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--- strutture:lnf:da:btf:beam_characteristics [2023/09/21 13:19] – taruggi@infn.it
+++ strutture:lnf:da:btf:beam_characteristics [2026/11/09 13:20] (current) – diociaiu@infn.it
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+====== BTF Beam Characteristics ======
+The **DAΦNE Beam Test Facility (BTF)** provides electron and positron beams with adjustable energy, intensity, transverse dimensions, and divergence.
+Beam parameters can be optimized according to experimental requirements, covering a wide range of operating conditions, from single-particle beams to high-intensity pulses.
+The achievable beam characteristics depend on the particle species, requested energy and multiplicity, experimental hall, and DAΦNE LINAC operating conditions.
+===== Main Beam Parameters =====
+BTF consists of two experimental halls, **BTFEH1** and **BTFEH2**, with complementary operating capabilities.
+^ Parameter ^ BTFEH1 ^ BTFEH2 ^
+| Particle species | Electrons / Positrons | Electrons / Positrons |
+| Electron energy | Approximately 25–780 MeV | Dependent on the selected beamline configuration, up to the facility electron energy limit |
+| Maximum positron energy | Approximately 550 MeV | Dependent on the selected beamline configuration, up to the facility positron energy limit |
+| Beam intensity | From single particles up to approximately 10<sup>10</sup> particles/pulse | Up to approximately 10<sup>6</sup> particles/s |
+| Maximum repetition rate | 49 Hz | 49 Hz |
+| Typical pulse duration | 10 ns | 10 ns |
+| Beam configuration | Primary and secondary beams | Primarily secondary beams |
+| Main applications | High-intensity and long-duration experiments | Low-intensity detector tests and calibration |
+**Note:** These values describe the overall capabilities of the facility and should not be interpreted as simultaneously achievable operating conditions.
+Beam energy, intensity, spot size, divergence, and repetition rate are correlated and depend on the DAΦNE LINAC operating conditions and the selected beam transport configuration.
+===== Beam Operating Modes =====
+BTF has historically operated in two main configurations: time-sharing and dedicated mode.
+==== Time-Sharing Mode — Currently Suspended ====
+**Status: Currently suspended.**
+Historically, during DAΦNE collider operation, BTF received LINAC pulses not required for injection into the storage rings.
+In this configuration, the primary LINAC energy was determined by DAΦNE injection requirements, typically 510 MeV, while beam availability and repetition rate depended on the collider injection cycles.
+**Time-sharing operation is currently suspended, as injection into the DAΦNE storage rings is no longer performed.**
+==== Dedicated Mode — Current Operation ====
+BTF currently operates in dedicated mode, with the LINAC configured according to the requirements of scheduled experimental activities.
+This configuration provides flexibility in:
+  * Electron and positron beam energy
+  * Beam intensity and particle multiplicity
+  * Pulse repetition rate
+  * Pulse duration, within the available LINAC configurations
+  * Beam transport and focusing conditions
+Beam parameters are optimized according to experimental requirements and the operational constraints of the facility.
+===== Beam Intensity and Multiplicity =====
+The facility can deliver both high-intensity primary beams and low-intensity secondary beams.
+==== Primary Beam ====
+In primary beam operation, the LINAC beam is transported directly towards the experimental area without interception by the intensity-reduction target.
+The primary LINAC beam can reach intensities of approximately 10<sup>10</sup> electrons per pulse or 10<sup>9</sup> positrons per pulse, depending on the accelerator configuration.
+This operating mode is particularly suitable for high-intensity applications and dedicated experimental campaigns.
+==== Secondary Beam ====
+Secondary beams are produced by inserting a copper target into the primary LINAC beam.
+The target thickness can be selected according to the required attenuation and beam conditions.
+Interactions in the target produce a broad particle energy spectrum. A momentum-selection system, consisting of dipole magnets and adjustable collimators, selects the required energy and controls the transmitted particle intensity.
+The remaining transport line includes quadrupole magnets and steering correctors, which allow the beam trajectory and transverse properties to be adjusted.
+This configuration enables the production of low-multiplicity beams, including single-particle operation.
+The achievable multiplicity depends on the selected energy, primary beam intensity, target configuration, and beamline acceptance.
+===== Particle Multiplicity Statistics =====
+In low-intensity secondary beam operation, the number of particles delivered in each pulse can be approximately described by a **Poisson distribution**:
+<code>
+P(k; λ) = exp(-λ) × λ<sup>k</sup> / k!
+</code>
+where:
+  * **k** is the number of particles in a pulse;
+  * **λ** is the average number of particles per pulse;
+  * **P(k; λ)** is the probability of observing exactly k particles.
+For an average multiplicity of λ = 1:
+  * Approximately 36.8% of pulses contain no particles.
+  * Approximately 36.8% contain exactly one particle.
+  * Approximately 18.4% contain exactly two particles.
+  * Approximately 8.0% contain three or more particles.
+The probability of obtaining exactly one particle per pulse is maximized at λ = 1.
+The following table illustrates the expected probabilities for different average multiplicities.
