Update on FFC Measurements at PIP-II Injector Test€¦ · PIP-II Injector Test Beamline (MEBT...

Update on FFC Measurements at PIP-II Injector Test

J.-P. Carneiro et al.

PIP-II Technical Meeting

06 February 2018

Outline

• Part I : Experimental Layout

– Description of the Fast Faraday Cup, Beamline description, Scope

remote operation

– FFC scope signal as observed in the control room

– FFC signal analysis to estimate the RMS bunch length

• Part II: PARMTEQM/TRACK RFQ Simulation

• Part III: Experimental Results

– RMS bunch length as a function of Buncher 2 and Buncher 3 field for

0.6 mA (Pencil Beam) and 5.0 mA beam

– Estimation of the long. Emittance at the RFQ exit for 0.6 mA and 5 mA

beam current. Reconstruction of Twiss parameters.

– Comparison of the measured RMS Bunch Length with the codes

Tracewin and Track.

J.-P. Carneiro et al. | Update on FFC Injector at PIP-II Injector Test 2/6/20182


Part I

Experimental Layout

3

• The FFC has an aperture of about 0.8 mm and it has a 50 Ω termination.

• According to Sasha’s estimate: the FFC has a time response of 30 ps to a point particle (20

mm/ns beam with 2 mm gap, ~100 ps)

Description of the Fast Faraday Cup

(Designed by Ding Sun)

J.-P. Carneiro et al. | Update on FFC Injector at PIP-II Injector Test

FFC 2017_VCheck holes’ alignment with a pin

TZM disk with a

collimating

aperture of about

0.8 mm diameter

Teflon

Center conductor (Brass) with a receiving hole (keep secondary electrons from

escaping)

Al Body

~ 1 inch

~ 1 inch

BEAM

2/6/20184

2 mm Gap

PIP-II Injector Test Beamline (MEBT V3.1, as of Jan 2018)

J.-P. Carneiro et al. | Update on FFC Injector at PIP-II Injector Test

• The FFC is presently the only diagnostic available at PIP-II Injector Test to estimate

bunch lengths.

• The data presented in this talk were taken with the FFC located after the fifth triplet (in

the MEBT v3.0 version) and with the FFC located at the end of the beamline (in the

MEBT v3.1 version).

• When installed after the fifth triplet, the FFC data were taken as function of the field in

Buncher 2 for different beam current (0.6 mA to 5 mA, 10/11/2017)

• The same type of measurement were performed with the FFC installed at the end of

the beamline (same 0.6 mA to 10 mA, 12/18 and 12/26 2017, 01/18 and 01/19 2018)

2/6/2018

~10 m

5

2/6/2018J.-P. Carneiro et al. | Update on FFC Injector at PIP-II Injector Test

Buncher 3

Remotely operated 6GHz scope(D. Slimmer)

FFC

Fast Faraday Cup as installed in the cave with scope connection

(As of Friday, January 19th, 2018)

6


Fast Faraday Cup signal from the scope as seen from the control

room for a 5mA beam kickers off (left) and both kickers on (right)

• The FFC requires a precise alignment with the beam (Bruce tuned the injector for all

the data in this talk). Once an optimized signal is obtained, data are saved directly in

the shift folder in the format of an excel file of about 100 kb.

Kickers OffB1=60kV, B2=50kV and B3=60kV

12/26/2017

Both 50Ω and 200 Ω kickers onB1=60kV, B2=50kV and B3=60kV

12/26/2017

7


Gaussian Fit of the signal from the FFC and estimate of the

corresponding RMS bunch length. (Below 9.3 mA pulse, 01/19/2018)

• A simple matlab macro read the FFC raw excel data file and computes for 10

consecutive pulses (5 consecutive pulses if both kickers are tuned on) the RMS

bunch length in pico-second by performing a Gaussian fit of the data.

8


FFC Signal as a function of B3 with both 50Ω and 200Ω kickers on

For a 5mA. Data taken on 12/26/2017.

