Progress on an Electron Beam Profile Monitor at theFermilab Main Injector*

FERMILAB-POSTER-23-299-AD

R. Thurman-Keup#, T. Folan, M. Mwaniki, S. Sas-Pawlik,Fermi National Accelerator Laboratory, Batavia, USA

WEP023
Abstract
The current program at Fermilab involves the construction of a
new superconducting linear accelerator (LINAC) to replace theexisting warm version. The new LINAC, together with otherplanned improvements, is in support of proton beam
intensities in the Main Injector (MI) that will exceed 2 MW.
Measuring the transverse profiles of these high intensity
beams in a ring requires non-invasive techniques. The MI uses
ionization profile monitors as its only profile system. An
alternative technique involves measuring the deflection of aprobe beam of electrons with a trajectory perpendicular to theproton beam. This type of device was installed in MI and initialstudies of it have been previously presented. This paper will
present the status and recent studies of the device utilizing
different techniques.

Experimental Device
Ion Gauge

OpticalBreadboard~ 60 cm x 150 cm

Ion Pump

60 keV Electron Gun
Pneumatic
Beam Valve
ElectrostaticDeflector

Main Injector
Beampipe

Ion Gauge

Introduction
Historically, thin wires were rapidly swept through the beam anddownstream losses recorded as a function of the position of thewire to construct the profile. These were called flying wires [1]. In
the Main Injector (MI) at Fermilab, they were removed around2012 due to wire breakage which was not understood.
The concept of a probe beam of charged particles to determine acharge distribution has been around since at least the early
1970’s [2-4]. Several conceptual and experimental devices havebeen associated with accelerators around the world [5-9]. An
operational device is presently in the accumulator ring at theSpallation Neutron Source at Oak Ridge National Lab [10]. The EBP
was constructed and installed in the Main Injector (MI) in 2014 andinitial results have been presented previously [11].

PneumaticInsertion Device
with OTR StainlessSteel Mirror

OpticalComponents
Box

Phosphor Screen

Electrostatic deflector

Faraday Cup

CID Camera

TheoryxTarget
Beamq(b)ybPhosphor Screen

Assume 𝛾 ≫ 1, no magnetic field, 𝜌 ≠ 𝑓 𝑧∞𝑟Ԧ−𝑟′Ԧ∆𝑝Ԧ = න 𝑑𝑡 𝐹Ԧ 𝑟Ԧ 𝑡𝐹Ԧ 𝑟Ԧ ∝ න 𝑑 2 𝑟′𝜌Ԧ 𝑟′Ԧ
2𝑟Ԧ − 𝑟′Ԧ−∞Assume deflection is very small such that 𝑟Ԧ ≈ 𝑏, 𝑣𝑡∞∞∆𝑝Ԧ ∝ න 𝑑𝑥′ න−∞∞∞𝑑𝑦′ 𝜌 𝑥 ′ , 𝑦′

න 𝑑𝑡

−∞

−∞

𝑏 − 𝑥 ′ , 𝑣𝑡 − 𝑦′𝑏 − 𝑥′ 2 + 𝑣𝑡 − 𝑦′ 2

Four 15 cm long
curved plates

Image Intensifier Housing

Fiberoptic
Taper

∞

∆𝑝Ԧ ∝ න 𝑑𝑥′ න 𝑑𝑦′ 𝜌 𝑥 ′ , 𝑦 ′ sgn 𝑏 − 𝑥′ 1,0−∞−∞Assume again that deflection is very small such that 𝑝Ԧ ≈ 0, 𝑝 and 𝜃 ≈∞

∞
−∞

∞

𝑑𝜃 𝑏∝ න 𝑑𝑦′ 𝜌 𝑏, 𝑦 ′𝑑𝑏−∞

x profile

Slow Sweep𝑑sgn 𝑏 − 𝑥′ ∝ 𝛿 𝑏 − 𝑥′𝑑𝑏

𝜃 𝑏 ∝ න 𝑑𝑥′ න 𝑑𝑦′ 𝜌 𝑥 ′ , 𝑦 ′ sgn 𝑏 − 𝑥′−∞∆𝑝Ԧ𝑝Ԧ𝑑𝜃 𝑏= 𝐺𝑎𝑢𝑠𝑠𝑖𝑎𝑛 𝑏
𝜌=2𝐷 𝑔𝑎𝑢𝑠𝑠𝑖𝑎𝑛𝑑𝑏

Slow Sweep Waveform
Slow sweep of electron beam. The individual spots are image
intensifier gates. A slight enhancement from the electron
deflection is visible in (a) where the proton beam is present.

