Characterizing the EBIS-C Spectrometer

Leah VanNahmenREU 2006

Kansas State University

Introduction

Spectrometer BasicsRecoil IonsBeam FragmentsSummaryApplications

Spectrometer Basics

EBIS-C Sp ec trom ete r

inte ra c tionre g ion

x-d irec tiony-d

irec

tion

De

tec

tor

Pa rtic le Bea m

GOAL: Determine initial momentum of all products from a collision

Gas Jet = Recoil Ions Particle Beam = Beam Fragments Detector MCP and PSD collect TOF and Final Position

Recoil Ions

We find recoil ions’ initial momentum from TOF using momentum conversion

Problem: Particles with different initial momenta can have the same TOF -50

13.98

14.04

14.10

different intial momentumand position can result in the same TOF

Comparison of Two Recoil Ions with Different Initial X Positions

TO

F (

use

c)

Momentum parallel to spectrometer (a.u.)

xi = 57.5 mm

xi = 57.4 mm

Recoil Ions

Make “voltage hill”

Best focusing if 2nd applied voltage is 82.8% of 1st voltage

Solution: Space and Time Focusing

5 10 15 20 25 30

0

200

400

600

800

1000

Voltage Decrease of Focusing Spectrometer (typical pattern)

Vo

ltag

e o

n P

late

(V

)

Plate Number

Recoil Ions

The EBIS-C spectrometer has great focusing!

82.0 82.5 83.0 83.5 84.0

-0.020.000.020.040.060.080.100.120.140.160.180.200.220.240.260.280.300.320.34

Best Space Focusing: 82.82%

Percent of Vs on 11th Plate vs. Error in Space Focusing

Err

or

(mm

)

Vf as a percent of V

s

82.5 82.6 82.7 82.8 82.9 83.0 83.1

20

40

60

80

100

120

140

160

Best Time Focusing: 82.75%

Percent of Vs on 11th Plate vs. Error in Time Focusing

Err

or

(pic

ose

con

ds)

Vf as a percent of V

s (Volts)

Beam Fragments

Magnification of Y Position

Magnification of Y Velocity

Problem: Magnification

Spectrometer AxisSpectrometer Axis

D = vt

Beam Fragments

0 1 2 3 4 5

1.06

1.08

1.10

1.12

1.14

1.16

1.18

1.20

1.22

1.24

1.26

1.28Data: EsclvsMagYPos_MyoModel: Upside-down Morse Potential Chi^2/DoF = 1.7187E-6R^2 = 0.99972 P1 0.12996 ±0.00359P2 2.34253 ±0.04856P3 0.39072 ±0.0099P4 1.0552 ±0.00847P5 0.29636 ±0.01993

Magnification of Y Position as a Function of E

scl

Mag

nif

icat

ion

of

Y P

osi

tio

n

Escl

Solution: Find an equation to correct for both kinds of magnification

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.51.021.031.041.051.061.071.081.091.101.111.121.131.141.151.161.171.181.191.201.21

Data: EsclvsMagVelo_MvelocityModel: ExpDec2 Chi^2/DoF = 7.3441E-7R^2 = 0.99989 y0 0.99362 ±0.08449A1 0.0908 ±0.052t1 6.23221 ±11.61012A2 0.14413 ±0.03213t2 0.81316 ±0.13532

Magnification of Y Velocity as a Function of E

scl

Mag

nif

icat

ion

of

Y V

elo

city

Escl

Beam Fragments

Overall Magnification Solution:Overall magnified Y position =

magnification of Y position x initial y position + magnification of Y velocity x initial Y velocity x TOF

Ym = MYi x Yi + MVy x vy x TOF

Summary

Apply two voltages to spectrometer to focus recoil ions

Correct for magnification of beam fragments

End up with enough equations to find the initial momentum of all the products from a collision

Applications

This characterization will allow experimenters to quickly and easily focus the EBIS-C spectrometer and correct for the magnification it causes

The spectrometer will be used in the EBIS-C beamline for future experiments…..

Applications

Gas JetParticle Beam

Physics

CO Ar11+ Dissociation of CO2+

Ar/He HD+ and H2+ CID and DC

He H2+ Vibrational State

Effects

Applications

In Ar/He experiment:

Ar + H2+

H+ + H + ArH + H + Ar+

De

tec

tor

Sp ec trom ete r a xis