Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 50 (2017)

Simultaneous acceleration of ions with different charge-to-mass ratio
in the SLOWRI post accelerator
S. Arai䠆1 and M. Wada䠆1
To accelerate beams from SLOWRI, 1) a post accelerator
consisting of a split-coaxial RFQ, a medium energy beamtransport (MEBT) and an interdigital-H linac (IH) has been
designed. 2) The main parameters of the accelerator are
listed in Table 1. For the sake of experimental convenience,
there is a demand to simultaneously accelerate the sameelement having different charges. Then, the transmission
efficiencies of ions with charge-to-mass ratio (q/A)
deviating from the design value of 0.125 are investigated bybeam simulations. A calculation code PARMTEQ is usedfor RFQ simulation, and a calculation code TRACEP 3) isused for MEBT and IH simulations. PARMTEQ cannot
calculate the motion of ions with q/A as a variable without
Table 1. Main parameters of the SLOWRI post accelerator.
Parameter
Frequency (MHz)
Mass to charge ratio: A/q
Normalized emittance (ʌ·cm mrad)
Energy (MeV/u)
Synchronous phase (deg)Electrode voltage (kV)
Number of cavities
Number of acceleration cells
in each cavity
Length (m)Cavity diameter (cm)

RFQ
79
80.06
0.005 - 0.5-25
81.5
1MEBT
79
80.06
0.5-90
82.5
1IH
158
80.06
0.5 - 5-25
140-250
18244

48 - 16

5.19
40

2.52
25

23.48
40Fig. 1. From top to bottom, results of RFQ, MEBT and IH.

changing the vane parameters from the design values.
However, the calculation with vane voltage as a variable ispossible. Since the vane voltage is inversely proportional tothe charge-to-mass ratio, for example, the simulation result
obtained with a normalized vane voltage (Vn=V/Vdesign) of
1.08 can be regarded the same as the simulation result
obtained with Vn=1 and q/A=0.135. By using the above
characteristic, a beam simulation of the post accelerator,
which accelerates ions with q/A different from the design
value, is conducted using 500 ions as follows: 1) The
operating parameters such as accelerating voltage,
Q-magnet field strength, etc. are fixed to accelerate thedesign ions. 2) The phase space distributions of the output
ions of RFQ calculated with Vn as a variable and the q/A
corresponding to Vn are used as input data for MEBT
simulation. 3) The phase space distributions and q/A of theoutput ions of MEBT are used as input data for IH
simulation. Figure 1 shows the simulation result for theq/A=0.135 ions. From the number (297) of ions distributedin the IH output phase spaces, the beam transmission isfound to be 59.4%. By using the above method, beam
䠆1RIKEN Nishina Center- 161 -transmission is examined in the range of 0.1125ӊq/Aӊ
0.1525. The result drawn in red in Fig. 2 is obtained byassuming that the input energy of RFQ is 5 keV/u even forions different from design ions. However, the kinetic energy
per nucleon of ions extracted from the same ion source
depends on the charge number of ions. The result ofconsidering this is drawn in green in Fig. 2. The full widthat half maximum of the transmission indicated by the green
line is mainly determined by the acceleration characteristicof RFQ related to the input energy of ions. 4)

Fig. 2. The q/A dependence of the transmission.
References1) M. Wada et al., Hyp. Int. 199, 269-277 (2011).
2) S. Arai, RIKEN-NC-AC-3, 2016.
3) S. Yamada, NIRS HIMAC program manual No. 1, May, 1990,
unpublished.
4) S. Arai, RIKEN-NC-AC-6, 2017.