𝜃 𝑏 = erf(𝑏)200 μsa) Beam

Experimental TechniqueDeflections

Measure the deflection for a range of impact parameters.
There are various approaches to accomplishing this.

Deflections

Fast sweeps diagonally through bunch
Sweep time much shorter than bunch length

Beam – No Beam

Sweep time longer than bunch
length. This is main injector.

b) No Beam

Deflection
Direction

Now find the maximum pixel value ineach column as well as the maximum
pixel in each column of the no-beam
image. Here these two curves ofmaximum pixels are overlayed.
Undeflected

One trace to adjacent pairsof deflecting plates

Deflected

Fast Sweep Test
Slow sweep diagonallythrough many bunches

Deflection shape isfunction of bunch
lengthSimilar to above, but instead of a long bunch, it
is a train of short bunches, so the gap between
the deflected and non-deflected fills in.

80 ns

Fast deflection
waveforms.

The undeflected curve shows the step structure of thediscrete spots in the original no-beam image . The difference
between these two curves is the deflection distance. We
evaluate the average deflection distance for each step region,
together with the impact parameter for each step to produce
the 𝜃 𝑏 = erf(𝑏) curve below. For reference, the ionization
profile monitor measured 1.71 mm.

Multiple fast sweeps along bunch
Peak deflection is not function of bunch length

Electron Sweep

Proton Beam

Bunch Center

Electron deflection
replicates thelongitudinal bunch
structure. Might bepossible to measuretransverse size vs.
longitudinal position.

Simulations of the deflectionsin this approach. Successive
sweeps along the proton
direction at different impact
parameters are displayed in
the same image. One can seethat the central deflections
may overlap each other andneed to be separated, perhaps
in different camera frames.

* This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359
with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
# keup@fnal.gov

Deflected
Down
Sweep
Direction
Not
Deflected

Deflected
UpREFERENCES[1] M. Hu et al., “Beam profile measurement with flying wires at the Fermilab Recycler Ring”, in Proc. PAC’05, Knoxville, TN, USA, May 2005, p. 2182. doi:10.1109/PAC.2005.1591050[2] Paul D. Goldan, “Collisionless sheath – An experimental investigation”, Phys. Fluids, vol. 13, p. 1055, 1970. doi:10.1063/1.1693008[3] C. H. Stallings, “Electron beam as a method of finding the potential distribution in a cylindrically symmetric plasma”, J. Appl. Phys., vol. 42, p. 2831, 1971. doi:10.1063/1.1660634[4] C. W. Mendel Jr., “Apparatus for measuring rapidly varying electric fields in plasmas”, Rev. Sci. Instrum., vol. 46, p. 847, 1975. doi:10.1063/1.1134351[5] J. Shiloh, M. Lampel and R. Sah, “Electron beam probe for charge neutralization studies of heavy ion beams”, Rev. Sci. Instrum., vol. 54, p. 46, 1983. doi:10.1063/1.1137213[6] V. Shestak, C.J. Kost, R. Burge, D.B. Steski and S. Kornak, “Electron beam probe for ion beam diagnostics”, TRIUMF, Rep. TRI-DN-87-36, 1987.
[7] P. Gross et al., “An electron beam probe for ion beam diagnosis”, in Proc. EPAC’90, Nice, France, June 1990, p. 806. https://accelconf.web.cern.ch/e90/PDF/EPAC1990_0806.PDF[8] J. Bosser, C. Dimopoulou, A. Feschenko and R. Maccaferri, “Transverse profile monitor using ion probe beams”, Nucl. Instrum. Methods Phys. Res. A, vol. 484, p. 1, 2002. doi:10.1016/S0168-9002(01)01965-9[9] P. V. Logatchov et al., “Non-destructive singlepass monitor of longitudinal charge distribution in an ultrarelativistic electron bunch”, in Proc. PAC’99, New York, NY, USA, March 1999. doi:10.1109/PAC.1999.794408[10] W. Blokland and S. Cousineau, “A non-destructive profile monitor for high intensity beams”, in Proc. PAC’11, New York, NY, USA, March 2011. https://accelconf.web.cern.ch/PAC2011/papers/weocn2.pdf[11] R. Thurman-Keup et al., “Commissioning and first results of the electron beam profiler in the Main Injector at Fermilab”, in Proc. IBIC'17, Grand Rapids, MI, USA, Aug. 2017, pp. 330-334. doi:10.18429/JACoW-IBIC2017-WE3AB3[12] A. Aleksandrov et al., “Feasibility study of using an electron beam for profile measurements in the SNS accumulator ring”, in Proc. PAC’05, Knoxville, TN, USA, May 2005, pp. 2586-2588. doi:10.1109/PAC.2005.1591191