B3=1kV B3=10 kV B3=20 kV B3=30kV

B3=40kV B3=50kV B3=60kV B3=70kV

B3=80kV B3=90kV B3=100kV

9


Part II

PARMTEQM / TRACK RFQ SIMULATIONS

10


Longitudinal emittance at the RFQ exit Vs beam current

(From PIP-II CDR and TRACK simulations on Grid)

Fig. 2.6 CDR / 1keV-ns=0.32mm-mrad(with measured input dist. in LEBT)

5mA, 100k

TRACK with 3D Fields on FermiGridReference WB Input DistAlpha=1.6, Beta=7 cm/rad

1mA to 10 mA in 0.1 mA steps

[kev

-ns]

11

Alpha at RFQ exit Vs Beam Current(Alpha Z < 0 means diverging) Beta at RFQ exit Vs Beam Current

Corresponding Longitudinal Twiss at the RFQ exit Vs beam current

(From TRACK simulations on Grid)

• From Fig. 2.6 of the CRD document and from TRACK simulation, the long. emittance

at the RFQ exits seems to decrease as a function of the beam current from about 0.4

mm-mrad at 0 mA to a minima of about 0.26 mm-mrad at 5mA.

• According to TRACK, the corresponding long. Beta function (plot on the right) seems

to increase as a function of the beam current (a factor of 2 from 0 mA to 5 mA)

2/6/2018J.-P. Carneiro et al. | Update on FFC Injector at PIP-II Injector Test12


Impact of a mismatch beam at the RFQ entrance on the

transverse and longitudinal emittance (J. Staple talk, 2012).

• On the slide below (forwarded by J. Steimel) we can see that a matching allowing

small transverse emittance at the RFQ exit does not necessary lead to a small

longitudinal emittance.

13


Part II

Comparing experimental results with TRACK and TRACEWIN

14


FFC Signal as a function of B3 with both 50Ω and 200Ω kickers on

For a 5mA. Data taken on 12/26/2017.

• On 11/10/2017 we took data with the FFC located downstream of Buncher 2 for a fixed field of

Buncher 1. These FFC data were taken for different beam current (0.6 mA, 1.3 mA, 2 mA, 3

mA, 4 mA, 5 mA and 10 mA). For each one of these beam current we could observe a waist

when plotting the RMS bunch length as a function of the Buncher 2 field. The goal of this

measurement was to reconstruct the long. emittance and Twiss at the RFQ exit as a function of

beam current.

• On 12/18/2017, 01/18 and 01/19 2018 we took data with the FFC located at the end of the

beamline for a fixed field on Buncher 1 and Buncher 2 and as a function of Buncher 3. These

data were taken as a function of the beam current (0.6 mA to 9.8 mA). The goal of this

experiment was to benchmark the long Twiss from 11/10/2017 reconstructed at the RFQ exit.

• On 12/26/2017 we took FFC data with the FFC located at the end of the beamline for a fixed

field on Buncher 1 and Buncher 2 and for a kickers on / kickers off.

• For each beam current, Bruce tuned the ion source (gas flow, arc current, ..) and the LEBT

solenoids + correctors. Each current therefore corresponds to a new LEBT tune. Also the RFQ

for all these data was set to 60 kV. For beam currents < 5mA, we used MEBT lattice#1540, for

beam current of 6 mA and higher we used MEBT lattice#1527. When using kickers we

uploaded MEBT lattice #1534.

15


Measured RMS bunch length at the FFC Vs B2 at 0.6mA

Estimate of the Long. Emittance and Long. Twiss at B

• The plot below on the left shows the measured RMS bunch length at the FFC located

after the fifth triplet as a function of the field in Buncher 2. A Matlab macro (no space

charge) has been written which permits the reconstruction of the long. Twiss at the

Buncher 2 from the RMS bunch length Vs Buncher 2 field data (right plot).

: Transfer-matrix elements

Long. emittance:

Twiss:

RMS Bunch length Vs B2

0.6 mA

Twiss reconstruction at B2

Measured RMS Bunch at the FFC Vs B2 at 0.6mA and

corresponding TRACK simulation. (Data of 11/10/2017)


• Matching has been performed in Tracewin in order to find the Twiss at the RFQ exit

that would match the Twiss at the Buncher 2 entrance (shown in previous slide)

• Below a plot showing RMS bunch length Vs B2 at 0.6 mA and TRACK simulations

17


• Below a plot showing RMS bunch length Vs Buncher 3 at 0.6 mA and Tracewin

simulations using the Twiss reconstructed on 11/10/2017.

