RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-8. Accelerator

Commissioning of the Laser Ion Source for RHIC EBIS †M. Okamura＊1,＊2 and T. Kanesue＊1
The electron beam ion Source (EBIS)-based heavy ion
preinjector (RHIC-EBIS) served for RHIC and NASASpace Radiation Laboratory (NSRL) at Brookhaven
National Laboratory (BNL)1). The NSRL is a facility thatsimulates the effect of galactic cosmic radiation (GCR),
which consists of highly energetic heavy ions of various
kinds in space. The RHIC-EBIS is required to provide fastswitching between heavy-ion species for this purpose. Anew laser ion source (LIS), named “LION,” is funded byNASA to expanding the range of ion species available forfast switching. Fast switching can be accomplished byswitching the laser-irradiation position on different target
materials2,3).
LION consists of a high-power pulsed laser, a target
chamber, a 3-m-long plasma drift region with a solenoid
magnet, and an extraction chamber. The ion extraction
voltage may be up to 40 kV. The laser is equipped with two
identical Q-switched Nd:YAG laser oscillators (850 mJ/6 ns
at FWHM, 1062 nm wavelength ). A built-in laser combiner
merges the two laser beams into one laser path to aim at thesame position. The laser is focused on a solid state target
plate. The laser spot on the target is 5 mm in diameter.
Different laser energies in the range 500 ~ 700 mJ is used
depending on the species to achieve singly charged ions. Ina target chamber, several targets are held on a tungsten
target holder, as shown in Fig.1, which is mounted on anx-y linear stage. The stage allows the laser to irradiate
different positions on different target materials. The
solenoid magnet is used to reduce the diverging angle of theexpanding plasma. The typical magnetic field to be used isonly several Gauss. With this drift length, an ion beam witha pulse width of a few hundred microseconds is achieved.
The commissioning of the beam was started on March 7,2014 with an Fe target. LION was isolated from the EBIS
beam line to prevent RHIC gold run as a precaution. Theplatform voltage was set to 12 kV for the first beam test.
The Fe beam extracted from the LION was very close towhat we expected. No breakdown caused by the generated
plasma was observed.
From March 14, the operation mode of EBIS wasadjusted for LION. The transport line and the EBIS
injection timing were investigated to capture ions. The firstbeam extracted from the EBIS was observed on March 16.
On March 26, the first beam at the NSRL target room
was observed with a Ta beam. The beam intensity wassufficiently high for an NSRL run. Hence, we decided touse the LION for an NSRL run.
†Condensed from the article in Proceeding of IPAC2014
Collider-Accelerator Department, BNL＊2
RIKEN Nishina CenterFig. 1 Target holder with Au, C, Fe, and Ta targets from leftto right. Aluminium plates are used to hold the Au target.
The user operation with LION was started from March 27,
and it was very successful. Since then, LION has provided
most of beams for NSRL. This is beyond our initial plan touse the LIS for several days for commissioning. After all, C,Si, Ti, Fe, Ta, and Au beams are provided for NSRL userruns.
As predicted, lighter species show less tolerance of thenumber of shots on a single spot to maintain long-term
stability. The target scan step of 0.1 mm / 80 s was used forC while 0.1 mm / 540 s was used for Fe. These numbers areconservative and should be investigated further for efficientuse of target materials.
The EBIS injection efficiency and the EBIS setting had
been improved continuously. Since June 3, LION with aplatform voltage of 18 kV started to provide Au beams for
RHIC instead of providing beams for NSRL. Until the endof the run, LIS has been working continuously. The target
scan step for the Au target was set at 0.5 mm / 20 s. Thetarget was 1-mm thick with 25 mm x 25 mm area, and thetarget consumed approximately 50% of its life.
LION was used to provide C, Si, Ti, Fe, Ta, and Au
beams for NSRL and RHIC user operation. This is the first
LIS for low-charge-state ion production to be combinedwith an EBIS-type heavy-ion source for long term user
operation.
References

1) J. Alessi et al., New York, 2011, p. 1966 (2011)2) T. Kanesue et al., Rev. Sci. Instrum., 79, 02B102 (2008)
3) K. Kondo et al., Rev. Sci. Instrum., 81, 02A511 (2010)(2000)＊1- 196 -

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