A high acceleration gradient deuteron linac for the EURISOL driver

J. Rodnizki, D. Berkovits and A. Facco
1/5/2006
Introduction
In this study we propose for the EURISOL driver injector a proton / deuteron linac, up to 60 MeV, based on the SARAF linac. The linac is optimized to deliver a 4 mA CW deuterons beam at 176 MHz, with a moderate increase in beam emittance.  The lattice includes an ion source with output energy of 20 keV/u, LEBT, RFQ with output energy of 1.5 MeV/u, MEBT and a SC linac. The MEBT matches the RFQ output beam in to the SC linac using three quadropole magnets and nondestructive beam diagnostics. Two linac lattices were considered. One with only two cavity-type at 176 MHz were the linac is composed of two cryostats each of 6 HWR of 0=0.09 and seven cryostats each of 8 HWR of 0=0.15.  The cryostat lattice includes three periods each consists of first a cavity then a solenoid and a second cavity at the end of the period. The second lattice consists of three cavity-type. This lattice is similar to the SARAF linac up to 50 MeV with an extension based on the LNL 0=0.31 cavities. In both lattices the HWR bore diameter is 30 mm while in the solenoids it is 38 mm. We have simulated the linac starting at the RFQ exit using a 40000 particle distribution obtained by Accels' simulation of the RFQ. We have used for the simulations Accels' HWR 3D fields and the simulation code TRACK (ANL).   

Beam dynamics simulation results
The simulation results for the two-cavity-type linac are shown in table 1.
The results show that the deuteron energy gain at the 7th cryostat decreases, due to the decrease in TTF, to 80% of the maximum. We didn't simulate protons yet through this lattice but it is clear that the last two cryostats will have even smaller acceleration efficiency for protons. If the next Spoke cavity of 0=0.36 is efficient enough for deuterons at 58 MeV (=24.3%) the driver efficiency may increase (mainly for protons) if the HWR linac will end after the 6th 0=0.15 cryostat. 
The simulation results for the two-cavity-type lattice includes misalignments values, as described at the EURISOL April 2006 meeting at Soreq, are shown in figure 1. In all plots the upper "max" envelops are of 40000 particles.

Table 1: Typical beam values as function of linac length for two modules of 0=0.09 and up to seven modules of 0=0.15.  

position (from RFQ exit) [m]
Energy [MeV/u]
4  RMS long. emittance [ keV/u-ns] 
4  RMS normalized transverse emittance x [ cm mrad]
4  RMS normalized transverse emittance y [ cm mrad]
RFQ exit






0.0        
1.5
3.14
0.0699             
0.0711
End of 0=0.15 cryostat 





4th 
21.1
21.1
3.53
0.0782
0.0794
5th 
24.9       
25.1
3.51
0.0818             
0.0760
6th 
28.7       
29.0
3.61
0.0785             
0.0777
7th 
32.5      
32.5
3.75
0.0755                      
0.0814

The simulation results for the three-cavity-type linac are shown in table 2.

Table 2: Typical beam values as function of linac length for two modules of 0=0.09, five modules of 0=0.15 and two modules of 0=0.31 cryostat.

Length from RFQ exit [m]
Energy [MeV/u]
4  RMS long. emittance [ keV/u-ns] 
4  RMS normalized transverse emittance x [ cm mrad]
4  RMS normalized transverse emittance y [ cm mrad]
RFQ exit






0.0        
1.5
3.14
0.0699             
0.0711
End of 0=0.15 cryostat





4th 
21.3               
21. 4
3.19
0.0839             
0.0887
5th 
25.1       
25.3        
3.21            
0.0901             
0.0811
End of 0=0.31 cryostat





1st 
29.4       
29.8       
3.15
0.0914             
0.0839
2nd 
33.6       
34.5
3.34
0.0827             
0.0903

The simulation results for the three-cavity-type lattice, including misalignments, are shown in figure 2.   


Figure 1a: TRACK simulation of the SARAF lattice extended to 60 MeV.

Figure 1b: TRACK simulation of misalignments for the SARAF lattice extended to 60 MeV.




Figure 1c: TRACK simulation of misalignments for the SARAF lattice extended to 60 MeV TRACK output.


Figure 2a: TRACK simulation of the SARAF lattice extended by LNL 0.31 cavities to 90 MeV.



Figure 2b: TRACK simulation of miss alignments for the SARAF lattice extended by LNL 0.31 cavities to 90 MeV.

Figure 2c: TRACK simulation of miss alignments for the SARAF lattice extended by LNL 0.31 cavities to 90 MeV.