SPEAR3 at 500mA
July 19, 2005 For the first time, on July 19, 2005, a beam line on SPEAR3 was opened and successfully operated at a current of 500 mA. This is a significant milestone along the path of bringing all the beam lines to sustained 500 mA operation. Furthermore, the previous evening saw successful first operation of SPEAR3 at 500 mA with all insertion device gaps closed.
Beam Line 6-2, which was rebuilt for 500 mA last year, was used for this test. Rocking curve measurements and radiation surveys were conducted at 25, 100, 200, 300, 400, and 500 mA. These measurements were made using both the Si(111) and Si(333) reflections to observe any changes in the rocking curve widths due to power loading on the monochromator crystals. At 500 mA, the power on the first LN monochromator crystal was calculated to be 1580 Watts with a peak power density of 14.4 Watt/mm^2. No major problems with the beam line optics were encountered and no concerns resulted from the radiation surveys. Overall, the monochromator performance was significantly better than anticipated from our modeling studies.
During the next months, we will continue to work on both the safety and operational aspects to enable 500 mA operations before the end of the 2006 run.
June 21, 2005 With help from the SLAC RF people we were able to eliminate beam instabilities that were being driven by the SPEAR RF system during the first evening of high-current operation on June 20. By increasing the chromaticity in both the horizontal and vertical planes we were able to suppress all harmful multibunch instabilities at 500 mA. The lifetime was ~9-10 h. More work will be done in 2 weeks to improve the RF system performance.
Once again, thanks to all who have worked hard to enable this great success for SPEAR 3 - Bob H
Photo from SPEAR Control Room (left to right): James Safranek, Andrei Terebilo, Jeff Corbett, Peter McIntosh, PJ Boussina, Ed Guerra, Fernando Rafael, Don Martin, Clemens Wermelskirchen, Hesham Khater (SLAC RP), Ray Russ (SLAC RP).
Shift members not shown - Stephanie Allison, Jim Sebek, Heinz Schwarz, John Schmerge, Bob Hettel
June 20, 2005 Initial tests for 500 mA operations in SPEAR3 began on Monday, June 20th. At 11:08 pm, we reached 500 mA in SPEAR3 for the first time. No significant problems were encountered. Vacuum pressure remained low, and the maximum temperature that was monitored on any component was an acceptable 64 C (on the BL 11 chamber upstream bellows). Other bellows temperatures were within expected ranges, but will be reduced with fans in the future. The lifetime at 500 mA was initially an unexpectedly high 15 hours. The high lifetime was attributed to vertical beam instability due to chamber impedance and ions. This instability was reduced substantially, and the lifetime reduced to the expected 8.5 hours, by increasing the vertical chromaticity. Although longitudinal oscillations were also seen, we believe it may be possible to attenuate them with the RF low level control system. More studies on beam instabilities and cures will be conducted on Tuesday evening, June 21st. This initial test follows the Accelerator Readiness Review (ARR) which was held on June 7, 2005. The final ARR report is expected to be completed in July. With the concurrence of the DOE and with the oversight of the SLAC safety representatives, tests to reach higher current in SPEAR were begun and will continue during the evening shifts of the next scheduled Accelerator Physics periods (July 5, 18, 19). This is an important milestone that will enable SPEAR3 to be run at its performance potential. Many thanks and congratulations to the SSRL, SPEAR3, SLAC, Radiation Protection, ES&H and DOE SSO staff who worked very hard to enable this landmark test of SPEAR3 operation.
A video which chronicles
the installation activities is available at:
SSRL entered a new era of synchrotron radiation experimentation with the
completion of the SPEAR 3 upgrade project. The SPEAR 3 storage
ring, with parameters summarized in Table 1, produces beams having one
to two orders of magnitude higher brightness and flux density than the
old SPEAR 2 ring (Table 2), accommodates several new high performance
insertion devices and beam lines, and is capable of top-off operation
by virtue of its improved at-energy injection system. Brightness for
new undulators exceeds 1018 at 5 keV. The 4-year, 58 M$ upgrade project is administered by the DOE, with ~50% joint
funding from NIH.
The project has completely replaced the SPEAR vacuum chamber,
magnets, support rafts, RF, power supplies, cable plant and shielding
tunnel floor in a 7-month shutdown period that began March 31, 2003.
480 tons of SPEAR 2 magnet girders, vacuum chambers, power supplies,
and most cables and controls were removed from the SPEAR site. Shielding,
utilities and other ancillary systems were modified, a new cable plant
was installed in trays outside the tunnel, new power supplies were installed
in a refurbished building, a new concrete floor was poured and mounting
plates for SPEAR 3 magnet and vacuum chamber support girders were installed
and aligned. Pre-assembled girders were installed in the second week
of August, followed by straight section vacuum chamber, mode-damped
RF cavity, insertion device and beam line front end component installation
in September and early October. The vacuum system was be pumped down,
cable and utility connections completed, and the ring aligned in October.
System testing took place in November and beam commissioning took place in January 2004. Beam was available for users
March of 2004.
SPEAR3 has operated at 100 mA this first user run while beam line
optical components are upgraded and radiation shielding is added for
higher current operation. The accelerator physics and engineering groups
fully utilized the first run to characterize and optimize ring lattice
and beam parameters, develop the fast orbit feedback system (having
a 4 kHz orbit acquisition rate), and to ascertain beam stability issues
that might be encountered at higher currents.