+^ Average multiplicity (λ) ^ P(0) ^ P(1) ^ P(2) ^ P(≥3) ^
+| 0.1 | 90.48% | 9.05% | 0.45% | 0.02% |
+| 0.5 | 60.65% | 30.33% | 7.58% | 1.44% |
+| 1.0 | 36.79% | 36.79% | 18.39% | 8.03% |
+| 2.0 | 13.53% | 27.07% | 27.07% | 32.33% |
+| 3.0 | 4.98% | 14.94% | 22.40% | 57.68% |
+These probabilities describe an ideal Poisson process. Experimental distributions may deviate from this model due to beam fluctuations, detector acceptance, and other experimental effects.
+===== Transverse Beam Properties =====
+The transverse properties of the BTF beams depend on particle energy, multiplicity, focusing conditions, and the selected experimental hall.
+The beam transport system includes quadrupole magnets, steering correctors, and adjustable collimators, allowing the beam position, transverse dimensions, and divergence to be optimized.
+The achievable beam spot size can vary significantly according to the experimental configuration.
+Multiple Coulomb scattering in the target, beamline materials, and exit vacuum window can significantly affect the transverse beam distribution, particularly at low energies.
+Beam parameters at the experimental setup must therefore be evaluated for the specific operating configuration.
+===== Typical Beam Performance =====
+The following measurements illustrate representative BTF beam characteristics obtained under specific experimental conditions.
+These results are examples of measured beam performance and should not be interpreted as guaranteed operating specifications.
+==== Low-Intensity Beam Multiplicity ====
+**Measurement conditions:**
+  * Beam energy: 450 MeV
+  * Multiplicity: approximately 1.5 particles/pulse in LINAC positron mode and 10 particles/pulse in LINAC electron mode
+  * Detector: CALOBTF1, BTFDAQ (V965)
+  * Trigger: LINAC trigger
+  * Statistics: 3.84 × 10<sup>7</sup> secondary electrons
+  * Run leader: BTF Staff
+The measurement illustrates the dependence of secondary beam multiplicity on the primary LINAC beam conditions.
+The detector resolution was affected by scattering material installed upstream of the calorimeter, including approximately 400 µm of multilayer silicon detector material.
+{{:strutture:lnf:da:btf:multi_mult2.png?700|Measured low-intensity beam multiplicity distribution}}
+**Figure 1:** Measured secondary electron multiplicity distributions for different primary LINAC beam conditions.
+==== Low-Intensity Beam Profile ====
+**Measurement conditions:**
+  * Beam energy: 450 MeV
+  * Average multiplicity: 25 particles/pulse
+  * Detector: Medipix
+  * Trigger: LINAC trigger
+  * Acquisition gate: 200 ns
+  * Statistics: 3500 pulses
+Pixel detector measurements allow the transverse particle distribution to be reconstructed and the beam profile to be characterized.
+{{:strutture:lnf:da:btf:beamprofile.gif?700|Transverse beam profile measured with Medipix}}
+**Figure 2:** Transverse beam profile measured using a Medipix detector.
+Data courtesy of [[http://www.le.infn.it/~chiodini/allow_listing/BTF2014Oct/|Gabriele Chiodini]].
+==== Beam Position Stability ====
+Beam position stability can be studied by reconstructing the mean transverse position of successive beam pulses.
+**Measurement conditions:**
+  * Beam energy: 450 MeV
+  * Average multiplicity: 25 particles/pulse
+  * Detector: Medipix
+  * Repetition rate: 50 Hz (historical measurement)
+  * Acquisition gate: 200 ns
+  * Statistics: 3500 pulses
+{{:strutture:lnf:da:btf:beamcenterprofile.gif?700|Beam centroid position stability}}
+**Figure 3:** Beam centroid position reconstructed over successive LINAC pulses.
+Data courtesy of [[http://www.le.infn.it/~chiodini/allow_listing/BTF2014Oct/|Gabriele Chiodini]].
+==== High-Intensity Beam Time Structure ====
+The DAΦNE LINAC is an S-band accelerator operating at an RF frequency of approximately 2.856 GHz.
+The beam therefore exhibits a microbunch structure with a temporal separation of approximately 350 ps.
+A typical 10 ns macropulse contains approximately 29 microbunches. The actual number depends on the LINAC pulse configuration.
+{{:strutture:lnf:da:btf:amy.jpg?500|High-intensity beam microbunch time structure}}
+**Figure 4:** Example of the microbunch structure of a high-intensity LINAC beam.
+Data courtesy of the AMY Collaboration.
+===== Beam Diagnostics =====
+BTF is equipped with diagnostic devices for measuring and monitoring beam charge, intensity, transverse position, profile, and stability.
+Different instruments are employed depending on the beam operating conditions, from single-particle measurements to high-intensity beam diagnostics.
+Further information is available in the [[strutture:lnf:da:btf:dispositivi:btf_diagnostic|BTF Beam Diagnostics]] section.
+===== References =====
+[1] B. Buonomo, G. Mazzitelli, F. Murtas and L. Quintieri, "A Wide Range Electrons, Photons, Neutrons Beam Facility", EPAC 2008, Genoa, Italy.
+[2] B. Buonomo, G. Mazzitelli and P. Valente, "Performance and Upgrade of the DAΦNE Beam Test Facility (BTF)", IEEE Transactions on Nuclear Science, 52, 824–829 (2005).
+[3] B. Buonomo, G. Mazzitelli, F. Murtas, L. Quintieri and P. Valente, "Beam Diagnostics for a Wide Range Beam Test Facility (BTF)", Beam Instrumentation Workshop, Lake Tahoe, USA (2008).