• The conclusion from our low current FFC studies is that the estimated long.

emittance is low (at 0.26 mm-mrad) and the reconstructed Twiss at the RFQ exit

allow a reasonable measurement/simulation agreement for data taken 1 month apart.


corresponding Tracewin simulation. (Data of 12/18/2017)

18

Estimate of the impact of space charge on the reconstruction of the

Long. Emittance at B2 from the Matlab macro. From Tracewin.


• Tracewin simulation have been performed with fixed trans. and long. Twiss at the

Buncher 2 entrance and the bunch length has been recorded at the location of the

FFC as a function of the Buncher 2 field (~3.8 meters downstream buncher 2)

• Input at B2: ex=0.17 mm-mrad, ax=0.3, bx=1.38 mm/rad

ey=0.17 mm-mrad, ay=0.19, by=0.64 mm/mrad

ez=0.28 mm-mrad, az=-2, bz=9 mm/mrad

• Using these simulated data in the Matlab macro that allows Twiss reconstruction, we

estimate that at 5mA the recovered long. emittance will be affected by approximately

a factor of 2.

Impact of Space Charge

on recovery of the long. Emit.

Tracewin / Matlab Macro

(on a ~3.8 m drift)

~ factor of 2

Reconstruction of the Long. Twiss at B2 from the FFC data

taken as a function of Buncher 2 field for different current


Beam Current

[mA]

EmitZ at B2

[mm-mrad]

BetaZ at B2

[mm/mrad]

AlphaZ at B2

0.6 0.28 9.68 -2.09

1.3 0.31 6.60 -1.89

2 0.39 7.29 -2.04

3 0.59 7.74 -2.22

4 0.78 7.43 -2.56

5 0.91 8.47 -2.93

• Using the data collected at the FFC at the fifth triplet as a function of the Buncher 2

field for different beam current we could reconstruct, using the Matlab macro, the

long. emittance and Twiss at Buncher 2.

• The trend is that as the beam current increases the long. Emittance increases.

• A 5 mA, taking into account a factor of 2 due to space charge effects, the estimated

long. emittance is in the order of 0.5 mm-mrad.

From Analysis

of FFC data Vs B2



corresponding Tracewin simulation. (Data of 11/10/2017)

21

• The plot below shows the RMS bunch length measured at the FFC Vs B2 at 5 mA

and Tracewin simulation taking a long. Emittance at the RFQ exit of 0.5 mm-mrad, a

long. Beta of 1.2 mm/mrad and long. Alpha of +0.42.

• A reasonable agreement is found between measurement and simulation.



corresponding TRACK simulation. (Data of 11/10/2017)

22

• Below a plot showing RMS bunch length Vs B3 at 5 mA and Tracewin simulations

using the long. Twiss reconstructed on 11/10/2017 (ez=0.5 mm-mrad, bz=1.2

mm/mrad and az=+0.42).

• At 5mA, a reasonable good agreement is obtained between the FFC measurement

and the simulation code Tracewin. This, as of now, implies an emittance larger than

expected.

Summary

• A Fast Faraday Cup connected to a remotely operated scope is presently in use at the

PIP-II Injector Test. We believe that the FFC works properly.

• For a low beam current (0.6mA) the agreement between the measured RMS bunch

length at the FFC and the simulation code is reasonable. The estimated long.

emittance at 0.6 mA is in the order of 0.26 mm-mrad.

• From our RMS bunch size measurement at higher beam current (> 2mA) we suspect

that the long. emittance may be higher (0.5 mm-mrad at 5mA) than expected (about

0.3 mm-mrad at 5 mA)

• We will in the next shifts continue measuring the long. emittance. We will focusing at

5mA current and investigate how different tunes of the LEBT (ion source settings,

solenoid settings) could impact the long. and trans. emittance. We will try to optimize

the injector for both trans. and long. emittance at 5mA.


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