM ports providing broadband sources covering the IR, VUV, and soft x-ray ranges. Any of these ports can alternatively be replaced by a 3PW port covering the hard x-ray range.
  • 4 BM ports on large gap (90 mm) dipoles for very far-IR

Multiple IDs may be installed in a single straight section for additional beamline capacity.

The NSLS-II ring circumference is 792 m. Beamlines up to 72 m long can be built within the ring building in sectors with the extended experimental floor width, as compared to 66 m long beamlines in sectors with the standard floor width. Extra-long (>200 m) beamlines extending beyond the exterior walkway with endstations located outside the ring building are also possible, as can be seen in Figure 1. For more detailed parameters of the NSLS-II storage ring, see the NSLS-II Source Properties and Floor Layout documentation (PDF).

Table 1. Main parameters of the storage ring

  NSLS-II High Brightness
Ring energy (GeV) 3
Ring current (mA) 500
Ring circumference (m) 792
Number of DBA Cells 30
Number of 9.3 m straights 15
Number of 6.6 m straights 15
βh in 9.3 m straights (m) 20.1
βv in 9.3 m straights (m) 3.4
βh in 6.6 m straights (m) 1.8
βv in 6.6 m straights (m) 1.1
Vertical emittance (nm-rad) 0.008
Horizontal emittance (nm-rad) 0.55
RMS energy spread (%) 0.1
RMS pulse length (ps) 15-30
Time between bunches (ns) 2
Revolution period (us) 2.64
RF frequency (MHz) 500
Number of RF buckets 1320
Number of bunches 1056
Average bunch current (mA) 0.47
Average bunch charge (nC) 1.25
NSLS-II storage ring

Table 2. Basic Parameters of Current and Some Potential NSLS-II Radiation Sources for Operation at 3.0 eV and 500 mA

Table 2

Figure 1. Experimental floor space. Red lines indicate possible long beamlines.

experimental floor space