Transcript Second Harmonic capture in the IPNS RCS: Transition from

Second Harmonic capture in the IPNS RCS:
Transition from SH to fundamental rf operation during the
acceleration cycle using CAPTURE_SPC
Jeff Dooling
Presented at The Ninth
Second Harmonic RF/Low Output-Impedance Amplifier
Collaboration Meeting
Argonne National Laboratory,
June 14-15, 2004
Motivation
• Currently, we believe our ferrite will not allow second harmonic (SH) rf
operation up to the maximum acceleration frequency—
5.15 MHz x 2 = 10. 3 MHz
• Most loss occurs at injection
• Can we run SH early in cycle using the new 3rd cavity, switching to
fundamental later and still realize a net increase in current?
Guide field, b, and Vrf
0.8
1.0
a)
proton velocity relative to c
0.9
-- frequency data
0.7
0.8
0.7
b(t)
0.6
B(t)
0.5
0.5
extraction
time
0.4
0.4
0.3
0.3
0
8
10
time (ms)
2
4
6
2
4
6
8
time (ms)
12
14
12
14
16
25
b)
Vrf (kV)
20
15
10
5
0
0
PM
signal
c)
10
16
t
magnetic field (T)
0.6
Frequency and energy vs. time
600
12
t = 4.7 ms
10
8
400
W
300
6
200
f
4
2
100
0
0
0
2
4
6
8
10
time (ms)
12
14
W (MeV)
f (MHz)
500
2f
Bucket Area in the RCS
1.0
=0.55
12
 =0.55, =0, spc (3.6x10 inj)
 =0.55, =0, no spc, Pred. Cor.
 =0.55, =0, no spc, CAPT
bucket area (eV-sec)
0.8
0.6
fund.
0.4
=0, spc (3.6x1012inj)
=0, no spc, Pred. Cor.
=0, no spc, CAPT
0.2
0
0
2
4
6
8
time (ms)
10
12
14
I b ( )
40
1
4
2
V ( )
2
20
0
0
-20
I b ( )
b)
1
4
2
V ( )
40
20
2
0
0
Voltage (kV)
Bunch Current (A)
6
-20
6
=3.150
rad
2
I b ( )
c)
40
1
4
V ( )
2
20
0
0
-20
-3
-2
-1
0
 (rad)
1
2
3
Voltage (kV)
Bunch Current (A)
Fundamental and SH
voltage and current profiles
from Hofmann-Pedersen
elliptical distributions
b)
Voltage (kV)
Bunch Current (A)
6
Maximum bucket area vs. maximum bunching factor
1.2
bucket area (eV-sec)
1.0
0.8
0.6
0.4
0.2
0
0
2
4
6
8
10
time after injection (ms)
12
14
Capture Efficiency and Fundamental-SH phase
angle, 
0
=0.55, =0
-0.2
96
=0.55, = m
b)
-0.4
 (rad)
efficiency (%)
100
92
t = 8 ms
t = 10 ms
a)
-0.6
-0.8
fundamental
88
m
-1.0
-1.2
0
2
6
4
time (ms)
8
10
0
2
4
6
8
10
time (ms)
12
14
Goal: Full SH rf for the full acceleration cycle
(the following animation includes the phase ramp)
Potential benefit
100
90
Lost charge (nC)
80
0.5x1012 protons
70
60
CAPTURE
50
40
presently
inject
30
20
0.5 0.6
0.7
0.8 0.9
1.0
Injected charge (C)
1.1 1.2
Modify CAPTURE to include (t)
*
CALL CPfield( tn, evol,
fnuS,
omegaS,
&
flagrf, Nrfpoints, rf_time, rf_evol,
&
rf_sh_phase,
Imax,
secHarmPhase )
Delta versus time
0.60
*
0.50
V ratio
0.40
0.30
0.20
*
CALL CPfield( tn, evol,
fnuS,
omegaS,
&
flagrf, Nrfpoints, rf_time, rf_evol,
&
rf_sh_phase,
rf_sh_ampl, Imax,
&
secHarmPhase,
secHarmFactor )
*
0.10
0.00
0.00
2.00
4.00
6.00
8.00
tim e (m s)
10.00
12.00
14.00
16.00
Two cases
CASE 1:
CASE 2:
• Run SH at d=0.55 for
the first 4 ms
• Ramp SH to 0 between
4 and 5 ms
• Leave Vrf unchanged
• Run SH at d=0.55 for
the first 4 ms
• Ramp SH to 0 between
4 and 5 ms
• Ramp Vrf to 1.55*Vrf
between 5 and 6 ms
Ramping Vrf up after 5 ms
RF Voltage vs time
40.00
35.00
RF Voltage (kV)
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0.00
2.00
4.00
6.00
8.00
time (ms)
10.00
12.00
14.00
16.00
Second Harmonic rf early, =0.55
ramping off between 4 and 5 ms
Second Harmonic rf early, =0.55; ramping off between 4 and 5
ms; ramping back on in the fundamental between 5 and 6 ms (to
1.55*Vrf)
1.00
Vrf on
0.96
0.94
SH only
0.92
0.90
0.88
0
2
4
6
time (ms)
8
10
250
200
loss rate (A.U.)
Transmission
efficiency and
loss rate
efficiency
0.98
150
100
Vrf on
SH only
50
0
0
2
4
6
time (ms)
8
10
Observations
• Transmission efficiency improves with SH rf even
when no further rf is applied
• Ramping back on Vrf shuts off the loss by increasing
the bucket size
• Timing is important—implied in these simulations is
the fact that the third cavity is being made to go from
full SH voltage to full fundamental voltage in 2 ms.
• May not need to go to full 1.55*Vrf in the
fundamental to gain efficiency
Why does SH early improve capture efficiency
when no additional rf is applied
• According to Chao, the limiting tune shift is,
  
ro R
2 n b 2
• One way to look at this is to say that SH effectively
moves injection to higher energy
--A . W. Chao, Physics of Collective Beam Instabilities in High Energy
Accelerators, Wiley, New York, 1993, p. 14.
Conclusions
Third cavity, even with limited SH capability,
will allow for important capture studies.
Also, the 3rd cavity may provide a modest
improvement in RCS beam current limit.
Acknowledgement
This work would not be possible without the
dedication and hard work of the IPNS
Accelerator Operations Group.